Following Adsorbate Coverage on Anodes of High‐Temperature Polymer Electrolyte Membrane Fuel Cells in the Presence of CO and H2O by using In Operando X‐ray Absorption Spectroscopy

Application of the Δμ X-ray absorption near-edge spectroscopy analysis technique to a polybenzimidazole-membrane-based high-temperature (170 °C) polymer electrolyte membrane fuel cell (PEMFC) under varying conditions reveals binding-site details for H, CO, and biphosphate on a platinum nanoparticle anode surface. A synergistic interplay between CO and biphosphate adsorption is found, so that with increasing CO in the gas feed (below 3–4 % in H2), an increased biphosphate coverage becomes visible, apparently because small amounts of adsorbed CO force more localization of the phosphate species, which is believed to be adsorbed on top of the existing H overlayer. Increasing the concentration of CO (well above 4 %) causes CO poisoning to takeover and dramatically decrease the activity, though, compared to low-temperature PEMFCs, huge amounts of CO can still be tolerated. Adding small amounts of water (less than 7 mg min−1) with CO to the anode feed reduces the amount of adsorbed phosphate and, thereby, increases the activity.