Acta Phys. -Chim. Sin. ›› 2005, Vol. 21 ›› Issue (07): 786-791.doi: 10.3866/PKU.WHXB20050717

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Influence of Pore Structure of Phenolic Resin Based Activated Carbon Fibers on the Electrochemical Performance of Electrical Double-layer Capacitors

LIU Chun-ling; WEN Yue-hua; CHENG Jie; GUO Quan-gui; CAO Gao-ping; LIU Lang; YANG Yu-sheng   

  1. Key laboratory of carbon Materials, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan 030001;Research Institute of Chemical Defense, Beijing 100083
  • Received:2004-12-14 Revised:2005-03-11 Published:2005-07-15
  • Contact: LIU Lang E-mail:liulang@public.ty.sx.cn

Abstract: Phenolic resin based activated carbon fibers (ACF-H2O) prepared using steam activation at 800 ℃ were investigated by means of N2 adsorption, AC impedance and constant current discharge techniques. The relationship between the specific surface area and pore size distribution of ACF-H2O with their electrochemical performance as electrodes of electric double layer capacitors (EDLC) in 1 mol•L-1 LiClO4/PC was discussed in detail. It is found that the ultramicropores(d < 0.7 nm= cannot be accessed by electrolyte solution. With increasing steam activation time, the specific surface area and pore volume increase gradually, whereas the micropore (2.0 nm> d > 0.7 nm ) and meso-pore ratios change little due to the deepening and broadening of the micropore formed during carbonization. However, excessive activation destroyed the pore structure, causing a sharp decrease of both specific surface area and pore volume. For those samples with well-developed pore structure, there is a linear relationship between capacitance and specific surface area (C-S), and a maximum specific capacitance of 109.6 F•g-1 was achieved. The double layer capacitance per unit surface area is not the same for all porous surface, and the capacitances of 8.44 μF•cm-2 and 4.29 μF•cm-2 are obtained, for the micropore and mesopore surfaces respectively. The double layer capacitance and AC impedance data strongly depend on the porous structure, the bigger the pore, the easier and faster being accessed electrochemically, the less the time constant and resistance should be, and it can be discharged/charged at higher current density. ACF with larger pore surface and less ultramicropore is desirable for those applications either as energy devices or as power storage devices. Steam activation can only obtain carbon materials with small mesopore, thus the higher electrochemical behavior attainable in EDLC using non-aqueous electrolyte is restricted.

Key words: Phenolic resin based activated carbon fiber, Pore structure, Electrochemical performance