Upcycling sawdust into sustainable binder-free nitrogen-doped carbon nanofiber electrodes for high energy density supercapacitors

Electrochemical supercapacitors (ESCs) are emerging as key energy storage systems, enabling the integration of renewable energy and powering the next generation of electric vehicles. In this study, we present a sustainable and innovative approach to high-performance electrode materials by transforming pinewood sawdust (PWSD), an abundant agricultural waste, into carbon nanotubes/nanofibers (CNTs/CNFs) and then into nitrogen-doped carbon nanofibers (N-CNFs). The CNTs/CNFs and N-CNFs were rigorously characterized using XRD, FT-IR, TGA, EDS, XPS, SEM, and TEM, confirming their successful synthesis and robust structural integrity. Electrochemical evaluation through cyclic voltammetry (CV), galvanostatic charge/discharge (GCD), and electrochemical impedance spectroscopy (EIS) revealed exceptional performance of the N-CNFs. The N-CNF electrode achieved a remarkable specific capacitance of ≈1280 F g^-1 at 1 A g^-1. Furthermore, an assembled symmetric supercapacitor device delivered an outstanding energy density of 78.3 Wh kg^-1 and a power density of 750 W kg^-1, along with exceptional cycling stability, with 100% capacitance retention after 4000 cycles. This superior performance is attributed to the synergistic combination of high electrical conductivity, nanofiber architecture, and enhanced surface wettability. Our findings underscore the significant potential of this waste-derived composite as a premier electrode material for building high-capacity, sustainable electrochemical supercapacitors.