Sustainable production of nanostructured activated carbon from biowaste for next generation supercapacitors

The rapid growth of electrochemical energy storage technologies has intensified the demand for advanced carbon materials, which are traditionally derived from nonrenewable sources such as coal and petroleum. These fossil-based precursors raise significant concerns about resource depletion, environmental impacts, and long-term sustainability, thereby necessitating the exploration of alternative, greener carbon sources. Despite growing interest in sustainable materials, a consolidated understanding of how bio-waste resources can be systematically converted into high-performance carbon electrodes for supercapacitors remains limited. In this context, this review provides a comprehensive overview of the conversion of bio-waste into nanostructured activated carbon for supercapacitor applications. Various bio-waste feedstocks, including agricultural residues, food-processing by-products, and plant-derived biomass, are examined as renewable, low-cost, and environmentally benign carbon sources. Key synthesis routes, such as pyrolysis, hydrothermal carbonization, and chemical activation, are critically discussed with respect to their ability to tailor pore architecture, surface area, and electrical conductivity. Furthermore, strategies to enhance electrochemical performance, including heteroatom doping, nanoscale structuring, and hybridization with metal oxides or conductive polymers, are systematically reviewed. These approaches have been shown to significantly improve specific capacitance, charge–discharge efficiency, and long-term cycling stability. Beyond electrochemical performance, the environmental and economic implications of bio-waste-derived carbons are highlighted, emphasizing waste valorization, reduced greenhouse gas emissions, and decreased reliance on fossil-based materials. Overall, this review identifies current challenges and knowledge gaps while underscoring the potential of bio-waste-derived nanostructured carbon as a sustainable, scalable solution for next-generation supercapacitors, aligned with green chemistry principles and the circular economy framework.