Mechanochemically Assisted Microwave-Induced Plasma Synthesis of a N-Doped Graphitic Porous Carbon-Based Aqueous Symmetric Supercapacitor with Ultrahigh Volumetric Capacitance and Energy Density

Abstract

In the realm of affordable and yet efficient energy storage devices required for future portable electronic gadgets and electric vehicles, supercapacitors (SCs) have immense potential; however, the prime bottleneck is the low volumetric capacitance and energy density caused by the sluggish reaction kinetics and a limited potential window (<1.2 V) in aqueous electrolytes. Therefore, to address this challenge, we aim to design suitable biomass-derived nitrogen (N)-doped highly porous graphitic carbon (HP-NGC) via a mechanochemically assisted microwave plasma-induced quick synthesis process to deliver high volumetric capacitance and energy density. Detailed characterization of the developed electrode materials revealed that the structural and functional properties are highly influenced by the crucial role of mechanochemical treatment carried out just before carbonization through microwave irradiation under N-2 plasma. HP-NGC produces an almost 32% higher surface area (820 m(2) g(-1)) than the surface area (620 m(2) g(-1)) of N-doped graphitic carbon (NGC) prepared without mechanochemical treatment. Moreover, HP-NGC shows more N doping (ID/IG similar to 1.01)(IDIG similar to 1.01) than NGC (where N doping is 1.1 atom % and ID/IG is similar to 0.98), which significantly affects their electrochemical storage properties. The HP-NGC electrode exhibited similar to 145% higher volumetric capacitance (840 F cm(-3)) and energy density (168 Wh L-1) than the volumetric capacitance (308 F cm(-3)) and energy density (61.5 Wh L-1) of the NGC electrode within a wide potential window of 1.2 V measured at 0.5 A g(-1) in 6 M KOH. Finally, the assembled aqueous symmetric device (HP-NGC//HP-NGC) made of HP-NGC electrodes exhibits a volumetric capacitance of 630 F cm(-3) with excellent rate performance (similar to 81% capacitance retained even after increasing the current density by 10 times), high-energy density of 32 Wh L-1, and power density of 640 W L-1 at 0.5 A g(-1), which is higher than those of many reported porous carbon-based symmetric devices, making it a promising candidate for commercial applications.