Co-Adsorption of H2O, OH, and Cl on Aluminum and Intermetallic Surfaces and Its Effects on the Work Function Studied by DFT Calculations

The energetics of adsorption of H2O layers and H2O layers partially replaced with OH or Cl on an Al(111) surface and on selected surfaces of intermetallic phases, Mg2Si and Al2Cu, was studied by first-principle calculations using the density function theory (DFT). The results show that H2O molecules tended to bind to all investigated surfaces with an adsorption energy in a relatively narrow range, between -0.8 eV and -0.5 eV, at increased water coverage. This can be explained by the dominant role of networks of hydrogen bonds at higher H2O coverage. On the basis of the work function, the calculated Volta potential data suggest that both intermetallic phases became less noble than Al(111); also, the Volta potential difference was larger than 1 V when the coverage of the Cl-containing ad-layer reached one monolayer. The energetics of H2O dissociation and substitution by Cl as well as the corresponding work function of each surface were also calculated. The increase in the work function of the Al(111) surface was attributed to the oxidation effect during H2O adsorption, whereas the decrease of the work function for the Mg2Si(111)-Si surface upon H2O adsorption was explained by atomic and electronic rearrangements in the presence of H2O and Cl.