Three-dimensional scaffolding framework of porous carbon nanosheets derived from plant wastes for high-performance supercapacitors

Utilizing carbon materials derived from sustainable biomass on supercapacitors has become particularly attractive recently. High-performance activated carbons (ACs) based on inexpensive, abundant but unwanted natural wastes are highly preferred. In this work, using dry elm samara as the prototype, we demonstrate that three-dimensional (3-D) scaffolding frameworks of highly porous carbon nanosheets (PCNSs) can be derived from plant wastes having specific natural morphology, i.e. half-transparent thin flakes, through a facile carbonization and activation treatment. The products possess a high accessible surface area induced by the 3-D framework, and a high density of micro-pores, which benefit large ion storage and high-rate ion transfer. In addition to the electric double-layer capacitor, the heteroatom doping evokes the faradic contribution. PCNS activated by 6 mol L⁻¹ KOH (PCNS-6) exhibited a rather high specific capacitance of 470 F g⁻¹ and 310 F g⁻¹ at a current density of 1.0 A g⁻¹ respectively in a three- and two-electrode system using 6 mol L⁻¹ KOH electrolyte, among the highest ever reported for carbon materials derived from biomass. Furthermore, the high rate capability (72% and 64% capacitance retention at 200 mV s⁻¹ and 20 A g⁻¹, respectively) as well as the high cycling stability (2% loss over 50,000 cycles) significantly potentiate the supercapacitor properties of the product. Additionally, an energy density as high as 25.4 Wh kg⁻¹ at the power density of 15 kW kg⁻¹ was verified in 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF₄) electrolyte. Most importantly, it is demonstrated that 3-D scaffolding PCNS frameworks can be easily achieved from different plant wastes sharing common features. This work provides a clear strategy on how to select promising plant-waste candidates for high-performance ACs applied on energy storage.