The interfacial capacitance of a metal electrode in contact with a dilute electrolyte is generally expected to follow the behavior predicted by the Gouy-Chapman-Stern model. Recent experiments ... Show moreThe interfacial capacitance of a metal electrode in contact with a dilute electrolyte is generally expected to follow the behavior predicted by the Gouy-Chapman-Stern model. Recent experiments [Angew. Chem. Int. Ed. 2020, 59, 711], however, have shown that a deviation from the Gouy-Chapman behavior is observed even in dilute electrolytes on platinum and gold single-crystal electrodes. Such deviations are usually attributed to an interaction between the surface and the electrolyte ions. However, a quantitative model showing that the strong deviations from the Gouy-Champan behavior observed for Pt can be ascribed to such an effect is still lacking, particularly as other experimental observables do not indicate a strong ion adsorption. Here, we propose a double-layer model that is capable of reproducing the main experimental findings in a simple and (in parts) analytical way. The analytical model thereby includes the attractive ion-surface interaction via an additional capacitive element connected in parallel to the Gouy-Chapman capacitance. By comparing the model predictions to experiment, we subsequently infer characteristics of the ion-surface interaction. In particular, we find that the model predicts the attractive interaction to be weak (weaker than a typical chemical bond formed when contact adsorbing) and that the interaction has to be very similar for all ions. Furthermore, for a good agreement with experiment, ion-size effects are suggested to play a role in determining the potential of minimum capacitance. Show less
In this article, we investigate the poisoning reaction that occurs at platinum electrodes during the electrocatalytic hydrogenation of acetone. A better understanding of this poisoning reaction is... Show moreIn this article, we investigate the poisoning reaction that occurs at platinum electrodes during the electrocatalytic hydrogenation of acetone. A better understanding of this poisoning reaction is important to develop electrocatalysts that are both active for the hydrogenation of carbonyl compounds and resilient against poisoning side reactions. We adsorb acetone to Pt(331), Pt(911), Pt(510), and Pt(533) (i.e., Pt[2(111) x (110)], Pt[5(100) x (111)], [5(100) x (110)], and Pt[4(111) x (100), respectively])) as well as Pt(100) single-crystal electrodes and perform reductive and oxidative stripping experiments after electrolyte exchange. We found that acetone adsorbs molecularly intact on all sites apart from Pt(100) terrace sites and can be stripped reductively from the electrode surface at a potential positive of hydrogen evolution. However, at Pt(100) terraces, acetone adsorbs dissociatively as carbon monoxide, which remains attached to the electrode surface and leads to its poisoning. Strikingly, dissociative adsorption does not occur on step sites with (100) geometry, which suggests that the dissociative adsorption of acetone is limited to Pt(100) terraces featuring a certain minimum ensemble number of freely available Pt atoms. Show less
Tebyani, A.; Baalbergen, F.B.; Tromp, R.M.; Molen, S.J. van der 2021
Many polyols are abundant and cheap molecules highly spread in the biomass. These molecules have an enormous potential to be used in electrochemical devices to generate energy and/or value-added... Show moreMany polyols are abundant and cheap molecules highly spread in the biomass. These molecules have an enormous potential to be used in electrochemical devices to generate energy and/or value-added molecules. The electrooxidation of polyols can produce different substances of interest in the chemical industry concomitantly to high purity hydrogen in electrolyzers. The cost in the production of all these chemicals depends, among other factors, on the develop of more active and selective catalysts. However, in order to search for these materials using computational experiments, it is mandatory to have a better understanding of the fundamental aspect of the reactions, which permit to base the search on the adsorption energies of one or more key reaction intermediates. To contribute to this task, we performed (spectro)-electrochemical and computational experiments to study the electrooxidation of C-4 polyols. We show that the electrooxidation of polyols does not depend on the relative orientation of their OH groups. Besides, using Pt single crystals, we demonstrate that the trend for the oxidation of the primary carbon (relative to the secondary) increases in the order Pt(111) < Pt(100) < Pt(110) and that this result can be extended to polyols with longer carbon chains. Finally, computational experiments permit us to rationalize these trends looking at the relative stability of double dehydrogenated intermediates on the Pt basal planes. Show less
The specific reaction parameter (SRP) approach to density functional theory has been shown to model reactions of polyatomic molecules with metal surfaces important for heterogeneous catalysis in... Show moreThe specific reaction parameter (SRP) approach to density functional theory has been shown to model reactions of polyatomic molecules with metal surfaces important for heterogeneous catalysis in the industry with chemical accuracy. However, transferability of the SRP functional among systems in which methane interacts with group 10 metals remains unclear for methane + Pd(111). Therefore, in this work, predictions have been made for the reaction of CHD3 on Pd(111) using Born–Oppenheimer molecular dynamics while also performing a rough comparison with experimental data for CH4 + Pd(111) obtained for lower incidence energies. Hopefully, future experiments can test the transferability of the SRP functional among group 10 metals also for Pd(111). We found that the reactivity of CHD3 on Pd(111) is intermediate between and similar to either Pt(111) or Ni(111), depending on the incidence energy and the initial vibrational state distribution. This is surprising because the barrier height and experiments performed at lower incidence energies than investigated here suggest that the reactivity of Pd(111) should be similar to that of Pt(111) only. The relative decrease in the reactivity of Pd(111) at high incidence energies is attributed to site specificity of the reaction and to dynamical effects such as the bobsled effect and energy transfer from methane to the surface. Show less
