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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
    Performance of templated mesoporous carbons in supercapacitors
    (2007)
    Sevilla, M.
    ;
    Álvarez, S.
    ;
    Centeno, Teresa A.
    ;
    Fuertes, A. B.
    ;
    Stoeckli, Fritz 
    By analogy with other types of carbons, templated mesoporous carbons (TMCs) can be used as supercapacitors. Their contribution arises essentially from the double layer capacity formed on their surface, which corresponds to 0.14 F m−2 in aqueous electrolytes such as H2SO4 and KOH and 0.06 F m−2 for the aprotic medium (C2H5)4NBF4 in CH3CN. In the case of a series of 27 TMCs, it appears that the effective surface area determined by independent techniques can be as high as 1500–1600 m2 g−1, and therefore exceeds the value obtained for many activated carbons (typically 900–1300 m2 g−1). On the other hand, the relatively low amount of surface oxygen in the present TMCs, as opposed to activated carbons, reduces the contribution of pseudo-capacitance effects and limits the gravimetric capacitance to 200–220 F g−1 for aqueous electrolytes. In the case of non-aqueous electrolyte, it rarely exceeds 100 F g−1.

    It is also shown that the average mesopore diameter of these TMCs does not improve significantly the ionic mobility compared with typical activated carbons of pore-widths above 1.0–1.3 nm.

    This study suggests that activated carbons remain the more promising candidates for supercapacitors with high performances.
  • 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.