Nitrogen-doped porous carbon for supercapacitor with long-term electrochemical stability

Nitrogen-doped porous carbons have been prepared by a direct carbonization of the mixture of urea formaldehyde resins (abbr. UF resins) and calcium acetate monohydrate. The experimental results reveal that the mass ratios of UF resins-to-Ca(OAc)(2)center dot H2O and carbonization temperatures can play crucial roles in the formation of porous carbon with various surface area and structure as well as determining the carbons' surface areas, pore structures and capacitive performance. The UF-Ca-700-3:1 sample exhibits much large specific capacitances ca. 334.8 F g(-1) and 224.0 F g(-1) at the current density of 0.5 and 1.0 A g(-1) in 6.0 mol L-1 aqueous KOH aqueous electrolyte, respectively. The UF-Ca-900-3:1 displays more superior rate capability, which can possess high specific capacitance retention as ca. 67.1% and 51.4% at the high current densities of 20 and 40 A g(-1), respectively. In addition, a capacity fading lower than 1% after 5000 cycles of charging and discharging is obtained, indicating its long-term electrochemical stability. (C) 2012 Elsevier B.V. All rights reserved.