- Oxygen electroreduction on heat-treated multi-walled carbon nanotubes supported iron polyphthalocyanine in acid media
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Multi-walled carbon nanotubes (MWCNTs) supported iron phthalocyanine (FePc), binuclear iron phthalocyanine (bi-FePc) and iron polyphthalocyanine (FePPc) were prepared by a solvothermal process. The resulting FePc/MWCNTs, bi-FePc/MWCNTs and FePPc/MWCNTs were heat-treated in argon (Ar) atmosphere at various temperatures ranging from 500 to 900°C to obtain optimized catalysts for the oxygen reduction reaction (ORR). The crystal structure, morphology and chemical environment of the catalysts were examined by ultraviolet-visible (UV-Vis) spectroscopy, X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure spectroscopy (XAFS). The electrocatalytic activity of the obtained catalysts was measured using a rotating disk electrode (RDE) technique in 0.5 mol L-1 H2SO4 solution saturated with oxygen. The ORR activity of the heat-treated FePPc/MWCNTs was found to be better than that of the heat-treated bi-FePc/MWCNTs and FePc/MWCNTs. Furthermore, the heat-treatment temperature greatly influenced the catalytic ORR ability of the catalysts. The FePPc/MWCNTs heat-treated at 800°C exhibited a four-electron transfer process and the best ORR activity (EORR = 0.79 V vs. RHE), methanol resistance, and stability (current loss = 13% at -0.13 V vs. Hg/Hg2SO4 after 55 h). XPS indicated that pyridine-type nitrogen, not graphitic-N, played a critical role in determining the electrocatalytic ORR activity of the amples. XAFS showed that the coordination geometry around Fe was close to square planar in structure, suggesting that the Fe-N4 structure was produced by the high temperature treatment.
- Zhang, Rui,Peng, Yingxiang,Li, Zhipan,Li, Kai,Ma, Jie,Liao, Yi,Zheng, Lirong,Zuo, Xia,Xia, Dingguo
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- Ni2P hollow microspheres for electrocatalytic oxygen evolution and reduction reactions
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H2 generated by solar-driven water splitting is a clean and environmentally benign fuel and is an ideal alternative to replace fossil fuels, whose uses have caused a series of energy and environmental issues. The synthesis of Ni2P and its catalytic properties foroxygen evolution reduction (OER) and oxygen reduction reaction (ORR) was reported. The as-prepared Ni2P material has a hollow microsphere structure, which has a very high surface-to-volume ratio and is beneficial for fast charge transfer and mass diffusion. These features are useful for electrocatalysis. The high activities and stabilities of this Ni2P material for both OER and ORR were confirmed, representing a rare example of bifunctional OER and ORR catalysts among Ni phosphides. Results showed that NI2P can catalyze water oxidation, achieving a 10 mA cm-2 current density at a 280 mV overpotential and can catalyze the selective four-electron reduction of O2 to H2O at an onset potential of 0.92 V, making it one of the most active metal phosphide catalysts for OER and ORR.
- Lei, Haitao,Chen, Mingxing,Liang, Zuozhong,Liu, Chengyu,Zhang, Wei,Cao, Rui
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- Tuning Cobalt and Nitrogen Co-Doped Carbon to Maximize Catalytic Sites on a Superabsorbent Resin for Efficient Oxygen Reduction
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The electrocatalytic performance and cost of oxygen reduction reaction (ORR) catalysts are crucial to many renewable energy conversion and storage systems/devices. Recently, transition-metal/nitrogen-doping carbon catalysts (M–N–C) have attracted tremendous attention due to their low cost and excellent catalytic activities; however, they are restricted in large-scale commercial applications by complex preparation processing. Here, a facile strategy to prepare Co–N–C catalysts has been developed. A kind of superabsorbent resin normally found in diapers, poly(acrylic acid-acrylamide), is used to adsorb a transition-metal cobalt salt and a pyrolysis strategy at 800 °C under an argon atmosphere is followed. The resin simultaneously plays a multiple role, which includes structural support, dispersing cobalt ions by coordinate bonds, and providing a carbon and nitrogen source. Attributed to the conductive carbon frameworks and abundant catalytic sites, the Co–N–C catalyst exhibits an excellent electrocatalytic performance. High onset potential (0.96 V vs. reversible hydrogen electrode, RHE), half-wave potential (0.80 V vs. RHE), and a large diffusion-limited current density (4.65 mA cm?2) are achieved for the ORR, which are comparable or superior to the commercial 20 % Pt/C and reported M–N–C ORR electrocatalysts. This work provides a universal dispersion technology for Co–N–C catalyst, which makes it a very promising candidate toward the ORR.
- Liu, Mengran,Lin, Hai,Mei, Zongwei,Yang, Jinlong,Lin, Jie,Liu, Yidong,Pan, Feng
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- Synthesis, electrochemistry and electrocatalytic activity of cobalt phthalocyanine complexes – Effects of substituents for oxygen reduction reaction
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The synthesis, characterization, electrochemistry and electrocatalytic activity of the mono (pyridine-4-oxy)-tri (tert-butyl) phthalocyaninato Co(II) (Pc1) and mono (pyridine-4-oxy)-hexa (hexyl) phthalocyaninato Co(II) (Pc2) are reported here. One reversi
- Acar, Elif Turker,Tabakoglu, Tuba Akk?zlar,Atilla, Devrim,Yuksel, Fatma,Atun, Gulten
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- Mechanism of the low-temperature interaction of hydrogen with α-oxygen on FeZSM-5 zeolite
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The mechanism of a low-temperature reaction of hydrogen with the radical anion surface oxygen species (α-oxygen, Oα) formed by decomposing N2O over FeZSM-5 zeolite was studied using kinetic and isotope techniques. It was found that the reaction is of first order with respect to hydrogen and the rate of the reaction is proportional to the concentration of Oα. The activation energy of the reaction, which was measured for H2 or D2 over a temperature range from +20 to -100°C, is equal to 3.2 or 5.3 kcal/mol, respectively. The reaction occurs with a considerable kinetic isotope effect (kH/k D), which varies over the range of 3.4-41 depending on the temperature. This fact indicates that the rate-limiting step of the reaction includes the dissociation of the hydrogen molecule. The temperature dependence of the isotope effect gave a value of 2.1 kcal/mol, which is close to the difference between the zero bond energies in the molecules of H2 and D2; this fact suggests that a tunnel effect does not significantly contribute to the reaction. The dissociative mechanism is consistent with data obtained by in situ IR spectroscopy. The interaction of hydrogen with α-oxygen is accompanied by the formation of new hydroxyl groups O αH (absorption bands at 3635 and 3674 cm-1) at the surface of the zeolite. The identification of these groups was supported by an isotope shift either on the replacement of H2 by D2 or on the replacement of 16Oα by Oα,. The stoichiometric ratio H2:Oα, is consistent with the previously drawn conclusion on the paired arrangement of α-sites.
- Dubkov,Starokon',Paukshtis,Volodin,Panov
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- A four-electron O2-electroreduction biocatalyst superior to platinum and a biofuel cell operating at 0.88 V
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O2 was electroreduced to water, at a true-surface-area-based current density of 0.5 mA cm-2, at 37 °C and at pH 5 on a wired laccase bioelectrocatalyst-coated carbon fiber cathode. The polarization (potential vs the reversible potential of the O2 /H2O half-cell in the same electrolyte) of the cathode was only -0.07 V, approximately one-fifth of the -0.37 V polarization of a smooth platinum fiber cathode, operating in its optimal electrolyte, 0.5 M H2SO4. The bioelectrocatalyst was formed by wiring laccase to carbon through an electron conducting redox hydrogel, its redox functions tethered through long and flexible spacers to its cross-linked and hydrated polymer. Incorporation of the tethers increased the apparent electron diffusion coefficient 100-fold to (7.6 ± 0.3) × 10-7 cm 2 s-1. A miniature single-compartment glucose-O2 biofuel cell made with the novel cathode operated optimally at 0.88 V, the highest operating voltage for a compartmentless miniature fuel cell. Copyright
- Soukharev, Valentine,Mano, Nicolas,Heller, Adam
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- 2D Layered non-precious metal mesoporous electrocatalysts for enhanced oxygen reduction reaction
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Rational design of inexpensive, highly active, and long-term stable non-precious metal electrocatalysts for oxygen reduction reaction (ORR) is of significant importance for large-scale applications of fuel cells in practice. In this paper, we report, for the first time, the construction of 2D layered mesoporous transition metal-nitrogen-doped carbon/nitrogen-doped graphene (meso-M-N-C/N-G, M = Fe, Co, and Ni) electrocatalysts using 4,4-bipyridine as the nitrogen and carbon source and mesoporous KIT-6/N-G generated by in situ formation of KIT-6 on graphene nanosheets as a template. The meso-Fe-N-C/N-G electrocatalyst showed super electrocatalytic performance for ORR. Excitingly, its catalytic activity and durability were superior to those of Pt/C, making it a good candidate as an ORR electrocatalyst in fuel cells. The results suggested that the outstanding electrocatalytic performance of the electrocatalysts could be attributed to the unique mesoporous structure, high surface area, ultrasmall size of Fe or FeOx nanocrystals embedded in 2D layered N-G nanosheets, excellent electron transportation, homogeneous distribution of high-density pyridinic N and graphitic N, graphitic C, and abundant metal active sites (Fe-Nx). The synthesis approach can be used as a versatile route toward the construction of various 2D layered graphene-based mesoporous materials.
- Huo, Lili,Liu, Baocang,Zhang, Geng,Si, Rui,Liu, Jian,Zhang, Jun
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- Rational Design of Hierarchical, Porous, Co-Supported, N-Doped Carbon Architectures as Electrocatalyst for Oxygen Reduction
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Developing highly active nonprecious-metal catalysts for the oxygen reduction reaction (ORR) is of great significance for reducing the cost of fuel cells. 3D-ordered porous structures could substantially improve the performance of the catalysts because of their excellent mass-diffusion properties and high specific surface areas. Herein, ordered porous ZIF-67 was prepared by forced molding of a polystyrene template, and Co-supported, N-doped, 3D-ordered porous carbon (Co-NOPC) was obtained after further carbonization. Co-NOPC exhibited excellent performance for the ORR in an alkaline medium with a half-wave potential of 0.86 V vs. reversible hydrogen electrode (RHE), which is higher than that of the state-of-the-art Pt/C (0.85 V vs. RHE). Moreover, the substantially improved catalytic performance of Co-NOPC compared with Co-supported, N-doped carbon revealed the key role of its hierarchical porosity in boosting the ORR. Co-NOPC also exhibited a close-to-ideal four-electron transfer path, long-term durability, and resistance to methanol penetration, which make it promising for large-scale application.
- Qiao, Mengfei,Wang, Ying,Mamat, Xamxikamar,Chen, Anran,Zou, Guoan,Li, Lei,Hu, Guangzhi,Zhang, Shusheng,Hu, Xun,Voiry, Damien
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- 2H→1T Phase Engineering of Layered Tantalum Disulfides in Electrocatalysis: Oxygen Reduction Reaction
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Tremendous attention is currently being paid to renewable sources of energy. Transition-metal dichalcogenides (TMDs) have been intensively studied for their promising catalytic activities in the hydrogen evolution reaction (HER) and the oxygen reduction reaction (ORR). In this fundamental work, we explored the catalytic properties of TMD family members 2H TaS2 and 1T TaS2. Our findings reveal that both polytypes exhibit poor HER performance, which is even more pronounced after electrochemical reduction/oxidation. Our experimental data show that 1T TaS2 has a lower overpotential at a current density of ?10 mA cm?1, despite theoretical DFT calculations that indicated that the more favorable free energy of hydrogen adsorption should make “perfect” 2H TaS2 a better HER catalyst. Thorough characterization showed that the higher conductivity of 1T TaS2 and a slightly higher surface oxidation of 2H TaS2 explains this discrepancy. Moreover, changes in the catalytic activity after electrochemical treatment are addressed here. For the ORR in an alkaline environment, the electrochemical treatment led to an improvement in catalytic properties. With onset potentials similar to that of Pt/C catalysts, TaS2 was found to be an efficient catalyst for the ORR, rather than for proton reduction, in contrast to the behavior of Group 6 layered TMDs.
- Luxa, Jan,Mazánek, Vlastimil,Pumera, Martin,Lazar, Petr,Sedmidubsky, David,Callisti, Mauro,Polcar, Tomá?,Sofer, Zdeněk
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- Bifunctional gold-manganese oxide nanocomposites: Benign electrocatalysts toward water oxidation and oxygen reduction
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Gold-manganese oxide nanocomposites were synthesised by seed-mediated epitaxial growth at the water/n-heptane interface under mild reflux conditions. These nanocomposites exhibit efficient electrocatalytic activity toward the water oxidation reaction (WOR) and the simultaneous oxygen reduction reaction (ORR) at a low overpotential (η ≈ 370 mV) and under neutral pH conditions. This journal is
- Rahaman, Hasimur,Barman, Koushik,Jasimuddin, Sk,Ghosh, Sujit Kumar
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- Boosting the catalysis of AuCuMo for oxygen reduction: Important roles of an optimized electronic structure and surface electrochemical stability
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The slow kinetics of the oxygen reduction reaction (ORR) remains a great challenge in many energy storage and conversion devices, such as alkaline fuel cells and metal-air batteries. Herein, a self-supported Au-based alloy (AuCuMo) was successfully synthesized by a one-pot hydrothermal method. By combining Cu and Mo, the electronic structure of Au was finely tuned. Furthermore, the electrochemical stability of surface Cu was enhanced by the incorporation of Mo. Benefitting from these advantages, the reaction of oxygen and oxygenated intermediates on AuCuMo was optimized, and the intrinsic activity was improved. AuCuMo thereby exhibited superior ORR activity and stability compared to commercial Pt/C catalysts.
- Gong, Hongyu,Li, Fan,Li, Ling,Yang, Bo,Yang, Ruizhi
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- Kinetic characterization of the reduction of silica supported cobalt catalysts
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The reduction process of silica supported cobalt catalyst was studied by thermal analysis technique. The reduction of the catalyst proceeds in two steps: Co3O4 + H2 to 3CoO + H2O, 3CoO + 3H2 to 3Co + 3H2O which was validated by the TPR and in-situ XRD experiments. The kinetic parameters of the reduction process were obtained with a comparative method. For the first step, the activation energy, E a, and the pre-exponential factor, A, were found to be 104.35 kJ mol-1 and 1.18?106~2.45?109 s-1 respectively. The kinetic model was random nucleation and growth and the most probable mechanism function was found to be f(α)=3/2(1- α)[-ln(1-α)]1/3 or in the integral form: g(α)=[-ln(1-α)]2/3. For the second step, the activation energy, E a, and the pre-exponential factor, A, were found to be 118.20 kJ mol-1 and 1.75?107~2.45 ? 10 9s-1 respectively. The kinetic model was a second order reaction and the probable mechanism function was f(α)=(1-α) 2 or in the integral form: g(α)=[1-α]-1-1.
