Effect of Sn on the Reactivity of Cu Surfaces

Abstract

Periodic, density functional theory (DFT-GGA) calculations, using PW91 (self-consistently) and RPBE functionals, have been employed to determine preferred binding sites, adsorbate structures, and binding energies for the adsorption of atomic (H, N, O, S, and C), molecular (NO and CO), and radical (OH) species on Cu(111) and CuSn(0001) alloy surfaces. Our results indicate the following order in the binding energies from the least to the most strongly bound: NO < CO < H < OH < N < O < S < C for Cu-terminated CuSn(0001). On Cu(111), the corresponding relative order of adsorbates from the least strongly bound to the most strongly bound is CO < NO < H < OH < N < O < S < C. On the Sn-terminated CuSn(0001) surface, CO does not adsorb and the relative order of adsorbates from the least strongly bound to the most strongly bound is NO < H < OH < N < S < O < C. For all adsorbates, the binding on Cu-terminated CuSn (0001) is stronger than on Cu(111), resulting from a combination of electronic and strain effects caused by the addition of Sn to Cu. CO dissociation is endothermic on Cu-terminated CuSn(0001) and Cu(111) surfaces, while CO oxidation is exothermic on these surfaces. OH dissociation is endothermic on all three surfaces. On all surfaces studied, thermodynamics of NO decomposition are much more favorable than those of CO and OH dissociation on the corresponding surfaces. Our microcalorimetric studies of the interaction of NO with Cu/SiO 2 and Cu 6 Sn 5 /SiO 2 samples give initial heats of 270 (2.80 eV) and 130 (1.35 eV) kJ/mol, respectively. These values correspond to the decomposition of NO to give adsorbed oxygen plus gaseous N 2 on Cu/SiO 2 and adsorbed oxygen plus gaseous N 2 O on the Sn-terminated phase of Cu 6 Sn 5 /SiO 2 .

Ab initio analysis of sulfur tolerance of Ni, Cu, and Ni–Cu alloys for solid oxide fuel cells

“…Our estimated distance of 1.547Å on the fcc site is consistent with these experimental observations. The adsorption energies on the Cu surface estimated in this study are also in good agreement with previous predictions both by slab [10] and cluster [12] models. Weaker sulfur binding is exhibited by adsorption on Cu(1 1 1) than Ni (1 1 1).…”

“…composite have been identified using Raman spectroscopy after exposure to H 2 fuel containing 100 ppm H 2 S at 1000 K for 5 days [8]. Although various experimental and theoretical calculations have been performed [2,3,[9][10][11][12][13][14][15], to the best of our knowledge, a direct comparison of sulfur tolerance on Ni and Cu surfaces at the same level of periodic density functional theory (DFT)…”

Surfactant effect of Sb on GaN growth

“…For the close-packed, highly symmetric GaN(0 0 0 1) surface, the diffusion barrier for atomic species is estimated using the binding energy (BE) of these species at the high symmetry sites. This approach has been shown to give reasonably good estimates for the diffusion barrier of atomic species on various surfaces [35][36][37].…”

Trends in the Exchange Current for Hydrogen Evolution

“…We exploit the fact that the vibrational entropy in the adsorbed state is small meaning that the entropy of adsorption of 1/2 H 2 is ⌬S H Х Ϫ1/2S H 2 0 , where S H 2 0 is the entropy of H 2 in the gas phase at standard conditions. ⌬E ZPE is calculated to be 0.04 eV for H/Cu͑111͒, see the Appendix, 13 and we take this value to be representative for all the metals we study here. This means that ⌬G H* ϭ ⌬E H ϩ 0.24 eV.…”

“…2 13 We use gas phase H 2 O at 0.035 bar as the reference state because at this pressure gas phase H 2 O is in equilibrium with liquid water at 300 K. 16 We use the same values for the adsorbed species for all the metals, as vibrational frequencies have been found to depend much less on the metal than the bond strength. 17 …”