Structural kinetics of polymer electrolyte fuel cell electrocatalysts revealed by in situ time-resolved XAFS

Abstract

Structural transformations and the kinetics of Pt cathode electrocatalysts in a PEFC, which have historically been a black box, were successfully investigated using an in situ time-resolved XAFS technique. The XAFS analyses of Pt₃M/C (M = None, Co, Ni) electrocatalysts revealed that, the rate enhancements of the reductive transformation processes of the Pt valence change, the Pt-Pt bond reformation, and the Pt-O bond breaking, by second metal alloying, were some of the most critical factors of their superior ORR activity and durability. Different degradation aspects between Pt/C and Pt₃Co/C during ADT were also found, as well as that hard Pt agglomeration did not lead to a transformation rate loss in Pt/C, while suppressed Pt agglomeration with unavoidable Co dissolution led to a decrease of kinetic performance in Pt₃Co/C.