- Wan,Li,Chen
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- Effect of the Composition of Supported Copper-Containing Salt Catalysts on Their Activity in the Deacon Reaction: Dependence of the Rate of the Deacon Reaction on the Ratio between Copper and Potassium Chlorides in a Supported CuCl2–KCl Salt Catalyst
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Abstract: The effect of KCl/CuCl2 molar ratios from 0 to 2.5 in the СuCl2–KCl catalyst (support) on its activity in the Deacon reaction was studied by a gradientless method in a temperature range of 350–425°C. The essential role of the hydration processes of the salt catalyst components in the homogenization of a reaction layer was established. The experiments did not contradict the previously proposed reaction kinetics and mechanism. A possible explanation of the experimental results was given based on the polarization representations used earlier in the reaction mechanism.
- Aglulin
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- Enhanced oxygen reduction activity of platinum subnanocluster catalysts through charge redistribution
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Single-size platinum Pt6 subnanoclusters exhibit superior mass-specific and surface-specific activities for the oxygen reduction reaction. The enhanced activity is attributed to polarized electron distributions based on rigorous structure chara
- Tsunoyama, Hironori,Ohnuma, Akira,Takahashi, Koki,Velloth, Archana,Ehara, Masahiro,Ichikuni, Nobuyuki,Tabuchi, Masao,Nakajima, Atsushi
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- Core-Shell Nanocomposites Based on Gold Nanoparticle@Zinc-Iron-Embedded Porous Carbons Derived from Metal-Organic Frameworks as Efficient Dual Catalysts for Oxygen Reduction and Hydrogen Evolution Reactions
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Core-shell nanocomposites based on Au nanoparticle@zinc-iron-embedded porous carbons (Au@Zn-Fe-C) derived from metal-organic frameworks were prepared as bifunctional electrocatalysts for both oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER). A single Au nanoparticle of 50-100 nm in diameter was encapsulated within a porous carbon shell embedded with Zn-Fe compounds. The resulting Au@Zn-Fe-C hybrids exhibited apparent catalytic activity for ORR in 0.1 M KOH (with an onset potential of +0.94 V vs RHE, excellent stability and methanol tolerance) and for HER as well, which was evidenced by a low onset potential of -0.08 V vs RHE and a stable current density of 10 mA cm-2 at only -0.123 V vs RHE in 0.5 M H2SO4. The encapsulated Au nanoparticles played an important role in determining the electrocatalytic activity for ORR and HER by promoting electron transfer to the zinc-iron-embedded porous carbon layer, and the electrocatalytic activity was found to vary with both the loading of the gold nanoparticle cores and the thickness of the metal-carbon shells. The experimental results suggested that metal-embedded porous carbons derived from metal-organic frameworks might be viable alternative catalysts for both ORR and HER.
- Lu, Jia,Zhou, Weijia,Wang, Likai,Jia, Jin,Ke, Yunting,Yang, Linjing,Zhou, Kai,Liu, Xiaojun,Tang, Zhenghua,Li, Ligui,Chen, Shaowei
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- Factors affecting catalytic destruction of H2O2 by hydrogenation and decomposition over Pd catalysts supported on activated carbon cloth (ACC)
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Destruction of hydrogen peroxide by its decomposition and hydrogenation over Pd catalysts supported on activated carbon cloth has been investigated. The catalysts were prepared by the impregnation method using acidic solution of palladium dichloride (PdCl2) as a metal precursor. The reactions were performed batchwise in a Parr stainless steel autoclave. Tests were run at room temperature using either methanol or water as a reaction medium. The effects of oxidation pre-treatment of the support with different acids (nitric and acetic acid), the heat treatment of the catalysts in different atmospheres (H2 and air), and Pd content on the final properties and H2O2 destruction activity of the catalysts were investigated. The results indicated that oxygen-containing surface functional groups have an important role in determining the physicochemical properties and H2O2 destruction activity of the catalysts. In fact, the presence of these groups stabilizes H2O2 in the solution and reduces its decomposition and hydrogenation. Furthermore, the presence of the oxidized state of Pd (PdO) in the catalyst makes it less active in H2O2 decomposition when compared to the corresponding zero valences (Pd0) catalyst. Using water instead of methanol dramatically increased the H2O2 decomposition
- Gudarzi, Davood,Ratchananusorn, Warin,Turunen, Ilkka,Heinonen, Markku,Salmi, Tapio
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- Tungsten oxide in polymer electrolyte fuel cell electrodes - A thin-film model electrode study
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Thin films of WOx and Pt on WOx were evaporated onto the microporous layer of a gas diffusion layer (GDL) and served as model electrodes in the polymer electrolyte fuel cell (PEFC) as well as in liquid electrolyte measurements. In order to study the effects of introducing WO x in PEFC electrodes, precise amounts of WOx (films ranging from 0 to 40 nm) with or without a top layer of Pt (3 nm) were prepared. The structure of the thin-film model electrodes was characterized by scanning electron microscopy and X-ray photoelectron spectroscopy prior to the electrochemical investigations. The electrodes were analyzed by cyclic voltammetry and the electrocatalytic activity for hydrogen oxidation reaction (HOR) and CO oxidation was examined. The impact of Nafion in the electrode structure was examined by comparing samples with and without Nafion solution sprayed onto the electrode. Fuel cell measurements showed an increased amount of hydrogen tungsten bronzes formed for increasing WOx thicknesses and that Pt affected the intercalation/deintercalation process, but not the total amount of bronzes. The oxidation of pre-adsorbed CO was shifted to lower potentials for WOx containing electrodes, suggesting that Pt-WO x is a more CO-tolerant catalyst than Pt. For the HOR, Pt on thicker films of WOx showed an increased limiting current, most likely originating from the increased electrochemically active surface area due to proton conductivity and hydrogen permeability in the WOx film. From measurements in liquid electrolyte it was seen that the system behaved very differently compared to the fuel cell measurements. This exemplifies the large differences between the liquid electrolyte and fuel cell systems. The thin-film model electrodes are shown to be a very useful tool to study the effects of introducing new materials in the PEFC catalysts. The fact that a variety of different measurements can be performed with the same electrode structure is a particular strength.
- Wickman, Bj?rn,Wesselmark, Maria,Lagergren, Carina,Lindbergh, G?ran
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- Kinetics and Mechanism of the OH + HO2 Reaction
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A discharge flow reactor with laser magnetic resonance and resonance fluorescence detection axes is used to measure the rate constant for the raction of OH and HO2 radicals by measuring the decay of OH in excess HO2 under pseudo-first-order conditions.Particular care is taken to reduce impurity O and H atoms to low levels since their presence leads to an underestimate of the rate constant.The rate constant is measured to be (8.0 +3.0/-2.0) x 1E-11 cm3 molecule-1 s-1 at 298 K and 2 Torr after a small (3 percent) correction is made for the impurity atoms.It is argued that recent experimental and theoretical results indicate that the reaction mechanism is likely dominated by attack at the hydrogen and of HO2 and that the reaction is unusually fast due a long-range attractive interaction.
- Schwab, James J.,Brune, William H.,Anderson, James G.
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- Absolute Rate Constant of the Reaction OH + H2O2 -> HO2 + H2O from 245 to 423 K
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The absolute rate constant of the reaction between the hydroxyl radical and hydrogen peroxide was measured by using the discharge-flow resonance fluorescence technique at total pressures between 1 and 4 torr.At 298 K the results is (1.64+/-0.32)E-12 cmsu
- Keyser, L. F.
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- Significantly improved electrocatalytic oxygen reduction by an asymmetrical Pacman dinuclear cobalt(ii) porphyrin-porphyrin dyad
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Pacman dinuclear CoII triphenylporphyrin-tri(pentafluorophenyl)porphyrin 1 and dinuclear CoII bis-tri(pentafluorophenyl)porphyrin 2, anchored at the two meso-positions of a benzene linker, are synthesized and examined as electrocatalysts for the oxygen reduction reaction (ORR). Both dinuclear Co bisporphyrins are more efficient and selective than corresponding mononuclear CoII tetra(pentafluorophenyl)porphyrin 3 and CoII tetraphenylporphyrin 4 for the four-electron electrocatalytic reduction of O2 to water. Significantly, although the ORR selectivities of the two dinuclear Co bisporphyrins are similar to each other, 1 outperforms 2, in terms of larger catalytic ORR currents and lower overpotentials. Electrochemical studies showed different redox behaviors of the two Co sites of 1: the CoIII/CoII reduction of the Co-TPP (TPP = triphenylporphyrin) site is well-behind that of the Co-TPFP (TPFP = tri(pentafluorophenyl)porphyrin) site by 440 mV. This difference indicated their different roles in the ORR: CoII-TPFP is likely the O2 binding and reduction site, while CoIII-TPP, which is generated by the oxidation of CoII-TPP on electrodes, may function as a Lewis acid to assist the O2 binding and activation. The positively charged CoIII-TPP will have through-space charge interactions with the negatively charged O2-adduct unit, which will reduce the activation energy barrier for the ORR. This effect of Co-TPP closely resembles that of the CuB site of metalloenzyme cytochrome c oxidase (CcO), which catalyzes the biological reduction of O2. This work represents a rare example of asymmetrical dinuclear metal catalysts, which can catalyze the 4e reduction of O2 with high selectivity and significantly improved activity.
- Liu, Yanju,Zhou, Guojun,Zhang, Zongyao,Lei, Haitao,Yao, Zhen,Li, Jianfeng,Lin, Jun,Cao, Rui
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- Nitrogen/sulfur co-doped non-noble metal material as an efficient electrocatalyst for the oxygen reduction reaction in alkaline media
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This work demonstrates the feasibility of nitrogen/sulfur co-doped non-noble metal materials (Fe-N/C-TsOH) as platinum-free catalysts for the oxygen reduction reaction (ORR) in alkaline media. Electrochemical techniques such as cyclic voltammetry (CV), rotating disk electrodes (RDEs) and rotating ring-disk electrodes (RRDEs) are employed with the Koutecky-Levich theory to investigate the ORR kinetic constants and the reaction mechanism. It is found that the catalysts doped with TsOH (p-toluenesulfonic acid) show significantly improved ORR activity relative to a TsOH-free catalyst. The overall electron transfer numbers for the catalyzed ORR are determined to be 3.899 and 3.098, respectively, for the catalysts with and without TsOH-doping. Catalysts heat treated at 600 °C exhibit relatively higher activity. In addition, the catalyst doped with TsOH (Fe-N/C-TsOH-600) not only exhibits exceptional stability in 0.1 mol L-1 KOH solution but also has higher methanol tolerance compared to commercial Pt/C catalyst in 0.1 mol L-1 KOH. To some extent, increasing the Fe-N/C-TsOH-600 loading on the electrode favors a faster reduction of H2O2 to intermediate to H 2O. X-ray photoelectron spectroscopy analysis indicates that pyrrolic N groups are the most active sites, and that sulfur species are structurally bound to carbon in the forms of C-S(n)-C and oxidized -SO (n)- bonds, an additional beneficial factor for the ORR.
- Xu, Li,Pan, Guoshun,Liang, Xiaolu
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- Covalent Phenanthroline Framework Derived FeS@Fe3C Composite Nanoparticles Embedding in N-S-Codoped Carbons as Highly Efficient Trifunctional Electrocatalysts
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Efficient and earth-abundant materials with multifunctional electrocatalytic properties within a wide range of pH are the new darlings for developing green energy conversion and storage techniques. A novel porous covalent phenanthroline framework (Fe-Phen-COFs) that involved Fe-DMSO (dimethyl sulfoxide) coordination complexes is successfully synthesized using 3, 8-dibromophenanthroline and 1, 3, 5-benzenetriboronicacid trivalent alcohol ester as a rigid building block via Suzuki coupling reaction. Fe-Phen-COFs as the self-carrier enriched with Fe, S, N, and C is pyrolyzed to produce N-S-codoping carbons with embedded core–shell Fe3C and FeS composite nanostructures (FeS/Fe3C@N-S-C). The FeS/Fe3C@N-S-C-800 obtained by pyrolysis at 800 °C exhibits efficient trifunctional electrocatalytic activity for oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER) within a wide pH range. Impressively, the ORR half-potential of FeS/Fe3C@N-S-C-800 reaches 0.87 V in 0.1 m KOH, more positive than the previously reported Pt-free electrocatalysts. It could be utilized as the advanced air electrode materials in zinc–air batteries, which exhibit an excellent power density and cycling stability superior to those of Pt/C-based zinc–air battery. Thermal conversion of novel Fe-Phen-COFs provides an effective strategy to prepare high-performance trifunctional electrocatalytic materials for the new-generation powerful energy conversion technologies.
- Kong, Fantao,Fan, Xiaohong,Kong, Aiguo,Zhou, Ziqian,Zhang, Xiaoying,Shan, Yongkui
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- In situ growth of Pt3Ni nanoparticles on an A-site deficient perovskite with enhanced activity for the oxygen reduction reaction
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A novel A-site deficient perovskite, La0.9Mn0.9Pt0.075Ni0.025O3-δ, is developed as a catalyst for the oxygen reduction reaction in alkaline solution. Pt3Ni nanoparticles are exsolved in situ on the surface upon reduction. The catalytic activity improves significantly after exsolution. This improvement is attributed to the synergy between the host perovskite and the nanoparticles.
- Gao, Yang,Wang, Jian,Lyu, Yu-Qi,Lam, Kwunyu,Ciucci, Francesco
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- Accelerating the oxygen reduction reaction via a bioinspired carbon-supported zinc electrocatalyst
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Oxygen utilization in electrochemical energy generation systems requires to overcome the slow kinetics of oxygen reduction reaction (ORR). Herein, we have outstretched an efficient strategy in order for developing a bioinspired Zn (N4)/sulfur/graphitic carbon composite (Zn-S-Gc) with an effective performance for the ORR at low temperature. The catalyst composite was created by attaching the Zn (N4) centers in the form of zinc phthalocyanine on the sulfur-linked graphitic carbon surface. The most positive ORR onset potential of about 1.00 V versus a reversible hydrogen electrode (RHE) was obtained due to the unique structure of a new catalyst in KOH solution (pH = 13) at low temperature (T = 298 K). The catalyst was evaluated using the rotating-disk electrode method in the potential range of ?0.02–1.18 V versus RHE. The number of transferred electrons as one of the most important parameters (n > 3.70) is almost constant in a wide range of low overpotentials (0.1–0.6 V), which indicates a more efficient four-electron pathway from O2 to H2O on the catalyst surface. The estimated Tafel slope in an appropriate range is about ≈ ?133.3 mV/dec at a low current density and E1/2 of the electrocatalyst displays a negative shift of only 11 mV after 10,000 cycles. The mean size of the catalyst centers is on the nanoscale (50 nm).
