Correlation between heats of immersion and limiting capacitances in porous carbons

• Published in: Carbon (New York) 2008-06, Vol.46 (7), p.1025-1030
• Main Authors: Centeno, T.A., Fernandez, J.A., Stoeckli, F.
• Format: Article
• Language: English
• Subjects: Chemistry; Colloidal state and disperse state; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Fullerenes and related materials; diamonds, graphite; General and physical chemistry; Materials science; Physics; Porous materials; Specific materials
• ISSN: 0008-6223; 1873-3891
• DOI: 10.1016/j.carbon.2008.03.005

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 C o at low current densities in both acidic (2 M H 2SO 4) and aprotic (1 M tetraethyl ammonium tetrafluoroborate in acetonitrile) electrolytic solutions. The enthalpies of immersion Δ i H(C 6H 6) and Δ i H(H 2O) provide information on C o-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 C o-aprotic is directly related to Δ i H(C 6H 6) and Δ i H(CCl 4). Carbon tetrachloride has a critical dimension (0.65 nm), which is close to the size of the (C 2H 5) 4N + ion (0.68 nm) and therefore Δ i H(CCl 4) 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.