Highly Crystalline Iridium–Nickel Nanocages with Subnanopores for Acidic Bifunctional Water Splitting Electrolysis

Developing efficient bifunctional materials is highly desirable for overall proton membrane water splitting. However, the design of iridium materials with high overall acidic water splitting activity and durability, as well as an in-depth understanding of the catalytic mechanism, is challenging. Herein, we successfully developed subnanoporous Ir₃Ni ultrathin nanocages with high crystallinity as bifunctional materials for acidic water splitting. The subnanoporous shell enables Ir₃Ni NCs optimized exposure of active sites. Importantly, the nickel incorporation contributes to the favorable thermodynamics of the electrocatalysis of the OER after surface reconstruction and optimized hydrogen adsorption free energy in HER electrocatalysis, which induce enhanced intrinsic activity of the acidic oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Together, the Ir₃Ni nanocages achieve 3.72 A/mg_{Ir(η=350 mV)} and 4.47 A/mg_{Ir(η=40 mV)} OER and HER mass activity, which are 18.8 times and 3.3 times higher than that of commercial IrO₂ and Pt, respectively. In addition, their highly crystalline identity ensures a robust nanostructure, enabling good catalytic durability during the oxygen evolution reaction after surface oxidation. This work provides a new revenue toward the structural design and insightful understanding of metal alloy catalytic mechanisms for the bifunctional acidic water splitting electrocatalysis.