- Nahavandi, Faezeh,Seyyedi, Behnam
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- Water affects the stereochemistry and dioxygen reactivity of carboxylate-rich diiron(II) models for the diiron centers in dioxygen-dependent non-heme enzymes
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Carboxylate-bridged high-spin diiron(II) complexes with distinctive electronic transitions were prepared by using 4-cyanopyridine (4-NCC 5H4N) ligands to shift the charge-transfer bands to the visible region of the absorption spectrum. This property facilitated quantitation of water-dependent equilibria in the carboxylate-rich diiron(II) complex, [Fe2(μ-O2CArTol) 4(4-NCC5H4N)2] (1), where -O2CArTol is 2,6-di-(p-tolyl)benzoate. Addition of water to 1 reversibly shifts two of the bridging carboxylate ligands to chelating terminal coordination positions, converting the structure from a paddlewheel to a windmill geometry and generating [Fe2(μ-O 2CArTol)2(O2CArTol) 2(4-NCC5H4N)2(H2O) 2] (3). This process is temperature dependent in solution, rendering the system thermochromic. Quantitative treatment of the temperature-dependent spectroscopic changes over the temperature range from 188 to 298 K in CH 2Cl2 afforded thermodynamic parameters for the interconversion of 1 and 3. Stopped flow kinetic studies revealed that water reacts with the diiron(II) center ca. 1000 time faster than dioxygen and that the water-containing diiron(II) complex reacts with dioxygen ca. 10 times faster than anhydrous analogue 1. Addition of {H(OEt2)2} {BAr′4}, where BAr′4- is tetrakis(3,5- di(trifluoromethyl)phenyl)borate, to 1 converts it to [Fe2(μ- O2CArTol)3(4-NCC5H 4N)2]-(BAr′4) (5), which was also structurally characterized. Moessbauer spectroscopic investigations of solid samples of 1, 3, and 5, in conjunction with several literature values for high-spin iron(II) complexes in an oxygen-rich coordination environment, establish a correlation between isomer shift, coordination number, and N/O composition. The products of oxygenating 1 in CH2Cl2 were identified crystallographically to be [Fe2(μ-OH) 2(μ-O2CArTol)2(O 2CArTol)2(4-NCC5H4N) 2]·2(HO2CArTol) (6) and [Fe 6(μ-O)2(μ-OH)4(μ-O2CAr Tol)6(4-NCC5H4N)4Cl 2] (7).
- Yoon, Sungho,Lippard, Stephen J.
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- Direct NMR and luminescence observation of water exchange at cationic ytterbium and europium centres
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Cationic chiral Yb and Eu tetra-amide complexes, have been studied by VT NMR, luminescence and crystallography: the rate of dissociation of water is about 500 times faster at Yb than at the square antiprismatic Eu centre.
- Batsanov, Andrei S.,Beeby, Andrew,Bruce, James I.,Howard, Judith A. K.,Kenwright, Alan M.,Parker, David
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- The influence of ruthenium substitution in LaCoO3towards bi-functional electrocatalytic activity for rechargeable Zn-air batteries
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The rechargeable zinc-air battery is a clean technology for energy storage applications but is impeded by the slow kinetics of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) during its cycling. Herein, a series of lanthanum cobaltate based perovskites are synthesised with the B-site cation deficiencies in the structure occupied by Ru substitution: LaCo1-xRuxO3-δ (x = 0, 0.1, 0.2, 0.3 and 0.5). These compositions were designed to enhance the OER/ORR activities, which are two vital reactions for rechargeable Zn-air batteries. Powder X-ray diffraction analysis revealed that increasing the Ru substitution >20% (x > 0.2) alters the LaCoO3 crystal structure from rhombohedral to orthorhombic. Photoelectron spectroscopy studies reveal that the surface oxygen vacancies increased in the Ru substituted catalyst, a property important for enhancing the OER/ORR efficiency. The LaCo0.8Ru0.2O3-δ (LCRO82) catalyst exhibits promising electrocatalytic activities in both the OER and the ORR in 0.1 M KOH solution. Furthermore, the LCRO82 catalyst was evaluated as a cathode for rechargeable Zn-air battery applications displaying a high power density of 136 mW cm-2 at a current density of 175 mA cm-2 and a stable charge-discharge voltage gap of 0.78 V after 1440 cycles, with excellent cycling stability over 240 h.
- Caruso, Rachel A.,Chandrappa, Shivaraju Guddehalli,Chen, Dehong,Karkera, Guruprakash,Moni, Prabu,Prakash, Annigere S.,Prakasha, Kunkanadu R.
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- Accelerated diffusion of chain carriers and kinetic features of heterogeneous processes in gas-phase chain reactions
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In gas-phase combustion processes, the regeneration of free atoms and radicals in chain propagation reactions enhances the diffusion flux of these species from the flame zone. In flame propagation in tubular reactors and in filtration combustion, this eff
- Azatyan,Piloyan,Baimuratova,Masalova
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- Electroreduction of O2 to water on the wired laccase cathode
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Oxygen was electrocatalytically reduced to water at a current density of 5 mA/cm2 and at +0.7 V (NHE) in pH 5 citrate buffer at 37.5 ?°C. The electrocatalyst was a composite of laccase cross-linked with a redox polymer on a hydrophilic cloth of 10 ??m diameter carbon fibers. The redox polymer, PVI-Os(tpy)(dme-bpy)2+/3+, [poly-N-vinyl imidazole with 1/5th of the imidazoles complexed with [Os(tpy)(dme-bpy)]2+/3+ (tpy=terpyridine; dme-bpy= 4,4a?2-dimethyl-2,2a?2-bipyridine)], electrically connected ( wired ) the laccase reaction centers to the fibers.
- Barton, Scott Calabrese,Kim, Hyug-Han,Binyamin, Gary,Zhang, Yongchao,Heller, Adam
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- Oxygen Reduction Catalysis at a Dicobalt Center: The Relationship of Faradaic Efficiency to Overpotential
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The selective four electron, four proton, electrochemical reduction of O2 to H2O in the presence of a strong acid (TFA) is catalyzed at a dicobalt center. The faradaic efficiency of the oxygen reduction reaction (ORR) is furnished from a systematic electrochemical study by using rotating ring disk electrode (RRDE) methods over a wide potential range. We derive a thermodynamic cycle that gives access to the standard potential of O2 reduction to H2O in organic solvents, taking into account the presence of an exogenous proton donor. The difference in ORR selectivity for H2O vs H2O2 depends on the thermodynamic standard potential as dictated by the pKa of the proton donor. The model is general and rationalizes the faradaic efficiencies reported for many ORR catalytic systems.
- Passard, Guillaume,Ullman, Andrew M.,Brodsky, Casey N.,Nocera, Daniel G.
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- Functional Species Encapsulated in Nitrogen-Doped Porous Carbon as a Highly Efficient Catalyst for the Oxygen Reduction Reaction
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The scarcity, high cost, and poor stability of precious metal-based electrocatalysts have stimulated the development of novel non-precious metal catalysts for the oxygen reduction reaction (ORR) for use in fuel cells and metal–air batteries. Here, we fabricated in situ a hybrid material (Co-W-C/N) with functional species (tungsten carbide and cobalt nanoparticles) encapsulated in an N-doped porous carbon framework, through a facile multi-constituent co-assembly method combined with subsequent annealing treatment. The unique structure favors the anchoring active nanoparticles and facilitates mass transfer steps. The homogenously distributed carbide nanoparticles and adjacent Co-N-C sites lead to the electrocatalytic synergism for the ORR. The existence of Co and W can promote the graphitization of the carbon matrix. Benefiting from its structural and material superiority, the Co-W-C/N electrocatalyst exhibits excellent electrocatalytic activity (with a half-wave potential of 0.774 V vs. reversible hydrogen electrode (RHE)), high stability (96.3 % of the initial current remaining after 9000 s of continuous operation), and good immunity against methanol in alkaline media.
- Song, Li,Wang, Tao,Ma, Yiou,Xue, Hairong,Guo, Hu,Fan, Xiaoli,Xia, Wei,Gong, Hao,He, Jianping
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- Tannic acid decorated AuPd lavender-like nanochains for enhanced oxygen reduction electrocatalysis
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Benefiting from the interaction of inorganic and organic building blocks, the design of metal-organic nanohybrids is of great significance for the oxygen reduction reaction (ORR). Herein, a universal strategy is presented to controllably synthesize tannic acid (TA) functionalized AuPd lavender-like nanochains (AuPd@TA LCs) by a chemical reduction method at low temperature. Due to the unique structural characteristics and polyphenolic modification, the AuPd@TA LCs show superior ORR performance in an alkaline electrolyte. Moreover, the surface decorated TA polymers can act as a molecular screen window to prevent methanol molecules from accessing the active site of the catalyst, thus resulting in high methanol tolerance and catalytic stability. The presented molecular screen window strategy is highly valuable for designing ORR electrocatalysts with high methanol tolerance.
- Jiao, Shiqian,Li, Xiaonian,Liu, Songliang,Wang, Hongjing,Wang, Liang,Wang, Ziqiang,Xu, You,Yin, Shuli,Zhang, Hugang
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- Nitrogen-doped graphene supported cobalt oxide nanocomposite as high performance electrocatalyst for oxygen reduction reaction
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Nitrogen doped reduced graphene oxide-supported cobalt oxide catalyst has been synthesized by a simple one step chemical reduction method (denoted as NrGO-Co3O4) for electrocatalytic oxygen reduction reaction (ORR). This material has been characterized by various instrumental methods. The morphological analysis shows the Co3O4 nanocomposites are well set on to the reduced graphene oxide with better dispersion. The X-ray photoelectron spectroscopy (XPS) shows electrochemical reduction has been done successfully with the increasing C/O ratio. Also, the Raman data reveals that the Co is presents with the oxidized form. The electrocatalytic activities have been verified using cyclic voltammetry (CV) and hydrodynamic voltammetry techniques in 0.1 M KOH electrolyte. The as prepared catalyst has shown more positively shifted onset and half wave potential (-0.091 V and -0.276 vs. Ag/AgCl) and high cathodic current density 2.57 mA cm-2 and high methanol, ethanol crossover tolerance than Pt/C. It is the introduction of strongly bonded cobalt nanocomposite into the network of NrGO that modulate the electronic properties of the NrGO-Co3O4, resulting in the superb electrocatalytic performance. The reaction kinetics have confirmed that the ORR at NrGO-Co3O4 catalyst follows a four electron transfer reaction process.
- Yasmin, Sabina,Ahmed, Mohammad Shamsuddin,Jeon, Seungwon
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- Fe ultra-small particles anchored on carbon aerogels to enhance the oxygen reduction reaction in Zn-air batteries
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In this work, ultra-small Fe particles (Fe-UPs) anchored on carbon aerogel (CA) (Fe-UP/CA catalysts) are successfully prepared by the optimal pyrolysis of hollow composite particles of zeolitic imidazolate framework-8 (ZIF) coated with coordination complexes of tannic acid (TA) and Fe precursors. Within these Fe-UPs, each Fe-N4moiety is separated by one O atom while each Fe atom is coordinated with four N atoms and one O atom. The as-prepared Fe-UPs composed of the Fe-N4-O-Fe-N4moiety (FeFe-O-Fe-UPs) are proposed as a new type of active species for the first time, to the best of our knowledge. Moreover, different types of active species (such as Fe single atoms, FeFe-O-Fe-UPs, and Fe nanoparticles) in the CA can be controlled by rationally adjusting the Fe-to-TA molar ratios. More importantly, FeFe-O-Fe-UPs in Fe-UP/CA catalysts are realized at an Fe-to-TA molar ratio of 2.2. With the merits of both Fe-single atom and traditional Fe-NPs, the as-prepared FeFe-O-Fe-UP/CA catalysts are able to regulate properly the adsorption of reactants and the desorption of intermediates and products due to their increasing size and the presence of the multi-metal-atom structure. Accordingly, the as-prepared FeFe-O-Fe-UP/CA catalysts towards the oxygen reduction reaction (ORR) exhibit a higher half-wave potential (0.93 Vvs.0.89 V of Pt/C), a higher onset potential (1.08 Vvs.1.0 V of Pt/C), a higher kinetic current density (14.2 mA cm?2at 0.9 V) and better long-term stability in alkaline media. Additionally, Zn-air batteries assembled with such electrocatalysts also exhibit a higher power density of 140.1 mW cm?2and a larger specific capacity of 781.7 mA h g?1, which are better than those of the state-of-the-art the commercial Pt/C catalyst.
- Shi, Jinjin,Shu, Xinxin,Xiang, Chensheng,Li, Hong,Li, Yang,Du, Wei,An, Pengfei,Tian, He,Zhang, Jintao,Xia, Haibing
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- Four-electron reduction of dioxygen catalyzed by a decavanadium complex
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The electroreduction of O2 in acidic aqueous solutions at an electrode modified with a decavanadium cluster [(V=O)10(μ2-O)9(μ3-O) 3(C5H7O2)6] (1) revealed that it produces H2O with four electrons per O2 molecule near 0.5 V versus SCE. The usefulness of the complex as a reduction catalyst of O2 with a high selectivity was demonstrated.
- Dewi, Eniya Listiani,Oyaizu, Kenichi,Tsuchida, Eishun
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- Synergetic Metals on Carbocatalyst Shungite
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The naturally occurring Palaeoproterozoic carbon mineral shungite is a complex raw carbon microporous matrix, loaded with a wide range of elements. Shungite exhibits a disordered and amorphous structure with highly irregular building blocks. Shungite incorporates metals in its structure; typically catalytic elements such Fe and Ni are present, as well as the toxic elements Pb and As at mg g?1 levels. We show here that incorporation of the metals in the carbon matrix of shungite leads into synergistic catalytic effect. We investigate the application of shungite in energy related electrochemical catalytic reactions, such as the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR). All elements have a synergetic effect, thus contributing for shungite′s interesting catalytic performance towards a different range of electrochemical reactions, outperforming other tested carbon allotropes, such as carbon black, metal loaded carbon nanotubes, fullerene, and glassy carbon. These findings have profound impact on the application of the natural carbon materials for catalysis.
