Radical-driven nano-crystalline IrO2: resolving the activity-stability trade-off in acidic OER

Abstract

Improving the intrinsic activity of surface iridium sites without sacrificing stability remains a critical challenge, as conventional strategies often enhance one property at the expense of the other. Here, we report a hydroxyl radical (˙OH)-driven synthesis strategy that spontaneously converts Ir(OH)₆³⁻ into sub-2 nm rutile-phase IrO₂ nanocrystals in aqueous solution at 90 °C via a thermodynamically favorable radical-oxidation pathway (ΔG° = −257.05 kJ mol⁻¹). The nanoscale confinement induces lattice contraction and shortens Ir–O bonds, thereby elevating the intrinsic activity of surface Ir sites, while the stabilized rutile framework with robust [IrO₆] octahedra effectively suppresses Ir dissolution. The obtained IrO₂ catalyst exhibits a mass activity of 135 A g⁻¹ and a turnover frequency (TOF) of 0.254 s⁻¹ at an overpotential of 320 mV, outperforming commercial IrO₂ by 92% and 66%, respectively. When integrated into a PEMWE anode with a low Ir loading of 0.3 mg cm⁻², the single cell achieves an industrial-relevant current density of 3.0 A cm⁻² at 1.89 V and operates stably for over 500 h. This work not only offers a practical solution to the activity-stability dilemma in PEMWE catalyst design, but also presents a novel, and low-temperature synthetic platform for metal oxides.