Oxidation of Aqueous Phosphorous Acid Electrolyte in Contact with Pt Studied by X-ray Photoemission Spectroscopy.

The oxidation of the aqueous H 3 PO 3 in contact with Pt was investigated for a fundamental understanding of the Pt/aqueous H 3 PO 3 interaction with the goal of providing a comprehensive basis for the further optimization of high-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs). Ion-exchange chromatography (IEC) experiments suggested that in ambient conditions, Pt catalyzes H 3 PO 3 oxidation to H 3 PO 4 with H 2 O. X-ray photoelectron spectroscopy (XPS) on different substrates, including Au and Pt, previously treated in H 3 PO 3 solutions was conducted to determine the catalytic abilities of selected metals toward H 3 PO 3 oxidation. In situ ambient pressure hard X-ray photoelectron spectroscopy (AP-HAXPES) combined with the "dip-and-pull" method was performed to investigate the state of H 3 PO 3 at the Pt|H 3 PO 3 interface and in the bulk solution. It was shown that whereas H 3 PO 3 remains stable in the bulk solution, the catalyzed oxidation of H 3 PO 3 by H 2 O to H 3 PO 4 accompanied by H 2 generation occurs in contact with the Pt surface. This catalytic process likely involves H 3 PO 3 adsorption at the Pt surface in a highly reactive pyramidal tautomeric configuration.