Dissociative Adsorption Of Water Research Articles

Atomic structure and water arrangement on K-feldspar microcline (001).

The properties of clouds, such as their reflectivity or their likelihood to precipitate, depend on whether the cloud droplets are liquid or frozen. Thus, understanding the ice nucleation mechanisms is essential for the development of reliable climate models. Most ice nucleation in the atmosphere is heterogeneous, i.e., caused by ice nucleating particles such as mineral dusts or organic aerosols. In this regard, K-feldspar minerals have attracted great interest recently as they have been identified as one of the most important ice nucleating particles under mixed-phase cloud conditions. The mechanism by which feldspar minerals facilitate ice nucleation remains, however, elusive. Here, we present atomic force microscopy (AFM) experiments on microcline (001) performed in an ultrahigh vacuum and at the solid-water interface together with density functional theory (DFT) and molecular dynamics (MD) calculations. Our ultrahigh vacuum data reveal features consistent with a hydroxyl-terminated surface. This finding suggests that water in the residual gas readily reacts with the surface. Indeed, the corresponding DFT calculations confirm a dissociative water adsorption. Three-dimensional AFM measurements performed at the mineral-water interface unravel a layered hydration structure with two features per surface unit cell. A comparison with MD calculations suggests that the structure observed in AFM corresponds to the second hydration layer rather than the first water layer. In agreement with previous computation results, no ice-like structure is seen, questioning an explanation of the ice nucleation ability by lattice match. Our results provide an atomic-scale benchmark for the clean and water-covered microcline (001) plane, which is mandatory for understanding the ice nucleation mechanism on feldspar minerals.

Theoretical insights into the effect of surface structure and anion ordering on the properties of SrTaO2N for photocatalytic water splitting

AbstractAs one of the representative perovskite‐type oxynitride photocatalysts, SrTaO2N has the ability to split water in the visible‐light region. It was found that the surface modification and interfacial design of SrTaO2N‐based materials are closely related to the photocatalytic activity, but the microscopic mechanisms of these experimental phenomena are not well understood. In this work, we have utilized density functional theory (DFT) calculations to investigate the effect of anion ordering and exposed terminations on the electronic structures, optical absorption, water adsorption and the mechanisms of water oxidation and reduction reactions of SrTaO2N. Our results indicate that cis configurations are more stable than trans configurations. The anion ordering has an important effect on the band gap and optical absorption coefficient. The terminations with exposed Ta atoms are more stable and have bigger work functions than those with exposed Sr atoms possibly due to the bonding ionicity and surface dipoles. The dissociative adsorption of water is energetically more favorable than the molecular adsorption on most surfaces. The highly active sites of hydrogen evolution reaction (HER) are the exposed nonmetal atoms. Terminations with exposed Sr and N atoms have lower overpotentials (0.70–0.77 V) of oxygen evolution reaction (OER) than others. They are comparable to the calculated results of common photocatalysts, such as Co3O4 and TiO2. This study sheds light on the relationship between the termination structure with different anion orders and the photocatalysis‐related properties of SrTaO2N at a molecular level, which provides guidance for constructing highly active photocatalytic materials.

Molecular and Dissociative Adsorption of H2O on ZrO2/YSZ Surfaces

The work involves first-principles calculations to study the mechanism of adsorption of water molecules on the surface of ZrO2 and their yttrium-stabilized structures (YSZ). Calculations of the electronic properties of ZrO2 showed that during the m-t phase transformation of ZrO2, the Fermi level first shifts by 0.125 eV towards the conduction band, and then in the t-c region goes down by 0.08 eV. In this case, the band gaps for c-ZrO2, t-ZrO2 and m-ZrO2, respectively, are 5.140 eV, 5.898 eV and 5.288 eV. Calculations to determine the surface energy showed that t-ZrO2 (101) and m-ZrO2 (111) have the most stable structure, on the basis of which it was first discovered that the surface energy is somehow inversely related to the value of the band gap, since as the band gap increases, the surface energy tends to decrease. An analysis of the mechanism of water adsorption on the surface of t-ZrO2 (101) and t-YSZ (101) showed that H2O on unstabilized t-ZrO2 (101) is adsorbed dissociatively with an energy of −1.22 eV, as well as by the method of molecular chemisorption with an energy of −0.69 eV and the formation of a hydrogen bond with a bond length of 1.01 Å. In the case of t-YSZ (101), water is molecularly adsorbed onto the surface with an energy of −1.84 eV. Dissociative adsorption of water occurs at an energy of −1.23 eV, near the yttrium atom. The obtained results complement the database of research works carried out in the field of the application of biocompatible zirconium dioxide crystals and ceramics in green energy generation, and can be used in designing humidity-to-electricity converters and in creating solid oxide fuel cells based on ZrO2.

