Sustainable synthesis of highly porous carbons from lignocellulosic residues via oxalic acid-assisted hydrothermal carbonization for electrochemical capacitor applications

The development of sustainable synthesis strategies for high-performance porous carbons is increasingly important to reduce the environmental impact associated with conventional activation methods. In this study, highly porous carbon materials were synthesized from lignocellulosic biomass waste via hydrothermal carbonization (HTC) in the presence of oxalic acid (OA), followed by thermal treatment under an inert atmosphere. The resulting carbons exhibited well-developed porosity, with BET surface areas of up to 1620 m 2 g −1 , without the need for additional activating agents or subsequent washing steps. The effects of key process variables, including OA content, biomass-to-water ratio, and HTC time, on the physicochemical properties of the resulting carbons were systematically investigated. The complete decomposition of OA prevents the generation of solid inorganic residues, further enhancing the sustainability of the process. A life cycle assessment confirmed a lower environmental impact compared with conventional synthesis strategies. The results also suggest that OA contributes to preserving specific components of the lignocellulosic precursor during HTC. The optimized porous carbon was evaluated as a capacitor electrode and exhibited electrochemical behavior comparable to commercial activated carbon YP-50F, highlighting the potential of this sustainable route for energy-storage applications.