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Nitrogen-doped porous carbon derived from residuary shaddock peel: a promising and sustainable anode for high energy density asymmetric supercapacitors

Exploring high-performance negative electrode materials is one of the great challenges in the development of high-energy density asymmetric supercapacitors (ASCs). Herein, a new kind of high-performance nitrogen-doped nanoporous carbon (NPC) electrode with a large surface area and abundant micropores/mesopores was derived from conveniently available fruit waste (shaddock peel) via a facile pyrolysis process. Electrochemical measurements showed that the as-synthesized NPC electrodes possessed a remarkably large capacitance of 321.7 F g−1 with good rate capability and excellent long-term cycling stability. Such excellent electrochemical performance was achieved by shortening the diffusion distance, increasing the electrode–electrolyte contact area and improving the electron conductivity of the NPC electrode arising from its nanoporous architecture and nitrogen doping. As a prototype, an all-solid-state ASC device based on the NPC negative electrode and a MnO2 positive electrode achieved an ultrahigh energy density of 82.1 W h kg−1 at a power density of 899 W kg−1, which is considerably larger than most reported carbon based supercapacitor devices.