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Double-layer capacitance is the important characteristic of the electrical double layer [1] [2] which appears at the interface between a surface and a fluid (for example, between a conductive electrode and an adjacent liquid electrolyte).
In surface science, a double layer (DL, also called an electrical double layer, EDL) is a structure that appears on the surface of an object when it is exposed to a fluid. The object might be a solid particle, a gas bubble, a liquid droplet, or a porous body. The DL refers to two parallel layers of charge surrounding the object.
The electrochemical charge storage mechanisms in solid media can be roughly (there is an overlap in some systems) classified into 3 types: Electrostatic double-layer capacitors (EDLCs) use carbon electrodes or derivatives with much higher electrostatic double-layer capacitance than electrochemical pseudocapacitance, achieving separation of charge in a Helmholtz double layer at the interface ...
Double-layer capacitance – Storage is achieved by separation of charge in a Helmholtz double layer at the interface between the surface of a conductor and an electrolytic solution. The distance of separation of charge in a double-layer is on the order of a few Angstroms (0.3–0.8 nm). This storage is electrostatic in origin. [1]
One layer of ions on the electrode surface and the second layer of adjacent polarized and solvated ions in the electrolyte move to the opposite polarized electrode. The two ion layers are separated by a single layer of electrolyte molecules. Between the two layers, a static electric field forms that results in double-layer capacitance.
Randles circuit schematic. In electrochemistry, a Randles circuit is an equivalent electrical circuit that consists of an active electrolyte resistance R S in series with the parallel combination of the double-layer capacitance C dl and an impedance (Z w) of a faradaic reaction.
where C D = ε 0 ε κ is the diffuse layer capacitance and C I the inner (or regulation) capacitance. The CC conditions are found when p = 1 while the CP conditions for p = 0. The realistic case will be typically situated in between. By solving the DH equation one can show that diffuse layer potential varies upon approach as
In electronics, a constant phase element is an equivalent electrical circuit component that models the behaviour of a double layer, that is, an imperfect capacitor (see double-layer capacitance). Constant phase elements are also used in equivalent circuit modeling and data fitting of electrochemical impedance spectroscopy data.