Agro-waste based carbon dots for supercapacitors: A review of their role as electrode materials

The rapidly growing energy storage demands has intensified focus on supercapacitors, where design of advanced electrode materials remains a key challenge. Among emerging carbon-based nanomaterials, zero-dimensional carbon quantum dots (CQDs) are noted for their high surface area, rich functionalization, tunable conductivity and quantum confinement effects. Beyond intrinsic properties, the carbon precursor is crucial in determining CQDs structure, surface chemistry and electrochemical behaviour. In this context, agro-residues remain still as unexplored abundant class of carbon precursors for CQDs, aligns with both waste valorisation and high-performance energy storage demands. This review examines agro-residues derived CQDs as electrode materials in supercapacitors, including precursor composition, structural properties, electrochemical properties, and performance metrics. Rather than cataloguing individual studies, we extracted of design trends and benchmark reported performances against CQDs derived from pure molecular precursors and conventional carbon electrodes such as activated carbon and graphene. To quantitatively map the field, a bibliometric analysis was conducted to highlight the rising focus on agro-residue specific CQDs. Our findings reveals that many reported performances rely on three-electrode configurations with low mass loadings, leading to inflated capacitance and energy-density values. Practically, agro-residue derived CQDs acts effectively as functional modifiers in composite electrodes, rather than standalone materials. Key challenges include scalable synthesis, batch-to-batch uniformity, integration into thick electrodes, device-level validation, and long-term stability. This review provides a critical framework and future directions for advancing agro-residue derived CQDs from lab level concepts toward realistic supercapacitor technologies.