Nanocarbon of moderate microporosity doped with oxygenate redox pairs to achieve superior gravimetic/volumetric supercapacitor performances

Abstract

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 MICx were synthesized through catechol polymerization in the presence of molten FeCl3. 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 FeCx 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).