An embedded atom approach to underpotential deposition phenomena

We have performed embedded atom calculations for a number of systems of electrochemical interest involving a metallic single-crystal substrate and a metallic adsorbate. Different thermodynamic contributions to the so-called underpotential shift are calculated and analyzed comparatively, drawing some general trends. The metal pairs considered involve silver, gold, platinum, palladium and copper. We consider the possibility of underpotential deposition through the excess of binding energy, arriving at two novel conclusions. First, for some systems consisting of metal M(1) and M(2), underpotential deposition should be energetically possible in both cases, that is M(1) on M(2) and M(2) on M(1). Second, anions may play a decisive role in changing the energetics of some systems. In particular cases like copper on Au(lll) they may be responsible to a large extent for the existence of an underpotential deposition. Entropic contributions were neglected in the present analysis. (C) 1999 Elsevier Science B.V. All rights reserved.