Orientational Water Bonding on Pt(111): Beyond the Frontier Orbital Principle

For decades, our understanding of water-metal bonding has been dominated by the frontier orbital principle in which globally stable water-metal interactions are ruled by HOMO interacting with metal surfaces. Using density functional theory calculations, herein, we have revealed that the frontier orbital principle cannot be applied to metastable water bonding on Pt(111), where the decisive role of HOMO is replaced by HOMO-1 in terms of the greatest orbital shifts and depopulations as the two different bonding indicators. Unlike the stable water configuration in which both HOMO-1 and HOMO prefer to overlap with metal states through σ-like orbital interactions, metastable configurations exhibit delicate competition or balance between σ-like and π-like orbital interactions exerted by HOMO-1 and HOMO, respectively. These findings have significantly deepened our understanding of orbital roles in water-metal bonding interactions and bridged the gap between theoretical understanding of electrified waters at electrochemical interfaces and water science on metal surfaces.

A Review of Trends in Corrosion-Resistant Structural Steels Research-From Theoretical Simulation to Data-Driven Directions

This paper provides a review of models commonly used over the years in the study of microscopic models of material corrosion mechanisms, data mining methods and the corrosion-resistant performance control of structural steels. The virtual process of material corrosion is combined with experimental data to reflect the microscopic mechanism of material corrosion from a nano-scale to macro-scale, respectively. Data mining methods focus on predicting and modeling the corrosion rate and corrosion life of materials. Data-driven control of the corrosion resistance of structural steels is achieved through micro-alloying and organization structure control technology. Corrosion modeling has been used to assess the effects of alloying elements, grain size and organization purity on corrosion resistance, and to determine the contents of alloying elements.

Multifunctional Amphiphobic Coating toward Ultralow Interfacial Adhesion of Hydrates

Hydrate adhesion is a challenging issue in some practical applications. However, most current anti-hydrate coatings fail to maintain their properties when subject to crude oil and corrosive contaminants. In addition, the effect of surface properties on the nucleation of hydrates is still unexplored from a microscopic perspective. In this study, a multifunctional amphiphobic PF/ZSM-5 coating consisting of 1H, 1H, 2H, 2H-perfluorooctyltriethoxysilane modified ZSM-5 zeolite (F/ZSM-5) and adhesive polyethersulfone was fabricated by the spraying method. The interfacial nucleation and adhesion of hydrates on substrates were studied from a microscopic perspective. The coating exhibited excellent repellencies to various liquids, including water, edible oil, liquid paraffin, vacuum pump oil, n-hexadecane, and crude oil. The tetrabutylammonium bromide (TBAB) hydrate is readily nucleated on the bare Cu surface. In contrast, the coated substrate effectively inhibited the hydrate nucleation on the surface and even reduced the adhesion force to 0 mN/m. Furthermore, this coating was fouling- and corrosion-resistant and can maintain an ultralow hydrate adhesion force even after immersion in crude oil or TBAB solution for 20 and 300 d, respectively. The durable anti-hydrate performance of the coating was attributed mainly to the unique architecture and excellent amphiphobic properties enabling stable air cushions between the solid-liquid interface.

Crystal Facet Structure Dependence and Promising Pd-Based Catalytic Materials for Resistance toward Deactivation and Catalytic Performance in Direct Oxidative Esterification

