Comparative study of water dissociation on Rh(111) and Ni(111) studied with first principles calculations

Abstract

The dissociation and formation of water on the Rh(111) and Ni(111) surfaces have been studied using density functional theory with generalized gradient approximation and ultrasoft pseudopotentials. Calculations have been performed on 2x2 surface unit cells, corresponding to coverages of 0.25 ML, with spot checks on 3x3 surface unit cells (0.11 ML). On both surfaces, the authors find that water adsorbs flat on top of a surface atom, with binding energies of 0.35 and 0.25 eV, respectively, on Rh(111) and Ni(111), and is free to rotate in the surface plane. Barriers of 0.92 and 0.89 eV have to be overcome to dissociate the molecule into OH and H on the Rh(111) and Ni(111) surfaces, respectively. Further barriers of 1.03 and 0.97 eV need to be overcome to dissociate OH into O and H. The barriers for the formation of the OH molecule from isolated adsorbed O and H are found to be 1.1 and 1.3 eV, and the barriers for the formation of the water molecule from isolated adsorbed OH and H are 0.82 and 1.05 eV on the two surfaces. These barriers are found to vary very little as coverage is changed from 0.25 to 0.11 ML. The authors have also studied the dissociation of OH in the presence of coadsorbed H or O. The presence of a coadsorbed H atom only weakly affects the energy barriers, but the effect of O is significant, changing the dissociation barrier from 1.03 to 1.37 and 1.15 eV at 0.25 or 0.11 ML coverage on the Rh(111) surface. Finally, the authors have studied the dissociation of water in the presence of one O atom on Rh(111), at 0.11 ML coverage, and the authors find a barrier of 0.56 eV to dissociate the molecule into OH+OH.

First-Principles Modeling of Direct versus Oxygen-Assisted Water Dissociation on Fe(100) Surfaces

“…The O-H bond length of 0.98 Å and the =HOH bond angle of 105.4˝, as listed in Table 2, are almost identical to those of a free H 2 O molecule (0.98 Å and 104.4˝, respectively). Similar adsorption behaviors of H 2 O on Ni(111) [53][54][55], Ni(100) [55], Ni(110) [55], Cu(111) [56], Cu(100) [57] and Cu(110) [58,59] were observed.…”

First-principles study of oxygen coverage effect on hydrogen oxidation on Ni(111) surface

“…A lot of DFT studies have been carried out for different surface orientations of Ni, such as (1 1 1) [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28], (1 0 0) [15,[25][26][27][28][29][30], and (2 1 1) [21,22,31]. Most of the papers are discussed on the dissociation of H 2 O to OH and H [10][11][12][13]16,22], as a one of the steps of steam reforming reaction on Ni surface. Limited papers are reported about the oxidation reaction on Ni surface assuming the SOFC anode [21,[31][32][33][34][35].…”

Equilibrium geometric structure and electronic properties of Cl and H2O co-adsorption on Fe (100) surface

“…Therefore, it could be deduced that the most stable geometrical structure of H 2 O molecules and Cl atoms co-adsorbed on the Fe (100) surface is that the H 2 O molecule is located at the atop site and the Cl atom is located at the bridge site. Previous studies [14][15][16][17][18][19] The layer distance in the Fe (100)/H 2 O adsorption system decreases, compared with that in the clean Fe (100) substrate, which indicates that the relaxation of the Fe atoms in the second layer and the third layer occurs. Additionally, d 12 and d 23 both have two values, 1.05 Å and 1.21 Å respectively, which shows that the displacement of the atoms in the same layer varies greatly in the vertical direction.…”

“…Recently, the adsorption and dissociation of H 2 O monomers on metal surfaces were presented by scanning tunneling spectroscopy (STM) and theory calculation methods [11][12][13][14][15][16][17][18][19] . Some other studies focused on the properties of the metal/solution interface with an H 2 O molecules and chlorine atom co-adsorbed on the metal surface by experimental techniques, such as HREELS, ESDIAD and LEED.…”