Operando Time-Resolved X-ray Absorption Fine Structure Study for Pt Oxidation Kinetics on Pt/C and Pt₃Co/C Cathode Catalysts by Polymer Electrolyte Fuel Cell Voltage Operation Synchronized with Rapid O₂ Exposure

Abstract

The oxidation of a cathode catalyst surface is one of the major factors for cathode catalyst degradation under polymer electrolyte fuel cell (PEFC) operating conditions; however, the oxidation kinetics of Pt cathode catalysts in a membrane electrode assembly with O2 has not been investigated. We have investigated operando Pt LIII-edge time-resolved X-ray absorption fine structure analysis for the Pt oxidation processes on Pt/C and Pt3Co/C cathode catalysts controlled by transient PEFC voltage operation (0.4 V → 0.7–1.0 V) synchronized with the rapid exchange of cathode gas (N2 → 10% O2 in N2). We plotted Pt valence and the coordination numbers of Pt–Pt and Pt–O bonds every 20 ms, and the rate constants of the structural parameters for the Pt oxidation were successfully estimated. The structural kinetics of the Pt oxidation at the cathode suggested differences in the Pt oxidation kinetics between the Pt/C and Pt3Co/C cathode catalysts, showing the kinetic control of the Pt oxidation rate by the alloying with Co to Pt.