期刊
JOURNAL OF PHYSICAL CHEMISTRY C
卷 118, 期 31, 页码 17342-17350出版社
AMER CHEMICAL SOC
DOI: 10.1021/jp5039865
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资金
- Sandia National Laboratories [DE-AC04-94AL85000]
The role of Cu-ion doping in alpha-MnO2 electrocatalysts for the oxygen reduction reaction in alkaline electrolyte was investigated. Cu-doped alpha-MnO2 nanowires (Cu-alpha-MnO2) were prepared with varying amounts (up to similar to 3%) of Cu2+ using a hydrothermal method. The electrocatalytic data indicate that Cu-alpha-MnO2 nanowires have up to 74% higher terminal current densities, 2.5 times enhanced kinetic rate constants, and 66% lower charge transfer resistances that trend with Cu content, exceeding values attained by alpha-MnO2 alone. The observed improvement in catalytic behavior correlates with an increase in Mn3+ content at the surface of the Cu-alpha-MnO2 nanowires. The Mn3+/Mn4+ couple is the mediator for the rate-limiting redox-driven O-2/OH- exchange. O-2 adsorbs via an axial site (the e(g) orbital on the Mn3+ d(4) ion) at the surface or at edge defects of the nanowire, and the increase in covalent nature of the nanowire with Cu-ion doping leads to stabilization of O-2 adsorbates and faster rates of reduction. A smaller crystallite size (roughly half) for Cu-alpha-MnO2 leading to a higher density of (catalytic) edge defect sites was also observed. This work is applicable to other manganese oxide electrocatalysts and shows for the first time there is a correlation for manganese oxides between electrocatalytic activity for the oxygen reduction reaction (ORR) in alkaline electrolyte and an increase in Mn3+ character at the surface of the oxide.
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