Elucidation of Durability of Carbon-Supported PdIr Alloy Catalyst by Experimental and Theoretical Approaches in Polymer Electrolyte Membrane Fuel Cell

Abstract PdIr nanoparticles supported on carbon support are synthesized, and their oxygen reduction reaction (ORR) activity and durability in a half cell or membrane-electrode assembly (MEA) configuration for polymer electrolyte membrane fuel cell are examined. A synergistic effect of the combination of Pd possessing the effective ORR catalytic activity and Ir as one of the most stable elements in acidic media leads to a decrease in particle size, a higher particle dispersion, and a better ORR activity than Pd monometallic catalysts. It is expected that PdIr alloys would form phase-separated nanoalloys that have Pd-rich surface owing to the higher surface energy of Ir. The addition of Ir to Pd in PdIr/C increases the metallic Pd portion. Meanwhile, the Pd5Ir/C is the most durable compared to Pd/C and Pt/C over 3000 h of MEA operation. The ORR activity of PdIr alloy is expected to increase by reducing the oxygen binding energy of Pd in the presence of Ir from the first-principle calculation, and each contribution of compressive strain and ligand effects is quantified. The cohesive energy and the kinetic segregation energy are also calculated to support the improved stability of PdIr compared to Pd and Pt in the ORR condition.