Crucial structural parameters affecting electrochemical properties of activated electrospun carbon fibers as solid-state supercapacitor electrodes

Electrospun carbon fibers were chemically activated using KOH with various KOH/carbon weight ratios and activation times. The activated carbon fibers were assembled with H₃PO₄/poly(vinyl alcohol) electrolyte to form flexible solid-state supercapacitors. An increase in the KOH/carbon weight ratio or activation time facilitated the development of porous structures. Moreover, KOH activation caused increases in the quantities of oxygen- and nitrogen-containing functional groups on the fiber surface. This behavior increased the affinity of the electrode and electrolyte, which enabled close contact between the electrode and the electrolyte and resulted in a low charge-transfer resistance. However, activation with a high KOH/carbon ratio destroyed the internal structure of fibers, which caused a decrease in the specific surface area and pore volume. Electrochemical examinations revealed that the effect of porosity parameters (specific surface area and pore volume) was stronger than that of the surface functionalities on the specific capacitance of the activated carbon fibers. In particular, mesopore volume mainly determined the ion adsorption behavior. The capacitor composed of the electrospun carbon fibers and gel polymer electrolyte retained its integrity and electrochemical performance after repeated bending. Furthermore, the capacitor was nonflammable and thus, is a promising candidate for application as a flexible supercapacitor.