The Fabrication And Electrochemical Performance Of Nanoporous Nickel Tubes And Composite Films Electrode

As a new type of energy device between secondary batteries and conventional capacitors, supercapacitors have drawn considerable attention during recent years owing to their excellent characteristics, such as fast charge-discharge capability, long cycle life, high power density, environmentally friendly, wide temperature range, etc. Generally, the electrode material is the most critical factor affecting the performance of supercapacitors. In this paper, the nanoporous nickel tubes electrode is fabricated by an electrochemical dealloying method; the Ni(OH)2/NiO/Ni composite films electrode is further formed by the electrochemical oxidation of the nanoporous nickel tubes. Their electrochemical performance was explored in detail.The nanoporous nickel tubes were synthesized by the selectively anodic dissolution of copper from an electrodeposited Ni-Cu alloy film. Then, we explored the electroplating system and the quality of the active material affecting the capacitance of the electrodes, respectively. The results indicated that the diameter size of the nickel tubes, the distribution of pipes and the morphology of nickel tubes can be adjusted by controlling the concentration of CUSO4solution in the electroplating system; the length of pipes and film thickness can be tuned by controlling the quality of active material. SEM analysis showed that the optimal structure of nanoporous nickel tubes could be obtained in a plating system when the Cu2+was0.1mol·L-1, the diameter size of nanopouous nickel tube is200-250nm, the pipe length is1-2.5μm; When cyclic voltammetry and charge-discharge tested in1mol·L-1KOH, the nanoporous nickel with a mass of0.30mg which fabricated in the plating solution including0.1mol·L-1CuSO4,1mol·L-1NiSO4,0.5mol·L-1H3BO3, showed excellent charge-discharge cycle stability and a high specific capacitance of527.56F·g-1.Through a simple electrochemical oxidation method, the nanopourous nickel tubes with high-performance transformed into composite films electrode. Microstructural analysis indicated that the composite films electrode is Ni(OH)2/NiO/Ni. The Ni(OH)2, NiO and Ni phases are all crystal structure, and Ni(OH)2/NiO wrapped in the surface of porous nickel. Compared to its highest specific capacitance, the composite films electrode displayed a high capacity retention rate of98%after suffering10000cycles at a current density of3mA·cm-2; At a current density of15A·g-1, the cycled composite films electrode delivered a specific capacitance of1073F·g-1when calculated the mass of Ni(OH)2/NiO as the effective mass. At a higher current density of150A·g-1, the cycled composite electrode still hold a higher specific capacitance (848F·g-1), and the capacity retention was79.3%compared with the current density of15A·g-1, even showed a higher energy density (31.4Wh·kg-1) as same as a higher power density (11.1kW·kg-1), manifested a good rate capability and excellent energy storage characteristics.