Excellent electrochemical properties and large CO2 capture of nitrogen-doped activated porous carbon synthesised from waste longan shells

We present a low-cost approach for facile synthesis of nitrogen-doped porous carbons by utilising waste longan shell as carbon source and carbamide as additional nitrogen source through KOH activation at 600°C–900°C for 2hours under N2 atmosphere. The obtained porous carbons possess highly-developed ultra-micropores (approximately 0.6nm), an ultrahigh specific surface area (up to 3260 m2 g-1) and a nitrogen content of 2.3 at.%. The porous carbon exhibits excellent electrochemical properties (a high specific capacity up to 322 F g-1 and an energy density of up to 20.4W h kg-1) at a current density of 0.5 A g-1 in 6M KOH and an excellent cycle stability (retained almost 96.2% specific capacitance after 5000 cycles). In addition, the porous carbon shows high CO2 adsorption capacities of 5.6 mmol g-1 (at 0°C) and 4.3 mmol g-1 (at 25°C) and high CO2 selectivity against N2. These results indicate that the fabricated porous carbon is a promising electrode material for supercapacitors and a solid adsorbent for CO2 uptake.