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

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 IrO_x (Irⁿ⁺, n>4) combined with FeNi₃OOH via asymmetric electron transport is deliberately designed on carbon cloth (IrO_x-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 IrO_x-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 IrO_x-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.