Modeling surface segregation phenomena in the (111) surface of ordered Pt3Ti crystal.

We investigated the surface segregation phenomena in the (111) surface of ordered Pt(3)Ti crystal using density functional theory (DFT) calculation (with no configuration sampling) and Monte Carlo (MC) simulation method (employing modified embedded atom method potentials and with extensive configuration sampling). Our DFT study suggested that the off-stoichiometric effect (specifically, a Pt concentration higher than 75 at. %) accounted for the experimentally observed Pt segregation to the outermost layer of the Pt(3)Ti (111). Our MC simulations predicted that in a Pt(3)Ti (111) sample with a Pt concentration slightly above 75 at. %, Pt atoms would segregate to the surface to form a pure Pt outermost layer, while the ordered Pt(3)Ti crystal structure would be maintained in the second layer and below. Moreover, our DFT calculations revealed that the d-band center of the Pt-segregated Pt(3)Ti (111) surface would downshift by 0.21 eV as compared to that of a pure Pt (111) surface. As a result, O adsorption energy on the Pt-segregated Pt(3)Ti (111) surface was found to be at least 0.16 eV weaker than that on the pure Pt (111) surface. Thus, we theoretically modeled the geometric and electronic structures of the Pt-segregated Pt(3)Ti (111) surface and further suggested that the Pt surface segregation could lead to enhanced catalytic activity for oxygen reduction reactions on Pt(3)Ti alloy catalysts.