Ultrafine oxygen-defective iridium oxide nanoclusters for efficient and durable water oxidation at high current densities in acidic media

Abstract

Iridium oxide (IrO₂) is one of the best known electrocatalysts for the oxygen evolution reaction (OER) taking place in a strongly acidic solution. IrO₂ nanocatalysts with high activity as well as long-term catalytic stability, particularly at high current densities, are highly desirable for proton exchange membrane water electrolysis (PEM-WE). Here, we report a simple and cost-effective strategy for depositing ultrafine oxygen-defective IrO_x nanoclusters (1–2 nm) on a high-surface-area, acid-stable titanium current collector (H-Ti@IrO_x), through a repeated impregnation–annealing process. The high catalytically active surface area resulting from the small size of IrO_x and the preferable electronic structure originating from the presence of oxygen defects enable the outstanding OER performance of H-Ti@IrO_x, with low overpotentials of 277 and 336 mV to deliver 10 and 200 mA cm⁻² in 0.5 M H₂SO₄. Moreover, H-Ti@IrO_x also shows an intrinsic specific activity of 0.04 mA cm_catalyst⁻² and superior mass activity of 1500 A g_Ir⁻¹ at an overpotential of 350 mV. Comprehensive experimental studies and density functional theory calculations confirm the important role of oxygen defects in the enhanced OER performance. Remarkably, H-Ti@IrO_x can continuously catalyze the OER in 0.5 M H₂SO₄ at 200 mA cm⁻² for 130 hours with minimal degradation, and with a higher IrO_x loading, it can sustain at such a high current density for over 500 hours without significant performance decay, holding substantial promise for use in PEM-WE.