Eight-Component Nanoporous High-Entropy Oxides with Low Ru Contents as High-Performance Bifunctional Catalysts in Zn-Air Batteries

One major challenge in heterogeneous catalysis is to reduce the usage of noble metals while maintaining the overall catalytic stability and efficiency in various chemical environments. In this work, a series of high-entropy catalysts are synthesized by a chemical dealloying method and find the increased entropy effect and non-noble metal contents would facilitate the formation of complete oxides with low crystallinity. Importantly, an optimal eight-component high-entropy oxide (HEO, Al-Ni-Co-Ru-Mo-Cr-Fe-Ti) is identified, which exhibits further enhanced catalytic activity for the oxygen evolution reaction (OER) as compared to the previously reported quinary AlNiCoRuMo and the widely-used commercial RuO2 catalysts, and at the same time similar catalytic activity for the oxygen reduction reaction (ORR) as the commercial Pt/C with a half-wave potential of 0.87 V. Such high-performance bi-functional catalysts, however, only require a half loading amount of Ru as compared to the quinary AlNiCoRuMo, due to the underlying Cr-Fe synergistic effects on tuning the electronic structures at active surface sites, as revealed by the first-principles density functional theory calculations of the authors. The eight-component HEO also demonstrates excellent stability under continuous electrochemical working conditions, suitable for a wide range of applications such as metal-air batteries.