Control of Ir oxidation states to overcome the trade-off between activity and stability for the oxygen evolution reaction

To improve the efficiency of polymer electrolyte membrane water electrolyzers (PEMWEs), catalysts with high activity and stability in the oxygen evolution reaction (OER) have been extensively investigated. In this study, using a novel solution-reduction process, self-assembled Ir/IrOx OER catalysts are prepared, with a controlled Ir oxidation-state ratios. Spectroscopic and electron microscopic analyses confirm that these catalysts have a gradient oxidation state, which gradually decreases from the shell to the core. In half-cell tests, before and after the accelerated stress test (AST) at 10 mA cm−2, the optimized Ir/IrOx catalyst exhibits an overpotential change of approximately 21 mVRHE, which is 3.3 times lesser than that of the state-of-the-art IrO2 (approximately 69 mVRHE). Further, quantification of the dissolved Ir content during the AST shows that the Ir/IrOx catalyst has a strong corrosion resistance under acidic OER conditions. Single-cell testing of the as-prepared OER catalyst demonstrates a remarkable cell performance of 1.73 V at 1.0 A cm−2. After 48-h durability testing, the increase in the membrane electrode assembly cell voltage with the as-prepared OER catalyst is approximately 5.3 times lesser than that of the reference at 250 mA cm−2. The proposed novel catalyst with high activity and stability can aid the development of cost-effective PEMWE systems.