With the assistance of alkali metal carbonate M2CO3 (M is Na and K) as a carbon source and silicon as a displacement agent, an exothermic and self-sustaining reaction to produce two-dimensional (2-D) hierarchically porous carbon nanosheets (denoted as HP-CNSs) was achieved. The combustion reaction developed a temperature in the range of 1100-1400 degrees C and resulted in a two-phase product consisting of HP-CNSs and alkali metal silicate (M2O center dot nSiO(2)). After dissolving the M2O center dot nSiO(2) in distilled water, a black carbon powder was formed. Despite the simple synthesis process, the HP-CNSs had a BET surface area of about 178.6-860 m(2)g(-1) and a pore diameter in the range 0.5-150 nm. HP-CNSs based capacitors showed a specific capacity of about 85-240 Fg(-1) and good cyclic performance for over 1000 cycles. (C) 2018 Elsevier B.V. All rights reserved.