Temperature and potential-dependent structural changes in a Pt cathode electrocatalyst viewed by in situ XAFS

The paper presents an X-ray absorption fine structure (XAFS) investigation of Pt supported on Vulcan XC-72 operating as a cathode catalyst in a polymer electrolyte membrane fuel cell (PEM FC). XAFS spectroscopy was performed in situ using a cell developed by the authors and optimized for absorption measurements. Low-noise spectra were obtained using the transmission mode over the Pt L3 XAFS range, enabling multiple-scattering XAFS data-analysis for the Pt nanocrystalline system under operating conditions. Accurate measurements of the local structure were performed at various potentials and working temperatures. Changes in the near-edge structures reflecting variations in the Pt electronic structure were observed for various potential values in the cathode activation region. The Pt average local geometric structure was found to be practically potential-independent. The increase in structural disorder caused by the higher working FC temperature was not found to affect the catalyst’s performance in the kinetically controlled region.