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 (E_d) of 75.54 Wh kg⁻¹ at a power density (P_d) of 1.6 kW kg⁻¹ at 0.5 A g⁻¹. Surprisingly, there is a 2.5-fold enhancement in E_d (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.