Solvent-Controlled Synthesis of ZnCo2O4: Effect of Water/Ethanol Composition on Structural, Textural, and Electrochemical Properties

Solvent composition is an important synthesis parameter that can influence the microstructure and electrochemical performance of electrode materials. In this study, the effect of solvent composition on the structural, morphological, textural, and electrochemical properties of ZnCo2O4 electrodes for supercapacitors was systematically investigated. ZnCo2O4 was synthesized by a hydrothermal method using either pure deionized water or a 1:1 water/ethanol mixture under otherwise identical synthesis conditions. The resulting materials were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), scanning transmission electron microscopy (STEM), and Brunauer–Emmett–Teller (BET) analysis, while their electrochemical properties were evaluated by cyclic voltammetry (CV), galvanostatic charge–discharge (GCD), and electrochemical impedance spectroscopy (EIS). XRD confirmed the formation of the cubic spinel ZnCo2O4 phase without detectable secondary phases for both solvent systems, indicating that solvent composition did not change the fundamental crystal structure. In contrast, pronounced differences were observed in particle morphology and textural properties. The water/ethanol-derived sample exhibited a substantially higher specific surface area of 72.16 m2 g−1 compared with 32.14 m2 g−1 for the pure-water sample, together with a higher pore volume of 0.30 cm3 g−1 versus 0.12 cm3 g−1. The average pore diameter decreased from 15 nm for the pure-water sample to 8 nm for the water/ethanol sample, indicating the formation of a more uniform mesoporous structure. These structural advantages were accompanied by superior electrochemical behavior, including higher specific capacitance, lower charge-transfer resistance, and improved rate capability over the investigated current-density range. Overall, the results demonstrate that incorporation of ethanol into the hydrothermal reaction medium provides an effective means of controlling the morphology and porous architecture of ZnCo2O4, thereby enhancing its electrochemical performance as a supercapacitor electrode.