Environmental Engineering Reference
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reach thermodynamic equilibrium are not included. Those studies would require
extensive kinetic simulations, for which the results described here might be used as
starting point.
5.4 SUMMARY
We have described the extended ab initio atomistic thermodynamics method, which
allows structures and stabilities of electrode/electrolyte interfaces to be calculated
quantitatively as functions of temperature, activities/pressures, and external electrode
potential. Starting from the gas phase system, we have successively moved to the
electrochemical system by first describing the properties and characteristics of the
well-separated bulk electrolyte and bulk electrode independently, finally discussing
the changes introduced by bringing both into contact. We have shown that when
the electrochemical system is considered, i.e., the electrode/electrolyte interface,
the interfacial free energy, which describes the stability of a particular interface struc-
ture, depends almost exclusively on well-defined quantities, even being accessible
experimentally. Only the activity of one of the ionic electrolyte species depends on
accurate theoretical modeling.
We have also discussed two applications of the extended ab initio atomistic thermo-
dynamics approach. The first example is the potential-induced lifting of Au(100)
surface reconstruction, where we have focused on the electronic effects arising from
the potential-dependent surface excess charge. We have found that these are already
sufficient to cause lifting of the Au(100) surface reconstruction, but contributions
from specific electrolyte ion adsorption might also play a role. With the second
example, the electro-oxidation of a platinum electrode, we have discussed a system
where specific adsorption on the surface changes the surface structure and compo-
sition as the electrode potential is varied.
Although the extended ab initio atomistic thermodynamics approach provides an
exact expression for the interfacial stability, the formalism requires self-consistent
modeling of the entire electrochemical system, or electrode/electrolyte interface,
exceeding presently available computational capabilities. Therefore, certain assump-
tions had to be made that reduce the effort to the calculation of the electrode surface
only. Even with this simplified approach, which has been applied to the two examples
discussed in this chapter, the qualitative behavior can be reproduced.
REFERENCES
Abbas Z, Gunnarsson M, Ahlberg E, Nordholm S. 2002. Corrected Debye-H¨ckel (CDH)
analysis of surface complexation. J Phys Chem B 106: 1403 - 1420.
Abruna HD. 1991. Electrochemical Interfaces: Modern Techniques for In-Situ Interface
Characterization. Weinheim: Wiley-VCH.
Allen GC, Tucker PM, Capon A, Parsons R. 1974. X-ray photoelectron-spectroscopy of
adsorbed oxygen and carbonaceous species on platinum-electrodes. J Electroanal Chem
50: 335 - 343.
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