Tobacco stem-derived activated carbon via KOH-ZnCl2 dual activation: hierarchical pore structure and enhanced supercapacitive performance

With the growing demand for sustainable energy storage devices, biomass-derived carbon materials have emerged as promising electrode candidates for supercapacitors due to their renewability, low cost, and environmental benignity. Tobacco stems, an abundant agricultural waste, are often underutilized, making their conversion into high-value carbon materials a critical focus for waste recycling and energy storage applications. Herein, a synergistic KOH-ZnCl 2 dual activation strategy was proposed to synthesize tobacco stem-derived activated carbons (TSACs), which precisely tailors the pore structure and defect density for enhanced electrochemical performance. Specifically, high-temperature KOH activation can etch the carbon framework to create numerous micropores, whereas ZnCl 2 has a weaker etching effect and produces only a limited number of micropores. Leveraging the synergistic etching effect of the KOH-ZnCl 2 dual-activator system, a hierarchically porous structure comprising both micropores and mesopores can be generated within the carbon material. The optimized TSAC-1 (with a mass ratio of TSC:KOH:ZnCl 2  = 1:4:1) possesses a well-developed honeycomb-like interconnected porous network, a high BET specific surface area of 3257 m 2 g −1 , and appropriate proportions of micropores (72.3%) and mesopores (26.7%), thus offering abundant active sites and efficient ion transport channels. Electrochemical tests show that the TSAC-1 electrode delivers a high specific capacitance of 334 F g −1 at 1 A g −1 , retains 218 F g −1 at 20 A g −1 (corresponding to a rate capability of 65.3%), and maintains 91.4% capacitance after 5000 cycles, demonstrating excellent performance and stability. The symmetric supercapacitor (SSC) based on TSAC-1 and 6 M KOH operates stably at 1.3 V, achieving a maximum energy density of 13.3 Wh kg −1 at 162.5 W kg −1 , retaining 6.4 Wh kg −1 at 3250 W kg −1 , and maintaining 95.76% capacitance after 11,000 cycles with Coulombic efficiency above 99%. These results validate that tobacco stem-derived activated carbons prepared by dual activation are high-performance electrode materials for supercapacitors, offering a sustainable approach to waste valorization and advancing the development of green energy storage systems.