Iridium Based Metal Oxides: Catalysts for Advancing the Oxygen Evolution Reaction in Acid

In the face of a changing climate, it is clear that technologies that meet the world’s growing energy demand in a sustainable way are needed. Green hydrogen, produced from the electrochemical splitting of water, could play an important role in decarbonizing electricity production, allowing for the storage of energy from renewables on the timescale of months. But wide scale implementation of hydrogen production requires advances in performance and cost of water electrolyzers. Proton exchange membrane electrolyzers for hydrogen production achieve high performance, but require the use of iridium, one of the world’s rarest metals, as a catalyst at the anode. Mixed metal oxide structures can reduce the use of expensive iridium without compromising activity or stability, but the behavior of this broad class of chemicals in realistic oxygen evolution reaction (OER) conditions is poorly understood. Here, we investigate the performance of iridium containing double perovskites and strontium iridates and study their change in intrinsic activity and surface composition over time. All catalysts were synthesized via solid state reaction in air and characterized using X-ray diffraction. The activity was measured using chronoamperometry in 0.1M HClO₄ and normalized by the electrochemical surface area. In general, we find that both the double perovskites and strontium iridates converge to the same activity and the same surface composition, as confirmed by post-reaction X-ray photoelectron spectroscopy. Although these metal oxide surfaces can be made with an unlimited range of element compositions and stoichiometries, our results suggest that the post reaction activity and surface composition in acid do not depend on the pristine lattice.