Influence of oxygen treatment on electric double-layer capacitance of activated carbon fabrics

Oxygen treatment at 250degreesC on polyacrylonitrile-based activated carbon fabric was conducted to explore the influence of carbon-oxygen complexes on the performance of capacitors fabricated with the carbon fabric. Surface analysis showed that most of the oxygen functional groups created from the oxygen treatment were the carbonyl or quinone type. The performance of the capacitors was tested in 1 M H2SO4, using potential sweep cyclic voltammetry and constant current charge-discharge cycling. It was found that the Faradaic current, the contributor of pseudocapacitance, increased significantly with the extent of oxygen treatment, while the increase in the double-layer capacitance was minor. Due to the treatment the overall specific capacitance showed an increase up to 25% (e.g., from 120 to 150 F g(-1) at a current density of 0.5 mA cm(-2)). However, the distributed capacitance effect, the inner resistance and the leakage current were found to increase with the extent of oxidation. It is suggested that due to the local changes of charge density and the increase in redox activity the presence of the carbonyl- or quinone-type functional groups may induce double-layer formation, Faradaic current, surface polarity, and electrolyte decomposition. (C) 2002 Elsevier Science Ltd. All rights reserved.