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 degrees C-900 degrees C for 2 hours under N-2 atmosphere. The obtained porous carbons possess highly-developed ultra-micropores (approximately 0.6 nm), an ultrahigh specific surface area (up to 3260 m(2) 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 20.4 W h kg(-1)) at a current density of 0.5 A g(-1) in 6 M 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 degrees C) and 4.3 mmol g(-1) (at 25 degrees C) and high CO2 selectivity against N-2. These results indicate that the fabricated porous carbon is a promising electrode material for supercapacitors and a solid adsorbent for CO2 uptake. (C) 2017 Elsevier Ltd. All rights reserved.