High‐entropy oxides for electrochemical energy storage and conversion devices

Abstract High‐entropy oxides (HEOs) are complex oxides with a single‐phase crystal structure that contains five or more principal metal cations in their lattices. The multiple elements doping and configurational entropy stabilization could bring many beneficial effects, such as improved high‐temperature phase stability, ionic conductivity, and surface reactivity. Consequently, HEOs have novel prospects for the systematic design of functional oxides for diverse applications with enhanced performance. Conducting oxides, which are conductive for electrons or certain kinds of ion(s), are of particular interest among the various oxide materials. They are key materials in many electrochemical energy conversion and storage devices, such as electrodes for lithium‐ion batteries, electrolytes for solid‐state batteries (SSBs), air electrodes, and electrolytes for solid oxide fuel cells (SOFCs) and solid oxide electrolysis cells (SOECs). The conductivity, stability, electrocatalytic activity, and ion storage capability of these conducting oxides determine the practical use of the corresponding devices. During the past, considerable research has been conducted towards the application of HEOs. Thus, this review seeks to provide an intensive, critical, and accessible summary of HEOs and their influence over a wide temperature range, highlighting the role of entropy‐driven phase stabilization and multiple elements doping that support their distinctive characteristics. This review also rigorously delves into the core mechanisms that affect their functionality and hinder their broader implementation. It connects essential insights with practical aspects, detailing innovative strategies for conducting HEOs design and exploitability, and establishing a roadmap to expedite their shift from laboratory research to industrial applications in sustainable energy systems. image