Accurate descriptions of molecule-surface interactions for understanding CO2 capture by MgO-based sorbents in wet conditions

MgO shows promise as a CO2 sorbent material for the intermediate temperature range. Here, a hybrid computation scheme, xDH:GGA that combines the XYG3-type of doubly hybrid (xDH) and the generalized gradient approximation (GGA) functionals, is applied. It aims to provide an accurate description of molecular-surface interactions to reduce calculation uncertainties in exploring CO2 capture mechanisms for MgO-based systems. After validating the accuracy of the hybrid scheme by modeling CO adsorption on both MgO(100) and NaCl(100) surfaces against the experimental results, CO2 capture in wet conditions is examined. The results highlight the importance of competitive adsorption between CO2 and water, which undermines the significance of the conventionally identified active sites on MgO surfaces. In contrast, the intermediate Mg(OH)2 layer emerges as a more viable active phase, whose presence was experimentally observed, where the layered structure of Mg(OH)2 is found to kinetically retard water dissociative adsorption. In addition to surface areas and pore structures, our study emphasizes the pivotal role played by selective CO2 chemical adsorption in the development of effective CO2 sorbent materials.

A Detailed Comparative Analysis of the Structural Stability and Electron-Phonon Properties of ZrO2: Mechanisms of Water Adsorption on t-ZrO2 (101) and t-YSZ (101) Surfaces.

In this study, we considered the structural stability, electronic properties, and phonon dispersion of the cubic (c-ZrO2), tetragonal (t-ZrO2), and monoclinic (m-ZrO2) phases of ZrO2. We found that the monoclinic phase of zirconium dioxide is the most stable among the three phases in terms of total energy, lowest enthalpy, highest entropy, and other thermodynamic properties. The smallest negative modes were found for m-ZrO2. Our analysis of the electronic properties showed that during the m-t phase transformation of ZrO2, the Fermi level first shifts by 0.125 eV toward higher energies, and then decreases by 0.08 eV in the t-c cross-section. The band gaps for c-ZrO2, t-ZrO2, and m-ZrO2 are 5.140 eV, 5.898 eV, and 5.288 eV, respectively. Calculations based on the analysis of the influence of doping 3.23, 6.67, 10.35, and 16.15 mol. %Y2O3 onto the m-ZrO2 structure showed that the enthalpy of m-YSZ decreases linearly, which accompanies the further stabilization of monoclinic ZrO2 and an increase in its defectiveness. A doping-induced and concentration-dependent phase transition in ZrO2 under the influence of Y2O3 was discovered, due to which the position of the Fermi level changes and the energy gap decreases. It has been established that the main contribution to the formation of the conduction band is made by the p-states of electrons, not only for pure systems, but also those doped with Y2O3. The t-ZrO2 (101) and t-YSZ (101) surface models were selected as optimal surfaces for water adsorption based on a comparison of their surface energies. An analysis of the mechanism of water adsorption on the surface of t-ZrO2 (101) and t-YSZ (101) showed that H2O on unstabilized t-ZrO2 (101) is adsorbed dissociatively with an energy of -1.22 eV, as well as by the method of molecular chemisorption with an energy of -0.69 eV and the formation of a hydrogen bond with a bond length of 1.01 Å. In the case of t-YSZ (101), water is molecularly adsorbed onto the surface with an energy of -1.84 eV. Dissociative adsorption of water occurs at an energy of -1.23 eV, near the yttrium atom. The results show that ab initio approaches are able to describe the mechanism of doping-induced phase transitions in (ZrO2+Y2O3)-like systems, based on which it can be assumed that DFT calculations can also flawlessly evaluate other physical and chemical properties of YSZ, which have not yet been studied quantum chemical research. The obtained results complement the database of research works carried out in the field of the application of biocompatible zirconium dioxide crystals and ceramics in green energy generation, and can be used in designing humidity-to-electricity converters and in creating solid oxide fuel cells based on ZrO2.

