In the present paper the adsorption of Ag+ ions on polycrystalline gold studied by means of an in-situ radiotracer method and cyclic voltammetry is described. After reviewing some literature data on the underpotential deposition (UPD) of silver, a new detection procedure elaborated for the measurement of isotopes emitting β- and γ- radiations as well as experimental results of the time, potential and concentration dependent adsorption of Ag+ ions labelled with 110mAg is presented and discussed. From the results summarized in this work several implications naturally arise: (i) On the basis of measurements performed by using a β-plastic dE/dX scintillation detector, it can be stated that the dE/dX detector placed beneath the radioelectrochemical cell is suitable for the investigation of the sorption behaviour of species labelled with radioisotopes emitting either low (or medium) energy β-particles or β-and γ-radiations. Disturbing effects of the secondary radiations (γ-ray, characteristic X-ray or bremsstrahlung, Compton- and photoelectrons) upon detection are negligible or can be eliminated. (ii) Deposition of Ag+ ions on gold is significant in the entire potential range more negative than the onset of surface electrooxidation. The coverage of the surface (θ) in the underpotential region is essentially lower than the monolayer coverage (i.e. θ < 0.20) and is highly dependent upon the experimental conditions. (iii) Differences in the potential and concentration dependences of Ag adsorption measured in two (interrupted and continuous) polarization modes may most likely be due to the slow structural changes of the gold surface in association with strong interactions between Ag and Au. (iv) The electrosorption valency (γ) of Ag adatoms deposited on polycrystalline gold can be calculated from the surface excess concentrations and deposition change values determined by microcoulombmetry. It is probable that in the UPD region silver is deposited as a pure metal or silver oxide. The presence of Ag oxides on a gold surface is supported by the γ ≥ 1 values as well as by the standard potentials, which give an indication that Ag2O and AgO may be formed in the potential range 0,75 V to 1,30 V. (v) The results of the exchange of deposited Ag attest that no strong embedding (e.g. alloy formation) of Ag on gold at underpotentials takes place.
|Translated title of the contribution||Investigation of the surface properties of metals by radiotracer technique, X. An in-situ study of the adsorption of Ag+ ions on polycrystalline gold|
|Journal||Magyar Kemiai Folyoirat, Kemiai Kozlemenyek|
|Publication status||Published - Jul 1 1997|
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