1313-13-9Relevant articles and documents
Balarew, D.
, p. 73 - 77 (1942)
Mesoporous β-MnO2 air electrode modified with pd for rechargeability in lithium-air battery
Thapa, Arjun Kumar,Hidaka, Yuiko,Hagiwara, Hidehisa,Ida, Shintaro,Ishihara, Tatsumi
, p. A1483-A1489 (2011)
The electrochemical performance and electrode reactions using ordered mesoporous β-MnO2 modified with Pd as a cathode catalyst for rechargeable Li-air batteries was reported. Well-ordered mesoporous β-MnO2 was prepared using mesoporous silica KIT-6 as a template under hydrothermal synthesis of Mn(NO3)2H2O. The obtained mesoporous β-MnO2 shows narrow pore size distribution of 1 nm. With the dispersion of small amounts of Pd to β-MnO2, mesoporous β-MnO2 exhibited a high initial discharge capacity of 817 mAhg-cat. with high reversible capacity. Charging potential is suppressed at 3.6 V vs. LiLi, which is highly effective for preventing the decomposition of organic electrolyte. The mesoporous β-MnO2Pd electrode shows good rate capability and cycle stability. Ex-situ and in-situ XRD results suggested that the observed capacity comes primarily from the oxidation of Li to Li2O 2 followed by Li2O after discharge to 2.0 V vs. LiLi. Electron spin resonance measurements suggest that the formation of superoxide anion radicals contributs to the oxidation of Li and the radicals were recovered during charge. Ex-situ FTIR measurement suggested that no electrolyte decomposition was observed and no Li2CO3 was formed during discharge when ethylene carbonate (EC)-diethyl carbonate (DEC) (3:7), which is highly stable for Li-air battery, was used as the electrolyte.
Pinnow, J.
, p. 91 - 96 (1904)
Dymond, T. S.,Hughes, E.
, p. 314 - 318 (1897)
Local atomic arrangement and electronic structure of nanocrystalline transition metal oxides determined by X-ray absorption spectroscopy
Hwang, Seong-Ju,Choy, Jin-Ho
, p. 5791 - 5796 (2003)
The local crystal structure and electronic configuration of transition metal in X-ray amorphous MnO2 and CrO2 nanocrystals have been examined by using X-ray absorption (XAS) spectroscopy at Mn K and Cr K-edges. The Mn K-edge XAS study reveals that tetravalent manganese ions are stabilized in ?±-MnO2-type local atomic arrangement consisting of the intergrowth of edge- and corner-shared MnO6 octahedra. On the other hand, it is found from Cr K-edge XAS results that nanocrystalline CrO2 possesses two different kinds of local structures around chromium, that is, Cr2O3-type with octahedral site and CrO3-type with tetrahedral site. The presence of Cr+VI species on the surface would be helpful for Li grafting process, giving rise to excellent electrochemical performances. This work can be regarded as a strong evidence for the usefulness of XAS to study nanocrystalline electrode materials.
A novel self-assembly approach for synthesizing nanofiber aerogel supported platinum single atoms
Jiang, Zheng,Kato, Kenichi,Li, Xiaopeng,Lin, Chao,Sun, Yu,Xu, Qing,Yamauchi, Miho,Yang, Ruoou,Zhang, Hao,Zhang, Haojie,Zhao, Yonghui
, p. 15094 - 15102 (2020)
A great challenge in catalyst engineering is precisely assembling and positioning nanoscale active metals at desired locations while constructing robust functional architectures. This article presents a novel approach for constructing macroscopic Ag-doped manganese oxide aerogels (up to 2 L) while homogeneously incorporating active Pt single atoms (Pt/Ag-MnO2) based on a solution-solid-solid (SSS) mechanism. AgOx seeds were identified as key species for triggering the octopus-like growth of MnO2 nanofibers and inserting Ag and Pt into the MnO2 crystalline framework. The interconnection and entanglement among nanofibers allowed the formation of mechanically strengthened hierarchical structures, leading to one of the most robust manganese-based aerogels to date. Impressively, the Pt/Ag-MnO2 aerogel also possessed promising selectivity and stability toward the electrocatalytic oxygen reduction reaction, with Pt showing a high mass activity of 1.6 A/(mgPt) at 0.9 V vs. RHE. Experimental characterization and theoretical calculation confirmed Pt single atoms to be located at substitutional lattice sites, which reduced the overall oxygen reduction barriers. Our approach suggests that SSS or other analogous nanofiber or nanowire growth strategies are powerful in controlling structural formation over the entire range of length scales while being applicable to fabricating single-atom catalysts.