- Gusm?o, Rui,Sofer, Zdeněk,Bou?a, Daniel,Pumera, Martin
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- Facile synthesis of well dispersed spinel cobalt manganese oxides microsphere as efficient bi-functional electrocatalysts for oxygen reduction reaction and oxygen evolution reaction
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Developing catalysts with high bi-functional electrocatalytic activity for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is essential for the fuel cells and metal-air batteries because of the sluggish kinetics of oxygen electrochemical reaction. Herein, we prepared a porous and well dispersed spinel MnCo2O4 (MCO) catalyst through a facile solvothermal method followed by a calcination process. CH3COONH4 used in solvothermal process played an important role in control of the size and morphology of MCO. The as-prepared MCO submicrospheres feature a porous structure and a high specific surface area. Tested by the rotating ring disk electrode (RRDE) technique, the sample MCO-10 and MCO-5 shows best catalytic towards ORR and OER, respectively. In particular, MCO-10 exhibits a high diffusion limiting current density (5 mA cm?2) and a better stability comparable to commercial Pt/C (20 wt% Pt on carbon) catalyst.
- Yang, Shuting,Wang, Zhichao,Cao, Zhaoxia,Mao, Xinxin,Shi, Mengjiao,Li, Yanlei,Zhang, Ruirui,Yin, Yanhong
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- Designed nanostructured Pt film for electrocatalytic activities by underpotential deposition combined chemical replacement techniques
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Multiple-deposited Pt overlayer modified Pt nanoparticle (MD-Pt overlayer/PtNPs) films were deliberately constructed on glassy carbon electrodes through alternately multiple underpotential deposition (UPD) of Ag followed redox replacement reaction by Pt (II) cations. The linear and regular growth of the films characterized by cyclic voltammetry was observed. Atomic force spectroscopy (AFM) provides the surface morphology of the nanostructured Pt films. Rotating disk electrode (RDE) voltammetry and rotating ring-disk electrode (RRDE) voltammetry demonstrate that the MD-Pt overlayer/PtNPs films can catalyze an almost four-electron reduction of O2 to H 2O in air-saturated 0.1 M H2SO4. Thus-prepared Pt films behave as novel nanostructured electrocatalysts for dioxygen reduction and hydrogen evolution reaction (HER) with enhanced electrocatalytic activities, in terms of both reduction peak potential and peak current, when compared to that of the bulk polycrystalline Pt electrode. Additionally, it is noted that after multiple replacement cycles, the electrocatalytic activities improved remarkably, although the increased amount of Pt is very low in comparison to that of pre-modified PtNPs due to the intrinsic feature of the UPD-redox replacement technique. In other words, the electrocatalytic activities could be improved markedly without using very much Pt by the technique of tailoring the catalytic surface. These features may provide an interesting way to produce Pt catalysts with a reliable catalytic performance as well as a reduction in cost. ? 2005 American Chemical Society.
- Huang, Minghua,Jin, Yongdong,Jiang, Heqing,Sun, Xuping,Chen, Hongjun,Liu, Baifeng,Wang, Erkang,Dong, Shaojun
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- Rock-Salt-Type MnCo2O3/C as Efficient Oxygen Reduction Electrocatalysts for Alkaline Fuel Cells
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The search for nonprecious metal-based electrocatalysts with high activity and long durability for the oxygen reduction reaction (ORR) has been long pursued by the renewable energy material community. Here, we designed a new Mn-Co bimetallic oxide MnCo2O3/C with the rock-salt-type structure, derived from a spinel-type precursor MnCo2O4/C under mild reduction using NH3 at 300 °C. In-depth electron microscopic and spectroscopic investigations suggest that MnCo2O3/C predominantly has Mn(II) and Co(II) and can be written as MnO(CoO)2/C. Charge transfer between Mn and Co was probed by electron energy-loss near-edge structure (ELNES) analysis. MnCo2O3/C has a Co-rich core and a thin 1-3 nm Mn shell with a mesoporous morphology. MnCo2O3/C achieved a high ORR activity with a half-wave potential of 0.86 V in 1 M KOH, which was ascribed to the microstructure and the synergistic effects between Mn and Co, serving as co-active sites for the ORR.
- Yang, Yao,Zeng, Rui,Xiong, Yin,Disalvo, Francis J.,Abru?a, Héctor D.
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- Facile preparation of porous hollow CoxMn3-xO4 normal-reverse coexisted spinel for toluene oxidation
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A facile method for the preparation of porous hollow CoxMn3-xO4 normal-reverse coexisted spinel is developed. The CoxMn3-xO4 catalysts with different morphologies can be prepared via adjusting the Co/Mn molar ratio using mixed carbonates as the precursors. The as-prepared CoxMn3-xO4 catalysts exhibit excellent catalytic activities for toluene oxidation due to the synergistic effect of abundant oxygen vacancies and the optimal molar ratio of Co3+/Mn2+–Co2+/Mn3+ coupled redox ion pairs. The porous hollow hierarchical structure of CoxMn3-xO4 is conducive to maintain good long-term structural stability and activity stabilities. The catalytic activity of CoxMn3-xO4 shows no significant loss during the 100 h of on-stream stability test and the 5 vol% water vapor inhibition test, showing excellent anti-sintering ability, high-efficiency mass transfer ability and anti-moisture ability.
- Gu, Wenxiu,Li, Chenqi,Qiu, Jianhao,Yao, Jianfeng
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- Formation of Catalytically Active Nanoparticles under Thermolysis of Silver Chloroplatinate(II) and Chloroplatinate(IV)
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The thermal behaviour of Ag2 [PtCl4 ] and Ag2 [PtCl6 ] complex salts in inert and reducing atmospheres has been studied. The thermolysis of compounds in a helium atmosphere is shown to occur in two stages. At the first stage, the complexes decompose in the temperature range of 350–500?C with the formation of platinum and silver chloride and the release of chlorine gas. At the second stage, silver chloride is sublimated in the temperature range of 700–900?C, while metallic platinum remains in the solid phase. In contrast to the thermolysis of Ag2 [PtCl6 ], the thermal decomposition of Ag2 [PtCl4 ] at 350?C is accompanied by significant heat release, which is associated with disproportionation of the initial salt to Ag2 [PtCl6 ], silver chloride, and platinum metal. It is confirmed by DSC measurements, DFT calculations of a suggested reaction, and XRD. The thermolysis of Ag2 [PtCl4 ] and Ag2 [PtCl6 ] compounds is shown to occur in a hydrogen atmosphere in two poorly separable steps. The compounds are decomposed within 170–350?C, and silver and platinum are reduced to a metallic state, while a metastable single-phase solid solution of Ag0.67Pt0.33 is formed. The catalytic activity of the resulting nanoalloy Ag0.67Pt0.33 is studied in the reaction of CO total (TOX) and preferential (PROX) oxidation. Ag0.67Pt0.33 enhanced Pt nano-powder activity in CO TOX, but was not selective in CO PROX.
- Filatov, Evgeny,Smirnov, Pavel,Potemkin, Dmitry,Pishchur, Denis,Kryuchkova, Natalya,Plyusnin, Pavel,Korenev, Sergey
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- Investigating the effects of various synthesis routes on morphological, optical, photoelectrochemical and photocatalytic properties of single-phase perovskite BiFeO3
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Herein, various BiFeO3 morphologies, including sheet-like, coral-like and rod-like structures, were synthesized via co-precipitation (CP), hydrothermal (HT), and sol-gel (SG) synthesis routes, respectively. The as-synthesized samples were characterized by physicochemical techniques to investigate their crystal structure, optical and photoelectrochemical properties. The SG-BiFeO3 sample exhibited remarkable direct sunlight photocatalytic degradation of phenol (98.95%), superior to those of the HT-BiFeO3 (77.4%) and CP-BiFeO3 (66.9%) in 120 min. The SG-BiFeO3 sample was the most effective among all due to the lower energy band gap value and highest separation of photogenerated charge carriers, which was validated by the UV–vis absorption, photoluminescence (PL) and photoelectrochemical measurements. The recycling and ferric (Fe3+) ion leakage test suggested that the SG-BiFeO3 sample was highly stable for up to six consecutive runs. The radical scavenger studies implied that the photogenerated hole (h+), hydrogen peroxide (H2O2) and hydroxyl radicles (?OH) were the dominant reactive species. Finally, based on these, a possible photocatalytic mechanism for phenol degradation over SG-BiFeO3 sample was also postulated.
- Chang Chien, Shui-Wen,Jaffari, Zeeshan Haider,Kumar, Dileep,Lam, Sze-Mun,Ng, Ding-Quan
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- Syntheses of two copper metal-organic frameworks with tri(1,2,4-triazole) and biscarboxylate and graphene oxide composites for decomposition of dye by visible-light driven and ultrasonic assisted
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Two crystalline and nano-sized new Cu(II) MOFs {[Cu(ttpa)(1,3-bdc)(H2O)]·CH3OH}n (Cu(ttpa)-1) and {[Cu(ttpa)(mip)(H2O)]?2H2O} (Cu(ttpa)-2) were prepared and characterized (ttpa ?= ?tris(4-(1,2,4-triaz
- Hu, Chuan-Jiang,Li, Bao-Long,Li, Hai-Yan,Li, Le-Yan,Ma, Li-Xiao,Zha, Miao,Zhou, Wen-Jing
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- Hydrothermally grown α-MoO3 microfibers for photocatalytic degradation of methylene blue dye
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Adsorption and photodegradation efficiency of α-MoO3 microfibers towards methylene blue (MB) dye in the aqueous solution were reported. To obtain high-quality α-MoO3 microfibers, an aqueous solution of (NH4)6Mo7O24·4H2O and citric acid was hydrothermally treated (180 °C, 12 h) in the presence of HNO3. The possible growth mechanism of microfibers in the hydrothermal reaction is explained. XRD and TEM studies provide shreds of evidence that microfibers have crystallized in a pure orthorhombic phase and grown up in the direction of [0 0 1]. The structural bonding between molybdenum and oxygen constituent elements of microfibers was further confirmed by XPS, FTIR, and Raman techniques. The estimated optical band gap of α-MoO3 microfibers (Eg = 2.68 eV) lies in the visible region, making them suitable for visible light photocatalytic application. MB adsorption and degradation capacity of microfibers were performed in the dark and light, respectively. The photocatalytic properties revealed that 90 % MB dye was degraded within 120 min illumination. Moreover, the good photocatalytic recycling capability of α-MoO3 microfibers makes them a promising photocatalyst to eliminate organic pollutants from water.
- Dewangan, Khemchand,Singh, Dadan,Satpute, Nilesh,Singh, Ritika,Jaiswal, Adhish,Shrivas, Kamlesh,Bahadur, Indra
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- Fabrication of TlSnI3/C3N4 nanocomposites for enhanced photodegradation of toxic contaminants below visible light and investigation of kinetic and mechanism of photocatalytic reaction
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The use of sufficient solar irradiation for the semiconductor photodegradation of organic pollutants is an excellent technique to tackle worldwide water contamination. Photocatalysis is an eco-friendly method that is familiar for the breakdown of toxic pollutants in sewage. Many semiconductor heterojunctions have been widely employed to intensify photocatalytic efficiency compared to single semiconductors. Polymeric semiconductors such as graphitic carbon nitride (g-C3N4) have been considered inspirational applicants due to their easily adjustable electronic structure and adaptable optical absorption properties. Disadvantages of the current photocatalytic method, which limit their uses, include the rapid recombination, low emigration ability of the photo-generated electron-hole, and low use of visible radiation. The current study designates the preparation of novel TlSnI3/g-C3N4 nanocomposites by ultrasound-assisted coprecipitation technique. The bandgap was estimated at 2.7 eV for pristine g-C3N4. The bandgap of nanocomposite was decreased to 2.5 eV by enhancing TlSnI3 content due to the narrow bandgap of TlSnI3 (2.3 eV). This nanocomposite possesses a high ability to decompose organic dyes due to its relevant bandgap being a prominent catalyst for water treatment. The photocatalytic ability of TlSnI3/C3N4 was examined over the removal of Methylene Blue (MB), Malachite Green (MG), and Rhodamine B (RhB) under visible light. The as-synthesized TlSnI3/C3N4 nanocomposites exposed better photocatalytic performance than the pure TlSnI3 and C3N4.
- Ghanbari, Mojgan,Salavati-Niasari, Masoud,Yousefzadeh, Fatemeh,Yousif, Qahtan A.
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- Novel LaCr substituted Mhexaferrite photocatalyst for decontamination of organic pollutants by peroxymonosulfate activation
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Element engineering in Mhexaferrite system has been demonstrated as an effective technique to boost catalytic activation of peroxymonosulfate (PMS). This study aimed at catalytic activation of PMS under LED irradiation using a novel LaCr substituted Mhexaferrite photocatalyst (BLCF-NPs) for degradation of organic pollutants in water systems. The chemical and physical characteristics of BLCF catalysts, the effects of BLCF's heterogeneous catalyst, PMS, pH, and pollutant concentration on degradation performance, reusability and stability of BLCF-NPs were systematically investigated. Importantly, under LED illumination, the sample C3 activated PMS to degrade MO more efficiently (99.99% within 80 min) and stably than reported Mhexaferrite NPs, with a first-order-kinetic rate constant (k = 11.41 10?2 min?1). The PMS/LED/BLCF-NPs system was improved effectively in a wide pH range from 3 to 10. Radical quenching experiments demonstrated that SO4[rad]? played a dominant role in MO degradation. This research paves the way for developing high-efficiency catalysts, as well as making Mhexaferrites viable options for pollutants removal.
- Ali, Jazib,Ashraf, Ghulam Abbas,Chen, Jing,Guo, Hai,Hassan, Muhammad,Li, Lianjie,Rasool, Raqiqa Tur,Zhang, Lanting
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- CeO2 Facet-Dependent Surface Reactive Intermediates and Activity during Ketonization of Propionic Acid
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CeO2 rods, octahedrons, and cubes exposing well-defined (110), (111), and (100) surfaces, respectively, were synthesized and investigated for the catalytic ketonization of propionic acid. The intrinsic ketonization rates at 350 °C on the rods, octahedrons, and cubes are 54.3, 40.4, and 25.1 mmol·m-2·h-1, respectively, indicating that the (110) facet is the most active surface for ketonization. The reaction was tracked by both in situ infrared and mass spectroscopies under transient conditions, and the results showed that monodentate propionate, a minority surface species, is responsible for the formation of 3-pentanone. In contrast, bidentate propionate, a dominant species on all three surfaces, appears to a spectator for ketonization. Moreover, the ketonization activity can be correlated with relative concentration of monodentate propionate. A density functional theory study showed that the relative concentration of monodentate propionate (or the adsorption energy difference between monodentate and bidentate configurations) at high coverages is strongly dependent on the surface geometry. The stability of monodentate propionate on the (110) surface exposing both the O and Ce sites in the outermost layer with the well-separated Ce sites exhibits little dependence on the propionate coverage. In contrast, strong steric hindrance due to the top layer O atom and the closely packed Ce atoms in (111) destabilizes monodentate propionate significantly at high coverages. This study demonstrates that the surface geometrical structure of CeO2 can determine the abundance of the active monodentate propionate, which, in turn, will determine the catalytic activity of CeO2 for ketonization.
