Optimization of Active Sites via Crystal Phase, Composition, and Morphology for Efficient Low-Iridium Oxygen Evolution Catalysts.

Reducing the amount of iridium in oxygen evolution electrocatalysts without compromising their catalytic performances is one of the major requirements in proton-exchange-membrane water electrolyzers. Herein, with the help of theoretical studies, we show that anatase-type TiO2 -IrO2 solid solutions possess more active iridium catalytic sites for the oxygen evolution reaction (OER) than IrO2 , the benchmark OER catalyst. Note that the same is not observed for their rutile-type counterparts. However, owing to their thermodynamic metastability, anatase-type TiO2 -IrO2 solid solutions are generally hard to synthesize. Our theoretical studies demonstrate that such catalytically active anatase-type solid-solution phases can be created in situ on the surfaces of readily available SrTiO3 -SrIrO3 solid solutions during electrocatalysis in acidic solution as the solution can etch away Sr atoms. We experimentally show this with porous SrTiO3 -SrIrO3 solid-solution nanotubes synthesized by a facile synthetic route that contain 56 % less iridium than IrO2 yet show an order of magnitude higher apparent catalytic activity for OER in acidic solution.