Synthesis of NaxMnO2+δ by a reduction of aqueous sodium permanganate with sodium iodide
Jeong,Manthiram
, p. 331 - 338 (2001)
Reduction of sodium permanganate with sodium iodide in aqueous solutions has been investigated systematically. The products formed have been characterized by X-ray diffraction, wet-chemical analysis, and surface area and magnetic susceptibility measurements after firing at various temperatures. The results reveal that the sodium content x in the reduction products NaxMnO2+δ depends strongly on the reaction pH and mildly on the relative concentrations of the reactants. Na0.7MnO2+δ obtained at pH>11 followed by firing at T>500°C adopts the P2 layer structure (hexagonal) with cation vacancies arising from a δ≈0.3. Na0.7 MnO2+δ crystallizing in a distorted P2 structure (orthorhombic) without cation vacancies (δ≈0) could be obtained by annealing the hexagonal Na0.7MnO2+δ (δ≈0.3) in N2 atmosphere around 600°C. While the orthorhombic Na0.7MnO2+δ (δ0.7MnO2+δ (δ≈0.3) transforms to spinel-like phases due to the presence of cation vacancies. Na0.5MnO2+δ obtained at a controlled pH of 9.3 adopts a metastable layer structure on firing at 500°C and a tunnel structure isostructural with Na4Mn4Ti5O18 on firing at T≥600°C. The tunnel structure is stable to ion-exchange reactions without transforming to spinel-like phases. In addition, washing the reduction products with various organic solvents before firing at higher temperatures is found to influence the reaction kinetics, composition, and crystal chemistry.
Capacitive properties of PANI/MnO2 synthesized via simultaneous-oxidation route
Zhang, Jie,Shu, Dong,Zhang, Tianren,Chen, Hongyu,Zhao, Haimin,Wang, Yongsheng,Sun, Zhenjie,Tang, Shaoqing,Fang, Xueming,Cao, Xiufang
, p. 1 - 9 (2012)
Polyaniline (PANI) and manganese dioxide (MnO2) composite (PANI/MnO2) was synthesized via a simultaneous-oxidation route. In this route, all reactants were dispersed homogenously in precursor solution and existed as ions and molecules, and involved reactions of ions and molecules generating PANI and MnO2 simultaneously. In this way, PANI molecule and MnO2 molecule contact each other and arrange alternately in the composite. The inter-molecule contact improves the conductivity of the composite. The alternative arrangement of PANI molecules and MnO2 molecules separating each other, and prevents the aggregation of PANI and cluster of MnO2 so as to decrease the particle size of the composite. The morphology, structure, porous and capacitive properties are characterized by scanning electron microscopy, X-ray diffraction spectroscopy, X-ray photoelectron spectroscopy, Branauer-Emmett-Teller test, thermogravimetric analysis, Fourier transform infrared spectroscopy, cyclic voltammetry, charge-discharge test and the electrochemical impedance measurements. The results show that MnO2 is predominant in the PANI/MnO2 composite and the composite exhibits larger specific surface area than pure MnO2. The maximum specific capacitance of the composite electrode reaches up to 320 F/g by charge-discharge test, 1.56 times higher than that of MnO2 (125 F/g). The specific capacitance retains approximately 84% of the initial value after 10,000 cycles, indicating the good cycle stability.
A comparison study of MnO2and Mn2O3as zinc-ion battery cathodes: An experimental and computational investigation
Shen, Hongyuan,Liu, Binbin,Nie, Zanxiang,Li, Zixuan,Jin, Shunyu,Huang, Yuan,Zhou, Hang
, p. 14408 - 14414 (2021)
The high specific capacity, low cost and environmental friendliness make manganese dioxide materials promising cathode materials for zinc-ion batteries (ZIBs). In order to understand the difference between the electrochemical behavior of manganese dioxide materials with different valence states, i.e., Mn(iii) and Mn(iv), we investigated and compared the electrochemical properties of pure MnO2 and Mn2O3 as ZIB cathodes via a combined experimental and computational approach. The MnO2 electrode showed a higher discharging capacity (270.4 mA h g-1 at 0.1 A g-1) and a superior rate performance (125.7 mA h g-1 at 3 A g-1) than the Mn2O3 electrode (188.2 mA h g-1 at 0.1 A g-1 and 87 mA h g-1 at 3 A g-1, respectively). The superior performance of the MnO2 electrode was ascribed to its higher specific surface area, higher electronic conductivity and lower diffusion barrier of Zn2+ compared to the Mn2O3 electrode. This study provides a detailed picture of the diversity of manganese dioxide electrodes as ZIB cathodes. This journal is
Catalytic effects of metal oxides on the decomposition of Potassium perchlorate
Zhang, Yunchang,Kshirsagar, Girish,Ellison, John E.,Cannon, James C.
