Nanoscale High-Entropy Alloys and Oxides for Supercapacitor Electrodes: Size Effects, Structure–Property Relationships, and Energy Storage Potential

Abstract

High-entropy alloys and oxides (HEAs and HEOs), composed of multiple principal elements in near-equiatomic ratios, have emerged as promising candidates for supercapacitor electrodes. Their intrinsic features—configurational entropy stabilization, sluggish diffusion, and lattice distortion—enable unique structure–property relationships. When synthesized at the nanoscale, these materials exhibit enhanced surface area, high defect density, and finite-size effects that boost electrochemical activity and stability. This review outlines the evolution of high-entropy materials, their synthesis strategies, and the advantages of nanoscale design for energy storage. We highlight correlations between electronic structure, defect engineering, charge storage mechanisms, and device-level demonstrations in symmetric, asymmetric, and flexible supercapacitors. Remaining challenges include synthesis reproducibility, compositional control, and scalability, while emerging directions point toward hybrid composites, sustainable synthesis, and artificial intelligence–guided discovery. Nanoscale high-entropy alloys and oxides thus provide a versatile platform to advance supercapacitor performance through systematic tuning of size effects and structure–property relationships.