ABSTRACT
The adsorption of polyatomic oxyanions is ( SO 4 2 − , HSO 4 − , CIO 4 − , NO 3 − , PO 4 3 − , HCO 3 − , and CO 3 2 − ) https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780203750469/7b216794-c74b-4b63-98ec-850a4e8d1fd1/content/eq63_1.tif"/> https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780203750469/7b216794-c74b-4b63-98ec-850a4e8d1fd1/content/eq63_2.tif"/> investigated on low index single crystal silver surfaces using ab initio quantum mechanical calculations. The surfaces are modeled using metal clusters having from 50 to 100 atoms. The energetics and structural aspects associated with anion adsorption are discussed. Monovalent anions have binding energies in the range of 50–70 kcal/mol, divalent anions in the range of 160–230 kcal/mol, and trivalent phosphate has a binding energy of 343 kcal/mol. The highest binding energies are obtained on the more open 110 surface, whereas comparable binding energies are obtained on the 111 and 100 crystal faces. Both chemical and electrostatic processes contribute to the binding energy of the ions. For divalent and trivalent anions, the metal polarization is the most important contribution. Chemical contributions involve both charge donation to the surface and backdonation to empty levels in the adsórbate, the first one being the most important. The influence of external electric fields comparable with those present in electrochemical interfaces on several adsórbate properties such as binding energy, charge transfer, geometry, and vibrational frequencies is also considered. Positive electric fields increase the binding energy of the anions that leads to shorter anion–metal bond distances and a higher charge transfer to the surface. Although the anion geometry distorts in the presence of electric fields, it is always very close to that of typical salts.
