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

Abstract

A study based on a total of 41 nanoporous carbons shows that there exists a good correlation between the limiting gravimetric capacitances C o at low current densities j (1 mA cm À2 ) measured in aprotic (1 M (C 2 H 5 ) 4 NBF 4 in acetonitrile) and in acidic (2 M aqueous H 2 SO 4 ) electrolytes. The comparison of the surface-related capacitances (F m À2 ) 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 CO 2 generating surface groups are the main factors which limit the ionic mobility in both electrolytes.

Correlation between heats of immersion and limiting capacitances in porous carbons

“…As pointed out earlier [9,28,29], relatively good correlations can be found between the limiting capacitances C o-acidic and C o-aprotic of pure carbons and their enthalpies of immersion into benzene, ∆ i H(C 6 H 6 ). In the last analysis, this is not too surprising, since the electric double layer capacitance C o and immersion calorimetry are both related to surface effects.…”

“…Since the accessible surface area of the carbon and its oxygen content play a role in the specific capacitance, it is logical to correlate them with the information provided by immersion calorimetry and adsorption isotherms. The present study develops the approach outlined earlier [7][8][9][10][11] and shows that a good assessment of the gravimetric capacitance at low current densities can be achieved on the basis of immersion calorimetry. Both properties, given respectively in F g -1 and J g -1 , are related to the unit weight of carbon as opposed to other studies more oriented towards the study of surface related capacitances, such as Chmiola et al [12,13] …”

“…The latter expression applies to carbons with average micropore widths L o > 0.75-0.80 nm and it is found that the ratio C o-aprotic / C o-acidic is approximately 0.54 ± 0.09 [9].…”

“…The comparison of the various approaches provides a reliable picture for porous and non porous carbons of different origins [3,4,[7][8][9][10][11]21]. Typical results corresponding to well characterized carbons are shown in Table 1.…”

Microscopic Structure and Dynamics of Molecular Liquids and Electrolyte Solutions Confined by Carbon Nanotubes: Molecular Dynamics Simulations

“…Yang et al, 2008;Zhang et al, 2007). One of the most interesting and promising is application of CNTs as electrode materials (Centeno et al, 2007;Janes et al, 2007;R. Lin et al, 2009).…”