Synthesis and electrochemical properties of Mg-doped chromium-based metal organic framework/reduced graphene oxide composite for supercapacitor application

In this work, pristine and Mg-doped chromium-based metal organic frameworks (MIL-101(Cr)) were synthesized by hydrothermal method. Supercapacitive properties of the fabricated electrodes were studied using cyclic voltammetry, galvanostatic charge–discharge cycling and electrochemical impedance spectroscopy in 6 M KOH solution employing three-electrode system. The specific capacitance of the MIL-101(Cr,Mg)/rGO reached 261.41 F/g at a charging current density of 1 A/g. This value is more than twice of the value obtained for MIL-101(Cr)/rGO (137.46 F/g). This improvement in capacity can be due to additional redox processes induced by the Mg metal and synergistic effect between Cr and Mg in the MIL-101(Cr,Mg) structure. On the other hand, the specific capacitance of MIL-101 (Cr,Mg)/rGO decreased from 261.46 to 158.46 F/g as the current density increased from 1 to 30 A/g, indicating its excellent rate capability with an excellent retention rate. The asymmetric supercapacitor (ASC) was manufactured on the basis of MIL-101(Cr,Mg)/rGO and activated carbon (AC) as positive and negative electrodes, respectively. The designed ASC device exhibited good electrochemical performances with high power density and remarkable cycling stability (86% retention after 2000 cycles). All these results indicate that the MIL-101(Cr,Mg)/rGO composite has promising potential for being used in supercapacitors.