Work

Oxygen Reduction Reaction Performance in Phosphoric Acid of a Catalyst Library for a High-Temperature Proton Exchange Membrane Fuel Cell

Year: 2026

Type: article

Abstract: High-temperature proton exchange membrane fuel cells (HT-PEMFCs) are advantageous for heavy-duty vehicles owing to their operating temperature (150−200 °C), which facilitates the stack heat management and hence decreases the system global weight. A HT-PEMFC membrane electrode assembly (MEA) commonly relies on phosphoric acid-doped polybenzimidazole membranes. While H 3 PO 4 is optimal in terms of electrolyte and membrane properties in HT-PEMFC, it strongly impacts the activity of Pt-based electrocatalysts. In this work, a wide catalyst library highlights most of the material characteristics that, according to the literature, influence phosphate poisoning mechanisms and possibly mitigate the penalty in oxygen reduction reaction (ORR): carbon support, Pt loading on carbon, Pt nanoparticles size, Pt-alloying effect (strain effect), and nanoparticles morphology (octahedron (facet orientation), sponges, carbon cap). By electrochemically characterizing the catalyst library, this work aims to understand their ORR activity decline in 1 M H 3 PO 4 vs 1 M HClO 4 electrolytes at room temperature. The electrolyte used is relatively concentrated compared to the model study in RDE in which the H 3 PO 4 concentration does not exceed 0.1 M (often in a mix with HClO 4 ). Whatever the electrocatalyst, the electrochemical surface area available in H 3 PO 4 decreases by 20−40% compared to HClO 4, while a ca. tenfold decline in ORR specific activity is observed. The results highlight the leading-order parameter influencing the absolute catalyst activity in H 3 PO 4, namely, the adsorbate coverage rate by various phosphates species (θ(H x PO 4 (3− x )− ) and θ(H x PO 3 (3− x )− )), and a second order parameter, namely, the Pt−O, with O from OH*, binding energy on each catalyst (catalyst material-dependent). Both parameters follow a Butler−Volmer model with a Frumkin adsorption/desorption isotherm. The loss rate vs HClO 4 suggests that the SA retention in H 3 PO 4 also depends on a third order parameter, namely, interactions between adsorbates at the surface of the catalyst and in the electrochemical double-layer, described by the Frumkin correction, which is largely affected by operating conditions (electrolyte anion concentration and temperature).

Source: ACS Catalysis

DOI: 10.1021/acscatal.6c00952