Carbonization-enhanced bio-based multilayer electrodes for sustainable energy storage

The transition to renewable energy systems requires sustainable, high-performance energy storage materials. Here, we report a simple and scalable layer-by-layer assembly strategy to fabricate hybrid supercapacitor electrodes composed of lignin, multi-walled carbon nanotubes (MWCNTs), and Mn 2 C MXene, followed by controlled carbonization. Lignin, an abundant and renewable by-product of the pulp and paper industry, serves as a low-cost carbon precursor, enabling a circular and sustainable approach to electrode design. Carbonization at 900 K converts lignin into a conductive, graphitized carbon matrix while maintaining MXene's electrochemical functionality, resulting in a hierarchical architecture that suppresses MXene restacking and facilitates rapid ion and electron transport. The optimized electrode delivers a high specific capacitance of 186.7 F g −1 , representing a more than seven-fold improvement compared with non‑carbonized electrodes, along with an energy density of 6.48 Wh kg −1 at a power density of 2.33 kW kg −1 . Excellent cycling stability is achieved, with 87.7% capacitance retention after 1000 charge–discharge cycles. These results demonstrate the potential of lignin-derived MXene composites as sustainable and high-performance electrode materials for advanced supercapacitors, supporting the development of affordable and clean energy storage technologies in alignment with United Nations Sustainable Development Goal 7.