Binder-free textile PAN-based electrodes for aqueous-based and glycerol-based supercapacitors

Abstract

Amidst different types of energy storage systems, electric double-layer capacitors (EDLCs), also known as supercapacitors, have received considerable attention as energy storage alternatives due to their advantageous characteristics: high power density, long life cycle, lightweight, safe operation, and fast charge–discharge rates. This work addresses these EDLC devices and has been divided into two parts. In the former, the synthesis and characterization of activated carbon fiber felt (ACFF) electrodes from textile PAN fiber have been provided. In the latter, electrochemical characterization of the ACFF electrodes in potassium hydroxide solutions (aqueous-based) 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 mostly micropores (maximum pore width of 3 nm) and a specific surface area of 1875 m² 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-based EDLCs in aqueous-based electrolyte (2 M KOH) exhibited low electrolyte resistance (0.44 ± 0.04 Ω cm²) and high gravimetric capacitance (129 ± 6 F g⁻¹ at 1 mV s⁻¹). Although ACFF-based EDLCs in glycerol-based electrolytes exhibited high electrolyte resistance (>17 ± 2 Ω cm²), they are hybrid green electrolytes that support a large potential window (<2.5 V), which is greater than that of aqueous electrolytes (≈1 V). Crude glycerol, the main byproduct in biodiesel production, is non-toxic, relatively safe, and low-cost. The advantages and disadvantages of aqueous and glycerol-based electrolytes have been discussed.