A critical sustainability review of green carbon-based supercapacitors

Carbon-based supercapacitors (SCs) are widely regarded as sustainable energy storage devices, primarily due to the use of biomass-derived carbon precursors and their excellent cycle stability. However, such perceptions often overlook the broader environmental implications associated with material processing, activation strategies, and end-of-life management. This study re-analyzes the true sustainability of carbon-based energy storage systems by assimilating electrochemical, structural and lifecycle outlook. We unravel trade-offs across electric double-layer, pseudocapacitive, and hybrid SC classes, unfolding tensions between surface-area maximization, electrolyte intensity, critical mineral dependence and end-of-life complexity. A sustainable classification framework for carbon electrode sources is introduced, spanning fossil-derived, biomass-derived, waste-derived, and hybrid carbon architectures. Through schematic illustrations of activation and pore formation, elucidation of how carbonization pathways and activation chemistries hold pore dynamics, crystallinity, and charge storage behavior, while simultaneously shaping environmental off-sets. Comparative diagrams and novel tables systematically evaluate carbon categories based on activation techniques, carbonization routes, electrochemical efficiency, lifecycle energy demand, greenhouse gas emissions, toxicity potential, and technology readiness level (TRL). A dedicated lifecycle assessment framework quantifies the environmental impacts of activated carbon production, highlighting the decoupling between electrochemical performance metrics and sustainability indicators. Finally, we propose a standardized sustainability evaluation methodology for carbon-based supercapacitors that integrates normalized lifecycle metrics with structural-functional correlations. By bridging new materials like regenerative ones and sustainability analytics, this review provides a critical roadmap for designing next-generation carbon electrodes that are not only high-performing but also environmentally and industrially responsible.