Rational construction of a hollow bimetallic porous composite derived zeolite imidazole framework based reduced graphene oxide nanosheets for supercapacitor applications.

A porous electrode material consisting of NiCo2O4/RGO with an approximate diameter of 200 nm has been successfully fabricated. This promising porous material was derived from ZIF-67/RGO (zeolitic imidazolate framework-67 crystals doped with reduced graphene oxide sheets) through an ion exchange and etching process using Ni(NO3)2·6H2O followed by a thermal reaction. The composition was analyzed using spectroscopic and morphological techniques. The obtained porous and hollow structure of NiCo2O4/RGO contains rich active sites. Additionally, its improved performance and stability were demonstrated using potassium ferricyanide (K3[Fe(CN)]6) (PFC) and sodium hydroxide (NaOH) as an electrolyte. NiCo2O4/RGO in NaOH/PFC exhibited a maximum estimated specific capacitance of 212.5 F g−1 at 0.5 A g−1 and demonstrated excellent retention value reaching 91.7% after applying 10,000 cycles at 20 A g−1. This symmetric supercapacitor achieved an outstanding energy density (Ed) of 75.54 Wh kg−1 at a power density (Pd) of 1.6 kW kg−1 at 0.5 A g−1. Surprisingly, there is a 2.5-fold enhancement in Ed (from 32.44 to 75.54 Wh kg−1) of NiCo2O4/RGO through the addition of 0.3 M PFC into 3 M NaOH. The results indicate that the NiCo2O4/RGO electrode could be ideal for supercapacitors. [ABSTRACT FROM AUTHOR]