Tailoring the Electrochemical Properties of Transition Metal Oxides (ZNCO) With MOFs (ZIF-67) as an Electrode Materials for Hybrid Supercapacitors

Abstract

This study examines tailoring the electrochemical properties of transition metal oxides ZNCO, MOFs (ZIF-67) and their composite materials for hybrid supercapacitors. The pristine ZNCO has a good specific capacitance due to multi oxidation state but has the pulverization effect during charging-discharging of hybrid supercapacitor which limits its application in practical use. To mitigate these challenges, ZNCO/MOFs (ZIF-67) composite material was successfully synthesized by using wet chemistry which shows enhanced electrochemical performance of fabricated asymmetric HSC. The developed ZNCO@ZIF-67 was characterized by XRD, SEM, EDS, FTIR, TEM, HRTEM and XPS to confirm the successful incorporation of the ZNCO into ZIF-67. Further the electrochemical analysis including CV, GCD and EIS of composite material was evaluated through electrochemical workstation. The ZNCO@ZIF-67 composite materials showed enhanced specific capacitance of 4215.5 Fg⁻¹ at current density of 1.5 Ag-1 which is far better than pristine ZNCO and ZIF-67 is 2500 Fg-1 and 1400 Fg-1 respectively. Over 8500 charge discharge cycles for three electrode assembly the composite material maintains 98.2% capacity retention. The asymmetric HSC device fabricated using ZNCO@ZIF-67 (ZNCO@ZIF-67/A.C) which shows the high energy density of 59 Whkg -1 and power density of 1.072 kWg -1 with capacity retention of 97.3% over 10000 cycles. The better electrochemical properties of the composite can be attributed to the, Synergistics effects of both the components. ZNCO has high specific capacitance and excellent electrical conductivity while ZIF-67 provides many active sites and robust frameworks for ion transport during electrochemical performance. Further, in electrochemical impedance spectroscopy (EIS), ZNCO@ZIF-67 composite material demonstrated less Rct values than pristine for their higher kinetics at interface. From the results the composite material ZNCO@ZIF-67 shows enhanced and synergistic effect between ZNCO and ZIF-67, which is promising electrode material for next generation hybrid supercapacitor.