Dissociation Of H2O Molecules Research Articles

Adsorption, dissociation and diffusion behavior of H2O on the PuO2(111) surface from DFT + U-D3: the role of hydrogen bonding.

The interaction between H2O and plutonium oxide is an essential aspect of researching plutonium corrosion. We systematically studied the adsorption, dissociation, and diffusion of H2O molecules on the PuO2(111) surface with the DFT + U-D3 scheme. We find that the top of the Pu atom is the most stable adsorption site for H2O molecules on the PuO2(111) surface. When multiple H2O molecules are adsorbed, hydrogen bonding between molecules can increase the average adsorption energy. H2O molecules will dissociate into H atoms and O-H groups under certain conditions. We have paid special attention to the role of hydrogen bonds between H2O molecules. When the coverage of H2O molecules is low, hydrogen bonds can significantly promote the adsorption and dissociation of H2O molecules. And H2O tends to exist on the surface of plutonium oxide in dissociated and molecular mixed states. The H atoms produced by the dissociation of H2O molecules are not easily diffused, which may be related to the hydrogen bonding between O-H groups. This work has important theoretical significance for deepening the understanding of the corrosion mechanism of plutonium.

Theoretical investigation of adsorption and dissociation behaviors of H2O molecules on the surfaces of Transition-metal doped γ-graphyne

The characteristics of adsorption and dissociation of H2O molecules on the surfaces of γ-graphyne doped with transition metal atoms (TM-GY) were explored by the first-principles calculation. Transition metal single-atom could be confined firmly at the center of acetylene ring, and it is difficult to migrate to the adjacent center of benzene ring because of the very high diffusion energy barrier. The positions of doped atoms on the TM-GY surfaces could be used as active sites, and H2O molecules on the Sc/Ti/V/Cr/Mn/Fe-GY surfaces all are a typical chemical adsorption. All possible reaction pathways for H2O molecules dissociation on TM-GY surfaces were evaluated. Adsorbed H2O molecules on TM-GY surfaces are more likely to be dissociated into OH and H along the path1 with a lower reaction energy barrier (less than 1.248 eV). Especially, for V/Cr-GY surface, the dissociation energy barrier is as low as 0.317/0.312 eV, this process is exothermic along with a large amount of energy releasing of about 1.524/1.709 eV. Therefore, stable doped substrate together with the lower dissociation barrier promises that TM-GY may serve as a high efficiency catalyst for H2O dissociation.

An AIMD Study of Water on α-Uranium Surface

The ab-into molecular dynamics method (AIMD) was used to study the adsorption and dissociation of H2O molecules on the surface of α-U (110). The adsorption and dissociation of H2O molecules in different positions and different initial configurations were compared and analysed. For the case of dissociative adsorption, the radial distribution function (RDF) is analysed, and the bonding of U-O bond and U-H bond is studied.

In Situ Exsolution of Ba3(VO4)2 Nanoparticles on a V-Doped BaCoO3-δ Perovskite Oxide with Enhanced Activity for Electrocatalytic Hydrogen Evolution.

The successful preparation of a perovskite-based heterostructure is important for broadening the applications of perovskites in the field of electrocatalysis, especially in a hydrogen evolution reaction (HER). Nevertheless, the limited active sites of perovskites severely hindered the HER properties. Herein, an in situ exsolution method was used to construct a nanocomposite based on V-doped BaCoO3-δ decorated with Ba3(VO4)2 (BVCO19) for alkaline HER. The exsolved Ba3(VO4)2 can induce more Co4+ ions on BaCoO3-δ, which serves as active sites for the release of H2. Meanwhile, by regulating the valency of V and Co species, the catalyst can reach a charge balance by generating more oxygen vacancies, which greatly facilitates the adsorption and dissociation of H2O molecules. The synergistic effect between the oxygen vacancies and high-valence Co4+ leads to an enhanced HER performance of BVCO19. The as-obtained catalyst delivers a low overpotential of 194 mV at 10 mA cm-2 as well as impressive stability for 100 h in alkaline media, which outperforms pristine BaCoO3-δ and most of the nonprecious-based perovskite oxides. This work provides new insights into the preparation of perovskite-based heterostructure for boosting HER.

