Kraft and organosolv lignin-activated carbon composites for supercapacitor electrode materials

Abstract

Lignin-activated carbon (AC) composites were employed as electrode active materials to develop more environmentally friendly Supercapacitor (SC) materials with enhanced properties. This way, the hydroquinone/quinone moieties present in lignin molecules added Faradaic processes to the system, and the capacitance of the active material increased, making it appropriate for future applications requiring more efficient and sustainable active materials. Lignin, a sustainable biobased aromatic polymer high in carbon content, was deposited on AC surface employing ultrasound (US) system, and for a better deposition, AC was treated with HNO3. Since the composition and properties of lignin can vary depending on their isolation process, two different types of lignin were used: Kraft lignin (KL) and Organosolv lignin (OL), and the effects on the chemical and electrochemical composition were deduced. Physicochemical, morphological, and electrochemical analyses were carried out on the lignin-AC composite to determine the optimum material combination and treatment process. It was observed that the acid treatment was effective in enhancing the functionality and porosity of the surface. Additionally, it improved the deposition of lignin and facilitated the formation of hierarchically porous structures on the surface of treated activated carbon (TAC), with different tendencies depending on the lignin employed. The creation of highly porous structures also resulted in enhanced electrochemical performance in materials. This validated the process, where eco-innovative technologies like US forces and employment of lignocellulosic biomass compounds like lignin were used as sustainable and efficient alternatives for obtaining electrochemically active materials.