Nickel-shell assisted growth of nickel-cobalt hydroxide nanofibres and their symmetric/asymmetric supercapacitive characteristics

Abstract

Abstract Using polyurethane foam as template, we introduce a facile method to synthesize cost-effective macroporous nickel-shell (NS) which plays vital role in the synthesis of α-Ni-Co(OH) 2 . Nanofibrous morphology of α-Ni-Co(OH) 2 is obtained by the aid of polyethylene glycol (structure directing reagent) and no precipitating agent is used. Our results indicate that no metal (Ni/Co) hydroxides can be synthesized if NS is isolated from the reaction vessel which ensures the role of NS in formation of α-Ni-Co(OH) 2 nanofibres. Prepared α-Ni-Co(OH) 2 @NS electrode shows a typical enhanced interlayer spacing (∼8.0 A) which results in significantly high specific capacitance (2962 F g −1 at 5 mV s −1 ). Furthermore, the symmetric supercapacitor cell (α-Ni-Co(OH) 2 @NS‖α-Ni-Co(OH) 2 @NS) exhibits a maximum specific capacitance of 668 F g −1 with coulombic efficiency ∼98% over 3000 charge/discharge cycles at high current density (4 A g −1 ). The energy and power density obtained for α-Ni-Co(OH) 2 @NS‖α-Ni-Co(OH) 2 @NS cell are 18.2 Wh kg −1 at 242 W kg −1 and 1980 W kg −1 at 5.5 Wh kg −1 respectively. Moreover, in asymmetric supercapacitor using lacey reduced graphene oxide nanoribbon (LRGONR) as a negative electrode, a remarkable increase in energy (107 Wh kg −1 at 1610 W kg −1 ) and power density (7 kW kg −1 at 42 Wh kg −1 ) is observed.