Porous Structure Engineering of Iridium Oxide Nanoclusters on Atomic Scale for Efficient pH-Universal Overall Water Splitting

Water electrolysis, which is a promising high-purity H₂ production method, lacks pH-universality; moreover, highly efficient electrocatalysts that accelerate the sluggish anodic oxygen evolution reaction (OER) are scarce. Geometric structure engineering and electronic structure modulation can be efficiently used to improve catalyst activity. Herein, a facile Ar plasma treatment method to fabricate a composite of uniformly dispersed iridium-copper oxide nanoclusters supported on defective graphene (DG) to form IrCuO_x@DG, is described. Acid leaching can be used to remove Cu atoms and generate porous IrO_x nanoclusters supported on DG (P–IrO_x@DG), which can serve as efficient and robust pH-universal OER electrocatalysts. Moreover, when paired with commercial 20 wt% Pt/C, P–IrO_x@DG can deliver current densities of 350.0, 317.6, and 47.1 mA cm⁻² at a cell voltage of 2.2 V for overall water splitting in 0.5 m sulfuric acid, 1.0 m potassium hydroxide, and 1.0 m phosphate buffer solution, respectively, outperforming commercial IrO₂ and nonporous IrO_x nanoclusters supported on DG (O–IrO_x@DG). Probing experiment, X-ray absorption spectroscopy, and theoretical calculation results demonstrate that Cu removal can successfully create P–IrO_x nanoclusters and introduce unsaturated Ir atoms. The optimum binding energies of oxygenated intermediate species on unsaturated Ir sites and ultrafine IrO_x nanoclusters contribute to the high intrinsic OER catalytic activity of P–IrO_x@DG.