Structure of Pt(111)/Ionomer Membrane Interface and Its Bias-Induced Change in Membrane Electrode Assembly

The structure of the perfluorosulfonated ionomer (PFSI)/Pt(111) interface in a membrane electrode assembly (MEA)-like configuration of a polymer electrolyte membrane (PEM) fuel cell, that is, a vacuum evaporated Pt layer/PEM(Nafion membrane)/PFSI(adhesion Nafion layer)/Pt(111) single crystal, and its bias-induced change were investigated by surface X-ray scattering measurement at an atomic level. Crystal truncation rod measurement shows that PFSI adsorbed on the Pt(111)-(1 × 1) surface without bias. When the Pt(111) electrode was positively biased to form Pt oxide, the PFSI layer was detached from the Pt surface and oxygen atoms penetrated into the Pt lattice.