Nitrogen-rich Cu-MOF decorated on reduced graphene oxide nanosheets for hybrid supercapacitor applications with enhanced cycling stability

Abstract

High specific capacitance, enhanced power density, and high cyclic stability are the main requisites for a promising supercapacitor electrode material. This can be achieved by the combination of different active materials with a hierarchical structure. In this work, a highly biporous piperazine (N) functionalized Cu-MOF ({[Cu2(L)(H2O)2]·(3DMF)(4H2O)}n) (C) has been successfully anchored on chemically reduced graphene oxide (R) to fabricate a hybrid composite Cu-MOF/rGO (CR) by simple ultrasonication. Comparative electrochemical investigations reveal that, due to the synergistic effect of redox-active porous Cu-MOF and highly conductive rGO, the resulting composite exhibits excellent charge storage property with reduced charge transfer resistance compared to R and C. From the Galvanostatic Charge-Discharge (GCD) study, the calculated specific capacitance of the composite is found to be 867.09 F.g−1 at current density 1 A.g−1. The cyclic stability study suggests that the composite shows enhanced specific capacitance (131.65%) after 5000 cycles due to its electrochemical activation during repeated cycling. The kinetic study reveals the hybrid capacitive nature of the material, having major charge storage due to surface capacitance and a minor contribution from the diffusion capacitance resulting from its components R and C, respectively. Additionally, the fabricated hybrid symmetric supercapacitor (SSC) device exhibits a maximum energy density of 30.56 Wh.kg−1 at a power density of 0.6 kW.kg−1 and a maximum power density of 12 kW.kg−1 at 14.59 Wh.kg−1 energy density, with the capacity retention of 90.07% after 10,000 cycles. The robust and outstanding electrochemical performances of CR composite suggest it to be a promising electrode material for long cyclic life supercapacitors.