Single crystal surfaces, anion adsorption

Bi)sulfate Anion Adsorption on Platinum Single Crystal Surfaces... 

The spectroscopic verification of a stable alloy surface in UHV (ultrahigh vacuum conditions) has to be done at an open circuit, where, in the case of a single crystal surface, it means a stable double layer. However, when the single crystal has to be transferred to the electrochemical cell to perform adsorption or electrode reactions, the persistence of this situation is not obvious. A constant correlation between the open circuit potential and the electron binding energy of the double layer components (anion, solvent, etc.) has to be maintained [50]. When the rest potential lies at the onset of the oxide formation, there is a further stabilization, but this can produce spontaneous dissolution of the less noble metal of the alloy. Thus, air contact has to be avoided. 

The first applications of ab initio quantum-chemical calculations to systems of electrochemical interest were concerned with the adsorption of halides at metal surfaces. The adsorption of halides is of great experimental and practical importance as many electrolyte solutions contain halide anions, which tend to adsorb specifically at the metal-water interface, especially at more positive electrode potentials. Issues of interest in halide chemisorption are the nature of chemical bond with the surface ( . e., covalent or ionic), the strength of the interaction of the different halides on different substrates, the preferred binding geometry on single-crystal surfaces, the effect of the electrode potential, and the importance of including the solvent (water) in correctly modeling the properties of the chemisorption bond. 

The capacitance-potential dependences of Cd(OOOl) in dilute solutions of Cl04, N02, and NOs" were also studied [6]. A weak specific adsorption of anions increasing in the order Cl04 < N02 < N03 was observed. The adsorption of halides on the Cd(OOOl) single crystal electrode was studied [7], and was found to increase in the sequence Cl < Br < 1 [8]. Analysis of the impedance data does not point to the specific adsorption of Cl ions, and shows that the surface excess (T) of halide ions changes with potential and increases from Br to 1 (Fig. 1) [7]... 

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