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Abstract

The synthesis of a highly active and yet stable electrocatalyst for the anodic oxygen evolution reaction (OER) remains a major challenge for acidic water splitting on an industrial scale. To address this challenge, we obtained an outstanding high-performance OER catalyst by loading Ir on conductive antimony-doped tin oxide (ATO)-nanoparticles by a microwave (MW)-assisted hydrothermal route. The obtained Ir phase was identified by using XRD as amorphous (XRD-amorphous), highly hydrated Ir^III/IV oxohydroxide. To identify chemical and structural features responsible for the high activity and exceptional stability under acidic OER conditions with loadings as low as 20 µg_Ircm^-2, we used stepwise thermal treatment to gradually alter the XRD-amorphous Ir phase by dehydroxylation and crystallization of IrO₂. This resulted in dramatic depletion of OER performance, indicating that the outstanding electrocatalytic properties of the MW-produced Ir^III/IV oxohydroxide are prominently linked to the nature of the produced Ir phase. This finding is in contrast with the often reported stable but poor OER performance of crystalline IrO₂-based compounds produced through more classical calcination routes. Our investigation demonstrates the immense potential of Ir oxohydroxide- based OER electrocatalysts for stable high-current water electrolysis under acidic conditions.