Mathematical Modeling of Alkaline Direct Glycerol Fuel Cells

Mathematical modeling and computer simulation are tools of great importance for the development of fuel cells. Thus, the objective of this work is to carry out the kinetic modeling of glycerol oxidation in a DGFC (direct glycerol fuel cell), considering two different approaches: (1) realistic phenomenological models for the partial oxidation of glycerol in Pt/C, considering its adsorbed intermediates; (2) models of artificial neural networks (ANN—artificial neural networks) for oxidation mainly of PtAg/C and PtAg/MnOx/C. The models were fitted to experimental data already available for validation and determination of their parameters, both using Matlab software, v. R2018a (MathWorks, Natick, MA, USA). Results for the phenomenological models developed showed excellent fits for the polarization curve, with an RMSE (root mean squared error) value on the order of 0.352 to 0.404 mA/cm2, in addition to coverage fractions consistent with the literature for the adsorbed species. The kinetic parameters with the greatest influence on the response of the models were those associated with the consumption of glyceric acid and the formation of tartronic acid and with the dissociative adsorption of water and the formation of Pt-Oads active sites. Regarding the neural models, excellent prediction fits were obtained for all of them, with RMSE values on the order of 0.008 to 0.014 mA/cm2, indicating the possibility of representing the functional interdependence between input variables and the density cell current for cases where it would be too complex to do so via mechanistic modeling (i.e., for PtAg/C and PtAg/MnOx/C oxidation).

The Metal-Oxide Nanoparticle-Aqueous Solution Interface Studied by Liquid-Microjet Photoemission.

ConspectusThe liquid-microjet technique combined with soft X-ray photoelectron spectroscopy (PES) has become an exceptionally powerful experimental tool to investigate the electronic structure of liquid water and nonaqueous solvents and solutes, including nanoparticle (NP) suspensions, since its first implementation at the BESSY II synchrotron radiation facility 20 years ago. This Account focuses on NPs dispersed in water, offering a unique opportunity to access the solid-electrolyte interface for identifying interfacial species by their characteristic photoelectron spectral fingerprints. Generally, the applicability of PES to a solid-water interface is hampered due to the small mean free path of the photoelectrons in solution. Several approaches have been developed for the electrode-water system and will be reviewed briefly. The situation is different for the NP-water system. Our experiments imply that the transition-metal oxide (TMO) NPs used in our studies reside close enough to the solution-vacuum interface that electrons emitted from the NP-solution interface (and from the NP interior) can be detected.We were specifically exploring aqueous-phase TMO NPs that have a high potential for (photo)electrocatalytic applications, e.g., for solar fuel generation. The central question we address here is how H2O molecules interact with the respective TMO NP surface. Liquid-microjet PES experiments, performed from hematite (α-Fe2O3, iron(III) oxide) and anatase (TiO2, titanium(IV) oxide) NPs dispersed in aqueous solutions, exhibit sufficient sensitity to distinguish between free bulk-solution water molecules and those adsorbed at the NP surface. Moreover, hydroxyl species resulting from dissociative water adsorption can be identified in the photoemission spectra. An important aspect is that in the NP(aq) system the TMO surface is in contact with a true extended bulk electrolyte solution rather than with a few monolayers of water, as is the case in experiments using single-crystal samples. This has a decisive effect on the interfacial processes that can occur since NP-water interactions can be uniquely investigated as a function of pH and provides an environment allowing for unhindered proton migration. Our studies confirm that water is dissociatively adsorbed at the hematite surface and molecularly adsorbed at the TiO2 NP surface at low pH. In contrast, at near-basic pH the water interaction is dissociative at the TiO2 NP surface.The liquid-microjet measurements presented here also highlight the multiple aspects of photoemission necessary for a full characterization of TMO nanoparticle surfaces in aqueous environments. For instance, we exploit the ability to increase species-specific electron signals via resonant photoemission, so-called partial electron yield X-ray absorption (PEY-XA) spectra, and from valence photoelectron and resonant Auger-electron spectra. We also address the potential of these resonance processes and the associated ultrafast electronic relaxations for determining charge transfer or electron delocalization times, e.g., from Fe3+ located at the hematite nanoparticle interface into the aqueous-solution environment.

