Experimental and Theoretical Investigation of the Stability of Pt−3d−Pt(111) Bimetallic Surfaces under Oxygen Environment

Abstract

The stability of the Pt-3d-Pt(111) (3d = Ti, V, Cr, Mn, Fe, Co, or Ni) bimetallic surface structures in the presence of adsorbed oxygen has been investigated by means of density functional theory (DFT). The dissociative binding energies of oxygen on Pt-3d-Pt(111) (i.e., subsurface 3d monolayer) and 3d-Pt-Pt(111) (i.e., surface 3d monolayer) were calculated. All of the Pt-3d-Pt(111) surfaces were found to have weaker oxygen binding energies than pure Pt(111) whereas all of the 3d-Pt-Pt(111) surfaces were found to have stronger oxygen binding energies than pure Pt(111). The total heat of reaction was calculated for the segregation for 3d metal atoms from Pt-3d-Pt(111) to 3d-Pt-Pt(111) when exposed to a half monolayer of oxygen. All of the Pt-3d-Pt(111) subsurface structures were predicted to be thermodynamically unstable with adsorbed oxygen. In addition, the segregation of subsurface Ni and Co to the surfaces of Pt-Ni-Pt(111) and Pt-Co-Pt(111) was investigated experimentally using Auger electron spectroscopy (AES) and high-resolution electron energy loss spectroscopy (HREELS). AES and HREELS confirmed the trend predicted by DFT modeling and showed that both the Pt-Ni-Pt(111) and Pt-Co-Pt(111) surface structures were unstable in the presence of adsorbed oxygen. The activation barrier of the segregation of surbsurface Ni and Co atoms was determined to be 15 +/- 2 and 7 +/- 1 kcal/mol, respectively. These results are further discussed for their implication in the design and selection of cathode bimetallic electrocatalysts for the oxygen reduction reaction (ORR) in polymer electrode membrane (PEM) fuel cells.

Structure evolution of Pt–3d transition metal alloys under reductive and oxidizing conditions and effect on the CO oxidation: a first-principles study

“…The driven forces for this are the lower surface energy and larger atomic size of Pt than that of the 3d TMs. In this particular case, calculated E (so-called segregation energy) decreases from the left (0.75 eV for Cr) to the right (0.47 eV for Cu) of the periodic table, and the results agree well with previous DFT calculations and experiments [31,[40][41][42]. To study the structure evolution of Pt-3d TM surfaces in the presence of CO, we explore a number of high-symmetry sites, and it turns out that CO adsorption prefers exclusively to the top sites of exposed Pt atoms, irrespective of 3d TMs in the surface or subsurface layer.…”

“…Kinetically, Menning and Chen reported a small activation barrier of 15 ± 2 and 7 ± 1 kcal/mol for the segregation of Pt-Ni and Pt-Co subsurface alloys in the presence of adsorbed oxygen under ultra high vacuum (UHV) conditions [40], and likewise small activation barrier of 32 kcal/mol for the segregation of subsurface Ni in atmospheric O 2 [31]. These results together with present calculations indicate that the formation of the Pt-3d TM surface alloys is not only energetically favorable but also kinetically feasible under the oxidizing conditions.…”

Elucidating challenges of reactions with correlated reactant and product binding energies on an example of oxygen reduction reaction

“…15,16 It was shown for Pt-M-Pt (M = Ru, Rh, Pd, Re, Os, Ir, Pt) that the O and OH binding energies could possibly be non-correlated for these materials. 1, 17 Thus, we seek to find cases of high oxoasymmetry, and this class of catalysts was shown to display this property.…”

“…Comparing with experiments, the only study done on Pt-M-Pt catalysts involves M = 3d transition metals 16 and did not involve Ru. A related study looked at a Pt monolayer on pure Ru catalyst 30,31 .…”

Key Factors Affecting the Performance and Durability of Cathode Electrocatalysts in Polymer Electrolyte Fuel Cells Characterized by In Situ Real Time and Spatially Resolved XAFS Techniques

“…The promoting effects of alloying of Pt with Co, Ni, etc. have been studied by various techniques such as theoretical calculations [58][59][60][61][62], transmission electron microscopy [56][57][58][59][60][61][62][63][64][65][66][67], and photoelectron spectroscopy [55,68,69]. Although these studies have revealed relationships between the ORR enhancements and the bimetal structures, the details of dynamic surface events taking place at the cathode electrocatalyst surface remain unclear, including individual redox processes under PEFC working conditions.…”