Transient voltage with overshooting or undershooting behavior in PEFC is suggested to cause the acceleration of electrocatalyst degradation under PEFC operating conditions. The overreactions of Pt electrocatalyst during such transient voltages may be related to the catalyst degradation, however electronic and local structures of Pt electrocatalysts have not been directly observed yet. Operando time-resolved QXAFS is a powerful tool to investigate changes in local structures of Pt and Pt-alloy cathode electrocatalysts in MEAs under PEFC operating conditions. Here, we report the electronic and local structures of a Pt/C cathode electrocatalyst in MEA of PEFC for load processes with transient voltages studied by operando time-resolved XAFS with 100 ms of time resolution at BL36XU, SPring-8. Current loading periods were 0-30 s with current density from 0.11 to 0.83 and from 0.83 to 0.11 A cm-2 to induce transient voltages. Series of Pt LIII-edge XANES spectra and EXAFS Fourier transforms were successfully acquired with every 100 ms and 500 ms, respectively. The curve-fitting analysis of the XANES spectra and EXAFS Fourier transforms were performed to estimate the oxidation states and local structures of the Pt electrocatalyst during the transient voltages. Gradual changes in the white line height of Pt LIII-edge XANES were observed, suggesting gradual oxidation/reduction of the Pt electrocatalyst for the current load, and the coordination numbers of Pt-Pt bonding were almost constant for the load processes. These results of the operando time-resolved XAFS suggested that the overreactions of the redox processes and structural changes in the Pt electrocatalyst at the cathode were negligible for the current loading processes with transient voltages.

Electronic and local structures of Pt/C cathode electrocatalyst in MEA of PEFC during transient voltages studied by operando time-resolved XAFS

247th National Meeting (2014)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.