Effect of solvent-dependent morphology on charge storage mechanism of NiCo2O4 for aqueous supercapacitors

The physical and morphological properties of materials significantly affect the electrochemical performance of supercapacitor electrodes. Therefore, tremendous research efforts have been devoted to adjusting and fine-tuning the morphology of electrode materials. NiCo2O4 as a promising pseudocapacitive material has been commonly synthesized by a facile solvothermal method. While it is known that synthetic parameters such as reaction time, temperature, and solvent during the solvothermal processes influence the resulting materials, the full extent of their effects is not yet fully understood. This work aims to investigate the influence of solvent used during solvothermal process on the physical and electrochemical properties of NiCo2O4 using four solvents including water, isopropyl alcohol, ethanol, and methanol. The prepared NiCo2O4 electrode using water as a solvent (NCO-D) exhibits urchin-like morphologies with long nanowires covering its surface, offering a high surface area. NCO-D exhibits higher electrical conductivity due to its increased oxygen vacancies, consequently displaying the highest specific capacitance. Notably, it demonstrates remarkable rate capability, achieving 580 F/g at 1 A/g and 479 F/g at 15 A/g. All the NiCo2O4 samples showed excellent cycling stability over 1000 cycles. Thus, this work demonstrates a facile synthesis to obtain NiCo2O4 electrode material with high electrochemical performance and explores the effect of the solvent on the morphological change and charge storage mechanism of NiCo2O4. The finding here could benefit the future development of NiCo2O4, as well as other metal oxides for energy storage applications.