Characterizing Structure-Dependent TiS2/Water Interfaces Using Deep-Neural-Network-Assisted Molecular Dynamics

As a promising layered electrode material, TiS2-based capacitive deionization (CDI) devices for water desalination have attracted significant attention. However, TiS2/H2O interfacial features, potentially important for device optimization, remain unidentified. Using Deep Potential Molecular Dynamics (DPMD), we characterized distinct aqueous interfaces introduced by four TiS2 terminations expected to be present as water intercalates into TiS2, namely, Armchair, Zigzag, Zigzag-L, and Zigzag-R. First, we assessed important representative physical properties of the system to validate the deep potentials (DPs). DPMD simulations agree well with experiments and first-principles simulations, suggesting the DPs are accurate and reliable. Subsequent simulations of these TiS2/water interfaces revealed how TiS2 surface termination influences the structure of interfacial water. This effect is most evident in the first and second water layers close to the TiS2 surface, and more pronounced when spontaneous dissociative adsorption of water occurs. The extent of water dissociation on each surface was evaluated using enhanced sampling. Zigzag-L is the only interface where proton transfer from adsorbed water to TiS2 surface S atoms is thermodynamically and kinetically favored. The coexistence of surface four-fold-coordinated Ti (Ti4c) and one-fold-coordinated S (S1c) is found to be essential to making proton transfer feasible on the Zigzag-L surface. Furthermore, remaining unprotonated S1c atoms can act as good proton acceptors after water dissociation. Thus, TiS2 with Zigzag-L termination may be a surface to avoid in CDI device construction, given that pH fluctuations adversely affect performance. This work provides new understanding of TiS2/H2O interfacial features that could aid future design and optimization of TiS2-based CDI devices for water desalination.

Mechanistic Insights into the High Selectivity and Photocatalytic Activity of Brookite TiO2 toward NOX Abatement

TiO2 nanomaterials are promising photocatalysts for NOx depollution from air under sunlight irradiation. It commonly exists in three phases, i.e., anatase, rutile, and brookite. Anatase, rutile, and a mixture of them are heavily studied. Herein, we have tested the photocatalytic activity of the less studied brookite TiO2 for the NOx depollution from the air. Pure brookite and anatase/brookite mixtures have been synthesized and characterized. Interestingly, we found that brookite TiO2 photocatalyst has a comparable photocatalytic activity to that of the benchmark TiO2 P25, and more importantly, it has higher selectivity toward the conversion of NOx into nitrate ions. The selectivity of brookite TiO2 derived from the TALH precursor is 4.6- and 3.5-fold higher than that of pure anatase and TiO2 P25, respectively. Such impressive selectivity has been explained by measuring the content of physically and chemically adsorbed water, the relative density of defects, and the affinity of NO2 and water adsorption on different anatase and brookite surfaces. The EPR results indicated that brookite TiO2 exhibits a higher density of charge-trapping sites (defects) than anatase. The DFT calculation supported that these defects increase the tendency of brookite (001) surface toward the nondissociative adsorption of NO2, whereas the dissociative adsorption of water is preferred on the perfect surface. It seems that the coexistence of dual sites for the adsorption of molecular NO2 and water-dissociated molecules is crucial for the enhanced selectivity of DeNOx to nitrate ions on brookite TiO2.

