Electrochemical Fabrication Of Porous Nanostructured Nickel-Based Complex Film Electrodes And Their Pseudocapacitive Properties

As new energy storage devices, electrochemical capacitors have recently attracted increasing attention due to their high power densities, good electrochemical reversibility and long cycle life. The electrode materials are one of key factors to determine the capacitive properties of electrochemical capacitors. Nickel oxide/hydroxide is considered as a promising electrode material for ECs because of its low price and excellent electrochemical performance. This thesis focuses on the electrochemical preparation and pseudocapacitive performance of nickel-based film electrodes.A porous nickel film was prepared by selectively anodic dissolution of copper from an electrodeposited Ni-Cu alloy film. A porous nanostructured nickel hydroxide film electrode was further fabricated by the cathodic electrodeposition of Ni(OH)2 film on the obtained porous nickel film. The specific capacitances of the as-prepared porous nanostructured Ni(OH)2 film electrode at current densities of 2,5 and 10 A·g-1 are 1634,1563 and 1512 F·g-1, respectively. The nanoporous Ni substrate significantly improves the electrochemically cyclic stability of the electrodeposited nickel hydroxide film in 1.0 mol·L"1 KOH solution. The superior pseudocapacitive properties such as large specific capacitance, excellent rate capability and improved electrochemically cyclic stability of the as-prepared nickel hydroxide electrode suggest its potential application in electrochemical capacitors.A porous nanostructured nickel-based complex film electrode was fabricated by oxidating the obtained porous nickel film using a cyclic voltammetric method in 1 mol·L"1 KOH solution, and a NiO/Ni film electrode was further obtained by heating the complex film electrode 300℃. The physical properties and pseudocapacitive performance of the as-prepared film electrodes were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis, X-ray photoelectron spectroscopy (XPS) and various electrochemical techniques. The results of SEM, XRD and XPS showed that the obtained complex film electrode consists of Ni, Ni(OH)2 and NiOOH, with a porous nanostructure. The result shows that composition of the electroplating solution and the mass of the electrode have great influence on its capacitance property. The as-prepared porous nanostructured nickel-based complex film electrode presents a specific capacitance of 578 F·g-1 at a current density of 20 A-g"1 at the initial cycle, and it still delivers a specific capacitance of 544 F·g-1 after 1000 cycles, with a capacitance retention of 94%. The results of cyclic votammetry indicated that the specific capacitances of the NiO/Ni film electrode at 2 and 10 A·g-1 are 498 and 398 F·g-1, respectively. It was found that the NiO/Ni film electrode has an excellent long-term cycle stability.