7732-18-5

Oxygen electroreduction on heat-treated multi-walled carbon nanotubes supported iron polyphthalocyanine in acid media

Zhang, Rui,Peng, Yingxiang,Li, Zhipan,Li, Kai,Ma, Jie,Liao, Yi,Zheng, Lirong,Zuo, Xia,Xia, Dingguo

, p. 343 - 351 (2014)

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.

Ni2P hollow microspheres for electrocatalytic oxygen evolution and reduction reactions

Lei, Haitao,Chen, Mingxing,Liang, Zuozhong,Liu, Chengyu,Zhang, Wei,Cao, Rui

, p. 2289 - 2293 (2018)

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.

Caley,Brundin

, p. 142 (1953)

Mechanism of the low-temperature interaction of hydrogen with α-oxygen on FeZSM-5 zeolite

Dubkov,Starokon',Paukshtis,Volodin,Panov

, p. 202 - 208 (2004)

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.

2D Layered non-precious metal mesoporous electrocatalysts for enhanced oxygen reduction reaction

Huo, Lili,Liu, Baocang,Zhang, Geng,Si, Rui,Liu, Jian,Zhang, Jun

, p. 4868 - 4878 (2017)

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.

2H→1T Phase Engineering of Layered Tantalum Disulfides in Electrocatalysis: Oxygen Reduction Reaction

Luxa, Jan,Mazánek, Vlastimil,Pumera, Martin,Lazar, Petr,Sedmidubsky, David,Callisti, Mauro,Polcar, Tomá?,Sofer, Zdeněk

, p. 8082 - 8091 (2017)

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.

Boosting the catalysis of AuCuMo for oxygen reduction: Important roles of an optimized electronic structure and surface electrochemical stability

Gong, Hongyu,Li, Fan,Li, Ling,Yang, Bo,Yang, Ruizhi

, (2020)

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.

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

Aglulin

, p. 290 - 296 (2019)

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.

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

Lu, Jia,Zhou, Weijia,Wang, Likai,Jia, Jin,Ke, Yunting,Yang, Linjing,Zhou, Kai,Liu, Xiaojun,Tang, Zhenghua,Li, Ligui,Chen, Shaowei

, p. 1045 - 1053 (2016)

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.

Factors affecting catalytic destruction of H2O2 by hydrogenation and decomposition over Pd catalysts supported on activated carbon cloth (ACC)

Gudarzi, Davood,Ratchananusorn, Warin,Turunen, Ilkka,Heinonen, Markku,Salmi, Tapio

, p. 69 - 79 (2015)

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

Tungsten oxide in polymer electrolyte fuel cell electrodes - A thin-film model electrode study

Wickman, Bj?rn,Wesselmark, Maria,Lagergren, Carina,Lindbergh, G?ran

, p. 9496 - 9503 (2011)

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.

Absolute Rate Constant of the Reaction OH + H2O2 -> HO2 + H2O from 245 to 423 K

Keyser, L. F.

, p. 1659 - 1663 (1980)

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

Nitrogen/sulfur co-doped non-noble metal material as an efficient electrocatalyst for the oxygen reduction reaction in alkaline media

Xu, Li,Pan, Guoshun,Liang, Xiaolu

, p. 19756 - 19765 (2014)

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.

Nelson, H. H.,Marinelli, W. J.,Johnston, H. S.

, p. 495 - 499 (1981)

In situ growth of Pt3Ni nanoparticles on an A-site deficient perovskite with enhanced activity for the oxygen reduction reaction

Gao, Yang,Wang, Jian,Lyu, Yu-Qi,Lam, Kwunyu,Ciucci, Francesco

, p. 6399 - 6404 (2017)

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.

Water affects the stereochemistry and dioxygen reactivity of carboxylate-rich diiron(II) models for the diiron centers in dioxygen-dependent non-heme enzymes

Yoon, Sungho,Lippard, Stephen J.

, p. 8386 - 8397 (2005)

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).

Giauque, W. F.,Johnston, H. L.

, p. 2300 - 2321 (1929)

Accelerated diffusion of chain carriers and kinetic features of heterogeneous processes in gas-phase chain reactions

Azatyan,Piloyan,Baimuratova,Masalova

, p. 178 - 185 (2008)

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

Oxygen Reduction Catalysis at a Dicobalt Center: The Relationship of Faradaic Efficiency to Overpotential

Passard, Guillaume,Ullman, Andrew M.,Brodsky, Casey N.,Nocera, Daniel G.

, p. 2925 - 2928 (2016)

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.

Tannic acid decorated AuPd lavender-like nanochains for enhanced oxygen reduction electrocatalysis

Jiao, Shiqian,Li, Xiaonian,Liu, Songliang,Wang, Hongjing,Wang, Liang,Wang, Ziqiang,Xu, You,Yin, Shuli,Zhang, Hugang

, p. 15678 - 15683 (2021)

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.

Fe ultra-small particles anchored on carbon aerogels to enhance the oxygen reduction reaction in Zn-air batteries

Shi, Jinjin,Shu, Xinxin,Xiang, Chensheng,Li, Hong,Li, Yang,Du, Wei,An, Pengfei,Tian, He,Zhang, Jintao,Xia, Haibing

, p. 6861 - 6871 (2021)

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.

Hill, G. R.

, p. 1306 - 1307 (1948)

Facile synthesis of well dispersed spinel cobalt manganese oxides microsphere as efficient bi-functional electrocatalysts for oxygen reduction reaction and oxygen evolution reaction

Yang, Shuting,Wang, Zhichao,Cao, Zhaoxia,Mao, Xinxin,Shi, Mengjiao,Li, Yanlei,Zhang, Ruirui,Yin, Yanhong

, p. 482 - 491 (2017)

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.

Wahnstroem, T.,Ljungstroem, S.,Rosen, A.,Kasemo, B.

, p. 439 - 451 (1990)

Frost, A. A.,Oldenberg, O.

, p. 781 - 784 (1936)

Facile preparation of porous hollow CoxMn3-xO4 normal-reverse coexisted spinel for toluene oxidation

Gu, Wenxiu,Li, Chenqi,Qiu, Jianhao,Yao, Jianfeng

, (2021/10/08)

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.

Investigating the effects of various synthesis routes on morphological, optical, photoelectrochemical and photocatalytic properties of single-phase perovskite BiFeO3

Chang Chien, Shui-Wen,Jaffari, Zeeshan Haider,Kumar, Dileep,Lam, Sze-Mun,Ng, Ding-Quan

, (2021/08/23)

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.

Fabrication of TlSnI3/C3N4 nanocomposites for enhanced photodegradation of toxic contaminants below visible light and investigation of kinetic and mechanism of photocatalytic reaction

Ghanbari, Mojgan,Salavati-Niasari, Masoud,Yousefzadeh, Fatemeh,Yousif, Qahtan A.

, (2022/01/26)

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.