High entropic engineering for sustainable energy and environmental applications

High-entropy alloys (HEAs) came into existence as a revolutionary class of advanced materials distinguished by their exceptional catalytic performance, which results from unique thermodynamic stability, a wide range of elemental compositions, and highly tunable structural and electronic properties. The inherent high-entropy state of HEAs can be explained by four main effects: (i) high configurational entropy, which helps to stabilize a single-phase solid solution; (ii) sluggish atomic diffusion, which increases long-term structural stability; (iii) significant lattice distortion, which modifies the electronic environment and influences charge distribution; and (iv) the cocktail effect, which synergistically modifies the d-band center about the Fermi level, so optimizing catalytic activity. These distinct characteristics provide HEAs with many active sites and complex surface electronic structures, resulting in remarkably high efficiency, stability, and low cost. Although much research has already been done on the synthesis and practical application of HEA-based electrocatalysts, there is still a lack of thorough knowledge and a systematic approach to the rational design of these catalysts for energy and environmental technologies. This review commences by providing an in-depth understanding of the fundamental principles guiding the development of HEAs, in addition to the present state-of-the-art engineering approaches used for performance optimization and innovative synthetic approaches for their scale production. Then, an in-depth investigation of advanced characterization techniques offers significant critical insights into the structural and functional characteristics of these materials. Moreover, the study of the properties is driven by their multi-elemental composition and advanced applications of well-defined HEA nanostructures in the framework of environmental, energy, and storage technologies. Finally, this review concludes the prevailing challenges within the field and delineates prospective research directions to facilitate the transition of HEAs from fundamental studies to practical applications of energy and environmental technologies, thereby serving as a valuable resource for emerging and established researchers in this discipline.