N-doped microporous carbon microspheres for high volumetric performance supercapacitors

N-doped highly dense uniform carbon microspheres of around 1 μm have been prepared by a nanocasting strategy using silica particles as template and a nitrogen-rich substance (i.e. pyrrole) as carbon precursor. These carbon microspheres possess a large number of nitrogen functional groups (∼ 9 wt % N), a high BET surface area of up to ∼ 1300 m2 g−1 with a porosity made up mostly of micropores (< 2 nm), and a high packing density of 0.97 g cm−3. They also show a remarkable volumetric capacitance of ca. 290 F cm−3 in H2SO4 as a result of pseudocapacitance effects arising from the N-groups, such that they are able to keep 50 % of the capacitance at a high current density of 40 A g−1. An additional chemical activation process with KOH has been performed to enhance the microporous network. These highly porous microspheres (2690 m2 g−1), that have a lower nitrogen content (∼ 2 % wt), can achieve 92 F cm−3 in TEABF4/AN while displaying 83 % of capacitance retention at a high current density of 40 A g−1.