Activated Carbons for High Power Energy Storage: Below the Surface of Non-Faradaic Reactions
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0973-BB07-02
Activated Carbons for High Power Energy Storage: Below the Surface of Non-Faradaic Reactions Prabeer Barpanda and Glenn G. Amatucci Department of Materials Science and Engineering, Rutgers University, North Brunswick, NJ, 08902 ABSTRACT The effect of iodine doping on the electrochemical performance of activated carbons for non-aqueous symmetric and asymmetric hybrid supercapacitors was investigated. The incorporation of iodine via high energy mechanical milling techniques significantly modified the physical and electrochemical properties of activated carbon precursors. The increasing amount of iodine into carbons leads to a unique combination of lower surface area coupled with higher volumetric and gravimetric electrochemical capacitance. Iodine modification of the carbon resulted in a 100% increase in volumetric capacitance. This improvement was a result of improved non-faradaic capacitance and the development of faradaic capacity. INTRODUCTION The electrochemical double layer capacitor (EDLC), widely known as the supercapacitor or ultracapacitor, is a promising energy storage device for high-power applications owing to its outstanding power density, extraordinary cycling stability and robustness [1]. These supercapacitors combine high surface area electrodes with very thin electrolytic dielectric layer to realize very high capacitance with appreciable energy and power density. In general, the electrodes of these high-performance supercapacitors are conducting materials with high surface area such as activated carbon [2], conducting metal oxide (e.g. RuO2) [3], nitrides etc. Activated carbons occupy a large share in supercapacitor market on account of its ultrahigh surface area and economic production. The chemical and mechanical modifications of high surface areas of activated carbons offer a unique pathway in order to tune their physical and electrochemical properties [4]. The activated carbon-based supercapacitors operate with non-Faradaic double layer electrochemical reaction at the surface area of the high surface area mesoporous activated carbons. The true capacitance of the activated carbon electrode is a parallel mechanism consisting of the Helmholtz double layer on the electrode-electrolyte interface and the space charge capacitance of solid electrode. Though the capacity in carbon supercapacitors is believed to be mainly governed by non-faradaic electrochemical double layer at electrode-electrolyte interface, thereby initiating much work into the optimization of the mesoporous architecture, the space charge of solid electrode can play a key role in mechano-chemically modified carbon. The current work investigates the relative effect of electrochemical double layer and space charge of carbon electrode in iodine modified activated carbons. While the former is directly related to the effective surface area and meso/ micro porosity of electrode-electrolyte interface,
the latter is a function of electronic properties of the solid electrode. The intrinsic change in the properties of carbon upon
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