Water sorption on pyrochlore – Niobium hydration and calcium susceptibility to leaching unraveled by DFT simulations

Hydration of pyrochlore is a preponderant step during its flotation well before any other surface-reagent interaction to take place. Water adsorption on low-index pyrochlore surfaces is investigated by Density Functional Theory (DFT) simulation, with a focus on the mechanisms of water interaction with surface sites and their coordination. As far as the pyrochlore (100) and (111) surfaces favor the associative physisorption of water, the dissociative chemisorption of water on the (110) surface is by far the most energetically favorable. The affinity of pyrochlore surface to water increases from −81.4 (111), −102.7 (100) to −331.6 kJ/mol (110) leading to decreasing hydrophilic surfaces: (110) ≫ (100) > (111). Water adsorption on the Nb sites located on the (100) surface is unlikely due to the full-coordination state of the exposed Nb. Moreover, the dissociative adsorption of water, driven by a lack of coordination on the (110) surface, would be at the origin of the selective (or non-congruent) dissolution of pyrochlore calcium by weakening its innate bonds. These primary results on the relationship between water and the atomic topology of pyrochlore cleavage planes will help guide the choice of aqueous chemical reagents to be used to address the challenges of this mineral's flotation.

Water adsorption on lead dioxide from abinitio molecular dynamics simulations.

The electrochemically active lead dioxide (β-PbO2) contains the hydrogen (H) species inside the bulk and on the surface. The loss of the surface H species is proposed to be one of the factors in lead-acid battery failure. In this study, water adsorption on β-PbO2 has been investigated using theoretical approaches to reveal the chemical forms of the surface H species and identify a probable cause of H loss mechanisms. For the single water-β-PbO2, density functional theory (DFT) calculations present intact water molecular adsorption on β-PbO2 (100) and dissociative water adsorption on β-PbO2 (110), (101), and (001) surfaces. The geometric distances and the number of hydrogen bonds contribute to the adsorption energy reduction of single water adsorption. For the liquid water-β-PbO2 slab models, DFT-based molecular dynamics simulations observe that the surface lead sites are fully occupied by a hydroxyl group or intact water molecule, and some of the surface oxygens are protonated at 300K. On the β-PbO2 (110) termination, dissociative water adsorption and intact molecular water adsorption occur competitively, leading to about 50% dissociation of adsorbed water molecules. On the β-PbO2 (100), (101), and (001) terminations, the water molecules adsorb preferably in the dissociative form. The surface dependence of water dissociation is explored in terms of hydrogen bonding interactions relevant to adsorbed aqueous species. It is indicated through the Wulff crystal shape that the increase in the β-PbO2 crystallite size may be one of the H loss mechanisms associated with the electrochemically inactive β-PbO2.

Photoinduced Dynamics at the Water/TiO_{2}(101) Interface.

We present a femtosecond time-resolved optical pump-soft x-ray probe photoemission study in which we follow the dynamics of charge transfer at the interface of water and anatase TiO_{2}(101). By combining our observation of transient oxygen O 1s core level peak shifts at submonolayer water coverages with Ehrenfest molecular dynamics simulations we find that ultrafast interfacial hole transfer from TiO_{2} to molecularly adsorbed water is completed within the 285fs time resolution of the experiment. This is facilitated by the formation of a new hydrogen bond between an O_{2c} site at the surface and a physisorbed water molecule. The calculations fully corroborate our experimental observations and further suggest that this process is preceded by the efficient trapping of the hole at the surface of TiO_{2} by hydroxyl species (-OH), that form following the dissociative adsorption of water. At a water coverage exceeding a monolayer, interfacial charge transfer is suppressed. Our findings are directly applicable to a wide range of photocatalytic systems in which water plays a critical role.

Coordination Inversion of the Tetrahedrally Coordinated Ru4f Surface Complex on RuO2(100) and Its Decisive Role in the Anodic Corrosion Process

The c(2 × 2) reconstruction of RuO2(100) leads to unusual and flexible surface functionality in the form of a tetrahedrally coordinated Ru4f surface complex with distinct chemical properties that are important for the anodic activity and stability in water electrolysis. We employ first-principles methods based on density functional theory calculations to elucidate the hybridization of this Ru4f surface species and its rich coordination chemistry. Under oxygen evolution reaction (OER) conditions, the consecutive breaking of structural Ru4f–O back bonds is shown to proceed via the back side attack of Ru4f (akin to the Walden inversion) by dissociative water adsorption and the release of two proton/electron pairs. This inversion step of the coordination environment of a surface transition metal cation is considered to be the key step in the anodic dissolution process. Oxygen evolution over Ru4f on RuO2(100)–c(2 × 2) competes with its dissolution. From ab initio thermodynamics, the inherent OER activity over Ru4f is shown to be lower than that of Ru surface sites on the unreconstructed RuO2(100), while the dissolution propensity of the Ru4f surface complex is higher. This finding calls into question the frequently stated hypothesis that higher activity is correlated with a lower stability of the active center.

