Bioinspired design of graphene-based N/O self-doped nanoporous carbon from carp scales for advanced Zn-ion hybrid supercapacitors

Integrating the superiorities of high power density of supercapacitors and high energy density of batteries, safe and low cost aqueous Zn-ion hybrid supercapacitors (ZIHSCs) are regarded as a promising alternative for next generation energy storage devices. As potential cathode materials for ZIHSCs, porous carbon/graphene have been widely investigated recently, whereas the adjustment of their composition and structure to achieve favorable features of sustainability, long lifespan and high activity remains a challenge. Herein, a graphene-based N/O co-doped porous carbon is successfully constructed via an efficient approach of the carbonization and sequent KOH activation using renewable carp scales as carbon source. The unique lamellar structure with the exterior layer of hydroxyapatite and the beneath well-arranged collagen fibrils (rich in N and O) functions as catalytic base for the growth of graphene structure over the exterior layer and affords the self-doping with N and O heteroatoms, respectively. Expectedly, the resultant carbon possesses a hybrid structure of graphene base and nanoporous amorphous carbon, together with a proper N/O co-doping, resulting in fast electrochemical kinetics and abundant Zn2+ storage active sites for high power and energy outputs. Consequently, as-assembled aqueous ZIHSC displays a high specific capacity of 138.8 mAh g -1 at 0.1 A g -1, admirable rate capability of 61.7% retention rate at a 200-fold higher current, and attractive energy density of 111.1 Wh kg -1 at 100 W kg -1. More excitingly, as-constructed quasi-solid ZIHSC exhibits a satisfactory specific capacity of 117.8 mAh g -1, a high energy density of 88.9 Wh kg -1 and a high power density of 10 kW kg -1, together with excellent cycling stability (capacity retention of 87.2% after 10,000 charge-discharge cycles at 5 A g -1) and outstanding mechanical flexibility. Therefore, the designed conversion of carp scales to advanced carbons by taking advantages of its inherent composition and structure opens up hereditary view to construct high performance ZIHSCs from biomass sources.