9.2: Mechanism of H2O‐induced Instability of Self‐Aligned Top‐Gate Amorphous InGaZnO TFTs

The influence of H2O on self‐aligned top‐gate (SATG) a‐ InGaZnO thin‐film transistor (TFT) was systematically investigated by performing the high‐temperature high‐humidity (HTHH) test (50 °C, 80% RH). Though initial electrical characteristics were well maintained, the stability under positive bias stress (PBS) was considerably deteriorated, including an abnormal negative Vth shift, degraded SS, and increased off current. The mechanism of H2O‐induced instability was proposed to be the dissociation of H2O molecules and the migration of hydrogen (H) atoms into the a‐IGZO channel. The hydrogen diffusion and doping effects in SATG a‐IGZO TFTs were further proved by SiNx‐passivated TFTs with regulated H content in SiNx layers.

IR Spectroscopic Degradation Study of Thin Organometal Halide Perovskite Films.

The advantages of IR spectroscopy include relatively fast analysis and sensitivity, which facilitate its wide application in the pharmaceutical, chemical and polymer sectors. Thus, IR spectroscopy provides an excellent opportunity to monitor the degradation and concomitant evolution of the molecular structure within a perovskite layer. As is well-known, one of the main limitations preventing the industrialization of perovskite solar cells is the relatively low resistance to various degradation factors. The aim of this work was to study the degradation of the surface of a perovskite thin film CH3NH3PbI3-xClx caused by atmosphere and light. To study the surface of CH3NH3PbI3-xClx, a scanning electron microscope, infrared (IR) spectroscopy and optical absorption were used. It is shown that the degradation of the functional layer of perovskite proceeds differently depending on the acting factor present in the surrounding atmosphere, whilst the chemical bonds are maintained within the perovskite crystal structure under nitrogen. However, when exposed to an ambient atmosphere, an expansion of the NH3+ band is observed, which is accompanied by a shift in the N-H stretching mode toward higher frequencies; this can be explained by the degradation of the perovskite surface due to hydration. This paper shows that the dissociation of H2O molecules under the influence of sunlight can adversely affect the efficiency and stability of the absorbing layer. This work presents an approach to the study of perovskite structural stability with the aim of developing alternative concepts to the fabrication of stable and sustainable perovskite solar cells.

Re-examining the role of subsurface oxygen vacancies in the dissociation of H2O molecules on anatase TiO2

Titanium (IV) oxide is a reference photocatalytic material for a number of chemical processes of interest in the energy transition, including the reduction of water into hydrogen gas. Density functional theory calculations have previously revealed that the decomposition into hydrogen and hydroxyl ions could be catalyzed by a subsurface oxygen vacancy (VO). However, these theoretical investigations have been carried out with models considering only isolated water molecules. We investigate the role of the subsurface VO at different levels of coverage up to full monolayer (ML) coverage. We observe that migration of the vacancy concomitantly to water decomposition is mandatory to obtain an exothermic pathway. Furthermore, the migration of the VO only occurs in the presence of an under-coordinated surface oxygen atom. As coverage and decomposition increase, surface oxygen atoms are saturated which inhibit further migration of the subsurface VO; hence the VO shows no catalytic effect on the splitting of water into hydrogen and hydroxyl ions at full water coverage.

Unravelling the synergy in platinum-nickel bimetal catalysts designed by atomic layer deposition for efficient hydrolytic dehydrogenation of ammonia borane

Bimetal catalysis has been one of the major categories in heterogeneous catalysis field, and the efficient and durable catalysts can be well achieved by the bimetal synergy. Herein we report a remarkable achievement of both dehydrogenation activity of ammonia borane and durability by controllably engineering Pt-Ni interfacial sites via the Pt and the following NiO atomic layer deposition strategy, which can also realize the controllable synthesis of other Pt-M (M=Co, Cu, Fe and Zn) bimetal catalysts. Multiple characterization techniques, kinetic-isotopic analyses and density functional theory calculations were employed to unravel the nature of the Pt-Ni synergy. Experimental and theoretical results reveal that the decoration of nickel species on the Pt nanoparticles constructing the targeted Pt-Ni interfacial sites could lower the reaction activation energy, promote the adsorption, activation and dissociation of H2O molecules, and facilitate the desorption of hydrogen atoms, resulting in the doubly enhanced activity with a turnover frequency value of 751.6 molH2 molPt-1 min-1 and the remarkably improved durability. Our work offers an alternative and general strategy for the rational design of bimetal catalysts with specific interfacial structure and provides fundamental guidance for in-depth understanding of the bimetal synergy.

