Understanding the Role of Electronic Interactions in Oxide–Supported Iridium Oxide Catalysts for the Oxygen Evolution Reaction

Abstract

As our society seeks increased energy security and resilience, the need for efficient, cost-effective, carbon-free hydrogen generation will continue to grow. Proton exchange membrane (PEM) water electrolysers are a promising technology to produce “green” hydrogen, however, at present, their large-scale commercialization is hindered by the high capital costs of critical components. The anodic membrane electrode assembly requires large quantities of iridium (Ir) to facilitate the kinetically demanding oxygen evolution reaction (OER). Owing to its scarcity, iridium is a severe bottleneck and expense in the widespread implementation of these technologies. The iridium content in electrolyser anodes can be lowered substantially by designing catalysts which consist of finely dispersed nanoparticles of iridium dioxide affixed onto suitable support materials. This approach enhances the active surface area and operational lifetime of these electrocatalysts towards the OER while utilising a fraction of the otherwise required iridium. To reap these benefits, the support needs to be a high surface area, corrosion-resistant material that is a good electronic conductor1,2. Metal oxides have dominated as oxygen evolution support materials for PEM electrolysis; however, they typically need to be doped with an impurity to demonstrate sufficient electronic conductivity. Iridium oxides supported on antimony−doped tin oxide (ATO) support have been found to behave as high-performing OER electrocatalysts in acidic conditions3,4. While there is no doubt that existing studies prove a link between the presence of ATO support and the improved performance of ATO-supported iridium oxides versus unsupported catalysts, an in-depth characterisation of the charge transfer between the ATO support and deposited IrO2 nanoparticles could prove useful in understanding the reason for these performance enhancements on the basis of the electronic properties of the catalyst and the support.In this study, we investigated the performance of highly dispersed IrO2 nanoparticles, supported on doped tin oxide supports, consisting of various metallic dopants and iridium loadings. The electronic interactions between the Ir-phase and the support were studied by measuring the valence band spectra of the prepared materials with X-ray and ultraviolet photoelectron spectroscopy, and Hall measurements were utilised to understand the nature of electronic conductivity in the prepared materials. The uncovered physicochemical and electronic characteristics are related to the electrochemical performance of these materials towards the OER. These novel findings contribute insights which can be used as the basis for the rational design of next-generation oxide-supported Ir-based catalysts with tunable electronic properties for sustainable PEM electrolysis applications.