Nitrogen-doped agar-derived porous carbon with long cycle life for high-performance ionic liquid-based supercapacitors

Reasonable design of electrode materials to match ionic liquid electrolytes is important for the development of high-performance supercapacitors in the future. Herein, we demonstrate a nitrogen-doped agar-derived porous carbon (NAGC) electrode material with high specific capacitance and long cycling life, which was prepared using agar as precursor, potassium carbonate as activator, and melamine as nitrogen source via one-step activation doping method. The combined action of melamine and potassium carbonate can regulate and control the physical and electrochemical properties of the prepared materials. NAGC presents a high specific surface area (3228 m 2 /g) and micropores-dominated hierarchical porous structure , which can provide more adsorption sites and benefit rapid ions transport. The NAGC electrode in 1-ethyl-3-methylimidazolium tetrafluoroborate ([Emim][BF 4 ]) ionic liquid electrolyte has a specific capacitance of 183 F/g at 1 A/g and 91 % capacitance retention from 1 to 10 A/g. Additionally, the assembled device with NAGC as both positive and negative electrode material has a wide operating voltage (3.6 V) and high energy density of 70.2 Wh/kg at a power density of 1.81 kW/kg. Also, it possesses a capacitance retention of 83.3 % after 50,000 cycles. This work provides a simple and effective way to achieve porous carbon materials with high specific capacitance and long cycle life.