A hierarchical CoMoO4@CoFe-LDH heterostructure as a highly effective catalyst to boost electrocatalytic water oxidation.

The oxygen evolution reaction (OER) has become the main barrier to electrochemical water splitting, owing to sluggish kinetics. To accelerate the OER process, a nature-abundant non-noble metal catalyst with outstanding catalytic activity is required. Here, a hierarchical CoMoO4@CoFe layered double hydroxide (LDH, denoted by CoMoO4@CoFe/NF) heterostructure supported on three-dimensional (3D) nickel foam (NF) was synthesised by electrodepositing CoFe-LDH nanosheets on the surface of CoMoO4 nanoplates to boost the electrocatalytic performance for the OER. The coupling between CoMoO4 and CoFe-LDH established abundant boundaries, which exposed abundant active sites. Furthermore, the electron transfer in the hierarchical heterostructure effectively promoted the adsorption and dissociation of H2O molecules. Harnessing the aforementioned synergistic effect significantly improved the intrinsic reaction kinetics of the OER. At 10 mA cm-2, CoMoO4@CoFe/NF reached a small overpotential of 245 mV at room temperature and exhibited outstanding stability for at least 47 h. Furthermore, the Tafel slope for CoMoO4@CoFe/NF was only 46 mV dec-1. This study provides new ideas for the rational design of hierarchical structures and the use of interface interactions.

Hexagonal Phase Ni3Fe Nanosheets toward High‐Performance Water Splitting by a Room‐Temperature Methane Plasma Method

AbstractIn addition to tuning the size and shape, exploring highly efficient and cost‐effective catalysts with active metastable phase represents an alternative strategy to improve electrocatalytic water splitting performance. However, it still remains a big challenge to synthesize unconventional crystal structures under mild conditions. Herein, a facile CH4 plasma assisted strategy to synthesize hexagonal close‐packed (hcp) Ni3Fe/C porous nanosheets by in situ topology reduction of Ni3Fe‐LDH nanosheets is successfully developed. Compared with its face‐centered cubic phase counterpart (fcc‐Ni3Fe/C), the resulting hcp‐Ni3Fe/C catalyst exhibits much enhanced activity with overpotentials of 70 and 201 mV at a current density of 10 mA cm−2 for the hydrogen evolution reaction and oxygen evolution reaction, respectively. Moreover, a small cell voltage of 1.54 V is realized to drive overall water splitting. Theoretical calculations further reveal that hcp‐Ni3Fe allows energetically favorable adsorption and dissociation of H2O molecules. This work presents a new strategy for designing advanced metastable phase electrocatalysts with high performance for energy and environmentally relevant reactions.

Construction of N-doped carbon frames anchored with Co single atoms and Co nanoparticles as robust electrocatalyst for hydrogen evolution in the entire pH range

The development of low-cost, efficient, and high atomic economy electrocatalysts for hydrogen evolution reaction (HER) in the entire pH range for sustainable hydrogen production is of great importance but still challenging. Herein, we synthesize a highly dispersed N-doped carbon frames (NCFs) anchored with Co single atoms (SAs) and Co nanoparticles (NPs) catalyst by a doping-adsorption-pyrolysis strategy for electrocatalytic hydrogen evolution. The Co SAs-Co NPs/NCFs catalyst exhibits an excellent HER activity with small overpotential, low Tafel slope, high turnover frequency as well as remarkable stability. It also exhibits a superior HER performance in the entire pH range. Combining with experimental and theoretical calculation, we find that Co SAs with Co-N3 coordination structure and Co NPs have a strong interaction for promoting synergistic HER electrocatalytic process. The H2O molecule is easily activated and dissociated on Co NPs, while the generated H* is easily adsorbed on Co SAs for HER, which makes the Co SAs-Co NPs/NCFs catalyst exhibit more suitable H adsorption strength and more conducive to the activation and dissociation of H2O molecules. This work not only proposes a novel idea for constructing coupling catalyst with atomic-level precision, but also provides strong reference for the development of high-efficiency HER electrocatalysts for practical application.

