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

Torsion-strained TaxTmyIr1-x-yO2-delta nanocatalyst with abundant grain boundaries is promising towards acidic oxygen evolution in practical proton exchange membrane electrolysers. The cost of H-2 is estimated to be reduced to US$1 per kg. 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 Ta0.1Tm0.1Ir0.8O2-delta 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 Ta0.1Tm0.1Ir0.8O2-delta 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 H-2, which is much lower than the target (US$2 per kg of H-2) set by the US Department of Energy.