Advanced supercapacitor electrodes: Lignin-derived carbonaceous materials and graphene composites with inorganic additives for enhanced energy storage

Recently, sustainable supercapacitors have received much more attention as potential energy storage devices than fossil fuel-derived one because of their high power density, long life cycle, broad range of operating temperatures and environmentally friendly nature. However, developing environmentally friendly supercapacitors with impressive electrochemical stability at low cost is a significant challenge. Lignin, a readily accessible noncarbohydrate, is an interesting and promising electrode material for supercapacitor applications because of its low cost, high carbon content, and multifunctionality. This review article explores the recent progress of lignin/lignin-derived graphene or carbon-inorganic additive-based electrodes for supercapacitor applications. Initially, a brief overview of lignin categorisation, synthesis techniques, and properties is provided. Then, the most recent advancements in the synthesis methodologies and potential of lignin-derived graphene-like sheet electrodes and lignin-derived carbon/graphene-metal oxide or hydroxides/graphene oxide-based composite electrodes for supercapacitors are thoroughly discussed. Finally, the study is summarised, and the future challenges of lignin-based supercapacitors are addressed.