How oxidation state and lattice distortion influence the oxygen evolution activity in acid of iridium double perovskites

Abstract

In view of iridium's scarceness and high cost, Ir-containing catalysts for water electrolyzers should have low loadings and maximal utilization. Here, we studied low-Ir-content, highly active, double perovskites (Sr₂MIrO₆, M = Ni, Co, Sc and Fe) for the oxygen evolution reaction (OER) in acid combining electrochemical experiments, DFT, and advanced characterization techniques. The initial OER performance depends on Ir's oxidation state and the geometric features of IrO₆ frameworks, which are tuned by the choice of M. Higher oxidation states, particularly Ir⁶⁺, enhance the OER activity: Sr₂NiIrO₆ and Sr₂CoIrO₆ display potentials of ∼1.53 V at 10 mA cm⁻², comparable to the best Ir-based catalysts in the literature. However, because of their less symmetric structures, perovskites with Ir⁶⁺ are less stable, prone to surface reconstruction and their cations leach under OER conditions. These results show that improved iridium-based OER electrocatalysts in acid can be designed by balancing their activity and stability.