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On the specific double-layer capacitance of activated carbons, in relation to their structural and chemical properties
Auteur(s)
Centeno, Teresa A.
Date de parution
2006
In
Journal of Power Sources, Elsevier, 2006/154/1/314-320
Résumé
Twelve well-characterized activated carbons with average micropore widths between 0.7 and 2 nm, total surface areas of 378–1270 m<sup>2</sup>g<sup>−1</sup> and specific capacitances <i>C</i> up to 320 F g<sup>−1</sup> have been investigated, using H<sub>2</sub>SO<sub>4</sub> 2 M as electrolyte. Some of the carbons have also been oxidized with (NH<sub>4</sub>)2S<sub>2</sub>O<sub>8</sub>, which leads to specific oxygen contents between 0.4 and 7.1 μmol m<sup>−2</sup> of carbon surface area. It appears that <i>C</i><sub>o</sub>, the limiting capacitance at a current density of 1 mA cm<sup>−2</sup> 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 <i>d</i> (1–70 mA cm−2 of electrode surface), as a function of the oxygen content. <br><br> As suggested by different authors, <i>C</i><sub>o</sub> can be expressed as a sum of contributions from the external surface area <i>S</i><sub>e</sub> and the surface of the micropores <i>S</i><sub>mi</sub>. A closer investigation shows that <i>C</i><sub>o</sub>/<i>S</i><sub>mi</sub> increases with the pore size and reaches values as high as 0.250–0.270 F m<sup>−2</sup> for supermicropores. It is suggested that the volume <i>W</i><sub>o</sub><sup>*</sup> of the electrolyte found between the surface layers in pores wider than 0.7–0.8 nm contributes to <i>C</i><sub>o</sub>. However, this property is limited to microporosity, like the enthalpy of immersion of the carbons into benzene. The latter is also correlated to <i>C</i><sub>o</sub>, which provides a useful means to identify potential supercapacitors.
Identifiants
Type de publication
journal article
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