Heterogeneous activated carbon with graphitized shell and hydrophilic pores integrating high conductivity and pore affinity for excellent rate performance supercapacitors

High electrical conductivity and excellent pore affinity for electrolyte are the two necessary characteristics for high-rate performance supercapacitors based on activated carbon electrode. Nevertheless, it is fairly challenging to simultaneously improve them due to they are usually in the tug of war relationship in aqueous electrolyte. Herein, based on the different antioxidant abilities of graphitized carbon and amorphous carbon, a well-designed heterogeneous structure activated carbon (HGCAC) with graphitized carbon shell, amorphous carbon inner, and hydrophilic pores has been successfully prepared by a combined procedure of solid phase grinding, catalytic graphitization, and hydrothermal oxidation. Owing to the heterogeneous structure, HGCAC exhibits a joint improvement of electrical conductivity and the pore affinity for aqueous electrolyte, and thus leads to the remarkable enhancement of capacitance and rate capability, in comparison with the commercial coconut shell derived activated carbon (CAC) for supercapacitor. When the current density increases 100 times to 50 A g-1, the specific capacitance of as-made HGCAC is 203.4 F g-1, with the capacitance retention of 81.0%, being nearly 2.14 times of CAC's capacitance (95.2 F g-1) and 1.6 times of its capacitance retention (51.0%). Moreover, good rate capability is still maintained when HGCAC is assembled to a coin type supercapacitor, with the capacitance retention of 82.1% at 50 A g-1.