Origin of efficient oxygen reduction reaction on Pd monolayer supported on Pd-M (M=Ni, Fe) intermetallic alloy

Intermetallic alloy has become a hot topic in heterogeneous catalysis due to improved activity and stability. We report here the results of Pd monolayer supported on face-centered tetragonal (fct) Pd-M (M = Ni or Fe) intermetallic alloy as cathode materials by first principle calculations. Adsorbed O2 is found to undergo hydrogenation process into OOH instead of direct dissociative mechanism. The oxygen reduction reaction (ORR) proceeds via four-electron transfer pathway on both surfaces. The enhanced activities are ascribed to moderate adsorption strength for ORR intermediates due to compression strain and substrate electron transfer. The dissolution potential analysis indicates that both Pd/PdNi(111) and Pd/PdFe(111) are stable under operating condition. Gibbs free energy analysis and barrier calculations suggest that the proposed Pd monolayer structures are promising for cathode material. These results can be useful in designing intermetallic Pd-M alloy as ORR electrocatalysts.