- Guo, Yonghua,Qin, Yuyao,Liu, Huixian,Wang, Hua,Han, Jinyu,Zhu, Xinli,Ge, Qingfeng
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p. 2998 - 3012
(2022/03/03)
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- Acid treated Sr-substituted LaCoO3 perovskite for toluene oxidation
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For A-site substituted AA'BO3 perovskite, the doped A' element is easy to migrate to the surface and form segregation of A'Ox, which could partially block active B sites and thus reduce catalytic activity. In the present work a La0.8Sr0.2CoO3-δ perovskite-type solid was first prepared and then treated with acetic acid to eliminate SrO segregation on its surface. The obtained catalyst (LCSO-a) possessed a significantly enhanced catalytic activity for toluene oxidation in the 220–260 °C range. This promotion effect might be attributed to the increase in the concentration of active surface oxygen species and the reduction in their binding strength. In addition, the LCSO-a catalyst showed very good stability and water resistance.
- Wei, Yonghui,Ni, Lei,Li, Minxia,Zhao, Jili
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- Removal of volatile organic compounds from air using supported ionic liquid membrane containing ultraviolet-visible light-driven Nd-TiO2 nanoparticles
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Volatile organic compounds (VOCs) with toxicity properties discharged from industrial emissions and combustion engines threaten human health and cause environmental problems. Therefore, it is important to develop technologies to remove VOCs from air. In this study, the performance of Nd (neodymium) -TiO2 nanoparticles embedded in a supported ionic liquid membrane (SILM) for removal of VOCs from air was investigated. Aiming at functionalizing the ionic liquid membrane with photocatalytic capability, we developed a facile and effective approach for the removal of VOCs by coupling highly efficient photocatalysts with the SILM. Nd-TiO2 nanoparticles, which are ultraviolet-visible (UV–Vis) light-driven photocatalysts, were prepared by sol-gel and immersed in the SILM for use as a photocatalytic membrane-based reactor. The gaseous VOCs tested were toluene, acetone, chloroform, benzene, and xylene. We confirmed that at a loading of 50 wt% Nd-TiO2 nanoparticles (1 wt% Nd content) and 1-hexyl-3-methylimidazolium hexafluorophosphate ([HMIm]PF6) as SILM ([HMIm]PF6/Nd-TiO2 SILM), the as-prepared photocatalytic membrane-based reactor exhibited higher removal efficiency of VOCs from air (60~80% removal after 10 h) under UV–Vis light illumination than individual SILM or photocatalytic systems. Effluent gas analysis revealed that 25–55% of VOCs was decomposed and mineralized in the photocatalytic membrane reactor, which exhibited higher VOCs removal efficiency than membrane separation. These results indicate that the photocatalytic membrane-based reactor containing Nd-TiO2 nanoparticles and SILM designed in this study is highly active and stable. This study on [HMIm]PF6/Nd-TiO2 SILM was initiated to couple membrane separation with photocatalytic degradation of gaseous VOCs and can serve as a promising way for eliminating harmful VOCs with low concentration from air.
- Li, Jinlong,Li, Boxin,Sui, Guozhe,Du, Lijuan,Zhuang, Yan,Zhang, Yulin,Zou, Yuanfang
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- Pd-AlOOH/Al Honeycomb Monolith Catalysts Obtained from Pd(II) Complex Precursor with Different Ligands by a Facile One-Step Method
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The adopted ligand type of a palladium precursor has a great influence on the microstructure, morphology and catalytic performance of obtained Pd-based monolith catalysts by a onestep method with redox reactions of two galvanic cells. In the sequence of ligand type NH3, en, Gly and EDTA, the obtained Pd-AlOOH/Al-x (x = NH3, en, Gly, EDTA) monolith catalysts showed gradually increasing specific surface areas, micro/mesopore volumes and catalytic activities in toluene total oxidation reaction, because more AlOOH nanosheets and Pd nanoparticles were generated to form a more uniform and welldispersed three-dimensional-network structure film on the Al substrate surface.
- Dai, Zhentan,Dou, Yong Shen,Li, Yong Feng,Liu, Fang Fang,Liu, Sanmao,Wang, Hongmian,Wu, Jiahao
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p. 1631 - 1636
(2021/07/02)
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- Enhancement of Mass Transport for Oxygen Reduction Reaction Using Petal-Like Porous Fe-NC Nanosheet
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Nitrogen-coordinated single-atom catalysts (SACs) have emerged as a new frontier for accelerating oxygen reduction reaction (ORR) owing to the optimal atom efficiency and fascinating properties. However, augmenting the full exposure of active sites is a crucial challenge in terms of simultaneously pursuing high metal loading of SACs. Here, petal-like porous carbon nanosheets with densely accessible Fe-N4 moieties (FeNC-D) are constructed by combining the space-confinement of silica and the coordination of diethylenetriaminepentaacetic acid. The resulted FeNC-D catalyst possesses an enhanced mesoporosity and a balanced hydrophobicity/hydrophilicity, which can facilitate mass transport and advance the exposure of inaccessible Fe-N4 sites, resulting in efficient utilization of active sites. By virtue of the petal-like porous architecture with maximized active site density, FeNC-D demonstrates superior ORR performance in a broad pH range. Remarkably, when utilized as the air cathode in Zn-air battery (ZAB) and microbial fuel cell (MFC), the FeNC-D-based device displays a large power density (356 mW cm?2 for ZAB and 1041.3 mW m?2 for MFC) and possesses remarkable stability, substantially outperforming the commercial Pt/C catalyst.
- Shao, Chunfeng,Zhuang, Shiguang,Zhang, Haocheng,Jiang, Qike,Xu, Xiaoyan,Ye, Jianshan,Li, Baitao,Wang, Xiujun
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- A template-directed synthesis of metal-organic framework (MOF-74) ultrathin nanosheets for oxygen reduction electrocatalysis
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Metal-organic frameworks (MOFs) have received wide attention for their promising applications in numerous fields due to their tailorable structure, metal centers and porosity. However, the low mass permeability, poor conductivity and blockage of active metal centers severely restrict the utilization of MOF systems in electrocatalysis. Two-dimensionalization can endow MOF materials extra unsaturated metal centers and enhanced electron-transfer ability, and could be an effective strategy to achieve high-performance MOF-based electrocatalysts. Herein, Ni-MOF-74 nanosheets are synthesized using layered double hydroxide (LDH) as a template to directly grow ultrathin structures. Benefiting from the two-dimensional structure, Ni-MOF-74 nanosheets with carbon substrate exhibit an enhanced ORR electrocatalytic property with positive half-wave potential (+0.83 Vvs.RHE), a large current density (3.9 mA cm?2), four-electron selectivity and a promising long-term durability.
- Fan, Rui,Kang, Ning,Li, Yuzhen,Gao, Lizhen
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p. 9353 - 9360
(2021/03/16)
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- Enzyme-Inspired Iron Porphyrins for Improved Electrocatalytic Oxygen Reduction and Evolution Reactions
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Nature uses Fe porphyrin sites for the oxygen reduction reaction (ORR). Synthetic Fe porphyrins have been extensively studied as ORR catalysts, but activity improvement is required. On the other hand, Fe porphyrins have been rarely shown to be efficient for the oxygen evolution reaction (OER). We herein report an enzyme-inspired Fe porphyrin 1 as an efficient catalyst for both ORR and OER. Complex 1, which bears a tethered imidazole for Fe binding, beats imidazole-free analogue 2, with an anodic shift of ORR half-wave potential by 160 mV and a decrease of OER overpotential by 150 mV to get the benchmark current density at 10 mA cm?2. Theoretical studies suggested that hydroxide attack to a formal FeV=O form the O?O bond. The axial imidazole can prevent the formation of trans HO-FeV=O, which is less effective to form O?O bond with hydroxide. As a practical demonstration, we assembled rechargeable Zn-air battery with 1, which shows equal performance to that with Pt/Ir-based materials.
- Xie, Lisi,Zhang, Xue-Peng,Zhao, Bin,Li, Ping,Qi, Jing,Guo, Xinai,Wang, Bin,Lei, Haitao,Zhang, Wei,Apfel, Ulf-Peter,Cao, Rui
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p. 7576 - 7581
(2021/03/03)
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- Hemin-based conjugated effect synthesis of Fe-N/CNT catalysts for enhanced oxygen reduction
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Metal-nitrogen codoped cathode catalysts, such as M-N-C (M = Fe, Co, Mn,etc.) are considered most promising non-platinum group ORR catalysts, and have received widespread attention. However, the problem involving the high oxygen reduction performance and stability of the catalyst remains to be solved. The unique olefin oxidation polymerization and π-π stacking effect induced hemin to be evenly coated on polypyrrole nanotubes (PPy). Subsequent carbonization produces the Fe-NCNT catalyst with a monodispersed, uniform diameter and large inner cavity. The PPy not only serves as a template for the formation of the hemin polymer, but also provides C, N source to further improve the catalytic activity. The material exhibits excellent ORR activity attributed to the promotion of the π-π stacking effect between hemin and PPy, and the abundant active site of Fe-NXderived from hemin. Results show that the Fe-NCNT-800 catalyst with high performance exhibits a maximum onset potential (Eonset= 0.93 V) and half-wave potential (E1/2= 0.79 V). The RRDE measures points out the complete four-electron transfer pathway of the Fe-NCNT-800 catalyst. The Fe-NCNT catalysts have higher durability of a negligible negative shift (10 mV) ofE1/2after a 5000 cycle ADT, and a remarkable methanol tolerance capability that is superior to that of the Pt/C catalyst. The synergy between the PPy-derived N-doped carbon nanotubes and Fe-NXfacilitates oxygen reduction and electron conduction.
- Lu, Yue,Zhang, Han,Liu, Shaojun,Li, Chenglong,Li, Lixiang,An, Baigang,Sun, Chengguo
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supporting information
p. 6940 - 6949
(2021/04/22)
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- Green synthesis of nitrogen-doped multiporous carbons for oxygen reduction reaction using water-caltrop shells and eggshell waste
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A green synthesis method is proposed for the preparation of nitrogen-doped multiporous carbons (denoted as N-MPCs) from water-caltrop shell (WCS) using eggshell waste as both a nitrogen-dopant and an activating agent. It is shown that the surface area, porosity, yield and nitrogen content of the as-prepared N-MPCs can be easily controlled by adjusting the activation temperature. Moreover, in oxygen reduction reaction (ORR) tests performed in O2-saturated 0.1 M KOH(aq) electrolyte containing 1.0 M methanol, the N-MPC catalysts show a high ORR stability and good resistance to methanol corrosion. In addition, as a cathode material in Al-air battery tests, the N-MPCs achieve a power density of 16 mW g-1 in a saturated NaCl(aq) electrolyte. Overall, the results show that the N-MPCs have a promising potential as a green and sustainable material for ORR catalysis applications.
- Hsu, Chun-Han,Pan, Zheng-Bang,Qu, Hau-Ting,Chen, Chuan-Ren,Lin, Hong-Ping,Sun, I-Wen,Huang, Ching-Ying,Li, Chun-Han
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p. 15738 - 15747
(2021/05/19)
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- Developing Iron-Nickel Bimetallic Oxides with Nanocage Structures As High-Performance Bifunctional Catalysts via the Ensemble Effect from Nitrogen Sources
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Metal-air batteries will serve as renewable and ecofriendly energy-storage systems in the future because of their high theoretical energy-density performance and unlimited resources, using oxygen as fuel materials compared with commercial lithium-ion batteries. However, the unsuitable inactive reactions at the air-electrode interface (the oxygen reduction reaction and the oxygen evolution reaction) in the metal-air battery are major challenges. In this study, we report nitrogen (N)-doped iron (Fe) and nickel (Ni) bimetallic catalysts with a hollow structure (Fe-Ni nanocage) as outstanding bifunctional catalysts, which have not been reported previously. The open structure in the catalysts simultaneously has an active inner cavity and an outer shell; catalysts have a high active surface area, resulting in remarkable electrochemical performance. Furthermore, the electron transfer phenomenon due to the ensemble effect generates a higher catalyst activation. Nitrogen has a higher electronegativity than the metal cations, so doped nitrogen sources draw the electron into iron and nickel cations, and the deprived oxidation state of the metal cations accelerates the electrocatalytic performance.
- Kang, Taeoh,Kim, Kwanwoo,Kim, Jooheon
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supporting information
p. 7490 - 7497
(2021/05/26)
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- Amplified Interfacial Effect in an Atomically Dispersed RuOx-on-Pd 2D Inverse Nanocatalyst for High-Performance Oxygen Reduction
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Atomically dispersed oxide-on-metal inverse nanocatalysts provide a blueprint to amplify the strong oxide–metal interactions for heterocatalysis but remain a grand challenge in fabrication. Here we report a 2D inverse nanocatalyst, RuOx-on-Pd nanosheets, by in situ creating atomically dispersed RuOx/Pd interfaces densely on ultrathin Pd nanosheets via a one-pot synthesis. The product displays unexpected performance toward the oxygen reduction reaction (ORR) in alkaline medium, which represents 8.0- and 22.4-fold enhancement in mass activity compared to the state-of-the-art Pt/C and Pd/C catalysts, respectively, showcasing an excellent Pt-alternative cathode electrocatalyst for fuel cells and metal–air batteries. Density functional theory calculations validate that the RuOx/Pd interface can accumulate partial charge from the 2D Pd host and subtly change the adsorption configuration of O2 to facilitate the O?O bond cleavage. Meanwhile, the d-band center of Pd nanosubstrates is effectively downshifted, realizing weakened oxygen binding strength.
