Study of hydrogen adsorption on Pt and Pt-based bimetallic surfaces by density functional theory

The surface energies and surface relaxation of Pt(100), (110), and (111) surfaces, as well as the hydrogen adsorption behavior on three Pt surfaces and M-Pt(111) (M=Al, Fe, Co, Ni, Cu, Pd) bimetallic surfaces with a coverage of 0.25 ML were calculated by density functional theory (DFT). The most favorable adsorption sites, adsorption energies, and relaxation during adsorption were obtained. The hydrogen local density of states before and after the adsorption, the positions of the d-band center of different bimetallic surfaces with respect to the Fermi level were analyzed and further related to hydrogen adsorption energies. The calculations showed that the easiest adsorption sites of hydrogen on Pt(100), Pt (110), and Pt(111) are, in order, the bridge site, the short bridge site, and the fcc hollow site. The Pt(111) surface has the lowest surface energy among the three Pt surfaces and the Pt(111) surface is the most stable structure. However, the fcc hollow site is the most stable adsorption site for different M- Pt(111) bimetallic surfaces. The Ni-Pt bimetallic surface showed the lowest hydrogen adsorption energy among the M- Pt(111) bimetallic surfaces. The Co-Pt bimetallic surface showed the next lowest hydrogen adsorption energy, indicating that hydrogen adsorption on Ni- Pt and Co- Pt bimetallic surfaces is more stable. In addition, the first layer and the second layer have an expanding tendency with some degree after hydrogen adsorption on Ni-Pt, Co-Pt, and Fe-Pt bimetallic surfaces. The addition of a 3d metal surface layer on Pt (111) was found to move the d-band center closer to the Fermi level when compared with the bulk Pt metal, and increases the hydrogen adsorption ability by means of the density of state analysis of the bimetallic surfaces model. This reveals that 3d- Pt bimetallic surfaces are likely to have better dehydrogenation activity than Pt.