Quantitative Analysis of the Synergy of Doping and Nanostructuring of Oxide Photocatalysts.

In this paper, the effect of doping and nanostructuring on the electrostatic potential across the electrochemical interface between a transition metal oxide and a water electrolyte is investigated by means of the Poisson-Boltzmann model. For spherical nanoparticles and nanorods, compact expressions for the limiting potentials at which the space charge layer includes the whole semiconductor are reported. We provide a quantitative analysis of the distribution of the potential drop between the solid and the liquid and show that the relative importance changes with doping.

Amorphous MoS2 from a machine learning inter-atomic potential.

Amorphous molybdenum disulfide has shown potential as a hydrogen evolution catalyst, but the origin of its high activity is unclear, as is its atomic structure. Here, we have developed a classical inter-atomic potential using the charge equilibration neural network method, and we have employed it to generate atomic models of amorphous MoS2 by melting and quenching processes. The amorphous phase contains an abundance of molybdenum and sulfur atoms in low coordination.

The Role of Water Molecules on Polaron Behavior at Rutile (110) Surface: A Constrained Density Functional Theory Study.

Understanding the behavior of a polaron in contact with water is of significant importance for many photocatalytic applications. We investigated the influence of water on the localization and transport properties of polarons at the rutile (110) surface by constrained density functional theory. An excess electron at a dry surface favors the formation of a small polaron at the subsurface Ti site, with a preferred transport direction along the [001] axis.

The carbonyl-lock mechanism underlying non-aromatic fluorescence in biological matter.

Challenging the basis of our chemical intuition, recent experimental evidence reveals the presence of a new type of intrinsic fluorescence in biomolecules that exists even in the absence of aromatic or electronically conjugated chemical compounds. The origin of this phenomenon has remained elusive so far. In the present study, we identify a mechanism underlying this new type of fluorescence in different biological aggregates.

High-Throughput Screening of Promising Redox-Active Molecules with MolGAT.

Redox flow batteries (RFBs) have emerged as a promising option for large-scale energy storage, owing to their high energy density, low cost, and environmental benefits. However, the identification of organic compounds with high redox activity, aqueous solubility, stability, and fast redox kinetics is a crucial and challenging step in developing an RFB technology. Density functional theory-based computational materials prediction and screening is a time-consuming and computationally expensive technique, yet it has a high success rate.

Heterostructures of ε-FeO and α-FeO: insights from density functional theory.

Many materials used in energy devices or applications suffer from the problem of electron-hole pair recombination. One promising way to overcome this problem is the use of heterostructures in place of a single material. If an electric dipole forms at the interface, such a structure can lead to a more efficient electron-hole pair separation and thus prevent recombination.

DFT insights into electrocatalytic CO reduction to methanol on α-FeO(0001) surfaces.

Electrocatalytic reduction of CO to manufacture fuels and other useful chemicals is one of the appealing methods to reuse CO. Herein, electrocatalytic CO reduction on a model α-FeO(0001) surface catalyst has been investigated by means of density functional theory. This systematic study, involving 20 reaction intermediates and 63 distinct elementary reaction steps, has allowed the identification of a novel mechanism for the decomposition of the key intermediate *COOH.

Catalytic properties of α-MnO for Li-air battery cathodes: a density functional investigation.

Details of the formation and dissociation of the first layer of LiO on the α-MnO(100) surface as the cathode in Li-air batteries have been studied using first principles density functional theory. The bias dependence of the electrochemical steps of charge (LiO dissociation) and discharge (LiO formation) via two different mechanisms has been studied. Discharge potential is found to be 2.

Tuning optoelectronic properties of triphenylamine based dyes through variation of pi-conjugated units and anchoring groups: A DFT/TD-DFT investigation.

Dye-sensitized solar cells (DSSCs) have attracted widespread attention due to their unique features. In the present work, molecular engineered triphenylamine based dyes featuring donor-bridge-acceptor architecture have been considered and investigated for suitable properties for DSSCs applications. Hydantoin anchoring group has been introduced replacing the commonly used cyanoacrylic acid to improve the long-term stability of the device.

Understanding the electrochemical double layer at the hematite/water interface: A first principles molecular dynamics study.

Using first principles molecular dynamics simulations, we probe the electrochemical double layer formed at the interface between the hematite surface and water. We consider two terminations of the (001) surface, viz., the fully hydroxylated (OH) and the stoichiometric (FeOFe) termination.

Characterization of peroxo reaction intermediates in the water oxidation process on hematite surfaces.

We use density functional theory-based calculations to study structural, electronic, and magnetic properties of two key reaction intermediates on a hematite, [Formula: see text]-FeO, photoanode during the solar-driven water splitting reaction. Both intermediates contain an oxygen atom bonded to a surface iron atom. In one case, the adsorbed oxygen also forms a peroxo bond with a lattice oxygen from hematite; in the second case no such bond is formed.

Substrate- to Laterally-Driven Self-Assembly Steered by Cu Nanoclusters: The Case of FePcs on an Ultrathin Alumina Film.