, p. 119 - 127 (1996)
Catalytic effects of metal oxides with comparable surface areas on the decomposition of potassium perchlorate were studied by thermogravimetric analysis. The catalytic mechanism is discussed based on the relative activity of the metal oxides. It is found
Ethanol tolerant precious metal free cathode catalyst for alkaline direct ethanol fuel cells
Grimmer, Ilena,Zorn, Paul,Weinberger, Stephan,Grimmer, Christoph,Pichler, Birgit,Cermenek, Bernd,Gebetsroither, Florian,Schenk, Alexander,Mautner, Franz-Andreas,Bitschnau, Brigitte,Hacker, Viktor
, p. 325 - 331 (2017)
La0.7Sr0.3(Fe0.2Co0.8)O3 and La0.7Sr0.3MnO3 ?based cathode catalysts are synthesized by the sol-gel method. These perovskite cathode catalysts are tested in half cell configuration and compared to MnO2 as reference material in alkaline direct ethanol fuel cells (ADEFCs). The best performing cathode is tested in single cell setup using a standard carbon supported Pt0.4Ru0.2 based anode. A backside Luggin capillary is used in order to register the anode potential during all measurements. Characteristic processes of the electrodes are investigated using electrochemical impedance spectroscopy. Physical characterizations of the perovskite based cathode catalysts are performed with a scanning electron microscope (SEM) and by X-ray diffraction showing phase pure materials. In half cell setup, La0.7Sr0.3MnO3 shows the highest tolerance toward ethanol with a performance of 614 mA cm?2 at 0.65 V vs. RHE in 6 M KOH and 1 M EtOH at RT. This catalyst outperforms the state-of-the-art precious metal-free MnO2 catalyst in presence of ethanol. In fuel cell setup, the peak power density is 27.6 mW cm?2 at a cell voltage of 0.345 V and a cathode potential of 0.873 V vs. RHE.
Factors influencing the structure of electrochemically prepared α-MnO2 and γ-MnO2 phases
Lin,Sun,Weng,Yang,Suen,Liao,Huang,Ho,Chong,Tang
, p. 6548 - 6553 (2007)
The α- and γ-phases of MnO2 prepared by electrolysis of MnSO4 and MxSO4 (where M = Li+, Na+, K+, Rb+, Cs+ or Mg2+) in aqueous solutions at various pH and voltage Ev values under ambient conditions have been systematically studied. The structures of powdery MnO2 produced are found to depend on the radius of the Mz+ counter cation in addition to the pH and Ev conditions. In order to achieve the α-phase for MnO2 formation under neutral pH condition, the radius of counter cation must be equal to or greater than 1.41 A?, the size of the K+ cation. The relative concentration ratio of [MnO4-]transient/[Mn2+], which is related to the pH-Ev conditions, also affects the structure of MnO2 produced with counter ions smaller than K+. For samples prepared in acidified solution with the counter ions of Li+, Na+ or Mg2+ at 2.2 V, the electrolysis products display the γ-MnO2 phase while those prepared at 2.8 V electrolysis produce a mixture of γ-MnO2 and α-MnO2 phases. Single phase of α-MnO2 is identified in the 5 V electrolysis products. Furthermore, the valence state of manganese was found to decrease as the applied voltage was reduced from 5.0 to 2.2 V. This implies that the lower [MnO4-]transient/[Mn2+] ratio or the less oxidative condition is responsible for the non-stoichiometric MnO2 structure with oxygen deficiency.
MnO2-coated Ni nanorods: Enhanced high rate behavior in pseudo-capacitive supercapacitor
Lei,Daffos,Taberna,Simon,Favier
, p. 7454 - 7459 (2010)
Ni nanorods prepared by electrochemical growth through an anodized aluminium oxide membrane were used as substrate for the electrodeposition of MnO2 either in potentiostatic mode or by a pulsed method. Electrochemical deposition parameters were chosen for an homogeneous deposit onto Ni nanorods. Resulting Ni supported MnO2 electrodes were tested for electrochemical performances as nanostructured negative electrodes for supercapacitors. They exhibited initial capacitances up to 190 F/g and remarkable performances at high charge/discharge rates.
