Improved double layer capacitors.

A double layer capacitor comprises a first and second electrode which electrodes comprise a high surface area constituent, and an electrolyte, and an ionically conductive separator means between and in contact with said electrodes electronically separating said electrodes from each other, the electrolyte having a pH above about 2 so that the capacitor exhibits low leakage current. A capacitor comprises 2 electrode assemblies (12),(14)(13) separated by separator means (15) the high surface area carbon electrodes (13) being impregnated with electrolyte.