Designing an effective Pd-based catalytic material with higher stability and catalytic performance for direct oxidative esterification is a great challenge. In this work, a systematic study on the activation mechanism of H₂O on the different crystal facets of monometallic Pd, bimetallic Pd-Pb(Bi), and trimetallic Pd-Pb-Bi catalysts was first performed, which showed that the (111) crystal facet of Pd-Pb-Bi had stronger stability of resistance toward deactivation induced by H₂O. Further, a detailed direct oxidative esterification mechanism on the screened crystal facet was investigated, where Pd-Pb-Bi catalytic materials showed higher stability and intrinsic catalytic performance for direct oxidation esterification, which was attributed to a dimer Pd-active unit and the synergistic effect of Pb and Bi compared to that of Pd-Pb(Bi) and Pd and also applied to other aldehydes with electron-donating groups producing corresponding esters. Meanwhile, the essential relationship between structures of Pd-based catalytic materials and catalytic performance for direct oxidation esterification was obtained. This work opens up a new simultaneous path for improving the stability of resistance toward deactivation and catalytic performance for direct oxidative esterification of Pd-based catalytic materials, which can be realized by regulating the surface-active unit with dimer Pd adsorbed more O-preadsorbed using Pb and Bi promoters.

Rapid Water Diffusion at Cryogenic Temperatures through an Inchworm-like Mechanism

Water diffusion across the surfaces of materials is of importance to disparate processes such as water purification, ice formation, and more. Despite reports of rapid water diffusion on surfaces the molecular level, details of such processes remain unclear. Here, with scanning tunneling microscopy, we observe structural rearrangements and diffusion of water trimers at unexpectedly low temperatures (<10 K) on a copper surface, temperatures at which water monomers or other clusters do not diffuse. Density functional theory calculations reveal a facile trimer diffusion process involving transformations between elongated and almost cyclic conformers in an inchworm-like manner. These subtle intermolecular reorientations maintain an optimal balance of hydrogen-bonding and water-surface interactions throughout the process. This work shows that the diffusion of hydrogen-bonded clusters can occur at exceedingly low temperatures without the need for hydrogen bond breakage or exchange; findings that will influence Ostwald ripening of ice nanoclusters and hydrogen bonded clusters in general.

Origins of fast diffusion of water dimers on surfaces

The diffusion of water molecules and clusters across the surfaces of materials is important to a wide range of processes. Interestingly, experiments have shown that on certain substrates, water dimers can diffuse more rapidly than water monomers. Whilst explanations for anomalously fast diffusion have been presented for specific systems, the general underlying physical principles are not yet established. We investigate this through a systematic ab initio study of water monomer and dimer diffusion on a range of surfaces. Calculations reveal different mechanisms for fast water dimer diffusion, which is found to be more widespread than previously anticipated. The key factors affecting diffusion are the balance of water-water versus water-surface bonding and the ease with which hydrogen-bond exchange can occur (either through a classical over-the-barrier process or through quantum-mechanical tunnelling). We anticipate that the insights gained will be useful for understanding future experiments on the diffusion and clustering of hydrogen-bonded adsorbates.

The experimental observation that water dimers diffuse more rapidly than monomers across materials’ surfaces is yet to be clarified. Here the authors show by ab initio calculations classical and quantum mechanical mechanisms for faster water dimer diffusion on a broad range of metal and non-metal surfaces.

Bias-dependent local structure of water molecules at a metallic interface

Understanding the local structure of water at the interfaces of metallic electrodes is a key issue in aqueous-based electrochemistry. Nevertheless a realistic simulation of such a setup is challenging, particularly when the electrodes are maintained at different potentials. To correctly compute the effect of an external bias potential applied to truly semi-infinite surfaces, we combine Density Functional Theory (DFT) and Non-Equilibrium Green's Function (NEGF) methods. This framework allows for the out-of-equilibrium calculation of forces and dynamics, and directly correlates to the chemical potential of the electrodes, which is introduced experimentally. In this work, we apply this methodology to study the electronic properties and atomic forces of a water molecule at the interface of a gold surface. We find that the water molecule tends to align its dipole moment with the electric field, and it is either repelled or attracted to the metal depending on the sign and magnitude of the applied bias, in an asymmetric fashion.

Water aggregation and dissociation on the ZnO(101̄0) surface

DFT studies reveal a hierarchy of water aggregates including dimers, quasi-1D ladders and a novel honeycomb-double monolayer.

