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11.
Estimations of electric field effects on the oxygen reduction reaction based on the density functional theory 总被引:1,自引:0,他引:1
By varying the external electric field in density functional theory (DFT) calculations we have estimated the impact of the local electric field in the electric double layer on the oxygen reduction reaction (ORR). Potentially, including the local electric field could change adsorption energies and barriers substantially, thereby affecting the reaction mechanism predicted for ORR on different metals. To estimate the effect of local electric fields on ORR we combine the DFT results at various external electric field strengths with a previously developed model of electrochemical reactions which fully accounts for the effect of the electrode potential. We find that the local electric field only slightly affects the output of the model. Hence, the general picture obtained without inclusion of the electric field still persists. However, for accurate predictions at oxygen reduction potentials close to the volcano top local electric field effects may be of importance. 相似文献
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William J. Durand Andrew A. Peterson Felix Studt Frank Abild-Pedersen Jens K. Nørskov 《Surface science》2011,605(15-16):1354-1359
Polycrystalline copper electrocatalysts have been experimentally shown to be capable of reducing CO2 into CH4 and C2H4 with relatively high selectivity, and a mechanism has recently been proposed for this reduction on the fcc(211) surface of copper, which was assumed to be the most active facet. In the current work, we use computational methods to explore the effects of the nanostructure of the copper surface and compare the effects of the fcc(111), fcc(100) and fcc(211) facets of copper on the energetics of the electroreduction of CO2. The calculations performed in this study generally show that the intermediates in CO2 reduction are most stabilized by the (211) facet, followed by the (100) facet, with the (111) surface binding the adsorbates most weakly. This leads to the prediction that the (211) facet is the most active surface among the three in producing CH4 from CO2, as well as the by-products H2 and CO. HCOOH production may be mildly enhanced on the more close-packed surfaces ((111) and (100)) as compared to the (211) facet, due to a change in mechanism from a carboxyl intermediate to a formate intermediate. The results are compared to published experimental data on these same surfaces; the predicted trends in voltage requirements are consistent between the experimental and computational data. 相似文献
14.
Modification of the surface electronic and chemical properties of Pt(111) by subsurface 3d transition metals 总被引:2,自引:0,他引:2
The modification of the electronic and chemical properties of Pt(111) surfaces by subsurface 3d transition metals was studied using density-functional theory. In each case investigated, the Pt surface d-band was broadened and lowered in energy by interactions with the subsurface 3d metals, resulting in weaker dissociative adsorption energies of hydrogen and oxygen on these surfaces. The magnitude of the decrease in adsorption energy was largest for the early 3d transition metals and smallest for the late 3d transition metals. In some cases, dissociative adsorption was calculated to be endothermic. The surfaces investigated in this study had no lateral strain in them, demonstrating that strain is not a necessary factor in the modification of bimetallic surface properties. The implications of these findings are discussed in the context of catalyst design, particularly for fuel cell electrocatalysts. 相似文献
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A. Hellman K. Honkala I.N. Remediakis á. Logadóttir A. Carlsson S. Dahl C.H. Christensen J.K. N?rskov 《Surface science》2009,603(10-12):1731-1739
A recently published first-principles model for the ammonia synthesis on an unpromoted Ru-based catalyst is extended to also describe ammonia decomposition. In addition, further analysis concerning trends in ammonia productivity, surface conditions during the reaction, and macro-properties, such as apparent activation energies and reaction orders are provided. All observed trends in activity are captured by the model and the absolute value of ammonia synthesis/decomposition productivity is predicted to within a factor of 1–100 depending on the experimental conditions. Moreover it is shown: (i) that small changes in the relative adsorption potential energies are sufficient to get a quantitative agreement between theory and experiment (Appendix A) and (ii) that it is possible to reproduce results from the first-principles model by a simple micro-kinetic model (Appendix B). 相似文献
16.
Abild-Pedersen F Greeley J Studt F Rossmeisl J Munter TR Moses PG Skúlason E Bligaard T Nørskov JK 《Physical review letters》2007,99(1):016105
Density functional theory calculations are presented for CHx, x=0,1,2,3, NHx, x=0,1,2, OHx, x=0,1, and SHx, x=0,1 adsorption on a range of close-packed and stepped transition-metal surfaces. We find that the adsorption energy of any of the molecules considered scales approximately with the adsorption energy of the central, C, N, O, or S atom, the scaling constant depending only on x. A model is proposed to understand this behavior. The scaling model is developed into a general framework for estimating the reaction energies for hydrogenation and dehydrogenation reactions. 相似文献
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Frank Abild-Pedersen Ole Lytken Jakob Engbk Gunver Nielsen Ib Chorkendorff Jens K. Nrskov 《Surface science》2005,590(2-3):127-137
We have, theoretically and experimentally, investigated the dissociation of methane on the terraces and steps of a Ni(1 1 1) surface. Using Density Functional Theory (DFT) total energy calculations combined with Ultra High Vacuum (UHV) experiments, we find that the steps exhibit a higher activity than the terraces. We have, furthermore, investigated how carbon and sulfur present on the surface will deactivate the steps, leaving only the terraces active. We find the intrinsic sticking probabilities of methane on the steps and terraces at 500 K to be 2.8 × 10−7 for the steps and 2.1 × 10−9 for the terraces, in complete agreement with our calculated difference in activation energy of 17 kJ/mol. 相似文献
18.
J.K. Nørskov 《Solid State Communications》1977,24(9):691-693
The electronic structure of H and He impurities in metals is calculated using the Gunnarsson-Hjelmberg method of solving the Kohn-Sham equation. The jellium model is used for the metal. The differences between interstitial and substitutional impurity sites are emphasized. For normal metallic densities it is found that both impurities favour sites of lower than average conduction electron density because here the impurity electrons can relax to a situation of lower kinetic energy. 相似文献
19.
Extensive calculations of the ground state properties of hydrogen chemisorbed on transition metal surfaces are presented. The calculations are performed using the effective medium theory. The results for the chemisorption energies on all the 3d, 4d and 5d metals presented are in good agreement with experiment. The trends along a particular row are shown to be dominated by the degree of filling of the d band. The full adiabatic potential energy surface is presented for a number of experimentally interesting systems, including H/Ni(111), H/Ni(110), H/W(100) and H/W(110). Equilibrium sites, bond lengths, vibrational frequencies and surface diffusion energies are deduced and compared with experiment. Again, agreement is good. The surface and adsorbate parameters determining those observables are discussed. It is shown that a simple canonical relationship exists between the perpendicular vibrational frequency and the metal-hydrogen bond length. This formulation, which is not based on pair potentials, should be useful as a first estimate of bond lengths from measured vibrational data. 相似文献