In situ synthesis of a non-toxic cobalt–benzimidazole metal–organic framework decorated reduced graphene oxide composite for asymmetric supercapacitor applications

Abstract

In this article, we report an effective synthesis of a cobalt–benzimidazole metal organic framework (Co–Bi_m MOF), which belongs to the Zeolitic imidazolate framework-9 (ZIF-9) family, and a cobalt–benzimidazole MOF@reduced graphene oxide (Co–Bi_m@rGO) composite through hydrothermal treatment for supercapacitor application. The structural and morphological features of the Co–Bi_m MOF and Co–Bi_m@rGO composite were confirmed by using various physicochemical techniques such as FT-IR, Raman, XRD, SEM, TEM, BET and XPS analysis. The SEM and BET analysis of the Co–Bi_m@rGO composite shows a layer-like structure with abundant pores and a large surface area (543 m² g⁻¹). The supercapacitive performance of the prepared electrodes was investigated using CV (cyclic voltammetry), GCD (Galvanostatic Charge–Discharge) and electrochemical impedance spectroscopy (EIS) analyses in aq. 1 M KOH. The as-fabricated Co–Bi_m@rGO composite showed a specific capacity of 1488 C g⁻¹ at 1 A g⁻¹ and maintained 96% of its initial capacitance after 8000 GCD cycles at 4 A g⁻¹. The superior capacity performance of the Co–Bi_m@rGO composite is mainly ascribed to its mesoporous nature with an improved surface area, multiple redox sites and synergistic effect between the Co–Bi_m MOF and rGO moiety. The constructed Co–Bi_m@rGO//AC device showed an energy density of 90.55 W h kg⁻¹ at a power density of 2396.28 W kg⁻¹, and the device showed a cyclic stability of 88% even after 4000 GCD cycles at 3 A g⁻¹. Further, biocompatibility analysis of the Co–Bi_m MOF and Co–Bi_m@rGO composite proved the non-toxic nature of the as-prepared electrode material. Thus, the effective energy storage ability of the Co–Bi_m@rGO composite confirms it as a potential candidate for supercapacitors in day-to-day applications.