Torsion strained iridium oxide for efficient acidic water oxidation in proton exchange membrane electrolyzers

Acidic oxygen evolution reaction is crucial for practical proton exchange membrane water splitting electrolysers, which have been hindered by the high catalytic overpotential and high loading of noble metal catalysts. Here we present a torsion-strained Ta_0.1Tm_0.1Ir_0.8O_2-δ nanocatalyst with numerous grain boundaries that exhibit a low overpotential of 198 mV at 10 mA cm^-2 towards oxygen evolution reaction in 0.5 M H₂SO₄. Microstructural analyses, X-ray absorption spectroscopy and theoretical calculations reveal that the synergistic effects between grain boundaries that result in torsion-strained Ir-O bonds and the doping induced ligand effect collectively tune the adsorption energy of oxygen intermediates, thus enhancing the catalytic activity. A proton exchange membrane electrolyser using a Ta_0.1Tm_0.1Ir_0.8O_2-δ nanocatalyst with a low mass loading of 0.2 mg cm^-2 can operate stably at 1.5 A cm^-2 for 500 hours with an estimated cost of US$1 per kilogram of H₂, which is much lower than the target (US$2 per kg of H₂) set by the US Department of Energy.