Fabrication Of Nanoporous Nickel-based Composite Film And Their Electrochemical Properties

Electrochemical capacitors, often called super-capacitors, have recently attracted attracted worldwide research interest due to their high power density, long cycle life and high energy density as new energy storage devices. The electrode material is an important factor affecting the capacitive properties of electrochemical capacitors. Nickel hydroxide has recently attracted increasing attention because of its low price and excellent electrochemical performance. This thesis focuses on the electrochemical preparation and the electrochemical properties of porous nickel-based composite film electrodes.A porous nickel film was prepared by selectively anodic dissolution of zinc from an electrodeposited Ni-Zn coating film in 1 mol·L-1KOH solution. A porous nickel-based composite film electrode was fabricated by oxidating the obtained porous nickel film using a cyclic voltammetric method 1 mol·L-1KOH solution. The physical properties and electrochemical properties of the as-prepared film electrodes were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis, cyclic voltam-metry (CV) and galvanostatic charge-discharge tests. The results of SEM, XRD and CV showed that the obtained composite film electrode consists ofNi, Ni(OH)2, NiOOH and a small amount of Ni5Zn21 alloy, with a porous structure. The as-prepared composite film electrode presents a specific capacitance of 578 F·g-1 at the scan rate of 10 mV·s-1. It was found that the electrode has good capacity retention and long-term cycle stability.A NiZn alloy film was prepared by annealing an electrodeposited Ni-Zn coating film. A nanoporous nickel-based composite film electrode was fabricated by dealloying and oxidating at the same way. The results of XRD and SEM showed that the thermal diffusion between different metals was improved. The composite film electrode with smaller particle size and larger specific surface area was obtained at the higher annealling temperature. The as-prepared composite film electrodes annealed at 200℃and 300℃for 2h presented specific capacitance of 639 F·g-1 and 913 F·g-1 at the scan rate of 10 mV·s-1 and capacity retention of 92% and 95% after 1000 charge-discharge cycles, respectively. The specific capacitance of as-prepared composite film electrode annealed at 400℃decreased sharply due to the dense ZnO film over the surface. The thermal diffusion between different metals also can be improved by increasing the annealing time. The as-prepared composite film electrodes annealed at 300℃for 4h presented specific capacitance of 1211 F·g-1. The nanoporous nickel-based composite film electrodes obtained by annealing showed good capacity retention and long-term cycle stability.