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

Exploring high-performance negative electrodematerials 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.