- Liao, Xinyan,Liu, Kai,Lyu, Zixi,Qiu, Chunyu,Wang, Yucheng,Xie, Shuifen,Xie, Zhaoxiong,Yang, Weihua,Zhang, Xia-Guang
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supporting information
p. 16093 - 16100
(2021/06/14)
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- A hierarchical Co3O4/CoS microbox heterostructure as a highly efficient bifunctional electrocatalyst for rechargeable Zn-air batteries
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Herein, we report the synthesis of a strongly coupled Co3O4/CoS microbox heterostructure, prepared through an annealing treatment with the subsequent hydrothermal sulfidation of a Co-Co Prussian blue analog (PBA) precursor. The unique 3D hierarchical architecture and potential synergies of Co3O4 and CoS provide benefits to the Co3O4/CoS heterostructure for both oxygen reduction and evolution reactions (ORR and OER). It displays comparable ORR catalytic activity (half-wave potential of 0.820 V) to state-of-the-art Pt/C but better durability and methanol tolerance. The Co3O4/CoS electrocatalyst also shows high OER activity with a relatively low overpotential (349 mV at 10 mA cm-2) and small Tafel slope (66.6 mV dec-1), compared to those of commercial RuO2 (366 mV at 10 mA cm-2 and 86.3 mV dec-1, respectively), making it a potential bifunctional electrocatalyst for both the ORR and the OER. Moreover, a rechargeable Zn-air battery with a Co3O4/CoS cathode shows a higher cell voltage (1.51 V), higher power density (168 mW cm-2 at 269 mA cm-2), and better cycling stability (up to 150 cycles) than the same battery with the state-of-the-art Pt/C + RuO2 catalyst. This PBA-based material with a strongly coupled interface between Co3O4 and CoS offers insights into the development of low-cost and highly efficient electrocatalysts for diverse energy-related applications.
- Baeck, Sung-Hyeon,Ham, Hyung Chul,Kim, Sangjin,Lee, Eoyoon,Lim, Dongwook,Min, Kyeongseok,Shim, Sang Eun,Yoo, Geunsang
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supporting information
p. 17344 - 17352
(2021/08/24)
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- Simultaneously Engineering the Coordination Environment and Pore Architecture of Metal–Organic Framework-Derived Single-Atomic Iron Catalysts for Ultraefficient Oxygen Reduction
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Designing highly efficient and durable electrocatalysts that accelerate sluggish oxygen reduction reaction kinetics for fuel cells and metal–air batteries are highly desirable but challenging. Herein, a facile yet robust strategy is reported to rationally design single iron active centers synergized with local S atoms in metal–organic frameworks derived from hierarchically porous carbon nanorods (Fe/N,S-HC). The cooperative trithiocyanuric acid-based coating not only introduces S atoms that regulate the coordination environment of the active centers, but also facilitates the formation of a hierarchically porous structure. Benefiting from electronic modulation and architectural functionality, Fe/N,S-HC catalyst shows markedly enhanced ORR performance with a half-wave potential (E1/2) of 0.912?V and satisfactory long-term durability in alkaline medium, outperforming those of commercial Pt/C. Impressively, Fe/N,S-HC-based Zn–air battery also presents outstanding battery performance and long-term stability. Both electrochemical experimental and density functional theoretical (DFT) calculated results suggest that the FeN4 sites tailored with local S atoms are favorable for the adsorption/desorption of oxygen intermediate, resulting in lower activation energy barrier and ultraefficient oxygen reduction catalytic activity. This work provides an atomic-level combined with porous morphological-level insights into oxygen reduction catalytic property, promoting rational design and development of novel highly efficient single-atom catalysts for the renewable energy applications.
- Liu, Feng,Shi, Lei,Song, Shaofeng,Ge, Kai,Zhang, Xiaopeng,Guo, Yingchun,Liu, Dong
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- Preparation of a one-dimensional hierarchical MnO@CNT@Co-N/C ternary nanostructure as a high-performance bifunctional electrocatalyst for rechargeable Zn-air batteries
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Developing high-performance bifunctional electrocatalysts for both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is a significant challenge for the implementation of rechargeable Zn-air batteries. Herein, MnO2nanotubes (NTs) are prepared as both templates and oxidants to grow polypyrrole (PPy) nanotubes (NTs), on which a zeolite imidazole framework-67 (ZIF-67) is grown. Following that, a single calcination step transforms MnO2, PPy and ZIF-67 into MnO nanoparticles, carbon nanotubes (CNTs) and Co-N doped carbon materials (Co-N/C), respectively to form a one-dimensional (1D) hierarchical ternary nanocomposite. In this composite, the CNTs encapsulate the MnO particles to effectively prevent their further agglomeration. The separated MnO particles possess a mixed valence of Mn2+/4+inside the CNTs, which can greatly facilitate electrolyte diffusion and electron transfer during the redox reactions. Furthermore, the Co-N/C and micro-CNTs formed on the CNT provide multiple catalytic active sites (Co-Nx, Co-O, and C-N moieties). At the optimized calcination temperature of 700 °C, MnO@CNT@Co-N/C exhibits excellent ORR/OER catalytic performance with a ΔEvalue of 0.81 V while maintaining structural and compositional stability. Remarkably, the rechargeable Zn-air battery fabricated with MnO@CNT@Co-N/C as the air electrode catalyst displays a higher peak power density (200.8 mW cm?2) and improved cyclability (300 h) at 5 mA cm?2compared to a precious metal commercial catalyst, indicating the potential application of this composite in energy storage and conversion technology.
- Jiang, Renjun,Li, Fen,Liu, Xiaoqiang,O'Mullane, Anthony P.,Qin, Tengteng,Sun, Yuping,Yuan, Jiangfeng
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supporting information
p. 22533 - 22543
(2021/10/19)
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- Insights into the electronic structure of Fe penta-coordinated complexes. Spectroscopic examination and electrochemical analysis for the oxygen reduction and oxygen evolution reactions
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Fe phthalocyanine was coordinated to pyridine-modified carbon nanotubes and studied as a catalyst for the oxygen reduction (ORR) and oxygen evolution reactions (OER). X-ray photoelectron spectroscopy (XPS), M?ssbauer, and electron paramagnetic resonance spectroscopy (EPR) analysis supported that pyridine acts as an axial ligand to yield penta-coordinated catalytic active Fe sites. The impedance analyses show an increase in the double-layer capacitance (Cdl) value, corroborating the adsorption of the complexes to give FePc-Py-CNT. The evaluation of the electrocatalytic activity for the ORR was performed in both acid (0.1 M H2SO4) and basic (0.1 M KOH) media, while the evaluation of the OER activity was investigated only in alkaline medium. DFT studies revealed an increased length in the Fe-N binding of the pentacoordinate Fe-based site, leading to a decreased O2-Fe binding energy, explaining the higher ORR and OER activity of FePc-Py-CNT relative to FePc-CNT.
- Abarca, Gabriel,Aliaga, Carolina,Jaouen, Frédéric,Loyola, César Zú?iga,Orellana, Walter,Sougrati, Moulay Tahar,Tasca, Federico,Ureta-Za?artu, Soledad,Zagal, Jose H.
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supporting information
p. 23802 - 23816
(2021/11/12)
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- Uniformly dispersed platinum nanoparticles over nitrogen-doped reduced graphene oxide as an efficient electrocatalyst for the oxygen reduction reaction
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Oxygen reduction reaction (ORR) with efficient activity and stability is significant for fuel cells. Herein, platinum (Pt) nanoparticles dispersed on nitrogen-doped reduced graphene oxide (N-rGO) were prepared by a hydrothermal and carbonized approach for the electrocatalysis of ORR. Polyvinylpyrrolidone plays a significant role in the reduction and dispersion of platinum particles (about 2 nm). The obtained Pt-N-rGO hybrids exhibited superior activity with an electron transfer number of ~4.0, onset potential 0.90 eV of ORR, good stability and methanol tolerance in alkaline media. These results reveal the interactions between Pt-N-rGO and oxygen molecules, which may represent an oxygen modified growth in catalyst preparation. The excellent electrocatalysis may lead to the decreased consumption of expensive Pt and open up new opportunities for applications in lithium air batteries. This journal is
- Chen, Xiaohong,Liu, Xundao,Xue, Zhiyong,Zhang, Yongming,Zheng, Yafei
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p. 34125 - 34131
(2021/12/08)
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- Study on the Structure-Activity Relationship Between Single-Atom, Cluster and Nanoparticle Catalysts in a Hierarchical Structure for the Oxygen Reduction Reaction
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Literature reports have shown that in primary structures, single-atom catalysts exhibit better performance than cluster and nanoparticles due to their maximum atom utilization and the fine-tuning of the electronic structure of the active sites. Hierarchical structures have recently been extensively studied because of increased active sites and orderliness of channels significantly improves the catalytic performance compare to primary structures especially in nanoparticles, however, the different sized effect of catalysts research has not been reported. Herein, a unique hollow double-shell structure (a distinct cavity-containing) is used as a hierarchical model to study the possible difference between single atom, cluster, and nanoparticle and to establish the corresponding structure-activity relationship. Three Co catalysts are prepared: single atoms (Co-Catalyst-1), clusters (Co-Catalyst-2, 0.5–1?nm), and nanoparticles (Co-Catalyst-3, ≈5?nm) and their oxygen-reduction capacity is evaluated. The unique electronic interactions, the strong electron-withdrawing ability of N in Co–N4 (Co-Catalyst-1), attract electrons from the electrode to Co, specifically by expediting the generation and transformation of the rate-determining step intermediates *OOH. The variant spatial structure which is caused by Co atom aggregation, and led to surface area, pore size, and carbon disorder, is a distinct, therefore significant variation in mass and charge transport efficiency, and activities.
- Li, Fayan,Li, Lei,Li, Yafei,Li, Yanyan,Zhang, Xinyu,Zheng, Zhiping,Zhu, Xiaorong
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- High-Performance Zinc-Air Batteries Based on Bifunctional Hierarchically Porous Nitrogen-Doped Carbon
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Active and durable bifunctional electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) on the cathode are required for high-performance rechargeable metal-air batteries. Herein, the synthesis of hierarchically porous nitrogen-doped carbon (HPNC) with bifunctional oxygen electrocatalysis for Zn-air batteries is reported. The HPNC catalyst possesses a large surface area of 1459 m2 g?1 and exhibits superior electrocatalytic activity toward ORR and OER simultaneously with a low OER/ORR overpotential of 0.62?V, taking the difference between the potential at 10?mA cm?2 for OER and half-wave potential for ORR in 0.1 m KOH. Adopting HPNC as the air cathode, primary and rechargeable Zn-air batteries are fabricated. The primary batteries demonstrate a high open-circuit potential of 1.616?V, a specific capacity of 782.7 mAh gZn?1 and a superb peak power density of 201?mW cm?2. The rechargeable batteries can be cycled stably for over 360 cycles or 120 h at the current density of 5?mA cm?2. As elucidated by density functional theory, N-doping is preferred on defective sites with pentagon configuration and on the edge in the form of pyridinic-N-type. The high content of these two motifs in HPNC leads to the superior ORR and OER activities, respectively.
- Chen, Zheng,Gui, Fukang,Jin, Qiu,Li, Bing,Ming, Pingwen,Siahrostami, Samira,Tan, Qinggang,Xiao, Dongdong,Xiao, Qiangfeng,Xu, Xiaobin,Yang, Daijun,Zhang, Cunman
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- Facile fabrication of Bi2GeO5/Ag@Ag3PO4 for efficient photocatalytic RhB degradation
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In this study, Bi2GeO5/Ag3PO4 nano-composites were synthesized by simple two-step approach. Then, Bi2GeO5/Ag@Ag3PO4 Z-scheme heterojunction was assembled by subsequent photocatalytic processes. It was characterized using XRD, SEM, TEM, HR-TEM, EDX, SAED, XPS, PL, UV–Vis DRS, photoelectrochemical and photodegradation experiments. Results illustrated that the catalytic activity of Bi2GeO5/Ag3PO4 nano-composites is remarkably superior to those of Bi2GeO5 and Ag3PO4. The influence of Bi2GeO5 amount on the performance of the composites was also studied. Results showed that 0.1Bi2GeO5/Ag3PO4 composite exhibited the best photocatalytic efficiency for rhodamine B (RhB) degradation, and gave rise to a 96% degradation of RhB after 30 ?min visible-light irradiation. In the degradation of RhB, the apparent rate constant of 0.1Bi2GeO5/Ag3PO4 is the largest, which is 0.06836min?1. After 4 cycles, RhB degradation by 0.1Bi2GeO5/Ag3PO4 still maintained 84%, equivalent to 1.7-fold higher than that of Ag3PO4. The trapping experiments revealed that holes (h+) and superoxide anions (O- 2·) were the primary species responsible for the decomposition of RhB in 0.1Bi2GeO5/Ag3PO4. Furthermore, the mechanism of improving photocatalytic activity was proposed relied on the experiments and characterization results. The formation of Bi2GeO5/Ag@Ag3PO4 Z-scheme heterojunction by photocatalytic processes dramatically increased its photocatalytic activity and stability.
- Jin, Riya,Liu, Dengdeng,Tan, Junhua,Yin, Li,Zhang, Xinyu,Zhu, Kaijin,Zhu, Pengyu
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- Construction of Z-scheme NiO/NiC/g-C3N4composites using NiC as novel cocatalysts for the efficient photocatalytic degradation
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A novel composite consisting of NiO/NiC/g-C3N4with excellent photocatalytic properties was successfully synthesized by the simple calcination of layered double metal hydroxide (LDH) and melamine. The color and chemical composition of the as-prepared composites could be tailored by changing the mass ratio of NiAl-LDH and g-C3N4. For the L4C composite at the ratio of 1?:?1, it showed the desired dark color due to the generated NiC. It also showed high photodegradation efficiency under visible light irradiation, reaching 97.5% toward Rhodamine B and 92.6% toward tetracycline. The high photodegradation efficiency could be mainly attributed to the unique formation of NiC cocatalysts coupled with g-C3N4and NiO semiconductors, which constructed a Z-scheme system and facilitated the efficient separation of the photogenerated electron-hole pairs. The present findings provide a promising approach for fabricating the new types of composite photocatalysts for pollutant degradation.
- Gui, Wanrui,Song, Xiaojie,Yang, Can,Yang, Zhihong,Ye, Sisi,Zhou, Xin
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p. 24822 - 24835
(2021/07/29)
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- Simple preparation of chitosan-coated thallium lead iodide nanostructures as a new visible-light photocatalyst in decolorization of organic contamination
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Recently, semiconductor photocatalysts have gained significant awareness owing to their high potential for environmental protection and remediation. Suppression of charge carrier recombination and the effective harvesting of solar power are two main aspects of photocatalysis. Fabrication of nanostructured photocatalysts is an encouraging approach to enhance photocatalytic ability. In this research, Tl4PbI6 and chitosan-coated Tl4PbI6 nanostructures were fabricated via a simple coprecipitation method. The effect of stoichiometric ratio (TlI to PbI2), variety of surfactants, and Tl4PbI6 content was scrutinized on the shape and structure of products. The bandgap of Tl4PbI6 was estimated at 2.6 eV, which made it suitable for photocatalytic activity. The morphology of products was carried out by FESEM photographs, indicating that various parameters had a significant impact on the size and morphology of the products. This demonstrates the first investigation of the photocatalytic ability of Tl4PbI6 and chitosan-coated Tl4PbI6 nanostructures. The photocatalytic activity was considered to destruct several dyes such as thymol blue, rhodamine B, methyl orange, and methyl violet under visible light. The outcome showed that chitosan-coated Tl4PbI6 can eliminate thymol blue with high efficiency (76.3%). Based on reusability, chitosan-coated Tl4PbI6 is so durable and maintains its great photocatalytic performance across five reaction cycles. Indeed during the fifth period, the reduction in photocatalytic activity is 7.7%.
