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Université de Neuchâtel

Specific and non-specific interactions on non-porous carbon black surfaces

Andreu, A. ; Stoeckli, Fritz ; Bradleya, R. H.

In: Carbon, 2007, vol. 45, no. 9, p. 1854-1864

The interactions which occur between methanol, ethanol or propanol and the surfaces of non-porous carbon blacks with increasing levels of oxygen chemistry have been studied using adsorption isotherm analysis and immersion calorimetry. Surface oxygen has been controlled by ozone treatment and characterised using X-ray photoelectron spectroscopy, which gives a direct and quantitative measure of...

Université de Neuchâtel

The effect of the carbonization/activation procedure on the microporous texture of the subsequent chars and active carbons

Cagnon, Benoît ; Py, Xavier ; Guillot, André ; Stoeckli, Fritz

In: Microporous and Mesoporous Materials, 2003, vol. 57, no. 3, p. 273-282

Chars obtained by carbonizing coconut shells at different intermediate heat treatment temperatures (IHTT) between 400 and 800 °C were activated at 800 °C in a stream of N2+H2O, following two distinct procedures. In the first procedure, activation follows directly the carbonization, whereas in the second procedure, the sample was first brought back to 25 °C and...

Université de Neuchâtel

Contributions of hemicellulose, cellulose and lignin to the mass and the porous properties of chars and steam activated carbons from various lignocellulosic precursors

Cagnon, Benoît ; Py, Xavier ; Guillot, André ; Stoeckli, Fritz ; Chambat, Gérard

In: Bioresource Technology, 2009, vol. 100, no. 1, p. 292-298

In this study, contributions of hemicellulose, cellulose and lignin to the mass and the porous properties of chars and activated carbons from various lignocellulosic materials were studied. A predictive calculation was established using the experimental results obtained for the three components separately to evaluate the carbonization and activation yields and their respective contributions to...

Université de Neuchâtel

Water adsorption on activated carbons with different degrees of oxidation

Carrasco-Marín, Francisco ; Mueden, Abdelaziz ; Centeno, Teresa A. ; Stoeckli, Fritz ; Moreno-Castilla, Carlos

In: Journal of the Chemical Society, Faraday Transactions, 1997, vol. 93, no. 15, p. 2211-2215

A typical activated carbon, derived from olive stones, has been oxidized to different degrees with (NH4)2S2O8 and analysed by water vapour adsorption, immersion calorimetry, acid–base titration and temperature-programmed desorption of CO2 and CO monitored by mass spectrometry. These techniques led to a coherent description of the surfaces...

Université de Neuchâtel

Correlation between capacitances of porous carbons in acidic and aprotic EDLC electrolytes

Centeno, Teresa A. ; Hahn, M. ; Fernández, J. A. ; Kötz, R. ; Stoeckli, Fritz

In: Electrochemistry Communications, 2007, vol. 9, no. 6, p. 1242-1246

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...

Université de Neuchâtel

On the specific double-layer capacitance of activated carbons, in relation to their structural and chemical properties

Centeno, Teresa A. ; Stoeckli, Fritz

In: Journal of Power Sources, 2006, vol. 154, no. 1, p. 314-320

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,...

Université de Neuchâtel

The role of textural characteristics and oxygen-containing surface groups in the supercapacitor performances of activated carbons

Centeno, Teresa A. ; Stoeckli, Fritz

In: Electrochimica Acta, 2006, vol. 52, no. 2, p. 560-566

It is suggested that the specific capacitance C0 of activated carbons at low current densities (d ~ 1 mA cm−2) consists, to a good first approximation, of two contributions. For the H2SO4 electrolyte they correspond to approximately 0.080 F m−2 from the total accessible surface area and an additional pseudo-capacitance of 63 F...

Université de Neuchâtel

The oxidation of an Asturian bituminous coal in air and its influence on subsequent activation by steam

Centeno, Teresa A. ; Stoeckli, Fritz

In: Carbon, 1996, vol. 33, no. 5, p. 581-586

It is shown that the oxidation of an Asturian bituminous coal by air, at 150 ° and 270 °C, has a considerable influence on the microporous structure of the carbon obtained by subsequent carbonization and steam activation to 50% burn-off. The direct activation of the coal leads to an open micropore system of 0.2 cm3/g, with an average pore size near 0.8 nm. On the other hand, much larger systems...

Université de Neuchâtel

On the activation of Asturian anthracite following various pretreatments

Centeno, Teresa A. ; Stoeckli, Fritz

In: Carbon, 1994, vol. 32, no. 8, p. 1463-1467

An Asturian anthracite has been subjected to different pretreatments and subsequently activated by steam at 850°C to a total burn-off of 55 percent. The physical properties (micropore sizes and distributions, external surface areas, etc.) of the solids are compared with those of the carbon obtained by direct activation. Although the yield is generally low, it appears that better results are...