Preparation And Electrochemical Capacitance Properties Of Three-dimensional Ni(OH)₂, Co(OH)₂ Electrodes

With the growth of the world energy crisis and the environmental pollution, there is increasing requirement on the energy saving and environment protecting. Electrochemical capacitor, which is one of the newest innovations in the field of electrical energy storage, combining the advantages of both dielectric capacitors and conventional rechargeable batteries, has attracted much attention and become an international hotspot, once appeared. The electrode material is a key factor which determines the performance of the electrochemical capacitors, therefore, much work focuses on developing electrode materials with high capacity, low cost and environmentally friendly character.In this dissertation, we have reviewed the basic principle of the electrochemical capacitors, the advances of research on electrode materials and the prospects of electrochemical capacitors. Two kinds of electrodes based on nickel foam for electrochemical capacitors were prepared. X-ray powder diffraction (XRD) and field emission scanning electronic microscopy (FESEM) were used to characterize the structure and morphology of the coatings on the electrodes. The cyclic voltammetry (CV), chronopotentiometry and electrochemical impedance spectra (EIS) were used to systematically investigate the capacitance of the electrodes. The main content is as follows:(1) Three-dimensional Ni(OH)2 coatings were directly electrodeposited on nickel foam from aqueous solution of Ni(NO3)2 for electrochemical capacitor electrodes. The cyclic voltammetry (CV), chronopotentiometry, electrochemical impedance spectra (EIS) were used to systematically study the effects of electrodeposition parameters such as deposition temperatures and active material loading on the electrochemical capacitor behavior. The investigation showed that the deposition temperatures and active material loading have obviously affected the capacitance of the three-dimensional Ni(OH)2 electrode. At a charge/discharge current density of 4 A/g, an average specific capacitance as high as 3887 F/g can be achieved at the optimum deposition temperature of 65℃with the Ni(OH)2 loading of 0.7 mg.(2) Three-dimensional Co(OH)2 coatings were directly electrodeposited on nickel foam from aqueous solution of Co(NO3)2 for electrochemical capacitor electrodes. The cyclic voltammetry (CV), chronopotentiometry, electrochemical impedance spectra (EIS) were used to systematically study the effects of deposition temperatures and the Co(OH)2 loading on the electrochemical capacitance of the electrode. An average specific capacitance as high as 2469 F/g was obtained at a charge/discharge current density of 4 A/g, and the average specific capacitance was still up to 2003 F/g when the charge/discharge current density augments to 32 A/g, which is 81.12% of the average specific capacitance at the charge/discharge current density of 4 A/g. Thus it is obvious that the three-dimensional Co(OH)2 electrode has excellent electrochemical capacitance property.