- Alshamsi, Hassan Abbas,Baladi, Mahin,Ghanbari, Mojgan,Karami, Maryam,Rahimzade, Elahe,Salavati-Niasari, Masoud
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- Facile synthesis of nitrogen-defective g-C3N4for superior photocatalytic degradation of rhodamine B
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Developing a new photocatalyst for fast and highly efficient organic dye degradation plays an essential role in wastewater treatment. In this study, a photocatalyst graphite phase carbon nitride (g-C3N4) containing nitrogen defects (CN) is reported for the degradation of rhodamine B (RhB). The porous g-C3N4photocatalyst is facilely synthesized through a polycondensation method and then characterized by X-ray diffraction (XRD), infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), N2isotherm adsorption line, and X-ray photoelectron spectroscopy (XPS). The photocatalytic activity of the g-C3N4is evaluated through the degradation of RhB under visible light irradiation. The results show that photocatalytic activity of the nitrogen-defective g-C3N4can be improved by optimizating washing conditions, including washing temperature, washing dosage, drying time, and drying temperature. With the prepared nitrogen-defective g-C3N4, decolourization of RhB is able to be completed within 20 minutes, in which the degradation rate is 1.7 times higher than that of bulk g-C3N4. Moreover, the nitrogen-defective g-C3N4has high stability and reusability in the degradation of RhB. Photocatalytic degradation mechanism investigations by ultraviolet-visible absorption spectroscopy, radical trapping experiments and high-performance liquid chromatography (HPLC) reveal that RhB achieved complete mineralization through the photocatalytic degradation reaction mediated by superoxide radicals (˙O2?). This work thus provides a new approach for the preparation of photocatalysts for organic pollutants treatment in wastewater samples.
- Wang, Dan,Yang, Xiupei,Zeng, Jie,Zhang, Lin,Zhang, Qian,Zhang, Run
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p. 30503 - 30509
(2021/11/17)
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- Co-Cu Bimetallic Metal Organic Framework Catalyst Outperforms the Pt/C Benchmark for Oxygen Reduction
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Platinum (Pt)-based-nanomaterials are currently the most successful catalysts for the oxygen reduction reaction (ORR) in electrochemical energy conversion devices such as fuel cells and metal-air batteries. Nonetheless, Pt catalysts have serious drawbacks, including low abundance in nature, sluggish kinetics, and very high costs, which limit their practical applications. Herein, we report the first rationally designed nonprecious Co-Cu bimetallic metal-organic framework (MOF) using a low-temperature hydrothermal method that outperforms the electrocatalytic activity of Pt/C for ORR in alkaline environments. The MOF catalyst surpassed the ORR performance of Pt/C, exhibiting an onset potential of 1.06 V vs RHE, a half-wave potential of 0.95 V vs RHE, and a higher electrochemical stability (ΔE1/2 = 30 mV) after 1000 ORR cycles in 0.1 M NaOH. Additionally, it outperformed Pt/C in terms of power density and cyclability in zinc-air batteries. This outstanding behavior was attributed to the unique electronic synergy of the Co-Cu bimetallic centers in the MOF network, which was revealed by XPS and PDOS.
- Sanad, Mohamed Fathi,Puente Santiago, Alain R.,Tolba, Sarah A.,Ahsan, Md Ariful,Fernandez-Delgado, Olivia,Shawky Adly, Mina,Hashem, Elhussein M.,Mahrous Abodouh, Mohamed,El-Shall, M. Samy,Sreenivasan, Sreeprasad T.,Allam, Nageh K.,Echegoyen, Luis
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p. 4064 - 4073
(2021/04/06)
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- Electrocatalytic Reduction of Oxygen on Reduced Graphene Oxide/Iron Oxide (rGO/Fe3O4) Composite Electrode
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Abstract: Reduced graphene oxide/iron oxide (rGO/Fe3O4) nanocomposite was synthesized by facile one-pot process and its performance as electrocatalyst for oxygen reduction reaction (ORR) was investigated. The nanocomposite was physically and electrochemically characterized using Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), Brunauer–Emmett–Teller (BET) method, scanning electron microscopy (SEM), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). FT-IR, XRD, and SEM confirms the presence of rGO and Fe3O4 as whole. CV data shows increment in current responses nearly two and a half folds for rGO/Fe3O4/GCE. EIS analysis shows stable electron transfers with lower charge transfer resistance (Rct) of modified electrode due to synergistic effect between rGO and Fe3O4. The performance of the electrocatalyst in ORR was compared with bare GCE and rGO/GCE where higher catalytic performance and better stability were obtained. The analysis results shows that the compound could be a promising material for fuel cells.
- Yusoff,Suresh,Khairul,Noorashikin
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p. 834 - 842
(2021/04/22)
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- Catalytic Reduction of Dioxygen to Water by a Bioinspired Non-Heme Iron Complex via a 2+2 Mechanism
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We report a bioinspired non-heme Fe complex with a tripodal [N3O]- ligand framework (Fe(PMG)(Cl)2) that is electrocatalytically active toward dioxygen reduction with acetic acid as a proton source in acetonitrile solution. Under electrochemical and chemical conditions, Fe(PMG)(Cl)2 selectively produces water via a 2+2 mechanism, where H2O2 is generated as a discrete intermediate species before further reduction to two equivalents of H2O. Mechanistic studies support a catalytic cycle for dioxygen reduction where an off-cycle peroxo dimer species is the resting state of the catalyst. Spectroscopic analysis of the reduced complex FeII(PMG)Cl shows the stoichiometric formation of an Fe(III)-hydroxide species following exposure to H2O2; no catalytic activity for H2O2 disproportionation is observed, although the complex is electrochemically active for H2O2 reduction to H2O. Electrochemical studies, spectrochemical experiments, and DFT calculations suggest that the carboxylate moiety of the ligand is sensitive to hydrogen-bonding interactions with the acetic acid proton donor upon reduction from Fe(III)/(II), favoring chloride loss trans to the tris-alkyl amine moiety of the ligand framework. These results offer insight into how mononuclear non-heme Fe active sites in metalloproteins distribute added charge and poise proton donors during reactions with dioxygen.
- Cook, Emma N.,Dickie, Diane A.,Machan, Charles W.
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supporting information
p. 16411 - 16418
(2021/10/20)
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- Metal–Organic-Framework-Supported Molecular Electrocatalysis for the Oxygen Reduction Reaction
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Synthesizing molecule@support hybrids is appealing to improve molecular electrocatalysis. We report herein metal–organic framework (MOF)-supported Co porphyrins for the oxygen reduction reaction (ORR) with improved activity and selectivity. Co porphyrins can be grafted on MOF surfaces through ligand exchange. A variety of porphyrin@MOF hybrids were made using this method. Grafted Co porphyrins showed boosted ORR activity with large (>70 mV) anodic shift of the half-wave potential compared to ungrafted porphyrins. By using active MOFs for peroxide reduction, the number of electrons transferred per O2 increased from 2.65 to 3.70, showing significantly improved selectivity for the 4e ORR. It is demonstrated that H2O2 generated from O2 reduction at Co porphyrins is further reduced at MOF surfaces, leading to improved 4e ORR. As a practical demonstration, these hybrids were used as air electrode catalysts in Zn-air batteries, which exhibited equal performance to that with Pt-based materials.
- Liang, Zuozhong,Guo, Hongbo,Zhou, Guojun,Guo, Kai,Wang, Bin,Lei, Haitao,Zhang, Wei,Zheng, Haoquan,Apfel, Ulf-Peter,Cao, Rui
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supporting information
p. 8472 - 8476
(2021/03/08)
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- Unifying Concepts in Electro- And Thermocatalysis toward Hydrogen Peroxide Production
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We examine relationships between H2O2 and H2O formation on metal nanoparticles by the electrochemical oxygen reduction reaction (ORR) and the thermochemical direct synthesis of H2O2. The similar mechanisms of such reactions suggest that these catalysts should exhibit similar reaction rates and selectivities at equivalent electrochemical potentials (μˉ i), determined by reactant activities, electrode potential, and temperature. We quantitatively compare the kinetic parameters for 12 nanoparticle catalysts obtained in a thermocatalytic fixed-bed reactor and a ring-disk electrode cell. Koutecky-Levich and Butler-Volmer analyses yield electrochemical rate constants and transfer coefficients, which informed mixed-potential models that treat each nanoparticle as a short-circuited electrochemical cell. These models require that the hydrogen oxidation reaction (HOR) and ORR occur at equal rates to conserve the charge on nanoparticles. These kinetic relationships predict that nanoparticle catalysts operate at potentials that depend on reactant activities (H2, O2), H2O2 selectivity, and rate constants for the HOR and ORR, as confirmed by measurements of the operating potential during the direct synthesis of H2O2. The selectivities and rates of H2O2 formation during thermocatalysis and electrocatalysis correlate across all catalysts when operating at equivalent μˉ i values. This analysis provides quantitative relationships that guide the optimization of H2O2 formation rates and selectivities. Catalysts achieve the greatest H2O2 selectivities when they operate at high H atom coverages, low temperatures, and potentials that maximize electron transfer toward stable OOH? and H2O2? while preventing excessive occupation of O-O antibonding states that lead to H2O formation. These findings guide the design and operation of catalysts that maximize H2O2 formation, and these concepts may inform other liquid-phase chemistries.
- Adams, Jason S.,Flaherty, David W.,Kromer, Matthew L.,Rodríguez-López, Joaquín
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p. 7940 - 7957
(2021/06/27)
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- High temperature H2S selective oxidation on a copper-substituted hexaaluminate catalyst: A facile process for treating low concentration acid gas
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H2S selective catalytic oxidation technology is a prospective way for the treatment of low concentration acid gas with simple process operation and low investment. However, undesirable results such as large formation of SO2 and catalyst deactivation inevitably occur, due to the temperature rise of fixed reaction bed caused by the exothermic reaction. Catalyst with high activity in wide operating temperature window, especially in high temperature range, is urgently needed. In this paper, a series of copper-substituted hexaaluminate catalysts (LaCux, x = 0, 0.5, 1, 1.5, 2, 2.5) were prepared and investigated for the H2S selective oxidation reaction at high temperature conditions (300-550°C). The LaCu1 catalyst exhibited excellent catalytic performance and great stability, which was attributed to the best reductive properties and proper pore structure. Besides, two facile deep processing paths were proposed to eliminate the remaining H2S and SO2 in the tail gas.
- Hao, Zhengping,Jiang, Guoxia,Li, Ganggang,Xu, Xin,Zhang, Fenglian
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supporting information
(2021/09/22)
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- Dicyanamide Anion-Based Ionic Liquid-Functionalized Graphene-Supported Pt Catalysts for Boosting Methanol Electrooxidation
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As an environmentally friendly energy technology, direct methanol fuel cells (DMFCs) meet the needs of sustainable development. Herein, novel dicyanamide anion-based (N(CN)2-) ionic liquid (IL)-functionalized reduced graphene oxide (rGO)-supported Pt catalysts are synthesized via a facile one-pot room temperature reduction method, which show a boost in methanol oxidation performance compared with Pt/rGO. The mass activities of the as-prepared Pt/emimN(CN)2/rGO (863.6 mA mg-1Pt) and Pt/epyN(CN)2/rGO (524.9 mA mg-1Pt) are about five and three times higher than that of Pt/rGO (178.6 mA mg-1Pt), and about six and four times higher than that of Pt/C (140.2 mA mg-1Pt), respectively. The participation of ILs significantly improves the CO poisoning resistance, stability, and activity for methanol oxidation of catalysts. The relationship between the structures and conductivities of diverse ILs and the performance of Pt catalysts are studied systematically. These findings may offer a promising prospect of ILs in DMFCs.
- Guo, Yong,Hu, Xiaoqin,Lou, Mengran,Shi, Hongli,Sun, Zhipeng,Wang, Ruiying,Wang, Xingchao,Wen, Pengtao,Yang, Lili
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p. 13736 - 13747
(2021/09/13)
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- Effects of the Support-Crystal Size on the Catalytic Performance of RuO2/TiO2 in the Deacon Process
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RuO2/TiO2 catalysts with different TiO2 crystal sizes were prepared via a dry impregnation method, and these prepared catalysts were applied in the oxidation of HCl. The results show that decreasing the support-crystal size is an effective method to enhance the dispersion of RuO2 on TiO2, which is helpful to increase the catalytic activity significantly. Graphic Abstract: [Figure not available: see fulltext.].
- Wang, Xue,Liu, Yupei,Xu, Chunhui,Lu, Xinqing,Ma, Rui,Fu, Yanghe,Wang, Shuhua,Zhu, Weidong
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p. 2346 - 2354
(2021/01/07)
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- Pt-core silica shell nanostructure: a robust catalyst for the highly corrosive sulfuric acid decomposition reaction in sulfur iodine cycle to produce hydrogen
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The platinum core silica shell catalyst has facilitated stable sulfuric acid decomposition at higherature which was not possible over bare Pt nanoparticles due to sintering and agglomeration. Helium (He) gas supplies the heat (550-900 °C) in a high temperature gas cooled reactor (VHTR). The major challenge is designing a stable catalyst for the variable heat efficiency of He. Pt catalysts loaded on different supports, such as SiC, Al2O3, SiC-Al2O3, BaSO4, TiO2, SBA-15, and SiO2, have been extensively studied but they have not provided a simple method to form robust catalysts for sulfuric acid decomposition. The core-shell scheme, whereby nanoparticles are enclosed by protecting agents (CTAB) and are covered by a silica shell, delivered mesopores and exhibited higher activity and stability over testing for more than 100 h. TEM images confirmed that the Pt particles on the Pt@mSiO2 catalyst are more stable during sulfuric acid decomposition, and no significant evidence of agglomeration or sintering of the Pt core particles was found, despite some broken shells and dislocated Pt nanoparticles from the silica core. ICP-OES analysis of the spent catalysts after 100 h showed minimal Pt loss (9.0%). These types of catalysts are highly desirable for practical applications. This journal is
- Khan, Hassnain Abbas,Jung, Kwang-Deog,Ahamad, Tansir,Ubaidullah, Mohd,Imran, Muhammad,Alshehri, Saad M.
