Effect of Annealing Temperature on the Structural and Electrochemical Properties of Hydrothermally Synthesized NiCo 2 O 4 Electrodes.

In this study, a porous Ni-foam support was employed to enhance the capacitance of nickel cobaltite (NiCo 2 O 4 ) electrodes designed for supercapacitors. The hydrothermal synthesis method was employed to grow NiCo 2 O 4 as an active material on Ni-foam. The NiCo 2 O 4 sample derived from hydrothermal synthesis underwent subsequent post-heat treatment at temperatures of 250 °C, 300 °C, and 350 °C. Thermogravimetric analysis of the NiCo 2 O 4 showed that weight loss due to water evaporation occurs after 100 °C and enters the stabilization phase at temperatures above 400 °C. The XRD pattern indicated that NiCo 2 O 4 grew into a spinel structure, and the TEM results demonstrated that the diffraction spots (DSs) on the (111) plane of the sample annealed at 350 °C were more pronounced than those of other samples. The specific capacitance of the NiCo 2 O 4 electrodes exhibited a decrease with increasing current density across all samples, irrespective of the annealing temperature. The electrode annealed at 350 °C recorded the highest specific capacitance value. However, the capacity retention rate of the NiCo 2 O 4 electrode revealed a deteriorating trend, declining to 88% at 250 °C, 75% at 300 °C, and 63% at 350 °C, as the annealing temperature increased.