Controllable Synthesis Of NiCo₂O₄Nanoporous Films And Their Supercapacitor Properties

With the continuous development of science and technology, every field has new demands of energy storage devices. Researchers were asked to develop energy storage devices with high energy density and high power density. Among the various energy storage devices, supercapacitor is the most promising one. It is well known for its large energy density, high power density, good cycling stability, and no memory effect. However, the energy density and power density failed to meet the demands of practical application at the same time. The main objective in this research is to develop methods for enhancing electrode reaction kinetics of the electrode. We have developed methods such as hydrothermal synthesis method, chemical bath deposition method to fabricate NiCo2O4based porous structures on nickel foam and investigated their pseudocapacitive performance.Porous NiCo2O4nanoflake-nanowire structured arrays are produced by hydrothermal method. The morphology of the arrays changes with the growth time. After hydrothermal synthesis for8h in combination with annealing treatment, the NiCoa2O4array presents a nanoflake-nanowire hetero-structure. The formation of the interesting morphology was related with the solubility product (Ksp). The porous NiCo2O4hetero-structure array exhibits excellent pseudocapacitive properties in2M KOH, with a high capacitance of891F g-1at1A g-1and619F g-1at40A g-1before activation as well as excellent cycling stability. The specific capacitance can achieve a maximum of1089F g-1at a current density of2A g-1, which can still retain1058F g-1(97.2%retention) after8000cycles. The enhanced pseudocapacitive performances are mainly attributed to its unique hetero-structure which provides fast ion and electron transfer, large reaction surface area and good strain accommodation.Hierarchical NiCo2O4@NiCo2O4core/shell nanoflake arrays on nickel foam are fabricated by a two-step solution-based method which involves in hydrothermal process and chemical bath deposition. The obtained core/shell nanoflakes have a combined structure of nanoflake core and nanoflake shell as well as the hierarchical porosity morphologies. Compared with the bare NiCo2O4nanoflake arrays, the core/shell electrode displays better pseudocapacitive behaviors in2M KOH, which can achieve a maximum of2.20F cm-2at a current density of5mA cm-2. After4000cycles, it can still retain2.17F cm-2(98.6%retention). The electrode showed excellent pseudocapacitive behaviors owing to the unique porous core/shell nanoflake array architecture and synergistic effect.