Freestanding ZIF-9-Derived Cobalt Carbon Nanofibers for Supercapacitor Electrodes

Abstract

A zeolitic imidazolate framework (ZIF-9) was synthesized via solvothermal reaction using cobalt (Co) salt and benzimidazole ligands in the presence of polyacrylonitrile. The precursor was electrospun to form carbon nanofibers (CNFs) creating freestanding, binder-free supercapacitor electrodes. Polyvinylpyrrolidone (PVP) and NaCl were added to the precursor solution to reduce fiber diameter and improve structural integrity during high-temperature annealing. The Co/CNF sample achieved an areal capacitance of 316 mF cm⁻² and an energy density of 0.043 mWh cm⁻² at a current density of 1 mA cm⁻². The addition of NaCl and PVP reduced fiber diameter by 30% and increased capacitance by 3.6 times. The optimal sample maintained 96.2% of its capacitance over 10,000 charge/discharge cycles, demonstrating strong electrochemical stability. Symmetrical pouch cells with the developed electrodes powered a light-emitting diode and a humidity/temperature sensor, demonstrating their potential in portable electronics.