Characterization and supercapacitive performance of nanocomposite electrodes made of nickel oxide and activated carbon frpm oil palm shell

Abstract

Electrochemical capacitors or supercapacitors or ultracapacitors have been identified as a promising technology that has a significant role in the electrical energy storage device revolution. The quality of the electrode material is one of the key factors that determines the performance of supercapacitors. Among the commonly used electrode materials are carbon-based materials, transition metal oxide and conducting polymers. A combination of two or more of these electrode materials in a single electrode has been found to exploit the relative advantages of the two electrode materials and mitigate their relative disadvantages. However, the use of composite electrodes for supercapacitors have not been fully exploited due largely to the divergence in the synthesis technique of which none have been consolidated. This study synthesized nanocomposite electrodes with high power, high energy and long cycle life for supercapacitor applications using a simple, fast and economical technique. Activated carbon (AC) was prepared via microwave-induced CO2 activation of oil palm shell (OPS) using bed temperature as the control parameter. The response surface methodology (RSM) and Box-Behnken design (BBD) were utilized to optimize the operating parameters of the preparation process. The AC prepared at optimum conditions had a BET surface area of 574.37 m2 g-1, total pore volume of 0.244 cm3 min-1, micropore volume of 0.198 cm3 min-1 and yield of 74.06%. A novel green activated carbon-nickel oxide nanocomposite electrode was synthesized using electroless deposition method for supercapacitor applications. Investigation of the electrochemical performance of the nanocomposite electrodes was carried out using cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy. The results from electrochemical tests showed that the nanocomposite electrodes exhibit superior capacitive performance compared with the AC electrode. The specific capacitance, power density and energy density were found to increase by 114.92 – 276.84 F g-1, 29.88 – 250.68 W kg-1 and 3.99 – 9.61 Wh kg-1, respectively with respect to the AC electrode. In addition, the specific capacitance as well as the energy density was found to reduce with the increment in the calcination temperature from 300 oC to 500 oC and time from 1 h to 2 h, suggesting that high calcination temperature and long calcination time are detrimental to the electrochemical performance of the nanocomposite electrodes. The nanocomposite electrode calcinated at 300 oC for 1 hour offers the maximum enhancement of 205% in both specific capacitance and energy density, while the nanocomposite electrode calcinated at 500 oC for 2 hours offers the maximum power enhancement of 112%. This thesis has established the possibility of using temperature as a process parameter in microwave heating and proved that electroless plating method is a good synthesis method for organizing nanocomposite electrode materials. Furthermore, the good structure and superb electrochemical performance of the nanocomposite material revealed that it is a promising electrode for supercapacitor applications.