New Approach for the Calculation on the Entropic and Free EnergyContributions to Underpotential Deposition

L. FARIGLIANO; O. A. OVIEDO; M.A. VILLARREAL; E.P.M. LEIVA

ECS Transactions

The Electrochemical Society

Lugar: Pennington New Jersey 08534-2839 ; Año: 2014 vol. 58 p. 3 - 20

1938-6737

In the present work we have studied the electrochemical nonpseudomorphic formation of Pbbidimensional structures on Au(111) surfaces. Based on the two-phase thermodynamic method, we haveanalyzed, from a computational perspective, entropic and energetic contributions to underpotentialdeposition. The occurrence of incommensurate nanophase formation, rotation of the adsorbate withrespect to the substrate, and the effect of expansion and compression of the Pb monolayer were alsoanalyzed. Our results show that the entropic contribution to monolayer underpotential deposition of Pb onAu(111) at room temperature is approximately 20% of the total free energy excess. For very smallclusters, this contribution increases up to 45%. Simulations show that in the early stages of formation, Pbnanophases grow without rotation. When the size of the Pb islands is close 100 atoms, a rotation processtakes places. At relatively high coverage, a strong lateral compression of Pb monolayer sets on, evidencedby a sharp decrease in the distance between nearest neighbors.