Enhanced Performance of Symmetric Double Layer Capacitor by Flexible Binder-free SWCNT Membrane Electrodes
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Enhanced Performance of Symmetric Double Layer Capacitor by Flexible Binder-free SWCNT Membrane Electrodes Danhao Ma1, James Kalupson2, Pralav Shetty3, Kofi Adu2,4 and Ramakrishnan Rajagopalan2 1
Department of Energy Engineering, The Pennsylvania State University, University Park, PA 16802. U.S.A. 2 Materials Research Institute, The Pennsylvania State University, University Park, PA 16802, U.S.A. 3 Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, University Park, PA 16802, U.S.A. 4 Department of Physics, The Pennsylvania State University, Altoona College, Altoona, PA 16601, U.S.A.
ABSTRACT We present results on an aqueous symmetric double layer electrochemical capacitor (EDLC) constructed with a flexible binder-free single wall carbon (SWCNTs) membrane as electrodes. The capacitors were cycled from 0 to 1V @ 10 A/g for 10,000 cycles with 99.9% coulombic efficiency and 94% energy efficiency, and 100% depth of discharge. The power performance of the aqueous symmetric SWCNTs membrane capacitor is almost 100 –1000 times better than commercial non-aqueous EDLC capacitors. INTRODUCTION The carbon nanotube (CNT), a one dimensional filamentous structure formed by seamless rolling of 2-dimensional graphene into a tube, has been a significant focus of the scientific research community since its discovery by Ijima in 1991[1]. The broad interest stems from its unique properties (thermal, electric and mechanical), the diverse potential applications it offers, and the fact that CNTs are an ideal prototype to investigate quantum phenomena in onedimensional systems. Carbon nanotubes (CNTs) have been proposed as potential candidate for electrodes applications in electrochemical energy storage and conversion systems (fuel cells, Li ion batteries and supercapacitors)[2-18] due to their unique single atomic layer and internal structures, lightweight, high surface area, remarkable chemical stability and electronic conductivity and high aspect ratio, just to mention a few. In recent years, much of the emphasis have focused on the development of supercapacitors that have high power density and improved frequency response [2,20]. The major limiting factors to high power density and frequency response of a supercapacitor include the internal resistivity of the electrode itself, the resistivity between the electrode and current collector and the resistivity of the electrolyte within the porous structure of the electrode [2,20]. Several reports have focused on addressing these challenges to boost power density and frequency[2,5,14-20].
Conventionally, electrodes for electrochemical energy systems usually consist of a mixture of active material, electrically conducting material and binder to form a paste that is deposited on a metal substrate. The use of CNT as electrode in Li ion batteries, electrochemical capacitors and fuel cells[14,15] have been demonstrated where the CNT is either deposited electrophoretically on a metal collector[16,17] or grown directly on Ni support or graphitic foils[18, 19] or
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