Potential energy surfaces for H₂ dissociative adsorption on Pt(111) surface—effects of vacancies

Abstract

In this study, we determine the effects of having vacancies on the Pt(111) surface to the dissociative adsorption behavior of H 2 on Pt(111). We study the potential energy behaviors along the reaction paths based on the potential energy surfaces (PESs) we calculated that are relevant to these systems. Partial results of our current calculations, based on the density functional theory, reveal that vacancies on the substrate can significantly lower the barrier for the dissociative adsorption of H 2 on the Pt(111) surface. We attribute this behavior to the increased reactivity of the surface owing to the vacant sites. Of the substrate atoms, we find that those on the surface mainly influence the behavior of H 2 adsorption on Pt(111).

First Principles Investigations on Fuel Cell Reactions: H2-Pt(111) Interactions

“…3 and the slight difference in energies is due only to the reversal of depths of the second and the third layers of the substrate. These conform with our earlier conclusion [15] that the potential energy profile for H 2 dissociative adsorption strongly depends on the geometric structure of the surface Pt atoms and, hence, on the interactions of H 2 with the first-layer Pt atoms. Also, based on our previous analyses, the relatively high energy peaks in the bfb(3/4), tfb(1) and tfb(2) plots of Fig.…”

“…The consistent lowering of the activation barriers that characterize the systems of Figs. 2 and 3 further corroborates our earlier finding [15] that the creation of reaction paths which allow for spontaneous H 2 dissociative adsorption is a general effect that can be attributed to the enhanced reactivity of the surface as a result of the presence of the vacant sites. Of the reaction paths we have presented so far, the lowest potential energy (−1.289 eV) is still observed in the htf(1) case at s = 5.79Å (Z = 1.00Å, r = 3.94Å) [15].…”

“…The figure indicates that the activation barrier, measured by the height of the first peak in each plot preceding the first local energy minimum is highest for the tfb configuration, followed by that for the bfb, the tfb(1), the bfb(1), the tfb(2), the bfb(3/4), the tfb(3/4), and the bfb(2) configuration, showing that the barrier to H 2 dissociative adsorption decreases when there is vacancy on the Pt surface. The corresponding calculated numerical values for the barrier potentials are given in Table I, rows 7-8, along with those previously reported [15] for the cases of the H 2 CM above the top and bridge sites, i.e., rows 3-6. It can be seen that from the original values of 0.409 eV and 0.414 eV for the bfb and tfb configurations, respectively, the barrier potentials are greatly reduced to as low as 0.034 eV (bfb(2) and 0.043 eV (tfb(3/4)), respectively.…”

“…We have previously reported that in the case where the H 2 CM is above the top or bridge site, the vacant sites increase the surface reactivity of Pt(111) by lowering the activation barriers for the dissociative adsorption of H 2 on the substrate, as demonstrated by the emergence of a significant number of reactions paths corresponding to actual and near spontaneous reactions [15]. By introducing vacancies in the substrate, we showed that a Pt atom directly below the H 2 CM is very effective for H 2 dissociation and leads to the very low activation barrier in the ideal surface and to the absence of it in the defective surface.…”

First Principles Study on the Adsorption and Dehydrogenation of Borohydride on Mn(111)

“…An ideal alternative source must be highly renewable, environmental friendly, relatively inexpensive, easily accessible, and easy to manufacture [1]. Hydrogen has been foreseen as a viable source of alternative energy through fuel cells [2][3][4][5][6][7]. Improvements were attained through the use of different fuels such as methanol, ethanol, hydrocarbons, and hydrazine [8].…”