Pt3Co/C is known to be more efficient and durable electrocatalyst at cathode in PEFC than Pt/C. The role of Co has been theoretically investigated but differences in structural changes and their kinetics of the Pt electrocatalysts are not fully investigated under PEFC working conditions. Herein, we report the structural kinetics and surface reaction mechanism of Pt3Co/C and Pt/C elecrotrocatalysts in MEAs during PEFC voltage-cycling processes by operando time-resolved QXAFS.Operando Pt LIII-edge time-resolved QXAFS of Pt3Co/C and Pt/C cathode electrocatalysts were recorded during voltage-cycling processes at 0.4 V ? 1.0 V and 1.0 V ? 0.4 V at SPring-8 at 100-500 ms intervals. Changes in electronic and local coordination structures of Pt in the electrocatalysts were systematically analyzed by the time-resolved XAFS.Changes in Pt oxidation states, coordination numbers and bond distances of Pt-O and Pt-Pt were plotted against reaction time, and kinetic parameters of these events were successfully estimated (fig. 1). We found significant time lags between electrochemical reactions in PEFC and structural changes in the Pt3Co/C and Pt/C for the voltage-cycling processes. Significant rate enhancements of Pt redox and structural changes were observed on Pt3Co/C, especially in Pt-Pt bond reforming (kPt-Pt=0.3 s-1) and Pt-O cleavage (kPt-O=0.4 s-1), compared to those of Pt/C (kPt-Pt=0.078 s-1 and kPt-O=0.11 s-1). These differences in the kinetics would be contributed to the improvement of the durability of Pt electrocatalysts under PEFC operating conditions.  (A) Series of in situ time-resolved Pt LIII-edge XANES spectra and (B) time profiles of Pt valence, CN and bond lengths of Pt-Co, Pt-Pt, Pt-O for the voltage-cycling process of 1.0 V ? 0.4 V on Pt3Co/C.

Differences in structural kinetics of Pt<sub>3</sub>Co/C and Pt/C cathode electrocatalysts under PEFC operating conditions by operando time-resolved XAFS

247th National Meeting (2014)

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Differences in structural kinetics of Pt3Co/C and Pt/C cathode electrocatalysts under PEFC operating conditions by operando time-resolved XAFS

Differences in structural kinetics of Pt₃Co/C and Pt/C cathode electrocatalysts under PEFC operating conditions by operando time-resolved XAFS