Binder‑free textile PAN‑based electrodes for aqueous and glycerol‑based electrochemical supercapacitors

Abstract

Amidst different types of energy storage systems, electrochemical supercapacitors have received considerable attention as they close the gap between electrolytic capacitors and batteries. This work addresses electric double-layer capacitors (EDLCs), a type of electrochemical supercapacitor, and has been divided into two parts. In the former, the synthesis and characterization of activated carbon fiber-felt (ACFF) electrodes, derived from textile PAN-based fiber, have been provided. In the latter, the electrochemical characterization of EDLCs in potassium hydroxide solutions ( aqueous electrolytes) and in potassium hydroxide-glycerol hybrid electrolytes (glycerol-based electrolytes) have been investigated. The synthesis of ACFF electrodes via two-step oxidation, carbonization, and physical activation resulted in low-cost and binder-free electrodes containing 87% of the total volume of pores as micropores (maximum pore width of 3 nm) and a high specific surface area of 1875 m(2) g(-1). Electrochemical impedance spectroscopy, cyclic voltammetry, and galvanostatic charge-discharge techniques were carried out in a symmetric two-electrode setup at room temperature. The results showed that ACFF electrodes are suitable for aqueous electrolytes, particularly 2 M KOH, and KOH:GLY (3:1), a glycerol-based electrolyte. Although KOH:GLY (3:1) exhibited high electrolyte resistance (34 +/- 3 Omega), this hybrid green-electrolyte supports a potential window that is twice greater than that of aqueous electrolytes. In addition, glycerol, commonly called glycerin, is a by-product of FAME (fatty acid methyl ester) biodiesel, which is the major source of glycerol. Glycerol-based electrolytes are promising green electrolytes for EDLCs. Therefore, it is necessary to decrease its viscosity and resistance.