A high entropy oxide as high-activity electrocatalyst for water oxidation

High entropy materials are a new pathway in the development of high-activity (electro )catalysts because of the inherent tunability and coexistence of multiple potential active sites, which may lead to earth-abundant catalyst materials for energy-efficient electrochemical energy storage. In this report, we identify how the multi-cation composition in high entropy perovskite oxides (HEO) contributes to high catalytic activity for the oxygen evolution reaction (OER), i.e. the key kinetically limiting half-reactions in several electrochemical energy conversion technologies, including green hydrogen generation. We compare the activity of the (001) facet of LaCr0.2Mn0.2Fe0.2Co0.2Ni0.2O3-δ with the parent compounds (single B-site in the ABO3 perovskite). While the single B-site perovskites roughly follow the expected volcano-type activity trends, the HEO clearly outperforms all of its parent compounds with 2.8 to 100 times higher currents at fixed overpotential. As all samples were grown as an epitaxial layer, our results indicate an intrinsic composition–function relationships, avoiding the effects of complex geometries or unknown surface composition. In-depth X-ray photoemission studies reveal a synergistic effect of simultaneous oxidation and reduction of different transition metal cations during adsorption of reaction intermediates. The surprisingly high OER activity demonstrates that HEOs are a highly attractive, earth-abundant new material class for high-activity OER electrocatalysts, possibly allowing fine-tuning the activity beyond the scaling limits of mono- or bimetallic oxides.