摘要 : This work reviews the studies conducted in this laboratory of the oxygen reduction reaction (ORR) on electrocatalysts formed by Pt-M/C (M = V, Cr, Co) and Ag-Pt/C alloys and on different Mn oxides (MnO/C, Mn3O4/C, MnO2/C) in KOH e... 展开 This work reviews the studies conducted in this laboratory of the oxygen reduction reaction (ORR) on electrocatalysts formed by Pt-M/C (M = V, Cr, Co) and Ag-Pt/C alloys and on different Mn oxides (MnO/C, Mn3O4/C, MnO2/C) in KOH electrolyte. The physical and electronic properties of the materials are investigated by in situ XAS (x-ray absorption spectroscopy) in the XANES (x-ray absorption near edge structure) region. The electrocatalytic activity for the ORR on the different catalysts is compared through mass-transport-corrected Tafel plots. The XANES results for the Pt-M/C and Ag-Pt/C composites at high electrode potentials show lower vacancy of the Pt 5d band compared to pure Pt/C, while for the results indicate a chance of the Mn oxidation state as a function of the electrode potential. The electrochemical measurements evidence increased electrocatalytic activity of the Pt alloys compared to pure Pt and this is attributed to a lowering of the adsorption strength of adsorbed oxygen species caused by the reduced Pt reactivity. An activity enhancement of the Ag atoms on the Ag-Pt/C alloys compared to pure Ag is ascribed to an electronic effect induced by the presence of Pt, increasing the Ag-O adsorption strength. In the case of the MnyOx/C materials, the electrochemical results show low activity for MnO/C and higher activity for MnO2/C and Mn3O4/C. This is explained based on the activation for the ORR, which is higher for the material with higher MnO2 contents and the occurrence of a mediation processes involving the reduction of Mn(IV) to Mn(III), followed by the electron transfer of Mn(III) to oxygen. 收起