Crab shell-derived honeycomb-like graphitized hierarchically porous carbons for satisfactory rate performance of all-solid-state supercapacitors

Crab shells derived from discarded seafood bio-waste, are a naturally abundant and sustainable resource, but their difficult solubility limits their processing and applications, resulting in severe environmental pollution. It is very attractive to discover approaches for reducing the threats of crab shells to the environment and even to convert crab shells into useful materials. Herein, we attempted to convert crab shells into three-dimensional (3D) honeycomb-like graphitized hierarchically porous carbons (GHPCs) by a convenient one-step carbonization process simultaneously combining catalytic graphitization and chemical activation routes. The removal of abundant inorganics from crab shells resulted in a unique honeycomb-like structure, and meanwhile a high doping concentration of N element was inherited in the framework of GHPCs. Furthermore, the simultaneous activation/graphitization treatment developed interconnected hierarchical porosity with a large accessible surface area and highly graphitized skeleton. Benefiting from these unique structural characteristics, GHPCs exhibited a remarkable capacitive performance as supercapacitor electrodes. The GHPC electrode delivered a high gravimetric capacitance of 367.4 F g(-1) at 1 A g(-1) in 6 M KOH electrolyte. More importantly, the electrode showed satisfactory rate capability where an extremely high current density of 100 A g(-1) for charge-discharge operation was available in both KOH and Na2SO4 electrolytes. Furthermore, the assembled symmetric flexible all-solid-state capacitor exhibited a high energy density of 11.1 W h kg(-1) and a power density of 100.5 W kg(-1), as well as a good cycling stability of 90.8% capacitance retention after 10 000 cycles in a PVA/KOH gel electrolyte. Our approach not only relieved the environmental pollution caused by crab shells but also achieved the production of a high-performance supercapacitor electrode, which was promising for industrial energy conversion and storage. It therefore demonstrated an example of trashto- treasure transformation.