Ir-Pd nanoalloys with enhanced surface-microstructure-sensitive catalytic activity for oxygen evolution reaction in acidic and alkaline media

Abstract

Ir-based electrocatalysts have been systematically studied for a variety of applications, among which the electrocatalysis for oxygen evolution reaction (OER) is one of the most prominent. The investigation on surface-microstructure- sensitive catalytic activity in different pH media is of great significance for developing efficient electrocatalysts and corresponding mechanism research. Herein, shape-tunable Ir-Pd alloy nanocrystals, including nano-hollow-spheres (NHSs), nanowires (NWs), and nanotetrahedrons (NTs), are synthesized via a facile one-pot solvothermal method. Electrochemical studies show that the OER activity of the Ir-Pd alloy nanocatalysts exhibits surface-microstructure-sensitive enhancement in acidic and alkaline media. Ir-Pd NWs and NTs show more than five times higher mass activity than commercial Ir/C catalyst at an overpotential of 0.25 V in acidic and alkaline media. Post-XPS analyses reveal that surface Ir(VI) oxide generated at surface defective sites of Ir-Pd nanocatalysts is a possible key intermediate for OER. In acidic medium, the specific activity of Ir-Pd nanocatalysts has a positive correlation with the surface roughness of NWs > NHSs > NTs. However, the strong dissociation of surface Ir(VI) species (IrO42-) at surface defective sites is a possible obstacle for the formation of Ir(VI) oxide, which reverses the activity sequence for OER in alkaline medium.