Microwave-assisted synthesis of nanocrystalline NiMoO4 for hybrid supercapacitor applications

The synthesis of nanocrystalline materials with the use of microwave has become widespread in the last decade. Among many advantages of this synthesis, there are, such as short processing time, high reproducibility and purity of the synthesis products, and environmentally friendliness. Nanocrystalline NiMoO 4 in the form of hydrate was obtained as a result of 2.5 min microwave irradiation. To study the properties of the non-hydrated form of nickel molybdate, the initial hydrate was subjected to thermal treatment. As a result, NiMoO 4 , which is a mixture of α and β phases, was obtained. The phase composition, crystal structure, and optical properties of the obtained materials were investigated using X-ray analysis, Fourier-transform infrared, and Raman spectroscopy. The electrochemical behavior of nickel molybdates was investigated by cyclic voltammetry, galvanostatic charge/discharge testing, and impedance spectroscopy. The obtained NiMoO 4 hydrate had a specific capacitance of 652 F/g, whereas the specific capacitance of NiMoO 4 thermally treated was 372 F/g at a discharge current of 0.2 A/g. The impedance spectra of both nickel molybdates show a semicircular in the high-frequency range and a linear section in the low-frequency range, which is typical for battery-type materials. The high electrochemical activity of nickel molybdates obtained by microwave-assisted synthesis makes these materials promising for application as electrodes for hybrid supercapacitors.