High-Entropy Alloys and Oxides as Supercapacitor Electrodes: A Structural and Electrochemical Perspective for Energy Storage

This study investigates the performance of high entropy alloys [Fe₃Cr₃Mn₂NiV, HEA)] and high entropy oxides [(Fe₃Cr₃Mn₂NiV)O₄, HEO)] as electrode materials for supercapacitors. HEA is synthesized through mechanical alloying, followed by HEO forming via an oxidation process. XRD results demonstrate HEA comprises both amorphous and crystalline phases, whereas HEO has an entirely crystalline structure. SEM analyses showed HEA exhibits larger and irregular particles, whereas HEO displays a smaller and spherical morphology. EPR analyses revealed significant changes in defect structures and unpaired electron configurations during the transition from HEA to HEO. HEA is prone to diffusion-controlled processes due to their regular structure and strong magnetic interactions; however, HEO exhibits capacitive behavior based on surface redox reactions and pseudo-capacitive mechanisms due to their irregular structure and oxygen vacancies. CV analyses revealed that HEO contributes more capacitive via surface redox reactions, while GCPL results suggested that HEO demonstrated superior energy density (40.8 Wh kg⁻¹) and power density (14.3 kW kg⁻¹). Impedance analyses revealed that HEO exhibited reduced internal resistance and enhanced ion conductivity, whereas HEA demonstrated higher resistance and diffusion-controlled processes. In conclusion, HEA and HEO exhibit distinct energy storage mechanisms, and these materials can be optimized for supercapacitor applications.