Electrospun PAN/TEMPO nanofiber electrode: Dual charge storage mechanism for supercapacitor applications

ABSTRACT An advanced electrode material for asymmetric supercapacitors was created by electrospinning a polyacrylonitrile (PAN)/2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) composite. Strong interfacial interactions between the PAN chains and TEMPO nitroxide radicals were confirmed by Fourier transform infrared spectroscopy, which showed partial suppression of the PAN nitrile (–C≡N) vibrations. X-ray diffraction revealed increased short-range molecular ordering of PAN caused by TEMPO via dipole–dipole interactions, without changing the semicrystalline structure. In morphological studies, the incorporation of TEMPO showed decrease in the fiber diameter and enhanced surface roughness as compared to PAN fibers, resulting in the interconnected nanofibrous network with enhanced electrolyte accessibility. A mesoporous architecture with a quantifiable surface area and pore volume was characterized by BET analysis. A higher D-to-G band intensity ratio was found by Raman spectroscopy, which quantitatively indicated the formation of defects and improved electrochemically active sites in the PAN/TEMPO composite. The PAN/TEMPO electrode facilitates a dual charge storage mechanism that combines electrical double-layer capacitance from the nanofibrous PAN matrix and pseudocapacitance from reversible TEMPO redox activity due to these synergistic structural and chemical modifications. The assembled asymmetric supercapacitor exhibits a stable energy density of 7.71 Wh kg -1 and a power density of 365.33 W kg -1 , and the composite electrode provides improved capacitive performance in acidic electrolyte. Additionally, Raman and EIS studies were performed for the PAN/TEMPO electrode after performing 5000 galvanostatic charge/discharge cycles to check the stability of the material. Overall, this work provides a novel approach to design supercapacitor electrodes with a structure–defect–redox synergy in TEMPO-modified electrospun PAN nanofibers.