Capturing Solvation Effects at a Liquid/Nanoparticle Interface by Ab Initio Molecular Dynamics: Pt201 Immersed in Water

Solvation can substantially modify the adsorption properties of heterogeneous catalysts. Although essential for achieving realistic theoretical models, assessing such solvent effects over nanoparticles is challenging from a computational standpoint due to the complexity of those liquid/metal interfaces. This effect is investigated by ab initio molecular dynamics simulations at 350 K of a large platinum nanoparticle immersed in liquid water. The first solvation layer contains twice as much physisorbed water molecules above the terraces, than chemisorbed ones located only at edges and corners. The solvent stabilizes the binding energy of chemisorbates: 66% of the total gain comes from interactions with physisorbed molecules and 34% from the influence of bulk liquid.

Water at Interfaces

The interfaces of neat water and aqueous solutions play a prominent role in many technological processes and in the environment. Examples of aqueous interfaces are ultrathin water films that cover most hydrophilic surfaces under ambient relative humidities, the liquid/solid interface which drives many electrochemical reactions, and the liquid/vapor interface, which governs the uptake and release of trace gases by the oceans and cloud droplets. In this article we review some of the recent experimental and theoretical advances in our knowledge of the properties of aqueous interfaces and discuss open questions and gaps in our understanding.

A DFT study of the adsorption of O2 and H2O on Al(111) surfaces

Using first-principles calculations that are based on density functional theory, the molecular and dissociative adsorptions of O₂ and H₂O on a clean and O pre-adsorbed Al(111) surface were systematically investigated.

Dispersion corrected RPBE studies of liquid water

The structure of liquid water has been addressed by ab initio molecular dynamics simulations based on density functional theory. Exchange-correlation effects have been described by the popular PBE and RPBE functionals within the generalized gradient approximation as these functionals also yield satisfactory results for metals which is important to model electrochemical interfaces from first principles. In addition, dispersive interactions are included by using dispersion-corrected schemes. It turns out that the dispersion-corrected RPBE functional reproduces liquid water properties quite well in contrast to the PBE functional. This is caused by the replacement of the over-estimated directional hydrogen-bonding in the PBE functional by non-directional dispersive interactions.

Interaction of H2O and H2S with Cu(111) and the impact of the electric field: the rotating & translating adsorbate, and the rippled surface

The interactions of H₂O and H₂S monomers with Cu(111) in the absence and presence of an external electric field are studied using density functional theory.

Dramatic increase in the oxygen reduction reaction for platinum cathodes from tuning the solvent dielectric constant

Hydrogen fuel cells (FC) are considered essential for a sustainable economy based on carbon-free energy sources, but a major impediment are the costs. First-principles quantum mechanics (density functional theory including solvation) is used to predict how the energies and barriers for the mechanistic steps of the oxygen reduction reaction (ORR) over the fcc(111) platinum surface depend on the dielectric constant of the solvent. The ORR kinetics can be strongly accelerated by decreasing the effective medium polarizability from the high value it has in water. Possible ways to realize this experimentally are suggested. The calculated volcano structure for the dependence of rate on solvent polarization is considered to be general, and should be observed in other electrochemical systems.

Microscopic Perspective on the Adsorption Isotherm of a Heterogeneous Surface

Adsorption of dissolved molecules onto solid surfaces can be extremely sensitive to the atomic-scale properties of the solute and surface, causing difficulties for the design of fluidic systems in industrial, medical and technological applications. In this communication, we show that the Langmuir isotherm for adsorption of a small molecule to a realistic, heterogeneous surface can be predicted from atomic structures of the molecule and surface through molecular dynamics (MD) simulations. We highlight the method by studying the adsorption of dimethyl-methylphosphonate (DMMP) to amorphous silica substrates and show that subtle differences in the atomic-scale surface properties can have drastic effects on the Langmuir isotherm. The sensitivity of the method presented is sufficient to permit the optimization of fluidic devices and to determine fundamental design rules for controlling adsorption at the nanoscale.