Analysis of Surface Oxidation on Pt and Pt Core-Shell Electrocatalysts for PEFCs

• Published in: Journal of the Electrochemical Society Vol. 159; no. 5; pp. B554 - B563
• Main Authors: Mathew, Preethi, Meyers, Jeremy P., Srivastava, Ratndeep, Strasser, Peter
• Format: Journal Article
• Language: English
• Published: The Electrochemical Society, Inc 01.01.2012
• ISSN: 0013-4651; 1945-7111
• DOI: 10.1149/2.066205jes

Studies on the formation and reduction of surface oxide on Pt-Cu/C core-shell electrocatalysts have been carried out with reference to the nature and type of the adsorbed intermediates formed on the surface as a function of applied potential. In-situ measurements were made using EQCM coupled with cyclic voltammetry to monitor the surface changes. Comparisons between the novel "core-shell" electrocatalysts, conventional Pt/C electrocatalysts and unsupported Pt black electrocatalysts have been made. We find that interfacial mass of the adsorbed species increases in a continuous linear manner as the potential is increased during the anodic oxidation. We also find evidence to suggest that the oxide formation on the core-shell electrocatalyst occurs via the formation of adsorbed hydroxyl species involving one electron per surface site and that on pure Pt proceeds via adsorbed oxide involving two electrons per site. A different mechanism for oxide growth on these catalysts was confirmed by the change in the Tafel slopes for anodic oxidation of the surface. The results showed that the core-shell catalyst surface is less oxidized and that the surface strain imposes a barrier to surface oxidation. This also explains the shift in the oxide stripping peak that has been observed for the Pt binary alloy catalysts.