Moore, T. E.,Ellis, M.,Selwood, P. W.
, p. 856 - 866 (1950)
Photocurrent generation from semiconducting manganese oxide nanosheets in response to visible light
Sakai, Nobuyuki,Ebina, Yasuo,Takada, Kazunori,Sasaki, Takayoshi
, p. 9651 - 9655 (2005)
Unilamellar nanosheet crystallites of manganese oxide generated the anodic photocurrent under visible light irradiation (?? a??0.5 nm may facilitate the charge separation of excited electrons and holes, which is generally very difficult for strongly localized d-d transitions. The monolayer film of MnO2 nanosheets exhibited the incident photon-to-electron conversion efficiency of 0.16% in response to the monochromatic light irradiation (?? = 400 nm), which is comparable to those for sensitization of monolayer dyes adsorbed on a flat single-crystal surface. The efficiency declined with increasing the layer number of MnO2 nanosheets, although the optical absorption was enhanced. The recombination of the excited electron-hole pairs may become dominant when the carriers need to migrate a longer distance than 1 layer through multilayered nanosheets. ? 2005 American Chemical Society.
Udupa, M. R.
, p. 245 - 248 (1981)
Oxidative Cleavage of S–S Bond During the Reduction of Tris(pyridine-2-carboxylato)manganese(III) by Dithionite in Sodium Picolinate–Picolinic Acid Buffer Medium
Sen Gupta, Kalyan K.,Bhattacharjee, Nandini,Pal, Biswajit
, p. 635 - 643 (2016)
The reduction of tris(pyridine-2-carboxylato)manganese(III) by dithionite has been investigated within the temperature window 288–303 K and at pH range 5.22–6.10 in sodium picolinate–picolinic acid buffer medium. The reaction obeys the following stoichiometry: S2O2- 4 + 2MnIII + 2H2O → 2HSO- 3 + 2MnII + 2H+ The reaction is described in terms of a mechanism that involves an initial complex formation between S2O4 2? and [MnIII(C5H4NCO2)3] followed by S–S bond cleavage to give 2HSO3 ? and [MnII(C5H4NCO2)2(H2O)2] as the products via the formation of SO2 ●? radical anion. Kinetics and spectrophotometric evidences are cited in favor of the suggested mechanism. Thermodynamic parameters associated with the equilibrium step and the activation parameters with the rate-determining step have been computed.
Synthesis, spectroscopic characterization, thermal, and photostability studies of 2-(2′-hydroxy-5′-phenyl)-5-aminobenzotriazole complexes
Refat, Moamen S.
, p. 1095 - 1103 (2010)
Three Mn(II), Co(II), and Cu(II) new transition metal complexes of the fluorescence dye: 2-(2′-hydroxy-5′-phenyl)-5-aminobenzotriazole/PBT derived from o-aminophenol and m-phenylenediamine have been synthesized. The structural interpretations were confirmed from elemental analyses, magnetic susceptibility and molar conductivity, as well as from mass, IR, UV-Vis spectral studies. From the analytical, spectroscopic, and thermal data, the stoichiometry of the mentioned complexes was found to be 1:2 (metal:ligand). The molar conductance data revealed that all the metal chelates are non-electrolytes and the chloride ions exist inside the coordination sphere. The thermal stabilities of these complexes were studied by thermogravimetric (TG/DTG) and the decomposition steps of these three complexes are investigated. The kinetic parameters such as the energy of activation (E*), pre-exponential factor (A), activation entropy (ΔS*), activation enthalpy (ΔH*), and free energy of activation (ΔG*) have been reported. Photostability of phenyl benzotriazole as fluorescence dye and their metal complexes doped in polymethyl methacrylate/PMMA were exposed to UV-Vis radiation and the change in the absorption spectra was achieved at different times during irradiation period.
Synthesis, Crystal Structures, Reactivity, and Magnetochemistry of a Series of Binuclear Complexes of Manganese(II), -(III), and -(IV) of Biological Relevance. The Crystal Structure of IV(μ-O)3MnIVL'>(PF6)2*H2O Containing an Unprecedented Short Mn...Mn Distance of 2.296 Angs...
