From garden to grid: harnessing yard waste into carbon electrode with an insight into life cycle assessment

As the world grapples with increasing energy demands, transitioning away from fossil fuels is imperative for a sustainable future. Biomass-derived hard carbon materials, particularly from waste sources, offer a promising solution for energy storage applications. This study explores the potential of pyrolyzed yard waste hydrochar (pyrohydrochar) as an eco-friendly electrode material for supercapacitor. Given the pressing need to balance electrochemical performance with environmental sustainability, this study also combined rigorous electrochemical characterization with a comprehensive cradle-to-gate Life Cycle Assessment (LCA) to holistically evaluate material performance and environmental impact. The pyrohydrochar exhibited a BET surface area of 381 m² g^-1 with a predominantly micro- and mesoporous structure without any acid or alkali treatments. The symmetric supercapacitor revealed a specific capacitance of 110 F g^-1 at 1 A g^-1, with an energy density of 34.37 Wh kg^-1 and a power density of 773.43 W kg^-1. Also, a cycling stability of 12,000 cycles was attained at 3 A g^-1 with around 85 % capacity retention. The material demonstrated typical capacitive behavior, indicating its suitability for rapid charge-discharge cycles. Additionally, a cradle-to-gate LCA was conducted, which identified electricity consumption during the electrode fabrication process as one of the major environmental hotspots, contributing between 42 % and 94 % across all impact categories. The dual focus on performance and environmental sustainability underscores the potential of waste biomass-derived carbon as a viable electrode material for next-generation supercapacitors.