A dye-sensitized photoelectrochemical cell (DS-PEC) is a promising device for direct conversion of solar energy into fuel. The basic idea, inspired by natural photosynthesis, is to couple the... Show moreA dye-sensitized photoelectrochemical cell (DS-PEC) is a promising device for direct conversion of solar energy into fuel. The basic idea, inspired by natural photosynthesis, is to couple the photoinduced charge separation process to catalytic water splitting. The photo-oxidized dye coupled to a water oxidation catalyst (WOC) should exert a thermodynamic driving force for the catalytic cycle, while water provides the electrons for regenerating the oxidized dye. These conditions impose specific energetic constraints on the molecular components of the photoanode in the DS-PEC. Here, we consider a supramolecular complex integrating a mononuclear Ru-based WOC with a fully organic naphthalene-diimide (NDI) dye that is able to perform fast photoinduced electron injection into the conduction band of the titanium-dioxide semiconductor anode. By means of constrained ab initio molecular dynamics simulations in explicit water solvent, it is shown that the oxidized NDI provides enough driving force for the whole photocatalytic water splitting cycle. The results provide strong evidence for the significant role of spin alignment and solvent rearrangement in facilitating the proton-coupled electron transfer processes. The predicted activation free energy barriers confirm that the O–O bond formation is the rate-limiting step. Our results expand the current understanding of the photocatalytic water oxidation mechanism and provide guidelines for the optimization of high-performance DS-PEC devices. Show less
To be able to simulate activated heterogeneously catalyzed reactions on the edge and corner sites of nanoparticles, a method for calculating accurate activation barriers for the reactions is... Show moreTo be able to simulate activated heterogeneously catalyzed reactions on the edge and corner sites of nanoparticles, a method for calculating accurate activation barriers for the reactions is required. We have recently demonstrated that a semiempirical specific reaction parameter (SRP) density functional developed to describe CHD3 dissociation on a flat Ni(111) surface is transferable to describing the same reaction on a stepped Pt(211) surface. In the current work, we compare initial sticking coefficients measured using the King and Wells beam reflectivity technique and calculated from ab initio molecular dynamics trajectories using the same SRP functional for CHD3 dissociation on a kinked Pt(210) surface at a temperature of 650 K. The calculated sticking coefficients overestimate those determined experimentally, with an average energy shift between the two curves of 13.6 kJ/mol, which is over a factor of 3 times higher than the 4.2 kJ/mol limit that defines chemical accuracy. This suggests the SRP functional predicts an activation barrier that is too low for the dissociation on the least coordinated kink atom, which is the site of the lowest energy transition state and where most of the dissociation occurs in the calculations. Show less
Iridium oxide-based catalysts are uniquely active and stable in the oxygen evolution reaction. Theoretical work attributes their activity to oxyl or mu(1)-O species. Verifying this intermediate... Show moreIridium oxide-based catalysts are uniquely active and stable in the oxygen evolution reaction. Theoretical work attributes their activity to oxyl or mu(1)-O species. Verifying this intermediate experimentally has, however, been challenging. In the present study, these challenges were overcome by combining theory with new experimental strategies. Ab initio molecular dynamics of the solid-liquid interface were used to predict spectroscopic features, whereas sample architecture, developed for surface-sensitive X-ray spectroscopy of electrocatalysts in confined liquid, was used to search for these species under realistic conditions. Through this approach, we have identified mu(1)-O species during oxygen evolution. Potentiodynamic X-ray absorption additionally shows that these mu(1)-O species are created by electrochemical oxidation currents in a deprotonation reaction. Show less
It is important that theory is able to accurately describe dissociative chemisorption reactions on metal surfaces, as such reactions are often rate-controlling in heterogeneously catalyzed... Show moreIt is important that theory is able to accurately describe dissociative chemisorption reactions on metal surfaces, as such reactions are often rate-controlling in heterogeneously catalyzed processes. Chemically accurate theoretical descriptions have recently been obtained on the basis of the specific reaction parameter (SRP) approach to density functional (DF) theory (DFT), allowing reaction barriers to be obtained with chemical accuracy. However, being semiempirical, this approach suffers from two basic problems. The first is that sticking probabilities (to which SRP density functionals (DFs) are usually fitted) might show differences across experiments, of which the origins are not always clear. The second is that it has proven hard to use experiments on diffractive scattering of H2 from metals for validation purposes, as dynamics calculations using a SRP-DF may yield a rather poor description of the measured data, especially