Differential Capacity of the Double-Layer Formed at a Solid Electrode (Pt, Au)/Ionic Liquid Interface

Salts of low melting points, usually called ionic liquids (ILs), have been studied extensively during the last decade [1 – 3]. These liquid salts may serve as solvents for chemical reactions as well as electrolytes in electrochemical devices. The first extensively studied IL was 1-ethyl-3-methyl-imidazolium tetrachloroaluminate ([EMIm][AlCl4]). However such ionic liquids containing AlCl4− are easily hydrolyzed by water. Non-chloroaluminate ILs, more resistive to moisture, have been developed recently. At the same time electrochemical double-layer capacitors (EDLCs), based on carbon materials having a very high surface area, have been developed with very promising results. Both aqueous and non-aqueous liquid electrolytes, as well as solid polymer electrolytes, have been applied [4 – 16]. There are also very promising attempts to apply ionic liquids in EDLCs [17 – 25]. The papers mentioned above report the capacity of devices prepared of different types of activated carbons (AC). The specific capacity of the AC/electrolyte interface has usually been expressed versus the carbon total mass (in F/g) or versus the total carbon surface estimated from the BET isotherm (in μF/cm2). There are only a few publications about the double-layer capacity measured at a geometrically defined electrode/electrolyte surface. Apart from the report on ionic liquids based on the chloroaluminate ion [26], a paper on the specific capacitance for glassy carbon (GC), mercury and a commer-