Analyses of dispersive effects and the distributed capacitance in the time and frequency domains of activated carbon nanofiber electrodes as symmetric supercapacitors

• Published in: Electrochimica acta 2022-01, Vol.402, p.139299, Article 139299
• Main Authors: Real, Carla G., Vicentini, Rafael, Nunes, Willian G., Pascon, Aline M., Campos, Feik Amil, Da Silva, Leonardo M., Freitas, Renato Garcia, Zanin, Hudson
• Format: Article
• Language: English
• Subjects: Activated carbon; Activated carbon nanofiber electrodes; Anomalous transport of ionic charge in porous carbons; Aqueous electrolytes; Capacitance; Carbon fibers; Distributed capacitance in the time domain; Electrochemical analysis; Electrode polarization; Electrolytes; Electrospinning synthesis method; Liquid phases; Nanofibers; Operando Raman studies; Raman spectra; Solid phases; Supercapacitors; Symmetry; Transmission lines
• ISSN: 0013-4686; 1873-3859
• DOI: 10.1016/j.electacta.2021.139299

•Novel flexible and freestanding activated carbon nanofiber electrodes (aCNF) for supercapacitors.•The analysis of the distributed capacitance using the GCD method.•Raman transient spectra support the insertion of HSO4− into carbon micropores.•Operando Raman analyses suggest new symmetry at the electrode/electrolyte interface and electronic changes in the carbon structure.•Transmission line model for the study of charge transport anomalies in aCNF electrodes. A novel and scalable method is reported to produce flexible and freestanding fabrics composed of high surface area activated carbon nanofibers (aCNF) for applications in supercapacitors. The electrochemical behavior of a symmetric supercapacitor using the aCNF electrodes and the operando Raman spectra study accomplished under polarization conditions are reported. The evolution of Raman spectra during polarization supported the aCNF stability and suggested the insertion of the HSO4− ions in carbon micropores. These findings evidenced a new symmetry at the aCNF/electrolyte interface, where electronic and ionic charges accumulate. The distributed capacitance in the time domain was studied by numeric differentiation of galvanostatic charge-discharge findings. The impedance behavior of the solid and liquid phases composing the aCNF/solution interface was modeled using a macro homogeneous description of two closely mixed phases represented by a single-channel transmission line incorporating the anomalous transport of the ionic charges in the disordered structure of aCNF. Electrochemical findings revealed outstanding charge-storage properties in neutral aqueous electrolyte resulting in long lifespan, low equivalent series resistance (12 mΩ g), high coulombic efficiency (∼99.8 %), a maximum distributed capacitance of 82 F g−1 (0.25 A g−1-1.1 V), maximum specific energy and power of 2.98 W h kg−1 and 72,672 W kg−1, respectively. [Display omitted]