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Hierarchically porous carbons (HPCs) have attracted much attention because of their potential application in carbonbased supercapacitors. Here, we list a facile and green method to obtain HPCs by annealing a coal tar pitch with sodium bicarbonate. The produced gases and sodium carbonate template can guide the formation of carbon products with a multiscale pore structure. Further activation by KOH endows HPC with a surface area of 2851.7 m 2 g −1 and a total pore volume of 2.4 cm 3 g −1 . Accordingly, such an HPC electrode achieves a specific capacitance of 321.5 F g −1 (0.5 A g −1 ) and retains 230.0 F g −1 (100.0 A g −1 ). Moreover, the HPC-based symmetric supercapacitor exhibits superior cyclic stability (1.1% capacity decay after 30,000 cycles) in an aqueous electrolyte. In the TEABF 4 /acetonitrile electrolyte, the assembled device displays a high energy density of 53.0 Wh kg −1 and still retains 77.9% even when the power density is increased from 750.0 to 15,000.0 W kg −1 . We believe that the salt-assisted synthesis strategy for HPC paves a green way to developing high-performance supercapacitors.

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Nitrogen-doped porous carbons are attractive electrode materials for supercapacitors because of their high specific capacitance and desirable surface property. Here, we report a facile polymerization-pyrolysis strategy to construct hierarchical porous carbon, which is rich in surface redox nitrogen species. The polymeric precursor of phenolic resin cross-linked with polyaniline is produced by a mild hydrothermal process. The following calcination procedure yields hierarchical nitrogen-doped porous carbon, which presents a large specific surface area of 968.5 m 2 g −1 with multi-scale porous structures including micro-, meso-, and macropores. It is found that pyrrolic nitrogen and oxidized nitrogen are successfully introduced on the porous carbon surface, and they can supply extra pseudo-capacitance. The synergy of massive charge storage sites and interconnected ion transport channels enables the hierarchical nitrogen-doped porous carbon to exhibit a high specific capacitance of 320.6 and 250.0 F g −1 in the alkaline electrolyte at current densities of 0.5 and 100 A g −1 , respectively. In addition, the assembled symmetrical supercapacitor with organic electrolytes shows a huge energy density of 48.9 Wh kg −1 at a power density of 375.0 W kg −1 , with a capacitance retention close to 100% after 50,000 cycles.

High energy density combined with rapid mass transport is highly desired for carbon-based electrical double-layer capacitors. Here, multiscale porous carbon has been constructed by an efficient polymerization-pyrolysis strategy. The resorcinol-formaldehyde polymer anchored with Fe3+ is firstly prepared, and the in situ formed Fe3O4 nanoparticles act as mesoporous template during the pyrolysis process. The resultant hierarchically porous carbon achieves an extended surface area of 2260.3 m2 g-1 and wide pore size distributions including micro-, meso-, and macropores. The synergism of large surface area, high conductivity, and interconnected ion transport channels leads to superior energy storage performances of prepared multiscale porous carbon electrode. It delivers a high specific capacitance of 271.7 F g-1 at 0.5 A g-1 in KOH electrolyte, accompanied with a prominent capacitance retention of 88.5% when the current density is 10.0 A g-1. Besides, the assembled symmetric supercapacitor using organic electrolyte exhibits a maximum energy density of 54.0 Wh kg-1 at the power density of 750.0 W kg-1, as well as the superior cyclic stability with a capacitance retention of 88.2% after 10000 cycles.