N-doped highly microporous carbons have been successfully fabricated from N-rich microalgae by the combination of low-cost hydrothermal carbonization and industry-adopted KOH activation processes. The hydrothermal carbonization process was found to be an essential step for the successful conversion of microalgae into a carbon material. The materials thus synthesized showed BET surface areas in the range similar to 1800-2200 m(2) g(-1) exclusively ascribed to micropores. The carbons showed N contents in the 0.7-2.7 wt.%, owing to the use of N-rich microalgae as a carbon precursor. When tested in symmetric double layer capacitors (occasionally called supercapacitors) based on aqueous LiCl electrolytes, pseudocapacitance was only observable for the sample synthesized at the lowest temperature, 650 degrees C, which is the one exhibiting the largest amount of N- and O-containing groups. The samples synthesized at 700-750 degrees C exhibited excellent rate capability (only 20% of capacitance loose at 20 A g(-1)), with specific capacitances of 170-200 F g(-1) at 0.1 A g(-1). These materials showed excellent long-term cycling stability under high current densities. (C) 2014 Elsevier B.V. All rights reserved.