Interplay between Facets and Defects during the Dissociative and Molecular Adsorption of Water on Metal Oxide Surfaces

Surface terminations and defects play a central role in determining how water interacts with metal oxides, thereby setting important properties of the interface that govern reactivity such as the type and distribution of hydroxyl groups. However, the interconnections between facets and defects remain poorly understood. This limits the usefulness of conventional notions such as that hydroxylation is controlled by metal cation exposure at the surface. Here, using hematite (α-Fe2O3) as a model system, we show how oxygen vacancies overwhelm surface cation-dependent hydroxylation behavior. Synchrotron-based ambient-pressure X-ray photoelectron spectroscopy was used to monitor the adsorption of molecular water and its dissociation to form hydroxyl groups in situ on (001), (012), or (104) facet-engineered hematite nanoparticles. Supported by density functional theory calculations of the respective surface energies and oxygen vacancy formation energies, the findings show how oxygen vacancies are more prone to form on higher energy facets and induce surface hydroxylation at extremely low relative humidity values of 5 × 10-5%. When these vacancies are eliminated, the extent of surface hydroxylation across the facets is as expected from the areal density of exposed iron cations at the surface. These findings help answer fundamental questions about the nature of reducible metal oxide-water interfaces in natural and technological settings and lay the groundwork for rational design of improved oxide-based catalysts.

Capturing CO2 by ceria and ceria-zirconia nanomaterials of different origin.

Ceria and ceria-zirconia nanomaterials of different origin were studied in order to elucidate the role of their structural and textural characteristics in controlling the performance towards CO2 capture. Two commercial cerias and two home-prepared samples, CeO2 and CeO2-ZrO2 (75% CeO2) mixed oxide, were investigated. The samples were characterized by a number of analytical techniques including XRD, TEM, N2-adsorption, XPS, H2-TPR, Raman and FTIR spectroscopy. Static and dynamic CO2 adsorption experiments were applied to assess the CO2 capture performance. The type of surface species formed and their thermal stability were evaluated by in situ FTIR spectroscopy and CO2-TPD analysis. The two commercial ceria samples possessed similar structural and textural characteristics, formed the same types of carbonate-like surface species upon CO2 adsorption and, consequently, demonstrated almost identical CO2 capture performance under both static and dynamic conditions. The thermal stability of the adsorbed species increased in the order bidentate (B) carbonates, hydrogen carbonates (HC) and tridentate carbonates (T-III, T-II, T-I). Reduction of CeO2 increased the relative amount of the most strongly bonded T-I tridentate carbonates. Preadsorbed water led to hydroxylation and enhanced formation of hydrogen carbonates. Although the synthesized CeO2 sample had a higher surface area (by 30%) it showed a disadvantageous long mass transfer zone in the CO2-adsorption breakthrough curves. Because of its complex pore structure, this sample probably experiences severe intraparticle CO2 diffusion resistance. Having the same surface area as the synthesized CeO2, the mixed CeO2-ZrO2 oxide exhibited the highest CO2 capture capacity of 136 μmol g-1 under dynamic conditions. This was related to the highest concentration of CO2 adsorption sites (including defects) on this sample. The CeO2-ZrO2 system showed the lowest sensitivity to the presence of water vapor in the gas stream due to the lack of dissociative water adsorption on this material.

