Key Structural Kinetics for Carbon Effects on the Performance and Durability of Pt/Carbon Cathode Catalysts in Polymer Electrolyte Fuel Cells Characterized by In Situ Time-Resolved X-ray Absorption Fine Structure

Abstract

The structural kinetics (rate constants for electronic and structural transformations) of the Pt charging/discharging, Pt–Pt bond dissociation/re-formation, and Pt–O bond formation/dissociation of Pt/Ketjenblack, Pt/acetylene black, and Pt/multiwalled carbon nanotube cathode catalysts in polymer electrolyte fuel cell (PEFC) membrane electrode assemblies (MEAs) under transient potential operations (0.4 VRHE → 1.4 VRHE → 0.4 VRHE) has been studied by in situ/operando time-resolved quick X-ray absorption fine structure (QXAFS; 100 ms/spectrum), while measuring electrochemical currents/charges in the MEAs under the potential operations. From the systematic QXAFS analysis for potential-dependent surface structures and rate constants (k and k′) for the transformations of Pt nanoparticles under the operations (0.4 VRHE → 1.4 VRHE and 1.4 VRHE → 0.4 VRHE), respectively, we have found the structural kinetics (k′Pt–O and k′valence) controlling the oxygen reduction reaction (ORR) activity and also the structural kin...