To probe metal particle/reducible oxide interactions density functional theory based ab initio molecular dynamics studies were performed on a prototypical metal cluster (Au20) supported on reducible oxides (rutile TiO2(110)) to implicitly account for finite temperature effects and the role of excess surface charge in the metal oxide. It is found that the charge state of the Au particle is negative in a reducing chemical environment whereas in the presence of oxidizing species coadsorbed to the oxide surface the cluster obtained a net positive charge. In the context of the well-known CO oxidation reaction, charge transfer facilitates the plasticization of Au20, which allows for a strong adsorbate induced surface reconstruction upon addition of CO leading to the formation of mobile Au-CO species on the surface. The charging/discharging of the cluster during the catalytic cycle of CO oxidation enhances and controls the amount of O2 adsorbed at oxide/cluster interface and strongly influences the energetics of all redox steps in catalytic conversions. A detailed comparison of the current findings with previous studies is presented, and generalities about the role of surface-adsorbate charge transfer for metal cluster/reducible oxide interactions are discussed.

Conjugated polymers, such as polyfluorene and poly(phenylene vinylene), have been used to selectively disperse semiconducting single-walled carbon nanotubes (sc-sWnTs), but these polymers have limited applications in transistors and solar cells. Regioregular poly(3-alkylthiophene)s (rr-P3ATs) are the most widely used materials for organic electronics and have been observed to wrap around sWnTs. However, no sorting of sc-sWnTs has been achieved before. Here we report the application of rr-P3ATs to sort sc-sWnTs. Through rational selection of polymers, solvent and temperature, we achieved highly selective dispersion of sc-sWnTs. our approach enables direct film preparation after a simple centrifugation step. using the sorted sc-sWnTs, we fabricate high-performance sWnT network transistors with observed charge-carrier mobility as high as 12 cm 2 V − 1 s − 1 and on/off ratio of > 10 6 . our method offers a facile and a scalable route for separating sc-sWnTs and fabrication of electronic devices.

The effect of an aqueous phase on phenol hydrogenation over Pt and Ni catalysts was investigated using density functional theory-based ab initio molecular dynamics calculations. The adsorption of phenol and the addition of the first and second hydrogen adatoms to three, ring carbon positions (ortho, meta, and para with respect to the phenolic OH group) were explored in both vacuum and liquid water. The major change in the electronic structure of both Pt(111) and Ni(111) surfaces, between a gaseous and liquid phase environment, results from a repulsion between the electrons of the liquid water and the diffuse tail of electron density emanating from the metal surface. The redistribution of the metal's electrons toward the subsurface layer lowers the metal work function by about 1 eV. The lower work function gives the liquid-covered metal a higher chemical reduction strength and, in consequence, a lower oxidation strength, which, in turn lowers the phenol adsorption energy, despite the stabilizing influence of the solvation of the partly positively charged adsorbate. At both the solid/vapor and the solid/water interface, H adatom addition involves neutral H atom transfer hence the reaction barriers for adding H adatoms to phenol are lowered by only 10-20 kJ/mol, due to a small stabilizing at the transition state. More importantly, the liquid environment significantly influences the relative energetics of charged, surface-bound intermediates and of proton-transfer reactions like keto/enol isomerization. For phenol hydrogenation, solvation in water results in an energetic preference to form ketones as a result of tautomerization of surface-bound enol intermediates.

We present a multiscale modeling approach to study oxygen diffusion in cubic yttria‐stabilized zirconia. In this approach, we employ density functional theory methods to calculate activation energies for oxygen migration in different cation environments. These are used in a kinetic Monte Carlo framework to calculate long‐time oxygen diffusivities. Simulation results show that the oxygen diffusivity attains a maximum value at around 0.1 mole fraction yttria. This variation in the oxygen diffusivity with yttria mole fraction and the calculated values for the diffusivity agree well with experiment. The competing effects of increased oxygen vacancy concentration and increasing activation energy and correlation effects for oxygen diffusion with increasing yttria mole fraction are responsible for the observed dopant content dependence of the oxygen diffusivity. We provide a detailed analysis of cation‐dopant‐induced correlation effects in support of the above explanation.

A detailed mechanistic study of the electrochemical hydrogenation of aldehydes is presented toward the goal of identifying how organic molecules in solution behave at the interface with charged surfaces and what is the best manner to convert them. Specifically, this study focuses on designing an electrocatalytic route for ambient-temperature postpyrolysis treatment of bio-oil. Aldehyde reductions are needed to convert biomass into fuels or chemicals. A combined experimental and computational approach is taken toward catalyst design to provide testable hypotheses regarding catalyst composition, activity, and selectivity. Electrochemical hydrogenation mechanisms for benzaldehyde and pentanal reduction are found to proceed by a coupled proton−electron transfer process. Initial results show that Au, Ag, Cu, and C catalysts exhibit the highest conversion to alcohol products. These catalysts are suitable because they show high cathodic onset potentials for H 2 formation and low cathodic onset potentials for organic reduction. Conversion of aromatic aldehydes is found to be appreciably higher than that of aliphatic aldehydes. Classical molecular dynamics simulations of solvent and substrate mixtures in an electrolytic cell were performed to assess how species concentrations vary at the solid/liquid interface and in the bulk as a function of applied voltage. Results show that an increase in surface charge in the electrolytic cell decreases organic and increases water mole fractions at the solid/liquid interface. In this current study, charged cathodic surfaces result in carbonyl orientations at the surface that do not favor electron transfer. Repulsion of organic substrates to the bulk must be compensated by strong adhesion to the electrode surface. Implications on catalyst choice and process design are discussed.