From biomass to energy storage: sustainable carbon materials for next-generation supercapacitors

Global energy demand continues to grow, and the depletion of fossil fuels, coupled with increasing environmental concerns, underscores the importance of sustainable energy storage solutions. Supercapacitors are promising electrochemical energy storage devices due to their high power density, fast charge–discharge kinetics, and long cycle life. However, the use of conventional fossil-based or hazardous electrode materials limits their sustainability. Biomass-derived carbons (BDCs) offer a renewable, low-cost, and carbon–neutral alternative, with tunable hierarchical porosity, heteroatom doping, and tailored surface chemistry that enhance ion transport, wettability, and electrochemical performance. This review presents a comprehensive overview of recent advances in BDCs for next-generation supercapacitors, covering sources ranging from agricultural residues, fruit and nut peels, and wood to algae and industrial by-products. Synthesis strategies, including pyrolysis, hydrothermal treatment, carbonization, chemical and physical activation, templating, heteroatom doping, and composite formation, are critically discussed in relation to structure–function relationships. Case studies demonstrate the role of BDCs as electric double-layer capacitor hosts, conductive scaffolds, and hybrid electrodes for enhanced energy storage. Key challenges are discussed, including feedstock variability, reproducibility, and the environmental footprints of activation processes. Opportunities are identified in scalable continuous processing, circular economy integration, green activation methods, and hybrid device designs. Finally, standardized metrics, life-cycle and techno-economic assessments, and prototype-scale validations are proposed to accelerate the industrial translation of BDCs into sustainable, high-performance supercapacitor technologies.