ORR Activity Enhancement in Pd-based Alloy Catalysts and Its Underlying Mechanisms: A First Principles Study

摘要

Palladium(Pd) based binary and ternary alloy catalysts are known to improve the sluggish kinetics of the oxygen reduction reaction (ORR) in Polymer Electrolyte Membrane fuel cells (PEMFCs). For example, alloying Pd with transition metals like Fe, Co, Ni has been shown to improve the catalytic activity of Pd; in particular, Pd3Co substrates have been reported to enhance the ORR activity of Pd significantly. In this work, we present the mechanisms underlying the alloying effect in PdCo alloys and elucidate the synergetic interplay between the surface electronic structure modification due to the underlying Co atoms and the compressive strain caused by the Pd3Co substrate. Reactivity is evaluated on the basis of the surface adsorption strength towards the key intermediate species in ORR . We also discuss the alloying effects of a series of Pd/Pd3X (X=Sc, Ti, V, Fe, Ni) systems and selected Pd-based ternary systems, and provide some suggestions for the design of new ORR catalysts.