Ultrafine IrRu Nanoparticles toward Efficient Oxygen Evolution Reaction in Acidic Media

Proton exchange membrane water electrolyzers (PEMWEs) are capable of mass-producing green hydrogen with renewable and wave-trough electricity, but confront the challenge of the lack of advanced electrocatalysts to accelerate sluggish oxygen evolution reaction (OER). Herein, we report the synthesis of ultrafine IrRu alloy nanoparticles (1.6 ± 0.3 nm) by coprecipitation of IrCl₃, RuCl₃, and HCOONa in water to allow Ir³⁺ and Ru³⁺ to be well dispersed and enclosed in the matrix of crystalline HCOONa, followed by heat treatment of HCOONa to reduce Ir³⁺ and Ru³⁺. Remarkably, the overpotential of IrRu toward acidic OER at 10 mA cm^-2 is merely 230 and 194 mV at 51 and 204 μg_IrRu cm^-2, respectively. The high electrochemically active surface area (ECSA) of 577.1 m² g^-1 and high specific activity (SA) of 22.7 μA cm^-2 at 1.45 V vs RHE would contribute to the exceptional OER activity. In addition, the electron transfer from Ir to Ru in IrRu should significantly boost the OER activity according to X-ray photoelectron spectroscopy (XPS). IrRu also shows an excellent stability during 10 h of a chronopotentiometry (CP) test at 10 mA cm^-2. Eventually, the high OER activity of IrRu was verified in a PEMWE.