Structural Kinetics of Cathode Events on Polymer Electrolyte Fuel Cell Catalysts Studied by Operando Time-Resolved XAFS

Abstract

Operando time-resolved X-ray absorption fine structure (XAFS) analysis is promising to investigate the structural kinetics of cathode events on polymer electrolyte fuel cell (PEFC) electrocatalysts. Here we reviewed our recent reports on operando time-resolved XAFS analysis for PEFC cathode catalysts under PEFC operating conditions. Systematic analysis of a series of operando time-resolved XAFS (XANES and EXAFS) spectra showed details of the structural transformations of Pt cathode catalysts (Pt/C, Pt3Co/C, and Pt3Ni/C) in PEFC, and the rate constants of various structural parameters of the Pt cathode catalysts such as electron transfer from/to Pt (oxidative/reductive electron density change of Pt), Pt–O bond formation/breaking, and Pt–Pt bond breaking/reformation of the cathode catalysts were successfully obtained to discuss the mechanisms of the redox processes of the Pt cathode catalysts and the degradation behaviors of the Pt cathode catalysts in PEFC cells. In this paper, we discuss about structural kinetics of the Pt cathode catalysts in PEFC suggested by operando time-resolved XAFS analysis in the viewpoints of the effects of Pt alloying and degradation.