High-Entropy Oxides as Electrocatalysts for the Oxygen Evolution Reaction: A Mini Review

It is crucial to develop cost-effective and high-efficiency catalysts for electrochemical water splitting. High-entropy oxides (HEOs) are promising emerging catalysts for the oxygen evolution reaction (OER) with outstanding catalytic activity and remarkable durability because of their flexibility and structural stability, as well as the synergistic effect of various elements. Herein, a panoramic view of the mechanism of the OER of HEO and the evaluation criteria for the performance of the OER of HEO are discussed. A sequence of key discoveries and achievements of HEO-based OER electrocatalysts with different structures such as perovskite, spinel, and rock-salt structures has been summarized, together with special focuses on the modification strategies including increasing the number of sites with active edges, adjusting the structure of electrocatalysts, and the improvement of electrical conductivity. Then the main preparation methods of HEO electrocatalysts are reviewed. Moreover, theoretical calculations applied in the production of OER catalysts are summarized to guide material design and understand the catalytic mechanism. Finally, this review highlights existing challenges and future design directions of HEO-based OER electrocatalysts.