Vignette d'image

Stoeckli, Fritz

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

Résultat de la recherche

Filtres

5
5
Réinitialiser les filtres

Paramètres

Voici les éléments 1 - 5 sur 5
  • Publication
    Accès libre
    Cherry stones as precursor of activated carbons for supercapacitors
    (2009)
    Olivares-Marín, M.
    ;
    Fernández, J. A.
    ;
    Lázaro, M. J.
    ;
    Fernández-González, C.
    ;
    Macías-García, A.
    ;
    Gómez-Serrano, V.
    ;
    Stoeckli, Fritz 
    ;
    Centeno, Teresa A.
    It is shown that cherry stones-wastes can be recycled as activated carbons for electrode material in supercapacitors. KOH-activation of this precursor at 800–900 °C is an efficient process to obtain carbons with large specific surface areas (1100–1300 m2 g−1), average pore sizes around 0.9–1.3 nm, which makes them accessible to electrolyte ions, and conductivities between 1 and 2 S cm−1. These features lead to capacitances at low current density as high as 230 F g−1 in 2 M H2SO4 aqueous electrolyte and 120 F g−1 in the aprotic medium 1 M (C2H5)4NBF4/acetonitrile. Furthermore, high performance is also achieved at high current densities, which means that this type of materials competes well with commercial carbons used at present in supercapacitors.
  • Publication
    Accès libre
    Performance of mesoporous carbons derived from poly(vinyl alcohol) in electrochemical capacitors
    (2008)
    Fernández, J. A.
    ;
    Morishita, T.
    ;
    Toyoda, M.
    ;
    Inagaki, M.
    ;
    Stoeckli, Fritz 
    ;
    Centeno, Teresa A.
    The present work shows that mesoporous materials obtained by the carbonization of mixtures of poly(vinyl alcohol) with magnesium citrate are very promising candidates for electrodes in supercapacitors. Their high performance arises essentially from a double-layer mechanism through the extent of the total surface area and one obtains at low current density (1 mA cm−2) values as high as 180 F g−1 in aqueous 2 M H2SO4 electrolyte and around 100 F g−1 in 1 M (C2H5)4NBF4 in acetonitrile. Moreover, in most cases the specific capacitance is reduced only by 15% at 100 mA cm−2, as opposed to many other types of carbons which display much higher reductions.

    This study suggests that these novel carbons could be potentially more advantageous as electrodes in electrochemical capacitors than templated mesoporous carbons.
  • Publication
    Accès libre
    Correlation between heats of immersion and limiting capacitances in porous carbons
    (2008)
    Centeno, Teresa A.
    ;
    Fernández, J. A.
    ;
    Stoeckli, Fritz 
    Based on more than 80 carbons, the paper shows that immersion calorimetry into benzene, water and carbon tetrachloride can be used to assess with a good accuracy the limiting capacitance Co at low current densities in both acidic (2 M H2SO4) and aprotic (1M tetraethyl ammonium tetrafluoroborate in acetonitrile) electrolytic solutions. The enthalpies of immersion ΔiH(C6H6) and ΔiH(H2O) provide information on Co-acidic, where both the surface area and the oxygen content play a role. On the other hand, in the case of the organic electrolyte the oxygen content has only a small influence and Co-aprotic is directly related to ΔiH(C6H6) and ΔiH(CCl4). Carbon tetrachloride has a critical dimension (0.65 nm), which is close to the size of the (C2H5)4N+ ion (0.68 nm) and therefore ΔiH(CCl4) provides better information in the case of carbons with small micropores. The advantage of this approach lies in the fact that immersion calorimetry, in itself a useful tool for the structural and the chemical characterization of carbons, can also be used to evaluate directly the gravimetric capacitances of these solids at low current densities.Based on more than 80 carbons, the paper shows that immersion calorimetry into benzene, water and carbon tetrachloride can be used to assess with a good accuracy the limiting capacitance Co at low current densities in both acidic (2 M H2SO4) and aprotic (1M tetraethyl ammonium tetrafluoroborate in acetonitrile) electrolytic solutions. The enthalpies of immersion ΔiH(C6H6) and ΔiH(H2O) provide information on Co-acidic, where both the surface area and the oxygen content play a role. On the other hand, in the case of the organic electrolyte the oxygen content has only a small influence and Co-aprotic is directly related to ΔiH(C6H6) and ΔiH(CCl4). Carbon tetrachloride has a critical dimension (0.65 nm), which is close to the size of the (C2H5)4N+ ion (0.68 nm) and therefore ΔiH(CCl4) provides better information in the case of carbons with small micropores. The advantage of this approach lies in the fact that immersion calorimetry, in itself a useful tool for the structural and the chemical characterization of carbons, can also be used to evaluate directly the gravimetric capacitances of these solids at low current densities.
  • Publication
    Accès libre
    EDLC performance of carbide-derived carbons in aprotic and acidic electrolytes
    (2008)
    Fernández, J. A.
    ;
    Arulepp, M.
    ;
    Leis, J.
    ;
    Stoeckli, Fritz 
    ;
    Centeno, Teresa A.
    This study shows that carbide-derived carbons (CDCs) with average pore size distributions around 0.9–1 nm and effective surface areas of 1300–1400 m2 g−1 provide electrochemical double-layer capacitors with high performances in both aqueous (2M H2SO4) and aprotic (1M (C2H5)4NBF4 in acetonitrile) electrolytes.
    In the acidic electrolytic solution, the gravimetric capacitance at low current density (1 mA cm−2) can exceed 200 F g−1, whereas the volumetric capacitance reaches 90 F cm−3. In the aprotic electrolyte they reach 150 F g−1 and 60 F cm−3.
    A detailed comparison of the capacitive behaviour of CDCs at high current density (up to 100 mA cm−2) with other microporous and mesoporous carbons indicates better rate capabilities for the present materials in both electrolytes. This is due to the high surface area, the accessible porosity and the relatively low oxygen content.
    It also appears that the surface-related capacitances of the present CDCs in the aprotic electrolyte are in line with other carbons and show no anomalous behaviour.
  • Publication
    Accès libre
    Correlation between capacitances of porous carbons in acidic and aprotic EDLC electrolytes
    (2007)
    Centeno, Teresa A.
    ;
    Hahn, M.
    ;
    Fernández, J. A.
    ;
    Kötz, R.
    ;
    Stoeckli, Fritz 
    A study based on a total of 41 nanoporous carbons shows that there exists a good correlation between the limiting gravimetric capacitances Co at low current densities j (1 mA cm −2 ) measured in aprotic (1 M (C2H5)4NBF4 in acetonitrile) and in acidic (2 M aqueous H2SO4) electrolytes. The comparison of the surface-related capacitances (F m −2 ) of well characterized samples with the amount of thermodesorbed CO suggests a strong contribution of CO generating surface groups to charge storage in the acidic electrolyte, but a negligible contribution in the aprotic medium. It also appears that the decrease of the capacitance with current density is similar in both electrolytes. This confirms that the average micropore width and the CO2 generating surface groups are the main factors which limit the ionic mobility in both electrolytes.