Steric interaction of iridium sites towards efficient oxygen and hydrogen evolution

Abstract

Transition metal materials that loaded with trace of Iridium (Ir) are widely accepted as effective catalysts for oxygen evolution (OER) and hydrogen evolution reaction (HER), in which the Ir atoms exposed on the surface can directly affect the electrocatalytic reaction. However, this neglects the Ir – Ir interaction of distinct locations, which may be benefit for the fine-tuning of electronic structure. Herein, we changed the locations (surface and inside) of Ir atoms in the cobalt oxide (Co3O4@NC), and investigated their alkaline OER and HER performances. Combined with X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS) and theoretical calculations, we infer that the steric interaction induced by the surface – internal Ir sites can weaken the Ir-O bond and optimize the adsorption of intermediates on catalyst surface with a negative shift of d-band center, enabling the surface-Ir sites with lower energy barrier for water dissociation and hydrogen adsorption for HER. Therefore, the as-prepared Irw-Co3O4@NC with surface − inside Ir distribution significantly improve the HER without degrading OER performance, with low overpotential of −173 / −71 mV for HER at −10 mA/cm2 in 0.1 M KOH / 1.0 M KOH, and 244 / 249 mV at 10 mA/cm2 for OER.