Enhanced Structural and Electrochemical Properties of Zn-Doped NiCo₂O₄ Synthesized by Low-Temperature Microwave Hydrothermal Process

The specific capacitance (Cp) is an important parameter influencing the energy storage capacity of materials. In this study, a series of NiZnxCo2-x O4 (x = 0.0-0.10) nanoparticles were prepared using the microwave-hydrothermal (M-H) method. The samples were characterized by using X-ray diffraction (XRD), Scanning electron microscopy (SEM), Fourier transform Infrared (FTIR), X-ray photoelectron spectroscopy (XPS) and electrochemical studies. It is observed from X-ray diffraction that all the samples are cubic in nature with space group Fd-3m. The average lattice constant is varied in between 7.63 (x = 0.0) to 8.34 (x = 0.10). The linear increase in lattice constant is due to the difference in the ionic radii. The average grain size is in the range of 80 (x = 0.0) - 124 nm (x = 0.10) for all the samples, and grains are found to be spherical in nature. The characteristic metal oxygen vibration bands were observed at 578 cm(-1) and 661 cm(-1). The valence states of Ni2+/Ni3+, Co2+/Co3+ and Zn2+ were confirmed by X-ray photoelectron spectroscopy. The electrochemical studies were performed on all the samples. The high value of specific capacitance (C-p) 871.91 Fg(-1) is observed for sample x = 0.06. Therefore, Zn doped NiCo2O4 shows good impedance and electrochemical properties which is promising material for supercapacitor applications.