Experimental and theoretical investigation of the stability of Pt-3d-Pt(111) bimetallic surfaces under oxygen environment.
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.
Menning
Carl A
CA
Department of Chemical Engineering, Center for Catalytic Science and Technology, University of Delaware, Newark, Delaware 19716, USA.
Hwu
Henry H
HH
Chen
Jingguang G
JG