| Summary: | 碩士 === 國立中正大學 === 化學工程研究所 === 103 === Supercapacitor has excellent energy storage performance, and it can be charged in a short time with high power density. In recent years, many studies focused on the combination of different active materials into hybrid ones, and thus improve the capacitance for supercapacitor.
In this study, the porous nickel substrate was prepared as current collector. The large surface area of three-dimension structure electrode not only increased the contact area between active material and electrolyte, but also enhanced the ion diffusivity. The active material was fabricated by using ZnO nanorods as a soft template. When the Co2+ adsorbed on the ZnO nanorods, the ZnO reacted with H+ simultaneously, and Zn2+ were released into solution. As a result, the precipitation of the cobalt-zinc layered double hydroxide was found on the surface of the ZnO nanorods, and ZnO@CoxZn1-x(OH)2 core-shell structure was formed. In comparison, the specific capacitance of the porous substrate was nearly 4.5 times greater than the planar substrate.
The ZnO@CoxZn1-x(OH)2 core-shell structure can be converted into the CoxZn1-x(OH)2 hollow nanorod, because the ZnO was dissolved for different times by alkaline solution. The pretreatment of CoxZn1-x(OH)2 exhibits a high specific capacitance of 0.863 F/cm2, and an excellent capacitance performance with capacity retention of 80%. After cycling tests, the specific capacitance gradually increased to 1.418 F/cm2. Moreover, the Ni(OH)2 was generated on the Ni-based electrode during the continuous redox reactions in alkaline electrolyte.
Ni(OH)2 had a higher theoretical capacity, and Co(OH)2 had a good electrochemical reversibility. The CoxNi1-x(OH)2 binary-component metal hydroxide had been demonstrated the specific capacitance higher than the single metal hydroxide. The CoxNi1-x(OH)2 exhibied a high specific capacitance of 1.621 F/cm2, and an excellent capacitance performance with capacity retention of 89.38%, but was not suitable for the active material of the capacitor with charge/discharge plateau.
The positive electrode with CoxZn1-x(OH)2 exhibits a high specific capacitance of 826.30 F/g. The negative electrode with active carbon exhibits a high specific capacitance of 158.3 F/g. The asymmetric supercapacitor of active carbon//CoxZn1-x(OH)2 showed an excellent rate capability, and the specific capacitance was up to 74.43 F/g, and could be reached at a cell voltage of 1.6 V in the KOH aqueous solution. The asymmetric supercapacitor can still retain about 62.54% at a high current density of 5 A/g, and it had a high power density of 3724.3 W/kg with a energy density of 16.5 Wh/kg. The asymmetric supercapacitor of active carbon//CoxZn1-x(OH)2 had excellent cycling performance, and the specific capacitance retention was higher than 92.69% after 5000 charge/discharge cycles at a current density of 2 A/g.
|
|---|
