Dual role of carbon in the catalytic layers of perovskite/carbon composites for the electrocatalytic oxygen reduction reaction

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• 作者：T. Poux ; F.S. Napolskiy ; T. Dintzer ; G. K¨¦rangu¨¦ven ; S. Ya. Istomin ; G.A. Tsirlina ; E.V. Antipov ; E.R. Savinova
• 关键词：Oxygen reduction reaction (ORR) ; Perovskite ; Carbon ; Alkaline electrolyte ; Rotating disc electrode (RDE)
• 刊名：Catalysis Today
• 出版年：2012
• 出版时间：30 July, 2012
• 年：2012
• 卷：189
• 期：1
• 页码：83-92
• 全文大小：1667 K

文摘

Perovskite oxides are promising materials for the ORR in alkaline media. However, catalytic layers prepared from perovskite powders suffer from high Ohmic losses and low catalyst utilization. An addition of carbon to the catalytic layers greatly improves the performance of the electrodes in the ORR. In this work composite thin film electrodes comprised of a perovskite oxide (either LaCoO₃ or La_0.8Sr_0.2MnO₃) and pyrolytic carbon of the Sibunit family were investigated in aqueous 1 M NaOH electrolyte using cyclic voltammetry and rotating disc electrode (RDE) method with the objective to unveil the influence of carbon on the catalyst utilization and on the ORR electrocatalysis. By systematically varying the oxide to carbon ratio we arrive to the conclusion on the dual role of carbon in composite electrodes. On the one hand, it is required to improve the electrical contact between perovskite particles and the current collector, and to ensure maximum utilization of the perovskite surface. On the other hand, carbon plays an active role in the ORR by catalyzing the O₂ reduction to H₂O₂. Composite electrodes catalyze the 4e^? ORR in contrast to carbon which is only capable of catalyzing the 2e^? reduction. For LaCoO₃ composite electrodes, carbon is responsible for the catalysis of the first steps of the ORR, the role of LaCoO₃ being largely limited to the hydrogen peroxide decomposition and/or reduction. For La_0.8Sr_0.2MnO₃ composite electrodes, along with the catalysis of the chemical decomposition and/or reduction of H₂O₂ produced on carbon, the perovskite also significantly contributes to the first steps of the ORR. The results of this work suggest that the ORR on the carbon and the oxide components of composite cathodes must be considered as coupled reactions whose contributions cannot be always separated, and that neglecting the contribution of carbon to the ORR electrocatalysis may lead to erroneous values of the catalytic activity of perovskite materials.