Novel In Situ Synthesis of Freestanding Carbonized ZIF67/Polymer Nanofiber Electrodes for Supercapacitors via Electrospinning and Pyrolysis Techniques

Zeolitic imidazolate framework-67 (ZIF67) has been regarded as an effective energy storage material due to its high surface area and electroactive cobalt center. Carbonizing ZIF67 can enhance electrical conductivity by converting 2-methylimidazole (2-melm) to carbon with cobalt doping. In this work, a novel in situ electrospinning is proposed to fabricate carbonized ZIF67 on carbon fiber (C67@PAN-OC) as a freestanding supercapacitor electrode. Polyacrylonitrile solution containing a cobalt precursor is used for electrospinning, and produced fibers are immersed in 2-melm to form ZIF67. Individually grown carbonized ZIF67 on carbon fiber is obtained using the in situ electrospinning method, while the one-body mixed carbon electrode is formed using the ex situ electrospinning method. A highest specific capacitance (CF) of 386.3 F/g at 20 mV/s is obtained for the in situ synthesized C67@PAN-OC electrode due to the largest electrochemical surface area and the smallest resistance, while the ex situ synthesized electrode only shows a CF value of 27.7 F/g. A symmetric supercapacitor (SSC) assembled using the optimized C67@PAN-OC electrodes and gel electrolytes shows a maximum energy density of 9.64 kWh/kg at 0.55 kW/kg and a CF retention of 59.5% after 1000 times charge/discharge process. A CF retention of 75.6% after bending 100 times is also obtained for SSC.