N doped porous carbon nanosheets with enhanced zinc ion storage capability

Aqueous zinc ion hybrid capacitors are promising energy storage devices due to their high security, excellent environmentally friendly, big power density and zero carbon emissions. Herein, an aqueous zinc ion hybrid capacitor is designed using an N doped porous carbon nanosheet cathode, which prepares by in-situ self-activated and self-doped strategy from ethylenediamine tetraacetic acid tripotassium salt. The superior ions storage performance is owing to the electric dual layer capacitor deriving from ion adsorption/desorption, Zn2+ deposition/stripping and extra pseudo-capacitance of vibration in valence of nitrogen functionalities. Additionally, the results of theoretical calculation show that the adsorption energy between N-5, N-6 and zinc ions is −4.816 and −3.453 eV, respectively, and higher than those of other N groups. Consequently, the N doped porous carbon nanosheet cathode displays big discharge capacity of 204.7 mAh g−1 and high energy density of 143 Wh kg−1. Moreover, the Zn‖N doped porous carbon nanosheet zinc ion hybrid capacitor presents superior cycle stability with 95.5% of initial capacity after 20,000 cycles. This study opens up a universal method by incorporating reversible redox reactions through N functionalities to enhance the zinc ions storage properties of zinc ion hybrid capacitor.