Partial charge transfer during anion adsorption: Methodological aspects

Some problems of applying the Lippmann equation to ionic adsorption on solid electrodes are considered. The possibility of using a nonthermodynamic approach to certain thermodynamic problems (particularly, the role of elastic and plastic deformations of electrode surfaces in adsorption processes, the polarity of surface bonds during anion adsorption, and others) is discussed. The extremely thin electrode layer affected electrically and mechanically by adsorbate is considered to be free of dislocations because of volume discrepancy. The nearest structure-mechanical analogs of such layers are whiskers’-type crystals whose side surface could have point-, one- and two-dimensional defects, but not dislocations. Like whiskers, surface metal layers ought to possess an ultimate strength close to theoretical one (0.2E) and a purely elastic deformation up to 0.04. The surface electrode layer (affected by adsorbate only) should be considered as an absolutely elastic body, whose plastic deformation is impossible. It means that the simple Lippmann equation and other equations containing terms of plastic deformation cannot be used in thermodynamics of the solid metal surface. Coefficients of the partial charge transfer and electrosorption valence of anions, as well as the role of electron tunneling in the formation of the contact electric resistance (CER) signal are considered. The relation between the charge transfer during adsorption of anions and the surface reconstruction of monocrystalline electrodes is analyzed. The beginning of the substantial charge transfer is proposed to be a trigger of the surface reconstruction process. The nature and adsorption of solvent molecules are shown to play a decisive role in the charge transfer during anion adsorption. The results are compared to the available literature data.