Three-dimensional core-shell niobium-metal organic framework@carbon nanofiber mat as a binder-free positive electrode for asymmetric supercapacitor

Abstract

The metal-organic-frameworks (MOFs) have attracted considerable attention as potential electrode materials for energy storage devices. In the present work, niobium(pyridine-2,6-dicarboxylic acid) MOFs (Nb(PDCA)MOFs) are grown on the surface of electrospun porous carbon nanofiber (CNF) via in-situ solvothermal process. As prepared Nb(PDCA)MOF@CNF hybrid mats were characterized and used as working electrode for supercapacitor applications. To find out ideal electrolyte, the electrochemical characteristics of the Nb(PDCA)MOF@CNF electrode were investigated in different electrolytes such as 3 KOH and 1 M LiCl. The hybrid electrode delivered greater specific capacitance in KOH electrolyte, i.e., 1248.8 F/g at 0.5 A/g, compared to LiCl electrolyte (816.8 F/g), while it has a more stable cycling performance in LiCl electrolyte. The asymmetric supercapacitors (ASCs) were constructed with the as-prepared binder-free Nb(PDCA)MOF@CNF mat as a cathode and the CNF as an anode and investigated their electrochemical properties in both the electrolytes. The higher specific capacitance was achieved for the KOH electrolyte-based ASC. However, the LiCl electrolyte-based ASC delivered superior energy density (64.24 Wh kg−1) and greater cycling stability (98.3 % after 4000 cycles) compared to ASC in KOH electrolyte. The ionic conductivity, chemical nature, and hydrated ionic radius of the electrolyte were found to be important factors to the electrochemical performance of the ASC device.