Reaction Kinetics-Based Modeling and Parameter Sensitivity Analysis of Direct Ethanol Fuel Cells

Ethanol is considered an alternative fuel to power fuel cells, especially due to its ease of transport and storage and renewable production on a large scale. However, its use in direct ethanol fuel cells (DEFC) is still limited by incomplete electro-oxidation and slow reaction kinetics. Modeling approaches have focused on investigating different reaction mechanisms, but so far, no formal analysis of model parameter sensitivity has been conducted. This work modeled and identified sensitive parameters for different types of Pt–Sn catalysts previously prepared by our research group that displayed good performance in the 5–15 mW/cm2 range (relative to a performance of 12 mW/cm2 achieved by a commercial ETEK catalyst). Analyses to study the effect of these parameters on coverage fraction distribution, reaction rates and possible correlations were also performed. The model was developed based on Butler–Volmer kinetics and on a reaction mechanism previously reported in the literature. Statistical developments were considered to compute parameter uncertainties for a non-linear system with non-linear restrictions. The model achieved very good fits to experimental data, with low RMSE values between 0.22 × 10−4 and 4.2 × 10−4 A/cm2, while also showing surface coverage fraction distributions in agreement with other experiment-based works from the literature. All catalysts taken into account, the most sensitive parameters were the reaction rate constants associated with the formation of adsorbed CH3CO, and the direct and reverse water dissociative adsorption reactions, respectively. Additional analyses suggested that there is not much correlation between the parameters. The results from this work could contribute to the state-of-the-art DEFC models by providing insights into which variables may be assumed constant or which ones have the greatest impact on the model output, thus helping to reduce the model size and computational time for future broader DEFC models.

Dissociative Adsorption of Water on CaMn4O5 Cationic Clusters.

Water splitting is catalyzed by photosystem II, which comprises an inorganic core (CaMn4O5) and protein ligands. To understand the evolution of CaMn4O5 after attaching water molecules, an isolated CaMn4O5+ cluster was investigated using vibrational spectroscopy and density functional theory calculations. Computational findings suggest that when a water molecule adsorbs on the Ca atom through the O atom of water, one of the OH bonds forms a hydrogen bond with a μ-oxo bridge, which dissociates into two OH groups. This is consistent with the fact that no isomers with molecularly adsorbed water were experimentally observed.

Dynamics of Water Dissociative Adsorption on TiO2 Anatase (101) at Monolayer Coverage and Below

Dynamics of Water Dissociative Adsorption on TiO₂ Anatase (101) at Monolayer Coverage and Below

Chemical-Reaction-Induced deformation of Body-Centered cubic iron in supercritical water leading to high risk of cleavage Fracture: A reactive Molecular dynamics study

To improve the reliability of BCC iron-based steels in supercritical water, it is crucial to understand the atomic-scale deterioration mechanisms under stress coupled with chemical reactions at the iron/water interface. Molecular dynamics simulations with the reactive force field were employed to examine the atomic-scale deterioration mechanisms of BCC-iron and the role of chemical reactions with supercritical water. The simulation results revealed a lower yield stress and strain for BCC-iron in supercritical water than in vacuum. Yielding of the BCC-iron in both the vacuum and supercritical water occurred through the generation of partial dislocations at the surface. The deterioration of iron in supercritical water was found to originate from chemical reactions between the iron surface and water molecules; specifically, the formation of Fe–OH bonds on the iron surface due to the dissociative adsorption of water induces displacement of the surface iron atoms, accelerating the generation of partial dislocations.

Origin of Surface Reduction upon Water Adsorption on Oriented NiO Thin Films and Its Relation to Electrochemical Activity

The interaction of water with oriented NiO films is studied by using a combination of photoelectron spectroscopy with in situ sample preparation and electrochemical measurements in the stability window of water. In contrast to NiO(100), room temperature water exposure induces a downward band bending on the (110)- and (111)-oriented films, indicating a more positive surface charge. The surface charge is assigned to a dissociative adsorption of water accompanied by a removal of oxygen, which corresponds to a preferential adsorption of protons. Photoelectron spectroscopy suggests that the nonstoichiometric adsorption is related to the presence of adsorbed oxygen species prior to water exposure. For the NiO(110) surface, the stability of adsorbed bridging oxygen dimers is confirmed by density functional theory calculations. The preferential adsorption of protons, which requires interaction of two water molecules with the oxygen dimers, explains that water acts as an electron donor on many oxide surfaces. The different adsorption behavior is consistent with a lower electrochemical activity of the (110)- and (111)-oriented surfaces toward hydrogen adsorption due to an effective reduction of Lewis base sites.