Synthesis Of NiMoO₄ Nanocomposites As Electrode Material And Their Application For High- Performance Supercapacitors

With the rapid development of technology and society, the demand for high performance energy storage systems is growing. Under this background, the supercapacitors exhibit great application value and market potential in automotive, electric power, national defense and consumer electronic products field due to their high power density, excellent charge-discharge characteristics, long cycle life and environmental friendliness. However, low energy density limits the wide application of supercapacitors. Therefore, the research and development of high-performance electrode materials are the key to the answer. Nickel molybdate (NiMoO4) has attracted great interests due to its excellent electrochemical performance, low cost and environmental friendliness. Although considerable efforts have been made, there are still some problems such as low capacitance, poor cycle life and rate performance.Electrodes with rationally designed hybrid nanostructure composites can have superior electrochemical performance for supercapacitors than single-component electrode material. In this thesis, the new NiMoO4 nanocomposites were synthesized by hybrid nanoarchitecture with Co3O4 or reduced graphene oxide (rGO). The results are as follows:1. The uniform three dimensional hybrid Co3O4@ NiMoO4 core/shell arrays directly grown on carbon cloth, which was chosen as current collector with many advantages of soft, low-cost and good electrical conductivity. The core/shell nanostructure could enlarger surface areas of electrode material, facilitating the diffusion of active species and the transport of electrons. Moreover, the binder-free sturcture of Co3O4@ NiMoO4 composite also provides convenient pathways for electron transport. As a result, the hybrid nanocomposite exhibits a high areal capacitance of 3.61 F cm-2 at a current density of 3 mA cm-2 and a capacitance retention of 82% with the increase of current density from 3 to 15 mA cm-2, indicating high rate capability. The EIS tests show that the composite electrode has lower charge resistance. And the capacitance retention is 85% after 2500 cycles at a current density of 15 mA cm-2, displaying good cycle stability.2. The NiMoO4/rGO composite was successfully synthesized by a facile one-pot hydrothermal method. Compared with pure NiMoO4 nanowires(873 F g-1), the composite shows not only a maximum specific capacitance of 1202 F g-1, but also good rate capability and cycling performance. By a series of structure characterizations of XRD, SEM, TEM, Raman, XPS and EIS test, the high performance of the NiMoO4/rGO compsite could be attributed to the following reasons:the NiMoO4 nanowires are homogenously distributed into the interconnected rGO network, which prevent rGO nanosheets from agglomerating and restacking. At the same time, the large surface area and high electrical conducting of rGO nanosheets in the composite, provide more electroactive sites and allows for effecitive ion and electron transport in the whole electrode.