We show that, for the formation of a metallorganic monolayer, it is possible to artificially divert from substrate- to laterally-driven self-assembly mechanisms by properly tailoring the corrugation of the potential energy surface of the growth template. By exploiting the capability of an ultrathin alumina film to host metallic nanoparticle seeds, we tune the symmetry of a iron phthalocyanine (FePc) two-dimensional crystal, thus showing that it is possible to switch from trans to lateral dominating interactions in the controlled growth of an organic/inorganic heterostack. Finally, by selecting the size of the metallic clusters, we can also control the FePc-metal interaction strength.

Magnetoelectric ϵ-FeO: DFT study of a potential candidate for electrode material in photoelectrochemical cells.

The metastable iron oxide ϵ-FeO is rare but known for its magnetoelectric properties. While the more common alpha phase has been recognized for a long time as a suitable material for photoelectrochemical cells, its use is limited because of the electron-hole recombination problem when exposed to light. The indirect bandgap of the epsilon phase with its spontaneous polarization may offer a better potential for the application in photoelectrochemistry.

Ab initio simulations of water splitting on hematite.

In recent years, hematite has attracted great interest as a photocatalyst for water splitting, but many questions remain unanswered about the mechanisms and the main limiting factors. For this reason, density functional theory has been used to understand the optical, electronic and chemical properties of this material at an atomistic level. Bulk doping can be used to reduce the band gap, and to increase photoabsorption and charge mobility.

Passivation of surface states of α-Fe2O3(0001) surface by deposition of Ga2O3 overlayers: A density functional theory study.

There is a big debate in the community regarding the role of surface states of hematite in the photoelectrochemical water splitting. Experimental studies on non-catalytic overlayers passivating the hematite surface states claim a favorable reduction in the overpotential for the water splitting reaction. As a first step towards understanding the effect of these overlayers, we have studied the system Ga2O3 overlayers on hematite (0001) surfaces using first principles computations in the PBE+U framework.

CO2 conversion to methanol on Cu(I) oxide nanolayers and clusters: an electronic structure insight into the reaction mechanism.

The mechanism of carbon dioxide reduction to methanol on Cu(I) oxide nanolayers and clusters using water as the source of hydrogen was traced using density functional theory. The nature of the active sites is revealed, namely the role of surface copper dimers, which are present on the Cu2O(001) surface and in the nanoclusters of size Cu32O16 and Cu14O7. The major difference between metal catalysts and Cu2O is outlined: the CO2 molecule interacts strongly with the oxide and undergoes bending prior to hydrogenation.

Nitrogen electrochemically reduced to ammonia with hematite: density-functional insights.

Licht et al. (Science, 2014, 345, 637) recently proposed a procedure to synthesize NH3 from N2 and by steam electrolysis in molten hydroxide suspensions of nano-Fe2O3. This highly exciting investigation undoubtedly boosts the hope of the CO2-free and low-cost ammonia industry.

Defective α-Fe2O3(0001): an ab initio study.

By using density functional theory calculations at the PBE+U level, we investigated the properties of hematite (0001) surfaces decorated with adatoms/vacancies/substituents. For the most stable surface termination over a large range of oxygen chemical potentials (muO), the vacancy formation and adsorption energies were determined as a function of muO. Under oxygen-rich conditions, all defects are metastable with respect to the ideal surface.

Photo-driven oxidation of water on α-Fe2O3 surfaces: an ab initio study.

Adopting the theoretical scheme developed by the Nørskov group [see, for example, Nørskov et al., J. Phys.

Water adsorption and dissociation on α-Fe2O3(0001): PBE+U calculations.

Adsorption and dissociation of water on different oxygen- and iron-terminated hematite(0001) surfaces at monolayer coverage have been studied by density-functional theory calculations, including a Hubbard-like+U correction. We considered six possible surface terminations, including four oxygen- and two iron-terminations. Binding energy of water on these terminations can be as large as 1.

Ab initio parameterization of an all-atom polarizable and dissociable force field for water.

A novel all-atom, dissociative, and polarizable force field for water is presented. The force field is parameterized based on forces, stresses, and energies obtained form ab initio calculations of liquid water at ambient conditions. The accuracy of the force field is tested by calculating structural and dynamical properties of liquid water and the energetics of small water clusters.

A relation between kinetic-energy density and the band gap in alkali and alkaline-earth oxides.

Alkali and alkaline-earth oxides are analysed by means of Bader's atom-in-molecule theory and density functional theory. Particular attention is devoted to the analysis of properties of the bond critical points. A linear relation is found between the kinetic-energy density at the bond critical point between cation and anion and the electronic band gap.

Carbon in palladium catalysts: A metastable carbide.

The catalytic activity of palladium toward selective hydrogenation of hydrocarbons depends on the partial pressure of hydrogen. It has been suggested that the reaction proceeds selectively toward partial hydrogenation only when a carbon-rich film is present at the metal surface. On the basis of first-principles simulations, we show that carbon can dissolve into the metal because graphite formation is delayed by the large critical nucleus necessary for graphite nucleation.

Ab initio thermodynamics of lithium oxides: from bulk phases to nanoparticles.

Lithium ion batteries are nowadays key devices for energy storage, and a great research effort is under way to develop and apply new materials. Recently, new approaches have been proposed that rely on the reversible formation of either Li2O or Li2O2 at the electrodes. The details of their formation and dissolution are, however, still unclear.