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

A study based on a total of 41 nanoporous carbons shows that there exists a good correlation between the limiting gravimetric capacitances <i>C</i>o at low current densities <i>j</i> (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.