Fabrication Of Nanoporous Nickel Films By Dealloving And Their Electrochemical Properties

Porous nickel is a new kind of multi-function porous metallic materials with a three-dimensional network structure. It possesses unique features such as light weight, flame retardancy, corrosion resistance, strong absorbed energy ability and electromagnetic shielding. Alloy-deallloying is receiving increased attention recently because of its ease in processing. This method could effectively enhance specific surface area of metals and their performance in many fields. This thesis focuses on the electrochemical preparation of porous nickel electrodes by the alloy-dealloying method and their electrochemical properties.Three-dimensional (3D) nanoporous nickel films were fabricated via the alloy-dealloying method. The fabrication process involved the heat treatment of the electrodeposited zinc layer on smooth nickel substrates and the subsequent electrochemical dealloying. As the electrodeposited zinc amount increased, the thickness, pore diameter and pore density of the nanoporous nickel films became larger. In our experimental range, the thickest nanoporous nickel film presented a thickness of8μm and an average pore diameter of700nm. The as-prepared3D nanoporous nickel films exhibited much higher electrocatalytic activity for hydrogen evolution reaction (HER) than smooth nickel foil in lmol·L-1KOH solution, and their electrocatalytic activities for HER enhanced with increase in the porosity and thickness. For the porous nickel foam fabricated by the same strategy, it showed an average pore diameter of800nm. The porous nickel foam is more active with lower potential for HER and higher exchange current density compared untreated nickel foam.Porous nickel oxide (NiO) films were prepared also by the alloy-dealloying method. The fabrication process includes the heat treatment of the electrodeposited zinc layer on smooth nickel substrates and the subsequent dealloying in alkaline medium. The porous NiO films with a highly ordered nanoporous surface and an average pore diameter of200-300nm obtained after the heat treatment under350℃. In our experimental range, the as-prepared porous NiO films presented the larges specific capacitance at the current density of20mA·cm-2in1mol·-1KOH. The strategy was also applied to nickel foam and the porous NiO foam showed a pore diameter in the400-700nm range. Electrochemical data demonstrated that the hierarchical porous NiO nano-structures were capable of delivering a specific capacitance of11.917F·cm-2at30mA·cm-2and offered a good specific capacitance retention of ca.80%after1000continuous charge-discharge cycles.