DoppelSchichtKondensatoren

Doppelschicht, in electrochemistry often referred to as the electrical double layer (EDL), is a structure that forms at the interface between a conductive electrode and an adjacent liquid electrolyte. When an electrode is charged, ions in the solution rearrange to screen the electric field, producing a region of net charge that balances the electrode's surface charge.

The double layer consists of two regions: a compact layer near the surface, commonly called the Stern layer (or Helmholtz layer), where ions are specifically adsorbed or oriented; and a more diffuse region extending into the bulk solution, where ion concentrations decay with distance according to the Poisson–Boltzmann distribution. The combination ensures overall electrical neutrality beyond the outer boundary of the layer. The potential drops mainly across this region, with a characteristic length scale set by the Debye length.

Theoretical descriptions include the Helmholtz model, the Gouy–Chapman model, and the combined Stern model, which accounts for both adsorbed ions and diffuse screening. The double layer behaves as a capacitor, with capacitance depending on electrolyte concentration, temperature, and electrode material. In practice, this capacitance can vary with applied potential and frequency of perturbation.

Experimental techniques such as electrochemical impedance spectroscopy and cyclic voltammetry probe the double layer by measuring how charge storage and interfacial resistance respond to voltage. The electrical double layer is central to electrochemical reactions, battery and supercapacitor performance, sensing, corrosion, and colloidal stability (via DLVO theory). Its properties are influenced by ion size, specific adsorption, solvent properties, and temperature.

In sum, the electrical double layer is a key concept for understanding interfacial electrostatics in liquid environments, governing charge distribution, potential profiles, and interfacial reactions at electrode surfaces.