Biomass-derived nanostructured carbon materials for high-performance supercapacitor electrodes

To achieve a higher energy density for the supercapacitor without degrading cycle stability, functionalization of biomass based-AC with oxygen-containing groups was applied. Nanostructured carbon materials were produced from barley straw biomass waste using the activation-functionalization by FeCl₃ and urea via the pyrolysis method in a tubular reactor at 900 °C. The electrode made up of carbon BCF-U in the three-electrode cell in aqueous KOH electrolyte showed high-specific capacitance of 515 F g^–1 at current density of 2 A g⁻¹ and in aqueous Na₂SO₄ electrolyte the capacitance of 379 F g⁻¹ at 3 A g⁻¹. The BCF-U electrode showed cycling stability, retaining more than 99% capacitance after 5000 cycles in 1 M Na₂SO₄ electrolyte. The fabricated symmetric supercapacitor device with carbon BCF-U showed a high-energy density of 10.7 Wh kg^–1 and a power density of 720 W kg⁻¹ in aqueous 6 M KOH. Different characterizations were carried out to show that the functional group and morphological features of the activated carbon were closely related to the superior capacitive performance by enhancing diffusion of electrolyte ions. The analysis proved the formation of graphitic nature with mixed micro- and mesoporous textures in addition to carbon nanotube, carbon nano rod, and graphene. These unique features make synthetic activated and functionalized samples possess good adsorption capacity for electrical double layer capacitors. The results demonstrate that nanostructured carbon materials derived from a low-cost biomass waste can serve as an economical carbon feedstock for production of high-performance electrode material for supercapacitors.