Wieghardt, Karl,Bossek, Ursula,Nuber, Bernhard,Weiss, Johannes,Bonvoisin, J.,et al.
, p. 7398 - 7411 (1988)
The disproportionation reactions of two binuclear complexes of manganese(III) containing the oxo-bis(acetato)dimanganese(III) core and two 1,4,7-triazacyclononane (L) capping ligands (1) or two N,N',N''-trimethyl-1,4,7-triazacyclononane (L') ligands (2) in aqueous solution under anaerobic conditions lead to a variety of novel binuclear MnIIIMnIV and MnIV2 dimers.These are the following: IIIMnIV(μ-O)2(μ-CH3CO2)>2*CH3CN (5); IIIMnIV(μ-O)(μ-CH3CO2)2>(ClO4)3 (6); IV2(OH)2(μ-O)2>II3(C2O4)4(OH2)2>*6H2O (7); and IV2(μ-O)3>(PF6)2*H2O (9).A tetranuclear species IV4O6>Br4*5.5H2O (8) is generated as a thermodynamically very stable product from a MnII containing aqueous solution of L in the presence of oxygen.In the absence of oxygen methanolic solutions of Mn(ClO4)2*2H2O or manganese(II) acetate react with L' to form II2(μ-OH)(μ-CH3CO2)2>(ClO4) (3) and II2(μ-CH3CO2)3> (4).The oxo- and acetato-bridges in 1 and 2 are labile; addition of anions X- (X=Cl, Br, NCS, N3) to acetonitrile solutions of 1 or 2 yields the monomers LMnX3 and L'MnX3.The electrochemistry of all compounds has been investigated; for example, 2 is reversibly oxidized by two one-electron processes to generate MnIIIMnIV and MnIV2 dimers in liquid SO2.The crystal structures of 4, 7, 8, and 9 have been determined by X-ray crystallography: 4, orthorhombic Pcab, a = 17.368(5) Angstroem, b = 17.538(5) Angstroem, c = 33.21(1) Angstroem, Z = 8; 7, monoclinic C2/c, a = 13.391(3) Angstroem, b = 16.571(4) Angstroem, c = 19.312(4) Angstroem, β = 109.82(2) degree, Z = 4; 8, monoclinic P21/c, a = 17.548(8) Angstroem, b = 13.118(7) Angstroem, c = 212.56(1) Angstroem, β = 105.63(4) degree, Z = 4; 9, orthorhombic Pnma, a = 10.057(5) Angstroem, b = 16.12(1) Angstroem, c = 19.237(8) Angstroem, Z = 4. 9 consists of the cofacial bioctahedral cation IV(μ-O)3MnIVL'>2+ and PF6 anions.The Mn...Mn distance is unusually short (2.296(2) Angstroem).Bulk magnetic properties of all compouds have been studied between 100 and 298 K, and in some instances 4 and 298 K.In 2 the MnIII ions are ferromagnetically coupled, J = +18(1) cm-1; whereas the MnII centers in 4 are weakly antiferromagnetically coupled, J = -3.5(2) cm-1.Very strong intramolecular antiferromagnetic coupling is observed in 9 (J = -780 cm-1).
Bifunctional pyrimidine-amino-acid ligands: Solution study and crystal structure of a Mn(II) chain alternating six- and sevenfold coordination environments
López-Garzón,Arranz-Mascarós,Godino-Salido,Gutiérrez-Valero,Cuesta,Moreno
, p. 41 - 48 (2003)
The acid-base characterization in aqueous solution of the N-2-[4-amino-1,6-dihydro-1-methyl-5-nitroso-6-oxopyrimidinyl)methionine, a member of a family of bifunctional N-pyrimidine α-amino acids ligands, has been carried out by potentiometric and UV-Vis techniques in the 2.5-9.0 pH range, indicating a quasi-zwitterionic structure. The solution study of the HL/Mn(II) system at 1:2, 2:1 and 4:1 molar ratios (25°C and pHA solid complex with MnL2·612H2O stoichiometry was isolated from an aqueous 1:3 [HL]/[Mn(II)] mixture at pH 6. The X-ray single-crystal characterization has revealed that this complex can be formulated as {[Mn(H 2O)4(μ-L)2Mn(L)2(H 2O)]·8H2O}n, an infinite chain in which two different Mn(II) ions having six- and sevenfold coordination environments alternate along the chain. The asymmetric unit contains two ligands coordinating in different fashion. One of these coordinates monodentately through the oxygen atom belonging to the exocyclic nitroso group while the other exhibits a 3η-bridging pattern between the six- and sevenfold Mn(II) arrangements. The versatile coordination modes of this ligand is discussed and compared to other complexes of this bifunctional family of ligands.
