Reductive Segregation During the Synthesis of Sb−SnO2-Supported Iridium Electrocatalysts for the Oxygen Evolution Reaction

Abstract

A metal-organic chemical deposition approach using an Ir(acac)3 precursor was employed to synthesise oxide−supported iridium-based electrocatalysts for the oxygen evolution reaction (OER) in acidic media. Inert and oxidising deposition conditions were explored in two temperature regimes, and the influence of these parameters on the physicochemical and electrochemical properties of catalysts consisting of IrOx supported on Sb–SnO2 (ATO) were studied. Surprisingly, it was found that increasing the deposition temperature up to 620 °C favoured the formation of reduced iridium phases even in the presence of an oxidising reaction environment. This was explained by a thermodynamic preference for reduced phases at high temperatures, as well as the presence of acetylacetonate ligand decomposition products serving as reducing agents. Similarly, the reductive segregation of Sb from the ATO support at high temperatures leads to the loss of conductivity of the support, and the formation of Ir–Sb–Sn alloyed nanoparticles. These processes resulted in a loss of OER performance for the materials prepared under high-temperature conditions. Our findings highlight the importance of carefully selecting the temperature range during the synthesis of oxidic support materials and electrocatalysts for the OER.