Role of Cu-Ion Doping in Cu-伪-MnO2 Nanowire Electrocatalysts for the Oxygen Reduction Reaction

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• 作者：Danae J. Davis ; Timothy N. Lambert ; Julian A. Vigil ; Mark A. Rodriguez ; Michael T. Brumbach ; Eric N. Coker ; Steven J. Limmer
• 刊名：Journal of Physical Chemistry C
• 出版年：2014
• 出版时间：August 7, 2014
• 年：2014
• 卷：118
• 期：31
• 页码：17342-17350
• 全文大小：428K
• ISSN：1932-7455

文摘

The role of Cu-ion doping in 伪-MnO₂ electrocatalysts for the oxygen reduction reaction in alkaline electrolyte was investigated. Cu-doped 伪-MnO₂ nanowires (Cu-伪-MnO₂) were prepared with varying amounts (up to 3%) of Cu²⁺ using a hydrothermal method. The electrocatalytic data indicate that Cu-伪-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 伪-MnO₂ alone. The observed improvement in catalytic behavior correlates with an increase in Mn³⁺ content at the surface of the Cu-伪-MnO₂ nanowires. The Mn³⁺/Mn⁴⁺ couple is the mediator for the rate-limiting redox-driven O₂/OH^{鈥?/sup> exchange. O₂ adsorbs via an axial site (the e_g orbital on the Mn3+ d4 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 O₂ adsorbates and faster rates of reduction. A smaller crystallite size (roughly half) for Cu-伪-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.}