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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
    Accès libre
    The characterization of microporosity in carbons with molecular sieve effects
    (2002)
    Stoeckli, Fritz 
    ;
    Slasli, Abdou
    ;
    Hugi-Cleary, Deirdre
    ;
    Guillot, André
    The apparent and the real micropore size distributions (PSDs) of molecular sieve carbons can be assessed by combining the adsorption of CO2 at 273 K with immersion calorimetry into liquids of increasing molecular dimensions. On the basis of model isotherms resulting from computer simulations, the adsorption of carbon dioxide, a relatively small probe, leads to the overall PSD of the carbon (essentially the internal micropore system). Immersion calorimetry, on the other hand, reveals the distribution of the pores accessible directly from the liquid phase, that is without constrictions. Liquid CS2 probes the same volume as CO2 and can be used as a reference. The paper describes the case of an industrial molecular sieve carbon obtained by blocking partly the entrance to a relatively broad micropore system, thus limiting its accessibility to molecules with diameters below 0.5–0.6 nm. It is shown how activation by steam at 900 °C removes the constrictions and leads to a gradual overlap of the two PSDs. The distribution of the pore widths on the surface, observed directly by scanning tunnelling microscopy, is also given.
  • Publication
    Accès libre
    On the characterization of carbon blacks by various techniques
    (1994)
    Stoeckli, Fritz 
    ;
    Huguenin, Didier
    ;
    Laederach, A.
    It is shown how the use of various adsorption and calorimetric techniques can provide unambiguous information on the presence or the absence of porosity on the surface of carbon blacks. Dubinin's theory, its extension to immersion calorimetry, and gas-phase calorimetry can be applied successfully. As an example, the characterization of 6 porous and non-porous samples is described.
  • Publication
    Accès libre
    The physical and chemical characterization of a sulphur-impregnated active carbon, by combined adsorption and immersion techniques
    (1991)
    Rebstein, Patrick
    ;
    Stoeckli, Fritz 
    A commercially available active carbon, impregnated with sulphur, has been characterized and compared to the original carbon by using adsorption and immersion techniques. The specific reaction of liquid CS2 with sulphur, following the preadsorption of various amounts of n-nonane, shows that the accessibility of sulphur decreases rapidly. It is also found that the impregnated carbon becomes hydrophilic but, in the case of SO2 adsorption, no change in adsorption capacity is detected.