Adsorption and dissociation behavior of H2O on PuH2 (1 1 0) surface: A density functional theory study

The reaction between water and plutonium hydride plays a significant role in the oxidation and corrosion rate of plutonium materials. The adsorption and dissociation of water molecule on PuH2 (110) surface have been studied by first-principles GGA + U method. To search the more favorable adsorption sites and adsorption types of H2O in terms of energy, the adsorption energies of H2O on different active sites were compared. The results reveal that the adsorption of H2O molecule on the surface of PuH2 (110) basically presents chemical adsorption, while the adsorption direction of H2O molecule parallel to the PuH2 (110) surface appears to be preferentially adsorbed on the top of Pu atom. We analyze the vibrational frequencies of H2O molecule adsorbed on the surface. It is found that there is a red shift phenomenon under the action of surface atoms. Two possible dissociation pathways of H2O molecule on PuH2 (110) surface were studied by the climbing-image nudged elastic band (CI-NEB) method. The calculation result shows that the more favorable dissociation energy barrier is about 0.406 eV. This indicates that the dissociation of H2O molecule on the surface of PuH2 (110) is favorable, even at room temperature.

The roles of Cl− and OH− in the dissociation of H2O molecules on an Al surface: A first-principles calculation

Previous work has confirmed that O2 can promote the dissociation of H2O, but the effect of OH− on the dissociation of H2O is not clear, and the synergistic effect of Cl− in the dissociation process is also worthy of study. In this work, we have systematically studied the roles of Cl− and OH− in the process of H2O dissociation on an Al surface through first-principles calculations. Several typical H2O and OH− co-adsorption models have been designed, and the conditions of OH−-induced H2O dissociation are discussed. By comparing models without Cl− and with pre-adsorbed Cl−, the dissociation mechanism of H2O molecules can be well explained in terms of the ratio of the reaction energy to the binding energy of the adsorbate. Based on electronic structure analysis, we surmise that Cl− plays a catalytic role in H2O dissociation on an Al surface, even though it does not directly participate in the dissociation reaction.

The role of S and Mo doping on the dissociation of water molecule on FeOCl surface: Experimental and theoretical analysis

FeOCl is widely used in cathode of lithium ion battery, matrix material and reaction catalyst. In which, the interactive behavior of H2O on FeOCl surface is closely related with the property of FeOCl materials. In this study, the influences of S and Mo doping on H2O molecule adsorption and dissociation on FeOCl (010) were explored by DFT calculations and experiments. Both calculations and experimental proved S and Mo doping promote the adsorption and dissociation of H2O molecule on FeOCl (010) surface with different process mechanisms. The surface electronegativity decreases slightly due to S doping, which reduces the repulsion to H2O molecule and lower the adsorption energy compared with clean surface. While, after forming stable adsorption structure, S doping promotes the dissociation of H2O by changing the electrons distribution in H2O and competing the shared electrons to weak the O–H bond strength. In contrast, Mo doping enhances the electropositivity of the surface, which is more conducive to the molecular adsorption reaction and more exothermic via coulombic attraction. For dissociative adsorption, the strength of O-H bond is enhanced, and the dissociation process is inhibited by Mo doping due to the electrons polarization in H2O molecule. Furthermore, S and Mo atoms are proved to be incorporated into the FeOCl lattice which enhance of H2O dissociation on doped FeOCl nanosheets surface. This study presents a microscopic insight for effects of S and Mo doped FeOCl surface on H2O molecule behaviors, while provides a theoretical basis for further research of the FeOCl surface water.

Theoretical study on water behavior on the copper surfaces.

