High-entropy oxides: Emergent materials for electrochemical energy storage and conversion

High-entropy oxides (HEOs) have received considerable attention in the past few years due to their unique high configurational entropy and ideal elemental adjustability. HEOs are generally considered to be a special class of oxides containing five or more different metal cations. The attractive synergistic effect makes HEOs promising energy storage and conversion material. However, at present, the knowledge of HEOs and their practical applications on electrochemistry is still scattered without comprehensive report. In this review, we highlight the preparation methods, common crystal structures and their applications in the field of electrochemistry, which can be divided into two main categories: (1) electrochemical energy storage devices, including supercapacitors, lithium-ion batteries, sodium-ion batteries, and other batteries; (2) electrocatalysis reaction system, including hydrogen evolution reaction (HER), oxygen evolution reaction (OER), oxygen reduction reaction (ORR), and electrocatalytic CO₂ reduction reaction (CO₂RR). Finally, the remaining challenges and prospects in the future are envisioned in the related field, which will help to unlock the mysteries of HEOs for energy storage and conversion.