Asymmetric Electron Transport-Induced Formation of High-Valent IrOx in NiFeOOH Heterostructure for Efficient Water Oxidation

Abstract

Metal oxyhydroxides (MOOHs) as the active phase of transition metal-oxide (TMOs) electrodes in the oxygen evolution reaction (OER) are limited by unsatisfactory electrochemical activity and stability during high-current conditions. Herein, the heterostructure of high-valent IrOx (Irn+, n>4) combined with FeNi3OOH via asymmetric electron transport is deliberately designed on carbon cloth (IrOx-FeNi3OOH/CC) as a promising OER electrocatalyst for industrial deployments. Experimental and DFT calculations reveal that the asymmetric electron transfer from Ir to the low-spin orbital of Fe/Ni sites via bridged O2− sites (Ir─O─Ni/Fe bonds) at IrOx-FeNi3OOH heterostructure interfaces induces the formation of high-valent Ir species. This process tailors the d-band center of Ir sites, thereby reducing the energy barrier of the rate-determining step from O* to OOH* in OER. The elevated activity of high-valent Ir enables IrOx-FeNi3OOH/CC to achieve an ultra-low overpotential of 241 mV at 200 mA cm−2, along with remarkable stability for 160 h under large current conditions (outperforming commercial IrO2/CC). This work offers a basis for rationally designing and analyzing the potential role of precious-metal-based oxyhydroxides as electrocatalysts for the OER and related processes.