Iridium Single-Atom-Modulated Nickel Hydroxide for Boosting Overall Water Splitting

Developing bifunctional electrocatalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) with high activity and stability at industrial current density remains an urgent priority. Herein, we present a facile one-step hydrothermal strategy under mild conditions to fabricate Ir single-atom (SA)-modulated ultrathin nickel hydroxide nanosheets on nickel foam (denoted as Ir-Ni(OH)₂/NF), serving as a structurally integrated bifunctional electrode for robust water electrolysis. The incorporation of Ir triggers Ni(OH)₂ to transform from a p-type semiconductor to an n-type semiconductor, substantially increasing carrier concentration and creating abundant oxygen vacancy on the Ni(OH)₂ surface to immobilize Ir-SAs through strong Ir-O-Ni bonds, which optimizes the local electronic environments of Ir and Ni sites. Density functional theory calculations unveil that the Ir-SAs demonstrate an appropriate valve of ΔG_O*-ΔG_OH* and activate the Ni sites for the OER, following the adsorption evolution mechanism (AEM) pathway. Meanwhile, the Ni sites promote water dissociation and supply continuous protons to Ir sites for facilitating HER. Consequently, the Ir-Ni(OH)₂/NF electrode achieves overpotentials of only 23 mV for HER and 217 mV for the OER at 10 mA cm^-2 in a 1.0 M KOH solution. More importantly, an efficient anion exchange membrane water electrolysis (AEMWE) electrolyzer is assembled by the structurally integrated Ir-Ni(OH)₂/NF electrode as both liquid-gas diffusion layer and catalyst layer of the anode and cathode, which requires an ultrasmall cell voltage of 1.54 V to drive a high current density of 500 mA cm^-2 with long-term stability for over 225 h. This work may provide a pathway to the rational design of bifunctional electrocatalysts.