On the specific double-layer capacitance of activated carbons, in relation to their structural and chemical properties
Twelve well-characterized activated carbons with average micropore widths between 0.7 and 2 nm, total surface areas of 378–1270 m2 g−1 and specific capacitances C up to 320 F g−1 have been investigated, using H2SO4 2 M as electrolyte. Some of the carbons have also been oxidized with (NH4)2S2O8, whic...
| Autores: | , |
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| Tipo de recurso: | artículo |
| Estado: | Versión aceptada para publicación |
| Fecha de publicación: | 2006 |
| País: | España |
| Institución: | Consejo Superior de Investigaciones Científicas (CSIC) |
| Repositorio: | DIGITAL.CSIC. Repositorio Institucional del CSIC |
| OAI Identifier: | oai:digital.csic.es:10261/102187 |
| Acceso en línea: | http://hdl.handle.net/10261/102187 |
| Access Level: | acceso abierto |
| Palabra clave: | Electrochemical capacitor Activated carbons Microporosity Surface area Surface oxygen Calorimetry |
| Sumario: | Twelve well-characterized activated carbons with average micropore widths between 0.7 and 2 nm, total surface areas of 378–1270 m2 g−1 and specific capacitances C up to 320 F g−1 have been investigated, using H2SO4 2 M as electrolyte. Some of the carbons have also been oxidized with (NH4)2S2O8, which leads to specific oxygen contents between 0.4 and 7.1 μmol m−2 of carbon surface area. It appears that Co, the limiting capacitance at a current density of 1 mA cm−2 of electrode surface, does not depend significantly on the oxygen content. An empirical equation is proposed to describe the decrease of C with increasing current density d (1–70 mA cm−2 of electrode surface), as a function of the oxygen content. As suggested by different authors, C o can be expressed as a sum of contributions from the external surface area S e and the surface of the micropores S mi. A closer investigation shows that C o/S mi increases with the pore size and reaches values as high as 0.250–0.270 F m−2 for supermicropores. It is suggested that the volume View the MathML sourceWo* of the electrolyte found between the surface layers in pores wider than 0.7–0.8 nm contributes to Co. However, this property is limited to microporosity, like the enthalpy of immersion of the carbons into benzene. The latter is also correlated to Co, which provides a useful means to identify potential supercapacitors. |
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