Cathodic behavior of alkali manganese oxides from permanganate
Chen, Rongji,Whittingham, M. Stanley
, p. L64-L67 (1997)
The reaction of potassium, sodium, and lithium permanganate in water at 170°C leads directly to potassium, sodium, and lithium manganese dioxides, AyMnO · nH2O, with a R3m rhombohedral structure. These crystalline layered structures after dehydration readily and reversibly react with lithium through an intercalation mechanism. The capacity for lithium is a function of the alkali ion present, and the larger potassium ion maintains the capacity best. For lithium there is a tendency to convert to the spinel structure which leads to loss of capacity.
Euler, Karl-Joachim,Kirchhof, Robert
, p. 1383 - 1388 (1981)
Enhanced anode performance of manganese oxides with petal-like microsphere structures by optimizing the sintering conditions
Yu, Wei,Jiang, Xiaojian,Meng, Fanhui,Zhang, Zhonghua,Ma, Houyi,Liu, Xizheng
, p. 34501 - 34506 (2016)
Herein, the rational design and synthesis of manganese oxides (MnO2 and MnO) have been achieved and both of them show petal-like microsphere structures. As anodes for LIBs, MnO exhibits a higher capacity of 751.4 mA h g-1 after 400 cycles (492.7 mA h g-1 for MnO2 after 300 cycles) at 2000 mA g-1.
Incorporation of impurity metal ions in electrolytic manganese dioxide
Tamura,Ishizeki,Nagayama,Furuichi
, p. 2035 - 2040 (1994)
The amounts of impurity metal ions incorporated into electrolytic manganese dioxide (EMD) during its preparation were measured as a function of metal ion concentrations and current densities. The amount of incorporated ions increased in proportion to the concentration in solution, and at a fixed concentration it was different from ion to ion: Ni2+2+2+2+3+ 2+. The specific surface area of the formed EMD was larger for impurity ions with higher incorporation affinity. Further, the adsorption of ions on the surface of a ready-made manganese dioxide sample (IC12) was examined, and modeling of the adsorption behavior was attempted. The amounts of adsorbed ions at a fixed concentration in solution and pH 0.7 (where EMD is produced) were obtained by the ion-adsorption model. There was a strong correlation between the amount incorporated and the amount of adsorption, suggesting a mechanism in which EMD is contaminated through adsorption on its new growing surface. The increase in specific surface area of EMD with contaminants was interpreted to be due to a suppression of the growth of EMD at the adsorbed foreign ion sites, resulting in EMD with many defects or smaller particle sizes. The opposite effect of current density on incorporation for the two groups of metal ions was discussed.
Power loss and energy density of the asymmetric ultracapacitor loaded with molybdenum doped manganese oxide
Wang, Yue-Sheng,Tsai, Dah-Shyang,Chung, Wen-Hung,Syu, Yong-Sin,Huang, Ying-Sheng
, p. 95 - 102 (2012)
Ultracapacitors of asymmetric configuration have been prepared with activated carbon (AC) and undoped or Mo-doped manganese oxide (MnO2) in 1.0 M Na2SO4 electrolyte. Phase analysis shows the AC powder, 1-15 μm in size, contains both disordered and graphitic structures, and the undoped and Mo-doped oxide powder, 0.05-0.20 μm in particle size, mainly involves amorphous MnO2 and MoO2. CV results indicate the single electrode of AC plus 10 wt% Mo-doped MnO2 (A9OM1) is superior to the electrode with undoped MnO2 or high content of doped MnO2, exhibiting features of double layer capacitance at high scan rate and pseudocapacitance characteristics at low scan rate. When assembled with a negative electrode of AC, the capacitor of positive A9OM1 electrode demonstrates the least power loss among three asymmetric capacitors. This asymmetric capacitor also shows a higher capacitance than the symmetric AC capacitor when the current density is less than 8.0 A g-1 in 1.8 V potential window. But a higher electrode resistance of A9OM1, in contrast with AC, compromises its capacitance plus. When the energy density of A9OM1 asymmetric capacitor is compared with that of symmetric AC capacitor at the same power level, the capacitance benefit on energy density is restricted to current density ≤ 3.0 A g-1.
