Preparation And Electrochemical Performanceof Electrode Materials For Supercapacitor Based On NiO Composite Nanostructure

Energy is becoming a crucially important worldwide issue, though fossil fuels still play an important role in energy-supported systems. However, excessive depletion of fossil fuels causes tremendous environmental pollution and climate change. There is an urgent need to develop clean, sustainable, and efficient devices/systems for energy storage and conversion.Supercapacitors, also known as electrochemical capacitors(ECs), are new type energy storage/conversion devices, which have recently received considerable attention due to their unique properties, such as high specific capacitance, high energy/power densities, short charge/discharge time and long lifetime.Based on the nature of the charging/discharging mechanism, ECs can roughly be classified into two categories: the electrical double-layer capacitors(EDLCs) and pseudocapacitors. EDLCs exhibit the capacitance that comes from pure electrostatic charges accumulated at the interface between an electrolyte and an electrode; while the pseudocapacitors typically show higher capacitances owing to the fast and reversible faradic redox reactions of electro-active materials of the electrodes.Research results have indicated that conductivity and microstructures of an electrode are of importance in determining the capacitance. Porous microstructures usually provide a large surface area to benefit the ionic diffusions at the electrode/electrolyte interface.Specific research contents are as follows:(1) A three-dimensional nanoporous Ni O films were fabricated using a two-step process through the electrochemical route, including electrodeposition and electrochemical dealloying using pulse power and DC power. The textural characterization of the film and its electrochemical performance as electrochemical electrode were investigated, presenting that the nanoporous Ni O film dealloyed by pulse power showed better electrochemical performance. The electrode showed high specific capacitance(1776 F g-1), and stable specific capacitance retention after a long cycle test in KOH solution, only 2.1% loss after 1000 cycles.(2) 3D ultrafine nanoporous V2O5 nanowires on Ni porous films were fabricated via a facile process. The as-prepared samples were used as binder-free supercapacitor electrode to obtain high performance. The nanoporous V2O5 nanowires have a diameter range of about 30 nm to 150 nm. The specific surface area was 189 m2 g-1. The nanoporous products covered a large amount of pores in the mesopore range mainly at 5.13 nm. The electrode specific capacity was 832 F g-1 based on the total mass of the active materials.(3) A novel three dimensional nanomaterial, namely V2O5 nanocoin(VNC), was synthesized on nanoporous Ni thin film through a straightforward one-step liquid phase epitaxy approach. The VNCs(~100 nm in diameter) are linked and supported by the porous Ni thin film with good electronic conductivity. Additionally, the as-prepared samples can be used as ECs electrodes without binders, which can improve the electronic conductivity for the electrodes. The highest specific capacitance was calculated to be 713 F g-1 at a current density of 1 A g-1. The specific capacitance can be reserved about 66% even at a very fast current density of 100 A g-1.(4) The mesoporous La Ni O3/Ni O thin film electrodes were produced through a simple sol-gel method using PEG as an organic template. The electrodes annealed at 650°C show excellent electrochemical performance, including high specific capacitance at ultrahigh scan rates and high cycling stability. The binder-free materials with LNO have shown improved electrical conductivity and stability of the electrodes, and the porous structures have provided full accessibility of the electrolyte, enhancing the stable performance of the electrochemical capacitors. The electrode annealed at 650°C has the areal specific capacitance of about 9.5 m F cm-2 at a scan rate of 0.1 V s-1, exhibiting an excellent cycling performance with only 2.8% capacitance loss up to 1000 cycles.(5) A flexible hybrid film based on single-wall carbon nanotubes(SWNTs) was fabricated. The SWNTs@Mn O2/Polypyrrole film was used as a supercapacitor electrode without binders to achieve high capacitance. The binder-free electrode with SWNTs and PPy layers improved the conductivity of the electrode materials, as well as the ion diffusion rate and charge-transfer resistance, thus achieving excellent electrochemical performance compared with SWNTs@Mn O2 electrodes. The capacitance loss of the electrode was 5.6% after 10000 cycles.