Easy preparation of nitrogen-enriched carbon materials from peptides of silk fibroins and their use to produce a high volumetric energy density in supercapacitors

A novel nitrogen-rich carbon material, silk carbon, was prepared from Bombyx mori silk fibroins by simple heat-treatment under inert atmosphere. The nitrogen atoms were originated from copious peptide bonds contained in the silk fibroins. The adequate heat-treatment temperature turned the nitrogen atoms of the peptide bonds to the silk carbons in the form of nitrogen-containing functional groups. Furthermore, the activation of the silk carbons with steam and potassium hydroxide provided nitrogen-containing activated carbons (ACs) with different pore-size distribution. In the application to electric double layer capacitors, the silk carbon-based ACs showed a higher capacitance and an excellent electrochemical stability in the high voltage region, compared with a typical AC prepared from phenolic resin. More significantly, the steam-activated silk carbon showed the energy density that was comparable to that of the phenolic resin-based AC prepared by chemical activation. This indicates the superiority of steam-activated silk carbons to conventional KOH-activated carbon materials in supercapacitor application, due to the low production cost by the facilities of steam activation, and the relevant capacitance comparable with that of chemical activation. (C) 2007 Elsevier Ltd. All rights reserved.