Sol-gel synthesis and electrochemical performance of NiCo2O4 nanoparticles for supercapacitor applications

In this work, NiCo2O4 nanoparticles with enhanced supercapacitive performance have been successfully synthesized via a facile sol-gel method and subsequent calcination in air. The morphology and composition of as-prepared samples were characterized using scanning electron microscopy (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD), and Raman spectroscopy (Raman). The electrochemical performances of NiCo2O4 nanoparticles as supercapacitor electrode materials were evaluated by cyclic voltammetry (CV), galvanostatic charge/discharge (GCD) tests in 3 mol L-1 KOH aqueous solution. The results show that as-prepared NiCo2O4 nanoparticles have diameters of about 20-30 nm with uniform distribution. There are some interspaces between nanoparticles observed, which could increase the effective contact area with the electrolyte and provide fast path for the insertion and extraction of electrolyte ions. The electrochemical tests show that the prepared NiCo2O4 nanoparticles for supercapacitors exhibit excellent electrochemical performance with high specific capacitance and good cycle stability. The specific capacitance of NiCo2O4 electrode has been found as high as 1080, 800, 651, and 574 F g(-1) at current densities of 1, 4, 7, and 10 A g(-1), respectively. Notably, the capacitance retention rate (compared with 1 A g(-1)) is up to 74.1 %, 60.3 %, and 53.1 % at current densities of 4, 7, and 10 A g(-1), respectively. After 100 cycles, higher capacitance retention rate is also achieved. Therefore, the results indicate that NiCo2O4 material is the potential electrode material for supercapacitors.