One-step synthesis of hollow urchin-like Ag2Mn8O16 for long-life Li-O2 battery
Ci, Lijie,Dai, Linna,Guo, Huanhuan,Li, Deping,Li, Jianwei,Liao, Jialin,Lu, Jingyu,Nie, Xiangkun,Sun, Qing,Xiao, Shenyi,Yao, Yuqing
, (2021/10/12)
To solve the critical issues like high polarization and unstable cycle ability, it is vital to design low-cost, stable and efficient catalytic cathode material for nonaqueous Li-O2 batteries (LOBs). Herein, a hollow urchin-like hollandite Ag2Mn8O16 electrocatalyst is fabricated by one-step hydrothermal method. The mixed bimetallic oxide with diverse valences (Mn3+ and Mn4+) and active oxygen defects provide sufficient active sites, and Ag[sbnd]Mn[sbnd]O bonds accelerate charge transformation. LOBs with the well-designed porous Ag2Mn8O16 cathode show superior electrochemical performances in LOBs, including ultrahigh specific capacity (7912 mAh gc?1 at 100 mA gc?1), good rate performance (5076 mAh gc?1 at 250 mA gc?1, 64.16%) and long-term cycle stability (320 cycles at 100 mA gc?1 within a limited capacity of 250 mAh gc?1 and 133 cycles at 200 mA gc?1 within a limited capacity of 500 mAh gc?1). This work provides a positive effect on designing better catalytic cathode materials for LOBs and push forward the commercialization progress.
Effect of Manganese Valence on Specific Capacitance in Supercapacitors of Manganese Oxide Microspheres
Chen, Xing,Li, Lei,Wang, Xiaoli,Xie, Kun,Wang, Yuqiao
, p. 9152 - 9159 (2021/05/17)
Manganese oxides have attracted great interest in electrochemical energy storage due to high theoretical specific capacitance and abundant valence states. The multiple valence states in the redox reactions are beneficial for enhancing the electrochemical properties. Herein, three manganese microspheres were prepared by a one-pot hydrothermal method and subsequent calcination at different temperatures using carbon spheres as templates. The trivalent manganese of Mn2O3 exhibited multiple redox transitions of Mn3+/Mn2+ and Mn4+/Mn3+ during the intercalation/deintercalation of electrolyte ions. The possible redox reactions of Mn2O3 were proposed based on the cyclic voltammetry and differential pulse voltammogram results. Mn2O3 microsphere integrated the advantages of multiple redox couples and unique structure, demonstrating a high specific capacitance and long cycling stability. The symmetric Mn2O3//Mn2O3 device yielded a maximum energy density of 29.3 Wh kg?1 at 250 W kg?1.
Interfacial effect of Pd supported on mesoporous oxide for catalytic furfural hydrogenation
Lee, Hojeong,Nguyen-Huy, Chinh,Jeong Jang, Eun,Lee, Jihyeon,Yang, Euiseob,Lee, Man Sig,Kwak, Ja Hun,An, Kwangjin
, p. 291 - 300 (2020/03/05)
Highly dispersed Pd is loaded onto different types of mesoporous oxide supports to investigate the synergetic metal-support effect in catalytic furfural (FAL) hydrogenation. Ordered mesoporous Co3O4, MnO2, NiO, CeO2, and Fe2O3 are prepared by the nanocasting and the supported Pd on mesoporous oxide catalysts are obtained by the chemical reduction method. It is revealed that mesoporous oxides play an important role on Pd dispersion as well as the redox behavior of Pd, which determines the final FAL conversion. Among the catalysts used, Pd/Co3O4 shows the highest conversion in FAL hydrogenation and distinct product selectivity toward 2-methylfuran (MF). While FAL is converted via two distinct pathways to produce either furfuryl alcohol (FA) via aldehyde hydrogenation or MF via hydrogenolysis, MF as a secondary product is derived from FA via the hydrogenolysis of C–O over the Pd/Co3O4 catalyst. It is revealed that FAL is hydrogenated to FA preferentially on the Pd surface; then the secondary hydrogenolysis to MF from FA is further promoted at the interface between Pd and Co3O4. We confirm that the reaction pathway over Pd/Co3O4 is totally different from other catalysts such as Pd/MnO2, which produces FA dominantly. The characteristics of the mesoporous oxides influence the Pd-oxide interfaces, which determine the activity and selectivity in FAL hydrogenation.
