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Stoeckli, Fritz

Nom
Stoeckli, Fritz
Affiliation principale
Fonction
Professeur.e émérite
Email
fritz.stoeckli@unine.ch
Identifiants
https://libra.unine.ch/handle/123456789/471

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  • Publication
    Accès libre
    On the specific double-layer capacitance of activated carbons, in relation to their structural and chemical properties
    (2006)
    Centeno, Teresa A.
    ;
    Stoeckli, Fritz 
    Twelve well-characterized activated carbons with average micropore widths between 0.7 and 2 nm, total surface areas of 378–1270 m2g−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, Co can be expressed as a sum of contributions from the external surface area Se and the surface of the micropores Smi. A closer investigation shows that Co/Smi 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 Wo* 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.
  • Publication
    Métadonnées seulement
    Modelling of water adsorption by activated carbons: effects of microporous structure and oxygen content
    (2004)
    Slasli, A M
    ;
    Jorge, M
    ;
    Stoeckli, Fritz 
    ;
    Seaton, N A
    The present paper examines the adsorption of water by microporous carbons containing various amounts of surface oxygen and a smaller proportion of basic centres. The modelling of water adsorption for 293 and 310 K, using variable pore size distributions (PSD), confirms that the overall type IV isotherm is the sum of a type I isotherm associated with the specific interactions, and a type V isotherm reflecting the non-specific interactions. The principle of temperature invariance is followed by these isotherms, which indicates that modelling leads to the Dubinin-Astakhov equation. The present approach allows the prediction of water adsorption near room temperature, on the basis of the PSD and the density of oxygen present on the surface area of the micropores. It is assumed, to a first and good approximation, that the pores are slit-shaped and the oxygen distribution is random. (C) 2004 Elsevier Ltd. All rights reserved.