Tailoring non-stoichiometric spinel Mn0.5Co2.5O4via tunable microwave strategy toward advanced supercapacitor application

Abstract

Supercapacitors, owing to their ultrahigh power density, long cycling life, and rapid charge–discharge capability, have emerged as promising candidates for next-generation advanced energy storage systems. Non-stoichiometric spinel-type electrode materials have attracted increasing attention due to their tunable architecture, high structural stability, and defect-induced electronic optimization. Microwave-assisted synthesis, featuring rapid heating and unique thermal and non-thermal effects, offers an efficient route for fabricating such non-stoichiometric spinel structures. In this work, non-stoichiometric spinel Mn_0.5Co_2.5O₄ porous nanowire array electrodes were successfully synthesized via a microwave-assisted hydrothermal method combined with defect engineering. By systematically tuning the microwave synthesis parameters (reaction temperature, reaction time, and microwave power), the correlations between microstructural evolution and electrochemical performance were comprehensively investigated. The results reveal that the sample obtained under 140 °C, 1.5 h, and 900 W exhibits a uniform and dense porous nanowire array with the lowest Co²⁺/Co³⁺ ratio, the highest Mn incorporation, and the most favorable reaction kinetics. Consequently, it delivers significantly enhanced charge-storage capacity (716.5 F g⁻¹ at 1 A g⁻¹), excellent rate capability (425.8 F g⁻¹ at 10 A g⁻¹), a wide potential window of 1.13 V (−0.2 to 0.93 V vs. SCE), and outstanding cycling stability with 80.2% capacitance retention and nearly 100% coulombic efficiency after 12 000 cycles at 10 A g⁻¹. This study provides new insights into the controlled design of high-performance non-stoichiometric spinel electrode materials for advanced supercapacitors.