Influence of solvent-mediated morphology evolution on the electrochemical performance of nickel cobalt oxide nanoparticles for supercapacitor applications

Nickel cobalt oxide nanoparticles were prepared via the hydrothermal method, with water, ethanol, and a water–ethanol mixed solvent, to explore how the solvent-mediated growth affects characteristics of NiCo 2 O 4 nanoparticles, such as morphology and the supercapacitive response. The characteristics of prepared nanoparticles depend on differences in solvent polarity and dielectric constant. In the case of water, because it has high polarity and better ionic mobility, it helps anisotropic growth and ends up giving sheet-like nanostructures. But ethanol, which suppresses ion diffusion and slows down crystal growth, so you get aggregated nanoclusters. The mixed solvent system shows an intermediate nature, so it really supports that the growth is controlled by the solvent itself. For confirmation, structural and elemental analyses, including XRD, XPS, FESEM, HRTEM, EDAX and BET, were carried out. These results verified phase-pure mesoporous spinel NiCo 2 O 4 , a specific surface area of 53.49 m 2 g −1 , and many oxygen vacancies, which act as electroactive sites. Electrochemical testing with the electrode derived from water showed a specific capacitance of 512.63 F g −1 at 50 mVs −1 and 182.30 F g −1 at 1 A g −1 . The energy density is found to be 32.81 Wh/kg along with a power density of 1.08 kW kg −1 with the capacitance retention of 86.32% after 5000 cycles. This enhanced performance relates to the morphology of the prepared sample, which provides a larger electroactive surface, lower interfacial resistance, and ion transport routes that accelerate the charge transfer kinetics. Though the value of specific capacitance is not much superior to the earlier reports, the present work focuses on how a solvent-mediated morphology plays an important role.