Enhanced electrochemical performance of nickel intercalated ZIF-67/rGO composite electrode for solid-state supercapacitors

Abstract Ni (Nickel) doped zeolitic-imidazolate framework (ZIF-67) has been prepared in presence of reduced graphene oxide (rGO) to realize a ZIF-67/rGO composite. The doping level of Ni and the ratio of rGO (wt%) in the composite have been optimized to attain desirable redox activity and electrical conductivity. A partial incorporation of redox active Ni ions to substitute Co (cobalt) ions in ZIF-67 has resulted in better electrochemical characteristics by inducing additional pseudocapacitance. A finalized composite with 33% Ni and 20% of rGO (i.e, Ni33/ZIF-67/rGO20) has been used as a supercapacitor electrode material to achieve a high specific capacitance of 304 F/g at a current density of 1 A/g in the presence of 1 M H2SO4 as an aqueous electrolyte. The above electrode has also been tested for an all-solid-state symmetric supercapacitor in the presence of a polymer gel electrolyte (PVA/1 M H2SO4). This device delivered high values of power and energy densities, i.e., 1 kW/kg and 21.5 Wh/kg, respectively. The device also exhibited an excellent cyclic stability. About 87% of capacitance could be retained even after 4500 charge-discharge cycles. The device has shown superior results for a working potential window of 0–2 V. The practical usefulness of the device has been demonstrated by preparing a symmetrical supercapacitor, which could energize a white LED for 8 min upon a charging of only 40 s.