Electrochemical double-layer capacitors store electrical energy at the phase boundary between an electronic conductor (electrode) and a liquid ionic conductor (electrolyte solution). In contrast to that, electrostatic space charge layers at dielectric oxide films, formed anodically on etched aluminum or tantalum foils of conventional electrolytic capacitors, should not be confused with the electrochemical double layer. | Electrochemical Double-Layer Capacitors P Kurzweil University of Applied Sciences Amberg Germany 2009 Elsevier . All rights reserved. Energy Strorage in the Electrolytic Double Layer Electrochemical double-layer capacitors store electrical energy at the phase boundary between an electronic conductor electrode and a liquid ionic conductor electrolyte solution . In contrast to that electrostatic space charge layers at dielectric oxide films formed anodically on etched aluminum or tantalum foils of conventional electrolytic capacitors should not be confused with the electrochemical double layer. The Double Layer as a Nanodielectric Generally every electrochemical cell works as an electrical capacitor if two metallic oxidic or carboneous electrodes dip into an aqueous or organic solution. The electrolytic double layer at the phase boundary between every electrode and the electrolyte measures only a few nanometers of thickness. Simplified the electrolytic double layer behaves like a plate capacitor. The capacitor is formed because the uncharged electrode surface gives electrons into the inner electrode material and charged negatively through that attracts counterions from the electrolyte. The counterelectrode charges itself positively against the surrounding solution. Electrode and electrolyte reach different electric potentials. The molecular layer of absorbed ions at the electrode surface surrounded by solvent molecules forms the actual dielectric of the double-layer capacitor. The interfacial capacitance at a plane electrode equals 50 pF cm 2 if a plate capacitor is assumed see the section The Electrostatic Helmholtz Model . Rough electrodes yield capacitances up to some F cm 2. A practical supercapacitor requires two highly porous electrodes which build up an electric circuit of two double layers in parallel separated by the ohmic resistance of an electrolyte-filled gap as narrow as possible Figure 1 . Based on the specific surface area of active carbon of .