if the potential used contains a van der Waals well. We address the first problem by performing dynamics calculations on three sets of molecular beam experiments on D2 + Pt(111), using four sets of molecular beam parameters to obtain sticking probabilities, and the SRP-DF recently fitted to one set of experiments on D2 + Pt(111). It is possible to reproduce all three sets of experiments with chemical accuracy with the aid of two sets of molecular beam parameters. The theoretical simulations with the four different sets of beam parameters allow one to determine for which range of incidence conditions the experiments should agree well and for which conditions they should show specific differences. This allows one to arrive at conclusions about the quality of the experiments and about problems that might affect the experiments. Our calculations on diffraction of H2 scattering from Pt(111) show both quantitative and qualitative differences with previously measured diffraction probabilities, which were Debye–Waller (DW)-extrapolated to 0 K. We suggest that DW extrapolation, which is appropriate for direct scattering, might fail if the scattering is affected by the presence of a van der Waals well and that theory should attempt to model surface atom motion for reproducing diffraction experiments performed for surface temperatures of 500 K and higher. Show less
The HCl + Au(111) system has recently become a benchmark for highly activated dissociative chemisorption, which presumably is strongly affected by electron–hole pair excitation. Previous dynamics... Show moreThe HCl + Au(111) system has recently become a benchmark for highly activated dissociative chemisorption, which presumably is strongly affected by electron–hole pair excitation. Previous dynamics calculations, which were based on density functional theory at the generalized gradient approximation level (GGA-DFT) for the molecule–surface interaction, have all overestimated measured reaction probabilities by at least an order of magnitude. Here, we perform ab initio molecular dynamics (AIMD) and AIMD with electronic friction (AIMDEF) calculations employing a density functional that includes the attractive van der Waals interaction. Our calculations model the simultaneous and possibly synergistic effects of surface temperature, surface atom motion, electron–hole pair excitation, the molecular beam conditions of the experiments, and the van der Waals interaction on the reactivity. We find that reaction probabilities computed with AIMDEF and the SRP32-vdW functional still overestimate the measured reaction probabilities, by a factor 18 for the highest incidence energy at which measurements were performed (≈2.5 eV). Even granting that the experiment could have underestimated the sticking probability by about a factor three, this still translates into a considerable overestimation of the reactivity by the current theory. Likewise, scaled transition probabilities for vibrational excitation from ν = 1, j = 1 to ν = 2 are overestimated by the AIMDEF theory, by factors 3–8 depending on the initial conditions modeled. Energy losses to the surface and translational energy losses are, however, in good agreement with experimental values. Show less
To be able to simulate activated heterogeneously catalyzed reactions on the edge and corner sites of nanoparticles, a method for calculating accurate activation barriers for the reactions is... Show moreTo be able to simulate activated heterogeneously catalyzed reactions on the edge and corner sites of nanoparticles, a method for calculating accurate activation barriers for the reactions is required. We have recently demonstrated that a semiempirical specific reaction parameter (SRP) density functional developed to describe CHD3 dissociation on a flat Ni(111) surface is transferable to describing the same reaction on a stepped Pt(211) surface. In the current work, we compare initial sticking coefficients measured using the King and Wells beam reflectivity technique and calculated from ab initio molecular dynamics trajectories using the same SRP functional for CHD3 dissociation on a kinked Pt(210) surface at a temperature of 650 K. The calculated sticking coefficients overestimate those determined experimentally, with an average energy shift between the two curves of 13.6 kJ/mol, which is over a factor of 3 times higher than the 4.2 kJ/mol limit that defines chemical accuracy. This suggests the SRP functional predicts an activation barrier that is too low for the dissociation on the least coordinated kink atom, which is the site of the lowest energy transition state and where most of the dissociation occurs in the calculations. Show less
This paper reports on the preparation and characterization of nanostructured Re and Co–Re/Al2O3/NiAl(110) surfaces designed as model catalysts for operando studies of Fischer–Tropsch synthesis.... Show moreThis paper reports on the preparation and characterization of nanostructured Re and Co–Re/Al2O3/NiAl(110) surfaces designed as model catalysts for operando studies of Fischer–Tropsch synthesis. Scanning tunneling microscopy on pure Re particles identified strong Re–Al2O3 support interaction, resulting in uniform nucleation and growth on random point defects. X-ray photoelectron spectroscopy confirmed the strong interaction through a shift in the binding energy, in addition to size-dependent final state effects. Co–Re particles were prepared by sequential deposition of the two metals, resulting in core–shell structures in which the shell was (strongly) enriched with the metal deposited second. Annealing of bimetallic particles allowed for elemental redistribution, as was concluded from the XPS data and supported by modeling. The annealing also resulted in sintering of bimetallic clusters. Interestingly, the thermal stability of the Co–Re surfaces prepared by sequential deposition of Co, followed by Re, was better than that of both pure Co and pure Re. Show less
