Environmental Engineering Reference
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Figure 5.6 Capacity versus potential measurements on the lifting of surface reconstruction of
Au(100) in 0.1 M H 2 SO 4 [Kolb, 1996]. Whereas below 0.55 V the solid curve of Au(100)-hex
more or less coincides with separate measurements on Au(111) (dashed curve), increasing the
potential above þ 0.55 V lifts the reconstruction and gives Au(100)-(1 1) (dotted curve).
voltammogram [Gao et al., 1991] and an alteration in the capacity curve (Fig. 5.6). The
potential-induced reconstruction therefore appears to be largely reversible under these
conditions. Analysis of electrochemical data pertaining to the reconstruction of
Au(100) suggests that the driving force for lifting the “hex” reconstruction [hex !
(1 1)] is due to positive surface excess charge induced by the positive electrode
potential. Such surface excess charges might lower the activation barrier for changes
in the surface morphology.
Further STM and SXS studies [Wu et al., 1998] concerning this phenomenon indi-
cated that the presence of specifically and nonspecifically adsorbing anions as well as
organic molecules (e.g., pyridine, bipyridine, and uracil) may also lift the recon-
structed surface by exhibiting a structural transition, and it has been extensively
studied and reviewed in [Kolb, 1996].
Hence, the question arose whether the lifting of reconstruction is due to surface
charging (as a result of the electrode potential), adsorption of electrolyte ions (or mol-
ecules), or both. Although various experimental and theoretical investigations have
been carried out, the driving force for the lifting of reconstruction is not yet clear.
Assuming a simple capacitor model for the electric double layer, Santos and
Schmickler [2004] used experimentally measured capacity curves for different
electrolyte concentrations to evaluate the surface free energy g for reconstructed
and unreconstructed surfaces of Au(100) and Au(111). At around 0.6 V, they found
an intersection between g Au(100)-hex and g Au(100)-(1 1) , and concluded that positive
excess charge on the surface is responsible for the lifting of reconstruction in
the case of weakly adsorbing electrolytes. They also evaluated the influence of the
electrolyte concentration on the capacitance.
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