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

[Image: see text] 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.