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 IrCuOx @DG, is described. Acid leaching can be used to remove Cu atoms and generate porous IrOx nanoclusters supported on DG (P-IrOx @DG), which can serve as efficient and robust pH-universal OER electrocatalysts. Moreover, when paired with commercial 20 wt% Pt/C, P-IrOx @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 IrOx nanoclusters supported on DG (O-IrOx @DG). Probing experiment, X-ray absorption spectroscopy, and theoretical calculation results demonstrate that Cu removal can successfully create P-IrOx nanoclusters and introduce unsaturated Ir atoms. The optimum binding energies of oxygenated intermediate species on unsaturated Ir sites and ultrafine IrOx nanoclusters contribute to the high intrinsic OER catalytic activity of P-IrOx @DG.