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 (C
F) 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 C
F 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 C
F retention of 59.5% after 1000 times charge/discharge process.
A C
F retention of 75.6% after bending
100 times is also obtained for SSC.