Spatial imaging of catalyst poisoning with SO2 on Pt/C PEFC electrocatalyst by operando Pt LIII-edge XAFS-CT imaging

Sulfur dioxide (SO2), which is one of the air contaminants, causes drastic power loss of Pt electrocatalysts in polymer electrolyte fuel cells (PEFCs). Herein, we report spatial imaging of catalyst poisoning with SO2 on a Pt/C PEFC cathode electrocatalyst in a membrane electrode assembly (MEA) using operando Pt L-III-edge X-ray absorption fine structure (XAFS)-computed tomography (CT) imaging. The operando XAFS clearly suggested that SO2 is strongly adsorbed on active sites on the Pt cathode catalyst surface without the significant aggregation of Pt catalyst particles. However, it was found that subsequent electrochemical treatment at 1.0 V under 20% O-2/N-2 to remove the adsorbed S species induced not only the removal of S poisoning but also the degradative aggregation of the Pt electrocatalyst. The 3D imaging of the distribution and chemical states of the Pt electrocatalyst showed the degradative manner of the Pt electrocatalyst by the recovery process after the catalyst poisoning with SO2.