Design and Application of High-Entropy Oxide Spinel Nanostructures (Mg0.2Ni0.2Cu0.2Zn0.2Co0.2)Fe2O4 as Potential Materials for Electrochemical Hydrogen Storage

The growing interest in electric vehicles and sustainable energy has intensified the focus on hydrogen as a clean energy carrier. However, the development of efficient electrode materials remains a key challenge, as they are crucial for improving storage capacity and ensuring durability of hydrogen-based systems. This study explores, for the first time, the use of AB₂O₄-type high-entropy oxides (HEOs) for hydrogen storage, focusing on (Mg_0.2Ni_0.2Cu_0.2Zn_0.2Co_0.2)Fe₂O₄ as an electrocatalyst through redox and physisorption kinetics. Porous HEO spinel ferrite nanoparticles were successfully synthesized via coprecipitation using metal nitrates as precursors, followed by calcination at various temperatures. The electrochemical performance of (Mg_0.2Ni_0.2Cu_0.2Zn_0.2Co_0.2)Fe₂O₄ was evaluated as a function of the calcination temperature, phase purity, uniformity, and particle size using a range of physicochemical and electrochemical techniques, including XRD, TGA, Raman spectroscopy, FE-SEM, FT-IR spectroscopy, BET, CV, and chronopotentiometry. XRD and Rietveld refinement confirmed a single-phase cubic structure (Fd3̅m) with high crystallinity and configurational entropy above 1.5R. STA revealed excellent thermal stability compared with conventional ferrites, attributed to the high configurational entropy of the multicomponent system. Laser granulometry analysis revealed that HEO particle size increased with increasing calcination temperature, and EDS mapping/spectra confirmed the presence of Mg, Ni, Co, Cu, Zn, Fe, and O in the compound. Electrochemical studies show that HEOs-600 nanoparticles offer the highest discharge capacity of 3310 mAh/g after 15 cycles in 6 M KOH, attributed to enhanced surface reactivity and faster electron transfer. The electrode maintained high capacity and stability up to 4 mA, while a drop at 5 mA suggests structural degradation at high current.