Fabrication of 9.6 V High-performance Asymmetric Supercapacitors Stack Based on Nickel Hexacyanoferrate-derived Ni(OH)2 Nanosheets and Bio-derived Activated Carbon

Abstract Hydrated Ni(OH) 2 and activated carbon based electrodes are widely used in electrochemical applications. Here we report the fabrication of symmetric supercapacitors using Ni(OH) 2 nanosheets and activated carbon as positive and negative electrodes in aqueous electrolyte, respectively. The asymmetric supercapacitors stack connected in series exhibited a stable device voltage of 9.6 V and delivered a stored high energy and power of 30 mWh and 1632 mW, respectively. The fabricated device shows an excellent electrochemical stability and high retention of 81% initial capacitance after 100,000 charge-discharges cycling at high charging current of 500 mA. The positive electrode material Ni(OH) 2 nanosheets was prepared through chemical decomposition of nickel hexacyanoferrate complex. The XRD pattern revealed the high crystalline nature of Ni(OH) 2 with an average crystallite size of ~10 nm. The nitrogen adsorption-desorption isotherms of Ni(OH) 2 nanosheets indicate the formation of mesoporous Ni(OH) 2 nanosheets. The chemical synthesis of Ni(OH) 2 results the formation of hierarchical nanosheets that are randomly oriented which was confirmed by FE-SEM and HR-TEM analysis. The negative electrode, activated porous carbon (OPAA-700) was obtained from orange peel waste. The electrochemical properties of Ni(OH) 2 nanosheets and OPAA-700 were studied and exhibit a high specific capacity of 1126 C/g and high specific capacitance of 311 F/g at current density of 2 A/g, respectively. Ni(OH) 2 nanosheets delivered a good rate performance and remarkable capacitance retention of 96% at high current density of 32 A/g.