Optimized iridium-molybdenum oxides for acidic oxygen evolution reaction via potential control

The harsh working conditions of proton exchange membrane water electrolysis (PEMWE), particularly at the anode, necessitate the development of high-performance anode catalyst materials. Currently, iridium (Ir), one of the rarest elements on Earth, and its derived materials remain the only viable candidates with reasonable activity and stability. This limitation significantly hinders the commercialization of PEMWE technology. This study presents a nanocomposite catalyst that consists of well-dispersed Ir clusters loaded on an ultrathin phosphomolybdic acid substrate. The optimized catalyst with a low Ir loading of approximately 21 wt% exhibits an overpotential of 262 mV at 10 mA cm⁻² for oxygen evolution reaction in acid and a mass activity of 501 A g⁻¹_Ir at 300 mV overpotential, which is one order of magnitude higher than that of commercial Ir black. A PEMWE device using the developed catalyst with an Ir loading of 0.6 mg cm⁻² can drive a current density of 1 A cm⁻² at 1.72 V and demonstrates a degradation rate of 0.20 mV h⁻¹ over 250 h operation at 0.5 A cm⁻². The catalyst dissolution rate analysis reveals that mitigating the open-circuit potential of molybdenum-based supports is crucial for minimizing material dissolution. The potential control electrochemical system offers a potential strategy for developing cost-effective catalysts for electrolysis.