Mesoporous Carbon Materials as Electrodes for Electrochemical Double-Layer Capacitor
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Mesoporous Carbon Materials as Electrodes for Electrochemical Double-Layer Capacitor Sea Park1, Chengdu Liang2, Dai Sheng2, Nancy Dudney1, and David DePaoli3 1 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37830 2 Chemical Sciences Division, Oak Ridge National Laboratory, Bethel Valley Rd., Oak Ridge, TN, 37830 3 Nuclear Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37830 ABSTRACT Nanostructured carbon materials with a regular array and narrow size distribution of mesopores have been synthesized at Oak Ridge National Laboratory via the self-assembly of block copolymers as soft templates. One promising application for these materials is as electrodes for electrochemical double-layer capacitors. To evaluate the performance, electrodes were prepared by coating the precursor onto fibrous carbon paper, followed by curing and pyrolysis at 850°C. The resulting mesoporous carbon has a surface area of 310 m2/g and an average pore size of 8.5 nm. Results from cyclic voltammetry and impedance spectroscopy experiments using a sulfuric acid electrolyte showed high specific capacitance values of up to 300 F/g. For comparison, a commercially available aerogel carbon coated paper was also examined. INTRODUCTION Electrochemical double-layer capacitors (EDLC) are an important technology for storage of electrical energy particularly for grid and vehicle applications. Also known as supercapacitors or ultracapacitors, EDLC can store much more energy per unit volume or mass than traditional dielectric capacitors.[1] In the ideal case, when the EDLC is polarized, the energy is stored solely as the electrostatic field formed in the electric double layer at the surface of each electrode. Because faradaic processes are minimal, these capacitors typically have much longer cycle life than batteries or pseudo-capacitors, however the energy stored at the interface is also much smaller. A large surface area for the double layer formation is needed to maximize the specific capacity and energy density of the device. Porous activated carbons have been used almost exclusively for this application due to their huge surface area and low cost; however, the currently available materials are far from optimal. [2] Activated carbons typically have a wide pore size distribution from micro- to macro-pore sizes, which is difficult to control and tailor by macroscopic bulk processing. Overall the capacity of the current commercial activated carbon materials is well below the theoretical capacitance, presumably due to limited accessibility of the electrolyte ions into the smallest (less than 2 nm) micropores. In addition, activated carbon materials have a low electrical conductivity which slows the response time of the device. New nanostructured mesoporous carbon materials developed at Oak Ridge National Laboratory (ORNL) may alleviate some of these deficiencies and prompted us to test them as EDLC
electrodes. Here we report the use of advanced mesoporous carbon materials
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