We calculated the adsorption of H, O, OH, and H2O and the dissociation of H2O molecule on the Cu(111), Cu(100), and Cu(110) surfaces using density functional theory. H, O, and OH tend to adsorb stably at the highly coordinated dh and h sites on the Cu(111) and Cu(100) surfaces. OH and H tend to adsorb on sb site on the Cu(110) surface. The more charge transfer of the adsorbed substance, the more stable the adsorption. The dissociation product is O+H on the Cu(111) surface, while the dissociation product is OH+H on the Cu(100) and Cu(110) surfaces. Due to the different geometric structures of initial state (IS), transition state (TS), and final state (FS) in the dissociation reaction, the dissociation of water on the copper surface does not establish a linear Brønsted-Evans-Polanyi (BEP) relationship. These results provide theoretical support for the understanding of the interaction between water and metals as well as the behavior of water molecules.

Adsorption of Water Molecule on Calcium Fluoride and Magnesium Fluoride Surfaces: A Combined Theoretical and Experimental Study

The adsorption and dissociation of H2O molecule on various surfaces of MgF2 and CaF2 have been investigated theoretically by using a dispersion-corrected density functional theory based method. The...

Strain Effect on the Dissociation of Water Molecules on Silicene: Density Functional Theory Study

Dissociative adsorption of water molecules on silicene is an efficient way to open the band gap of silicene for electronic applications. However, the dissociation of H2O molecules on silicene is di...

Adsorption and dissociation of H2O molecule on the doped monolayer MoS2 with B/Si

Adsorption and dissociation of H2O on monolayer MoS2 surface doped with B/Si explored by first principle calculations coupled with climb image nudged elastic band method. The impurity B/Si atoms are more likely to occupy sulfur atom lattice positions with lower formation energies, which results in the breaking of surface chemically inertness of the MoS2 (001) plane. Free H2O molecules can be adsorbed on doped surfaces with lower adsorption energies, and form chemical bonds between oxygen and impurity atoms. Adsorbed H2O can be separated into OH radical and hydrogen adatom with a lower dissociation energy barrier on these doped systems (including impurity B/Si single doped, B and Si co-doped). Furthermore, the adsorbed OH radical can be further dissociated into oxygen and hydrogen adatoms on the surface of B and Si co-doped MoS2. Our theoretical study suggests that substrate of monolayer MoS2 doped with impurity B, Si may be a potential alternative choice for hydrogen evolution reaction.

Water dissociative adsorption on the precovered Fe (100) surface from DFT computation

The H2O adsorption and dissociation on two kinds of the precovered Fe surface were studied by density functional theory. On the surface-1, the water molecules prefer to adsorb on the bridge and hollow sites than top sites, but there are no obvious preferred adsorption sites on the surface-2. The impurity energy difference and adsorption energy of the adsorbates are not sensitive to the adsorption orientation and height relative to the surface. Moreover, the Hirshfeld charge and the electronic density of state were analyzed. The rotation and dissociation of H2O molecules occur on the two kinds of precovered surfaces. Some H2O molecules are dissociated into OH and H groups. The energy barriers are from 0.4 to 1.0 eV which are consistent with the experimental data. H2O molecule can be dissociated more easily at the Ha site on boron-precovered surface-1 than those on the phosphorus-precovered surface-1 and boron-precovered surface-2 due to the lower reaction barrier.

DFT study of the interactions of H2O, O2 and H2O + O2 with TiO2 (1 0 1) surface

The interactions of H2O, O2 and H2O+O2 with TiO2 (101) surface was studied using density functional theory (DFT). The adsorption energy of H2O+O2 on the TiO2 surface is the largest, followed by O2, and H2O. H2O molecule and O2 molecule adsorbed respectively on TiO2 surface are not dissociated, while the coadsorption of H2O and O2 results in the dissociation of H2O molecule and O2 molecule. H2O and O2 molecules not only interact respectively with TiO2 surface, but also interact with each other when H2O and O2 molecules adsorb simultaneously on the TiO2 surface. The interaction of H2O+O2 with TiO2 surface is more complex than those of single H2O or O2, including the formations of five new bonds and the cleavages of four bonds, which suggests the strong interaction between H2O+O2 and TiO2 surface. Two hydrogen-oxygen bonds of H2O molecule are all broken, and two hydrogen atoms interact with two oxygen atoms of TiO2 surface, respectively, while oxygen atom of H2O interacts simultaneously with a titanium atom of TiO2 surface and an oxygen atom of O2 molecule. Another oxygen atom of O2 molecule is bonded to another titanium atom of TiO2 surface.