Abstract
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.
On top of the volcano: The importance of the anatase crystal phase in TiO2‐IrO2 solid solutions in forming highly active Ir sites for the oxygen evolution reaction (OER), around the top of the volcano plot, is shown through theoretical and experimental studies. Such highly active Ir sites are indirectly obtained by creating Sr‐deficient surfaces on SrTiO3‐SrIrO3 solid solutions in situ.