Cation Substituted Entropy Driven Cu–Mn–Zn–Cr–O Metal Oxide for Efficient Seawater Splitting and Hybrid Supercapacitors

ABSTRACT Entropy‐stabilized single‐phase oxides represent a promising class of multifunctional catalysts, where entropy‐driven stability and oxygen vacancy‐induced lattice distortion synergistically enhance electronic structure and electroactivity. In this work, a Cu–Mn–Zn–Cr–O (CMZCO) medium entropy oxide (MEO) is synthesized via a facile solvothermal method. CuMn 2 O 4 is prepared as a structural analogue, sharing the same spinel framework. Strategic substitution of Zn 2+ for Cu 2+ and Cr 3+ for Mn 3+ is hypothesized to minimize lattice distortion due to comparable ionic radii and stable oxidation states, thereby improving CMZCO's structural and electrochemical properties. The CMZCO MEO exhibited a high specific capacity of 188 C/g (417.7 F/g) in 2 m KOH at 2 A/g. Integrated into a hybrid supercapacitor (HSC), it delivered power and energy densities of 600 W/kg and 33.33 Wh/kg, with ∼84% capacitance retention over 10 000 cycles. Electrocatalytic performance showed low overpotentials of 130 mV and 116 mV in 1 m KOH, with extended stability. In alkaline seawater, overpotentials further decreased to 53 mV and 100 mV. Density functional theory simulations validated the atomic level insights into electronic structure, reaction activity, and stability, aligning with experimental results. Overall water splitting required 1.7 V at 10 mA/cm 2 , remaining stable at 1.9 V for 48 h. Sustainable applicability is demonstrated using a photovoltaic module for seawater splitting and HSC charging.