Deciphering the Incredible Supercapacitor Performance of Conducting Biordered Ultramicroporous Graphitic Carbon

Nanostructured porous carbon and conducting graphitic carbon were previously explored for energy storage applications. However, a balance of graphitization and porosity with high electrical conductivity to percolate ions and their storage is challenging. In this work, we report the synthesis of electrically conducting biordered ultramicroporous graphitic carbon (BUGC) employing an activation methodology, wherein reduced graphene (RG) was infused with nonporous carbon (NC) along with porogen KOH to catalyze bulk graphitization. The nanoengineered material possesses superior properties such as a high electrical conductivity due to a biordered graphitic arrangement for enhanced ion percolation, large BET surface area (2472 m2/g) with ultramicropores/micropores (0.35-1.47 nm) for enhanced ion accumulation, a short-range graphitic interconnected network for ion diffusion, and oxygen functionalities for better wettability in the aqueous electrolyte. Consequently, specific capacitances of 732 F/g (0.5 A/g) in a three-electrode assembly and 534 F/g (0.2 A/g) in a two-electrode assembly have been obtained for BUGC with a superior energy density of 90 Wh/kg with an excellent cyclic stability of 94% after 10 »000 cycles. BUGC exhibited a small dielectric relaxation time constant of 0.18 s, i.e., the time required to achieve 50% specific capacitance. Electrochemical impedance spectroscopy (EIS) has been employed to estimate an upper limit of specific capacitance, which eliminates a series of potential drops due to cell configurations. The upper limit capacitance obtained from EIS and the specific capacitance obtained from a galvanostatic charge/discharge experiment have been utilized to define a parameter, i.e., supercapacitor performance efficiency (SPE). SPE was found to be 2.7 times higher for BUGC than that of even electrically conductive RG, which further validated the importance of the unique structural features in BUGC. Hence, this work demonstrates a significant surge toward the improvement of designing carbon-based material for supercapacitor (SC) applications correlating the structure-property relationship.