Ultra-high specific capacitance of self-doped 3D hierarchical porous turtle shell-derived activated carbon for high-performance supercapacitors

The turtle shell of biomass waste is used as raw material, and the natural inorganic salt contained in it is used as a salt template in combination with a chemical activation method to successfully prepare a high-performance activated carbon with hierarchical porous structure. The role of hydroxyapatite (HAP) and KOH in different stages of preparation was investigated. The prepared turtle shell-derived activated carbon (TSHC-5) has a welldeveloped honeycomb pore structure, which gives it a high specific surface area (SSA) of 2828 m2 g-1 with a pore volume of 1.91 cm3 g-1. The excellent hierarchical porous structure and high heteroatom content (O 6.88%, N 5.64%) allow it to have an ultra-high specific capacitance of 727.9 F g-1 at 0.5 A g-1 with 92.27% of capacitance retention even after 10,000 cycles. Excitingly, the symmetric supercapacitor assembled from TSHC-5 activated carbon exhibits excellent energy density and cycling stability in a 1 M Na2SO4 aqueous solution. The energy density is 45.1 Wh.kg- 1 at a power density of 450 W kg-1, with 92.05% capacitance retention after 10,000 cycles. Therefore, turtle shell-derived activated carbon is extremely competitive in sustainable new green supercapacitor electrode materials.