Nano high-entropy materials for bifunctional oxygen electrocatalysis: Rational design, structure-activity relationships, and applications in rechargeable metal-air batteries

High-entropy materials (HEMs) have emerged as promising oxygen electrocatalysts due to their compositional flexibility, tunable electronic structures, entropy-stabilized phases, and highly adjustable catalytic properties. These unique characteristics enable HEMs to effectively address the sluggish kinetics of the oxygen reduction (ORR) and oxygen evolution reactions (OER), reduce overpotentials, and overcome the bifunctional activity limitations imposed by scaling relationships that hinders their practical application in metal–air batteries. This review systematically examines design principles and synthesis methods for high-entropy oxygen electrocatalysts, emphasizing structure–activity correlations. It critically assesses recent advances across diverse HEM classes—including alloys, oxides , layered double hydroxides , phosphides, selenides, and fluorides—highlighting their bifunctional ORR/OER activity, multi-element synergistic effects, and mechanisms of catalytic enhancement. Key performance descriptors relevant to high-entropy oxygen catalysis are identified and discussed. The integration of HEMs into rechargeable zinc–air (both conventional and flexible solid-state) and lithium–oxygen batteries is also discussed, demonstrating their potential in next-generation energy storage. The review provides insights into rational design strategies and structure–property relationships to guide the development of high-performance high-entropy bifunctional electrocatalysts for electrochemical energy conversion and storage applications.