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[Display omitted] • Solvent-free strategy was developed to synthesize porous carbon (MIC x) doped with rich Faradaic active oxygen (5.8–8.2 atom%). • The resultant MICx owns surface area of 326–427 m2/g and large packing density of 1.12–1.28 g/cm3. • The MICx based electrode achieves superior supercapacitor performances with both high gravimetric and volumetric performances. In the selection of carbon-based electrode materials for supercapacitive energy storage, it is hard to get one that is high in both gravimetric and volumetric performance because there is a trade-off between them. In the presented work, microporous carbon materials denoted herein as MIC x were synthesized through catechol polymerization in the presence of molten FeCl 3. As complexing agent, the iron species coordinate with catechol oligomers, functioning as template as well as catalyst in the synthesis of the microporous carbon. The in situ formation of micropores and carbonaceous skeleton is induced by the carbonyl/hydroxyl redox pairs upon catalytic graphitization during carbonization. The derived nanocarbons have high microporosity (70.6 %–79.2 %) and rich oxygenate functionalities (carbonyl: 3.3–4.0 atom% and hydroxyl: 2.5–4.2 atom%). The FeC x materials are high in faradaic activity. For example, the FeC873-based electrode displays excellent supercapacitor performances: capacitance of 440F/g@1.0 A/g (equivalent to 537F/cm3@1.0 A/g) and 289F/g@20 A/g (equivalent to 353F/cm3@20 A/g), large energy density of 25.5 Wh/kg@900 W/kg (equivalent to 31.1 Wh/L@1098 W/L), and good cycling stability (ca.100 % capacitance retention after 20 000 continual charge/discharge cycles). [ABSTRACT FROM AUTHOR]

As an industrial material for supercapacitive energy storage, commercial activated carbons (AC) could achieve a satisfactory gravimetric performances by electric double layered capacitance (EDLC) due to their rich microporosity, but the volumetric performances are usually poor resulted from the low packing density. Herein, we presented a strategy to address this tradeoff relationship and to achieve both high gravimetric and volumetric performance by filling the macro/mesoporosity with extra nitrogen doped carbon. The reconstructed activated carbon could inherit most of microporosity from the parent AC, while the macro/mesoporosity of them was greatly decreased, resulting in increase of packing density and the improvement of surface hydrophilicity. Benefited from the increase of packing density and maintenance of microporosity, the resultant activated carbon achieves greatly enhanced energy storage level including three times higher capacitance of 384 F cm−3@ 1.0 A/g (vs 128 F cm−3@ 1.0 A/g for pristine AC), high rate capability of 73.4% (vs 59.2% for pristine AC), larger energy density of 27.5 Wh L−1@ 900 W L−1 (vs 10.0 Wh L−1@747 W L−1). Importantly, the present strategy provides a facile and unique method to process activated carbon, which offers a possibility improving the energy storage level of the commercial activated carbon. [Display omitted] • Commercial activated carbon (AC) was processed by filling the macro/mesoporosity. • The filled AC owns increased packing density and more nitrogen functionalities. • The filled AC achieves greatly enhanced supercapacitor performances. [ABSTRACT FROM AUTHOR]