Partial charge Grahame model

As explained in the description of the Grahame model for the double layer, specific adsorption is the adsorption of ions at the electrode surface after losing their solvation partially or completely. These ions can have the same charge or the opposite charge to the electrode. Bonds formed with the electrode in this way are stronger than for solvated ions. 

According to the Stem-Graham model, the dense part of the EDL, adjacent to the solid surface charged with the potential determining ions, may, in turn, consist of inner and outer layers. The inner part, located in the direct vicinity of the charged surface, is formed by the specifically adsorbed ions, which are completely, or partially dehydrated (the so-called inner Helmholtz plane). The outer part, referred to as the outer Helmholtz plane, consists of hydrated ions that do not reveal such strong specific adsorption. The ions, specifically adsorbed within the inner part of Stem- Helmholtz plane, may... 

The aforementioned diffuse-layer and discreteness-of-charge effects have been taken into consideration in the model proposed by Grahame and Parsons [26,250-252]. First, it was assumed (unlike in the Stern model) that the specifically adsorbed ions were located at the distance from the metal surface (in the inner Helmholtz plane ) ensuring their maximum bond strength, owing to the combination of forces of electrostatic and quantum-mechanical origins. It shows the need for the partial or even complete desolvation of the adsorbed species and its deep penetration into the compact layer. The position of this adsorption plane depends on all components of the system, metal, solvent, and adsorbed ion. 

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