Theoretical Prediction and Experimental Verification of Stability of Pt–3d–Pt Subsurface Bimetallic Structures: From Single Crystal Surfaces to Polycrystalline Films

Abstract

In this paper we will provide a review of our recent studies on the general stability of the Pt-3d-Pt (3d = Ti, V, Cr, Mn, Fe, Co and Ni) subsurface structures, which are the desirable structural configurations in several applications in heterogeneous catalysis and electrocatalysis. We will first provide a review of density functional theory (DFT) predictions of the thermodynamic stability of Pt-3d-Pt(111) and Pt-3d-Pt(100) in vacuum and with adsorbed hydrogen and oxygen. The DFT results predict that the Pt-3d-Pt subsurface structures are stable in vacuum and with adsorbed hydrogen, while with adsorbed oxygen the 3d atoms should segregate to the surface to produce the 3d-Pt-Pt surface structures. The DFT predictions are verified experimentally on selected Pt-3d-Pt(111) systems. The experimental efforts are further expanded by bridging the materials gap form single crystal Pt(111) to polycrystalline Pt to incorporate multiple crystal facets and to determine their effects on the kinetic barriers for the segregation of the subsurface 3d atoms. In order to further correlate DFT calculations with experimental results, a Brønsted-Evans-Polanyi relationship is derived to correlate thermodynamic stability from DFT calculations with kinetic barriers from experimental measurements for the Pt-3d-Pt systems. Finally, empirical equations have been developed for predicting the thermodynamic stability of other bimetallic systems both in vacuum and with adsorbed hydrogen and oxygen.

Effect of oxide supports in stabilizing desirable Pt–Ni bimetallic structures for hydrogenation and reforming reactions

“…8,13 The relative stability on the Ni-Pt(111) single crystal surface remains the same when introducing multiple grain boundaries and crystal planes when using a polycrystalline Ni-Pt foil. 56 Therefore, the trends predicted and found experimentally for the model single crystal surfaces will most likely hold when extended to nanoparticle catalysts. 57 Recently, Grass et al 58 carried out an in situ study of the interaction of a bimetallic Rh 0 .…”

Towards the elucidation of the high oxygen electroreduction activity of PtxY: surface science and electrochemical studies of Y/Pt(111)

“…57 Another is the high affinity of yttrium for oxygen (DH = À1905 kJ mol À1 or corresponding to a gain of 9.9 eV per yttrium atom for 2Y + 1.5O 2 = Y 2 O 3 ), 58 which could favour the formation of subsurface oxygen or segregation of Y, leading to a depletion of yttrium. [59][60][61] It is interesting to compare the UHV annealed Y/Pt(111) crystal with the UHV annealed Pt 3 Sc polycrystalline sample from our earlier work. For scandium the standard reduction potential (E 0 = À2.077 V for Sc ) Sc 3+ ) 57 and affinity for oxygen (DH = À1908 kJ mol À1 for 2Sc + 1.5O 2 = Sc 2 O 3 ) 58 are approximately as high as for yttrium.…”

Understanding the electrocatalysis of oxygen reduction on platinum and its alloys

“…99 They implicitly assume that the interaction between Ni and adsorbed O is insufficient to cause subsurface oxide formation or Ni segregation to the surface. 159,160 Perhaps the most likely cause of the increased stability of Ptalloys is the high temperatures used to anneal them. 128,149 Under these conditions, the particles would sinter, their average size would increase and the facets would become more ordered.…”