Electrodeposition Of 3D Ni?OH?₂/C Electrode Materials And Supercapacitor Performance Research

In recent years, the depletion of nonrenewable fossil fuels and the increasing environmental issues have increased the demand for renewable energy storage and conversion device. Supercapacitors have attracted more and more attention due to their superior characteristics, such as high power density and excellent cycling stability. Among them, the metal oxide/ hydroxide have become the focus of the present study because of their high specific capacity and energy density. But because of high temperature solid phase synthesis methods and chemical deposition methods commonly usually make metal oxide/ hydroxide poor dispersion, in addition, the inherent poor conductivity of metal oxide/hydroxide influences its electrochemical performance. Previous studies have shown that the hybridization of electrochemically active metal oxides/hydroxides with electrically conducting polymers or carbon materials is an effective method to overcome the instability of metal oxides/hydroxides. Based on the above considerations, we builded a three dimensional structure composite electrode materials by using high specific surface area activated carbon and excellent electrical conductivity graphite carbon as substrates for electrochemical deposition of Ni?OH?₂. Electrochemical tests show that the number of oxygen-containing functional groups, the specific surface area and the electrical conductivity of the carbon substrate both have influences on the Ni?OH?₂/C composite electrodes. In the research process, a series of test methods, such as scanning electron microscopy, transmission electron microscopy, nitrogen adsorption/deadsorption, cyclic voltammograms, constant current charge, discharge and electrochemical impedance have been used. The main results were as follows:?1? Three-dimensional Ni?OH?₂ nanoflakes were prepared via a facile and cost-effective electrodeposition method using commercial activated carbon?AC? as substrate. Nitric acid treatment?NT? and partial crystallization?PC? by metal nickel catalysis were applied for AC. The effects of the oxygen-containing functional groups and the degree of crystallization on the electrochemical performance of the electrode were investigated. The resulting Ni?OH?₂/PC–NT–AC/nickel foam electrode exhibits distinct performance with a specific capacitance of 2971 F/g?scaled to the mass of active Ni?OH?₂? at a current density of 6 A/g. A high capacitance of 1919 F/g was still achieved even at 40 A/g, which is much higher than Ni?OH?₂/AC/nickel foam electrode and Ni?OH?₂/NT–AC/nickel foam electrode. The excellent performance of Ni?OH?₂/PC–NT–AC/nickel foam electrode can be attributed to the presence of large surface area and highly conductive PC–NT–AC network on nickel foam. This study presents an effective method to improve the dispersion and rate capability of Ni?OH?₂ nanostructure electrodes.?2? Graphitic carbon with a graphitization degree of nearly 100 % as raw materials and were activated by potassium hydroxide with different proportions, then Ni?OH?₂ crystals with a well-developed pore structure were prepared by using the above materials as substrates for electrochemical deposition of Ni?OH?₂. The effects of different activation degree of the substrate and the deposited amount of Ni?OH?₂ on the electrochemical deposited Ni?OH?₂ were investigated. By comparison, commercial graphene nanosheets were introduced as substrate for electrochemical deposition of Ni?OH?₂. The effects of the substrate surface area and conductivity on the electrochemical deposition of Ni?OH?₂ crystals were discussed.