Binder-Free Textile PAN-Based Electrodes for Aqueous and Glycerol-Based Electrochemical 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 operations, 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 ber-felt (ACFF) electrodes from textile PAN ber 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 speci c 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-based EDLCs in aqueous-based electrolyte (2 M KOH) exhibited low electrolyte resistance (0.44 ± 0.04 Ω cm 2 ) 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 cm 2 ), they are hybrid green-electrolytes that support a large potential window (< 2.5), 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.