| In recent years, electrochemical capacitors, also called supercapacitors, have attracted tremendous interest as power sources for applications requiring quick bursts of energy. It is well known that electrode materials play a vital role in the electrochemical performance of supercapacitors, so research for the novel electrode materials is the key problem for supercapacitors. Spinel nickel cobaltite(Ni Co2O4) has been conceived as a promising cost-effective and scalable alternative since it offers many advantages such as high specific capacitance, excellent electronic conductivity and environmental friendliness. However, some obstacles such as low utilization ratio, non-uniform pore distribution and structural instability of Ni Co2O4 always harass the applications in energy storage. Therefore, we have developed some methods for enhancing the value of specific surface and electrode reaction kinetics of Ni Co2O4 materials so as to improve the storage ability of electrode materials. The research content and the main conclusion are listed as below:First, dandelion-like Ni Co2O4 mesoporous microspheres were uniformly assembled from slim nanowires via a large-scale and template-free method. Furthermore, the electrochemical properties of Ni Co2O4 microspheres were evaluated by cycle voltammetric(CV) and galvanostatic charge-discharge(GCD) measurements. The results demonstrated that the Ni Co2O4 microspheres exhibited high specific capacitance(372 F g-1 at 1 A g-1), good rate capability, and excellent cycling stability(88.3% retention after 2000 cycles).Second, an effective and rational strategy is developed for large-scale growth of firecracker-like Ni Co2O4 or Co3O4 nanosheets on β-Mn O2 nanowires(NWs) with robust adhesion as high performance electrode for electrochemical capacitors. The structure and morphology of as-synthesized Ni Co2O4-Mn O2 and Co3O4- Mn O2 NWs were characterized by nitrogen adsorption, X-ray diffraction, focus ion beam scanning electron microscopy(FIB/SEM) and transmission electron microscopy. The Ni Co2O4-Mn O2 nanostructures display much higher specific capacitance(343 F g-1 at current density of 0.5 A g-1), better rate capability(75.3% capacitance retention from 0.5 A g-1 to 8 A g-1) and excellent cycle stability(5% capacitance loss after 3000 cycles) than Co3O4-Mn O2 nanostructures.Third, we demonstrates a facile and tunable preparative strategy of porous Ni Co2O4 nanosheets-decorated Cu-based nanowires hybrids as high-performance supercapacitor electrodes. A fast faradic reaction has been realized by inducing elementary copper core in the composite, which assists in high electric conductivity of the cell and creates intimate channels for fast charge collection and electron transfer. As a result, this hybrid composite electrode displays high specific capacitance(578 F g-1 at current density of 1.0 A g-1) and rate capability(80.1% capacitance retention from 1 A g-1 to 10 A g-1). Additionally, asymmetric device is constructed from Cu/Cu Ox/Ni Co2O4 NWs and activated graphene(AG) with an operation potential from 0 to 1.4 V. The asymmetric device exhibits an energy density of 12.6 Wh kg-1 at a power density of 344 W kg-1 and excellent long-term cycling stability(only 1.8% loss of its initial capacitance after 10000 cycles). These attractive findings suggest that such unique Ni Co2O4/Cu-based NWs hybrid architecture is promising for electrochemical applications as efficient electrode material.In conclusion, an effective and rational strategy is developed for 3-dimensional Ni Co2O4 microspheres and one-dimensional Ni Co2O4 core-shell nanowires for high-performances supercapacitors and the obtained results can pave the solid way for the investigation and development of Ni Co2O4 materials at energy storage. Simultaneously, the obtained nanostructured one-dimensional Ni Co2O4 core-shell nanowires in this work exhibited excellent electrochemical performance and they could be the optimized nanomaterials for supercapacitors. |
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