Effect of Pore Morphology on the Electrochemical Properties of Electric Double Layer Carbon Cryogel Supercapacitors
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1056-HH08-19
Effect of Pore Morphology on the Electrochemical Properties of Electric Double Layer Carbon Cryogel Supercapacitors Betzaida Batalla Garcia1, Aaron M. Feaver2, Richard Champion1, Qifeng Zhang1, Tim T. Fister3, Kenneth P. Nagle3, Gerald T. Seidler3, and Guozhong Cao1 1 Materials Science and Engineering, University of Washington, 302M Roberts Hall, Box 352120, Seattle, WA, 98195-2120 2 EnerG2 LLC, 810 3rd Avenue, Suite 120, Seattle, WA, 98104 3 Physics, University of Washington, Seattle, WA, 98195 ABSTRACT In this study a group of resorcinol-formaldehyde carbon cryogels (CC) have been processed chemically, via catalysis and activation, to obtain varied nanostructures and pore size distributions. To understand the relation between structure and electrochemical properties the capacitor can be studied as a dielectric system composed of a porous electrode and the electrolyte (Tetraethylammonium tetrafluoroborate in propylene carbonate). Using Electrochemical impedance spectroscopy (EIS) the complex capacitance and power are used to study the behavior of the system below the relaxation frequency fo (φ = -45o). Therefore, the relaxation of the capacitor system at the low frequency range, f < fo, may be used as a measure of pore/electrolyte interaction. The approach here proposed also allows for a direct experimental characterization of the capacitance and power at low frequencies where small pores are likely to affect the diffusion dynamics of the electrolyte molecules. The results suggest a correlation between the occurrence of small micropores and that of high power losses that are related to the resistive element produced at the low frequency range. Moreover, the impact of the micropore structure upon the supercapacitor’s performance is apparent in its capacitance and energy as well. In addition to the complex power and capacitance other measurements including BET Nitrogen sorption, cyclic voltammetry, galvanic cycling and X-Ray Raman Scattering were used to characterize the samples and support these results. INTRODUCTION: Carbon cryogels (CC) produced from the polycondensation of resorcinol and formaldehyde are excellent precursor materials to use as electrodes in electric double layer supercapacitor (EDLS). Their tunable nanostructure, high surface area and good conductivity make them suitable for such application [1]. The ability to tune the pore sizes is a very important feature to optimize the formation of an ionic double layer. Although the tunable structure of these cryogels is highly attractive, unsuitable structures are often produced. Recent studies have addressed the structure/ charge issue by measuring both the total surface area and the capacitance [2,3]. Unfortunately, the use of absolute quantities does not include clear boundaries for specific structures, thus overlooking their role with regards to charge storage. Understanding this role is necessary to design better CC supercapacitors. Electrochemical impedance spectroscopy has been used in the past to study the relation of pore size and el
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