Asymmetric Electron Transport‐Induced Formation of High‐Valent IrO_x 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 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.