Nitrogen-doped porous carbon is synthesised through a low-cost approach that utilise water chestnut as a carbon source and melamine as a nitrogen source through potassium hydroxide (KOH) activation for 2 h at 600 degrees C-900 degrees C. The obtained samples exhibit predominant characteristics with highly developed micropores, an ultralarge specific surface area (3401 m(2) g(-1)) and a high nitrogen content (4.89 at.%). These characteristics endow nitrogen-doped porous carbon with a high specific capacity of 346 Fg(-1) and a high energy density of 22.4 W h kg(-1) at 0.5 A g(-1) in 6 mol dm(-3) KOH. It also exhibits an excellent cycling stability with a retention of nearly 97.6% capacity after 5000 cycles at 1 Ag-1. In addition, the unique pore structure and high nitrogen content of porous carbon provide an important contribution to CO2 adsorption capacity, which can reach up to 6.0 mmol g(-1) (at 0 degrees C and 1 bar) and 4.7 mmol g(-1) (at 25 degrees C and 1 bar), and to high CO2/N-2 selectivity. Results show that the synthesised porous carbon exhibit considerable potential in electrochemical energy storage and solid adsorption. (c) 2018 Published by Elsevier Ltd.