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p. 1247 - 1252
(2021/02/03)
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- Pendent Relay Enhances H2O2Selectivity during Dioxygen Reduction Mediated by Bipyridine-Based Co-N2O2Complexes
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Generally, cobalt-N2O2 complexes show selectivity for hydrogen peroxide during electrochemical dioxygen (O2) reduction. We recently reported a Co(III)-N2O2 complex with a 2,2′-bipyridine-based ligand backbone which showed alternative selectivity: H2O was observed as the primary reduction product from O2 (71 ± 5%) with decamethylferrocene as a chemical reductant and acetic acid as a proton donor in methanol solution. We hypothesized that the key selectivity difference in this case arises in part from increased favorability of protonation at the distal O position of the key intermediate Co(III)-hydroperoxide species. To interrogate this hypothesis, we have prepared a new Co(III) compound that contains pendent -OMe groups poised to direct protonation toward the proximal O atom of this hydroperoxo intermediate. Mechanistic studies in acetonitrile (MeCN) solution reveal two regimes are possible in the catalytic response, dependent on added acid strength and the presence of the pendent proton donor relay. In the presence of stronger acids, the activity of the complex containing pendent relays becomes O2 dependent, implying a shift to Co(III)-superoxide protonation as the rate-determining step. Interestingly, the inclusion of the relay results in primarily H2O2 production in MeCN, despite minimal difference between the standard reduction potentials of the three complexes tested. EPR spectroscopic studies indicate the formation of Co(III)-superoxide species in the presence of exogenous base, with greater O2 reactivity observed in the presence of the pendent -OMe groups.
- Cook, Emma N.,Dickie, Diane A.,Dressel, Julia M.,Gan, Yunqiao J.,Machan, Charles W.,Miedaner, Peter R.,Nichols, Asa W.,Shafaat, Hannah S.
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supporting information
p. 13065 - 13073
(2021/09/03)
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- A Nonoxide Catalyst System Study: Alkali Metal-Promoted Pt/AC Catalyst for Formaldehyde Oxidation at Ambient Temperature
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Metal oxides have been extensively used as supports in noble metal-based catalysts for formaldehyde (HCHO) oxidation, utilizing the benefit of the strong metal-support interaction (SMSI). Non-oxide supported noble metal catalysts are still rarely investigated in the field of HCHO oxidation. Herein, a series of Pt catalysts supported on a nonoxide, that is, activated carbon (AC), were studied in detail. Pt/AC catalysts with or without addition of the alkali metal Na were prepared and tested for HCHO oxidation. HCHO could be completely oxidized to form H2O and CO2 at 25 °C on the Na-Pt/AC-R (reduced Na-Pt/AC) catalyst, but in contrast, the Pt/AC-R catalyst only achieved 40% HCHO conversion under the same reaction conditions. The characterization results indicated that Na addition to the Na-Pt/AC-R catalyst could induce the formation of Pt-Ox-Na species, which improves the stability of Pt species, increases Pt dispersion, and enhances the activation of chemisorbed oxygen and water to form abundant surface-active hydroxyl groups. Meanwhile, HCHO-TPD confirmed that HCHO could be transformed into CO2 and H2O directly because of the presence of abundant OH groups on the Na-Pt/AC-R catalyst. In this study, the promotion effect of alkali metals on supported Pt catalysts for HCHO oxidation was further extended to a catalyst system with a nonoxide carrier.
- Wang, Chunying,Li, Yaobin,Zheng, Lirong,Zhang, Changbin,Wang, Yin,Shan, Wenpo,Liu, Fudong,He, Hong
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p. 456 - 465
(2021/01/12)
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- Cu-grafted TiO2 photocatalysts: effect of Cu on the action spectrum of composite materials
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This paper describes a simple technique for the modification of titania with copper to enhance its photocatalytic performance. In addition to the absorption of UV light resulted in band-to-band excitation of electrons, TiO2 grafted with copper species absorbs radiation in the visible region of spectrum, and it is able to completely oxidize volatile organic pollutants both under UV and visible light. The action spectra of pristine and Cu-grafted TiO2 photocatalysts are measured and discussed to elucidate the reasons for appearance of the activity under visible light.
- Kovalevskiy, Nikita S.,Kozlov, Denis V.,Lyulyukin, Mikhail N.,Selishchev, Dmitry S.
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p. 644 - 646
(2021/11/26)
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- Activity manifestationviaarchitectural manipulation by cubic silica-derived Co3O4electrocatalysts towards bifunctional oxygen electrode performance
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Electrocatalytic water splitting reaction utilizing non-renewable energy resources significantly leads to a sustainable energy infrastructure. Highly efficient bifunctional catalysts for oxygen reduction and oxygen evolution reactions (ORR/OER) are essential for the replacement of platinum, ruthenium and iridium metals. We used four different silica templates to create excellent mesoporous cobalt oxide (Co3O4) electrocatalysts in crystalline form. Various advanced techniques confirm the spinel structure composed of both Co3+and Co2+sites, which lead to an enhanced surface area, mesoporosity, and a rod morphology with a cubic-like network structure. Among these replicas, the Mobil composition of matter (MCM)-48-derived Co3O4(Co3O4-M8) material demonstrates remarkable OER activity with an observed potential of 1.76 V, a Tafel slope of 107 mV dec?1and a lower charge transfer resistance. Such a high performance is observed due to assistance of the Co3+to Co4+transition during the oxygen evolution reaction. The ORR was more active on the Korea advanced institute of science and technology (KIT)-6-derived Co3O4(Co3O4-K6) material, which displayed a more positive onset potential of 0.85 V, a half-wave potential of 0.56 V and a better current density in alkaline medium. In addition, we found that the stabilization of Co2+active sites in the Co3O4-K6 material is the reason for the enhanced oxygen reduction reaction. The observed bifunctional activity (ΔE=EOER@10 mA cm?2? ORR@E1/2) for the Co3O4-K6 catalyst is 1.22 V, which shows significant performance among all the catalysts prepared in this work. Such an earth-abundant mesoporous Co3O4catalyst obtainedviaan environmentally benign process is anticipated to revolutionize electrochemical energy conversion and storage devices.
- Duraisamy, Velu,Selvakumar, Karuppiah,Senthil Kumar, Sakkarapalayam Murugesan
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supporting information
p. 16913 - 16925
(2021/09/27)
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- Preparation of g-C3N4 Nanosheets/CuO with Enhanced Catalytic Activity on the Thermal Decomposition of Ammonium Perchlorate
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The thermal oxidation etching assisted g-C3N4 nanosheets/CuO was prepared through a facile co-precipitation strategy. In this work, the structure, morphology, and composition of g-C3N4 (UCN, prepared by urea), g-C3N4 nanosheets (TCN, prepared by thermal oxidation etching of UCN), g-C3N4/CuO (UCN/CuO), g-C3N4 nanosheets/CuO (TCN/CuO) were characterized via X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). Furthermore, the catalytic effect of the obtained samples on the thermal decomposition of ammonium perchlorate (AP) was examined by thermal gravimetric analysis (TGA). As a result, in the case of 5 wt% TCN/CuO, the high decomposition temperature of AP decreased by 120.6 °C, which is much lower than that of UCN, TCN, CuO and UCN/CuO. In addition, the exothermic heat released from the decomposition of AP increased from 430.64 J g?1 to 2856.08 J g?1. This evident catalytic activity may be related to the synergistic effect of CuO and TCN. This work provides a novel strategy for the construction of composite catalyst for the thermal decomposition of AP, which is supposed to possess significant potential in the solid propellant field.
- Ma, Dan Na,Li, Xiao Meng,Wang, Xiao Qing,Luo, Yun Jun
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p. 982 - 988
(2021/02/26)
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- Biochemical Characterization, Phytotoxic Effect and Antimicrobial Activity against Some Phytopathogens of New Gemifloxacin Schiff Base Metal Complexes
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String of Fe(III), Cu(II), Zn(II) and Zr(IV) complexes were synthesized with tetradentateamino Schiff base ligand derived by condensation of ethylene diamine with gemifloxacin. The novel Schiff base (4E,4′E)-4,4′-(ethane-1,2-diyldiazanylylidene)bis{7-[(4Z
- Mohamed, Amira A.,Elshafie, Hazem S.,Sadeek, Sadeek A.,Camele, Ippolito
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- Synthesis of Boroxine and Dioxaborole Covalent Organic Frameworks via Transesterification and Metathesis of Pinacol Boronates
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Boroxine and dioxaborole are the first and some of the most studied synthons of covalent organic frameworks (COFs). Despite their wide application in the design of functional COFs over the last 15 years, their synthesis still relies on the original Yaghi's condensation of boronic acids (with itself or with polyfunctional catechols), some of which are difficult to prepare, poorly soluble, or unstable in the presence of water. Here, we propose a new synthetic approach to boroxine COFs (on the basis of the transesterification of pinacol aryl boronates (aryl-Bpins) with methyl boronic acid (MBA) and dioxaborole COFs (through the metathesis of pinacol boronates with MBA-protected catechols). The aryl-Bpin and MBA-protected catechols are easy to purify, highly soluble, and bench-stable. Furthermore, the kinetic analysis of the two model reactions reveals high reversibility (Keq ~1) and facile control over the equilibrium. Unlike the conventional condensation, which forms water as a byproduct, the byproduct of the metathesis (MBA pinacolate) allows for easy kinetic measurements of the COF formation by conventional 1H NMR. We show the generality of this approach by the synthesis of seven known boroxine/dioxaborole COFs whose crystallinity is better or equal to those reported by conventional condensation. We also apply metathesis polymerization to obtain two new COFs, Py4THB and B2HHTP, whose synthesis was previously precluded by the insolubility and hydrolytic instability, respectively, of the boronic acid precursors.
- Hamzehpoor, Ehsan,Jonderian, Antranik,McCalla, Eric,Perepichka, Dmitrii F.
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supporting information
p. 13274 - 13280
(2021/09/07)
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- Protodeboronation of (Hetero)Arylboronic Esters: Direct versus Prehydrolytic Pathways and Self-/Auto-Catalysis
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The kinetics and mechanism of the base-catalyzed hydrolysis (ArB(OR)2→ ArB(OH)2) and protodeboronation (ArB(OR)2→ ArH) of a series of boronic esters, encompassing eight different polyols and 10 polyfluoroaryl and heteroaryl moieties, have been investigated by in situ and stopped-flow NMR spectroscopy (19F,1H, and11B), pH-rate dependence, isotope entrainment,2H KIEs, and KS-DFT computations. The study reveals the phenomenological stability of boronic esters under basic aqueous-organic conditions to be highly nuanced. In contrast to common assumption, esterification does not necessarily impart greater stability compared to the corresponding boronic acid. Moreover, hydrolysis of the ester to the boronic acid can be a dominant component of the overall protodeboronation process, augmented by self-, auto-, and oxidative (phenolic) catalysis when the pH is close to the pKaof the boronic acid/ester.
- Hayes, Hannah L. D.,Wei, Ran,Assante, Michele,Geogheghan, Katherine J.,Jin, Na,Tomasi, Simone,Noonan, Gary,Leach, Andrew G.,Lloyd-Jones, Guy C.
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supporting information
p. 14814 - 14826
(2021/09/13)
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- Concerted Multiproton-Multielectron Transfer for the Reduction of O2to H2O with a Polyoxovanadate Cluster
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The concerted transfer of protons and electrons enables the activation of small-molecule substrates by bypassing energetically costly intermediates. Here, we present the synthesis and characterization of several hydrogenated forms of an organofunctionalized vanadium oxide assembly, [V6O13(TRIOLNO2)2]2-, and their ability to facilitate the concerted transfer of protons and electrons to O2. Electrochemical analysis reveals that the fully reduced cluster is capable of mediating 2e-/2H+ transfer reactions from surface hydroxide ligands, with an average bond dissociation free energy (BDFE) of 61.6 kcal/mol. Complementary stoichiometric experiments with hydrogen-atom-accepting reagents of established bond strengths confirm that the electrochemically established BDFE predicts the 2H+/2e- transfer reactivity of the assembly. Finally, the reactivity of the reduced polyoxovanadate toward O2 reduction is summarized; our results indicate a stepwise reduction of the substrate, proceeding through H2O2 en route to the formation of H2O. Kinetic isotope effect experiments confirm the participation of hydrogen transfer in the rate-determining step of both the reduction of O2 and H2O2. This work constitutes the first example of hydrogen atom transfer for small-molecule activation with reduced polyoxometalates, where both electron and proton originate from the cluster.
- Brennessel, William W.,Fertig, Alex A.,Matson, Ellen M.,McKone, James R.
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p. 15756 - 15768
(2021/10/02)
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- Synthesis and Structure-Activity Characterization of a Single-Site MoO2Catalytic Center Anchored on Reduced Graphene Oxide
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Molecularly derived single-site heterogeneous catalysts can bridge the understanding and performance gaps between conventional homogeneous and heterogeneous catalysis, guiding the rational design of next-generation catalysts. While impressive advances have been made with well-defined oxide supports, the structural complexity of other supports and the nature of the grafted surface species present an intriguing challenge. In this study, single-site Mo(-O)2 species grafted onto reduced graphene oxide (rGO/MoO2) are characterized by XPS, DRIFTS, powder XRD, N2 physisorption, NH3-TPD, aqueous contact angle, active site poisoning assay, Mo EXAFS, model compound single-crystal XRD, DFT, and catalytic performance. NH3-TPD reveals that the anchored MoO2 moiety is not strongly acidic, while Mo 3d5/2 XPS assigns the oxidation state as Mo(VI), and XRD shows little rGO periodicity change on MoO2 grafting. Contact angle analysis shows that MoO2 grafting consumes rGO surface polar groups, yielding a more hydrophobic surface. The rGO/MoO2 DRIFTS assigns features at 959 and 927 cm-1 to the symmetric and antisymmetric Mo-O stretching modes, respectively, of an isolated cis-(O-Mo-O) moiety, in agreement with DFT computation. Moreover, the Mo EXAFS rGO/MoO2 structural data are consistent with isolated (C-O)2-Mo(-O)2 species having two Mo-O bonds and two Mo-O bonds at distances of 1.69(3) and 1.90(3) ?, respectively. rGO/MoO2 is also more active than the previously reported AC/MoO2 catalyst, with reductive carbonyl coupling TOFs approaching 1.81 × 103 h-1. rGO/MoO2 is environmentally robust and multiply recyclable with 69 ± 2% of the Mo sites catalytically significant. Overall, rGO/MoO2 is a structurally well-defined and versatile single-site Mo(VI) dioxo heterogeneous catalytic system.
- Bedzyk, Michael J.,Das, Anusheela,Jones, Leighton O.,Kim, Hacksung,Kratish, Yosi,Li, Jiaqi,Liu, Yiqi,Ma, Qing,Marks, Tobin J.,Schatz, George C.
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p. 21532 - 21540
(2022/01/03)
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