Elucidating the Complex Oxidation Behavior of Aqueous HPO on Pt Electrodes via Tender X-ray Absorption Near-Edge Structure Spectroscopy at the P -Edge.

tender X-ray absorption near-edge structure (XANES) spectroscopy at the P -edge was utilized to investigate the oxidation mechanism of aqueous HPO on Pt electrodes under various conditions relevant to high-temperature polymer electrolyte membrane fuel cell (HT-PEMFC) applications. XANES and electrochemical analysis were conducted under different tender X-ray irradiation doses, revealing that intense radiation induces the oxidation of aqueous HPO via HO yielding HPO and H. A broadly applicable experimental procedure was successfully developed to suppress these undesirable radiation-induced effects, enabling a more accurate determination of the aqueous HPO oxidation mechanism. XANES studies of aqueous 5 mol dm HPO on electrodes with varying Pt availability and surface roughness reveal that Pt catalyzes the oxidation of aqueous HPO to HPO. This oxidation is enhanced upon applying a positive potential to the Pt electrode or raising the electrolyte temperature, the latter being corroborated by complementary ion-exchange chromatography measurements. Notably, all of these oxidation processes involve reactions with HO, as further supported by XANES measurements of aqueous HPO of different concentrations, showing a more pronounced oxidation in electrolytes with a higher HO content. The significant role of water in the oxidation of HPO to HPO supports the reaction mechanisms proposed for various chemical processes observed in this work and provides valuable insights into potential strategies to mitigate Pt catalyst poisoning by HPO during HT-PEMFC operation.