Finite element analysis of the Poisson–Boltzmann equation coupled with chemical equilibriums: redistribution and transport of protons in nanophase separated polymeric acid–base proton exchange membranes

<p>The finite element analysis is applied to the study of the redistribution and transport of protons in model nanophase separated polymeric acid–base composite membranes by the Poisson–Boltzmann equation coupled with the acid and base dissociation equilibriums for the first time. Space charge redistribution in terms of proton and hydroxide redistributions is observed at the interfaces of acidic and basic domains. The space charge redistribution causes internal electrostatic potential, and thus, promotes the macroscopic transport of protons in the acid–base composite membranes.</p

Hydrogen Transfer Reaction in Polycyclic Aromatic Hydrocarbon Radicals

Density functional theory calculations have been successfully applied to investigate the formation of hydrocarbon radicals and hydrogen transfer pathways related to the chemical vapor infiltration process based on model molecules of phenanthrene, anthra­[2,1,9,8-<i>opqra</i>]­tetracene, dibenzo­[<i>a</i>,<i>ghi</i>]­perylene, benzo­[<i>uv</i>]­naphtho­[2,1,8,7-<i>defg</i>]­pentaphene, and dibenzo­[<i>bc</i>,<i>ef</i>]­ovalene. The hydrogen transfer reaction rate constants are calculated within the framework of the Rice–Ramsperger–Kassel–Marcus theory and the transition state theory by use of the density functional theory calculation results as input. From these calculations, it is concluded that the hydrogen transfer reaction between two bay sites can happen almost spontaneously with energy barrier as low as about 4.0 kcal mol^–1, and the hydrogen transfer reactions between two armchair sites possess lower energy barrier than those between two zigzag sites

Dynamic Fluctuation of U³⁺ Coordination Structure in the Molten LiCl–KCl Eutectic via First Principles Molecular Dynamics Simulations

The dynamic fluctuation of the U³⁺ coordination structure in a molten LiCl–KCl mixture was studied using first principles molecular dynamics (FPMD) simulations. The radial distribution function, probability distribution of coordination numbers, fluctuation of coordination number and cage volume, self-diffusion coefficient and solvodynamic mean radius of U³⁺, dynamics of the nearest U–Cl distances, and van Hove function were evaluated. It was revealed that fast exchange of Cl^– occurred between the first and second coordination shells of U³⁺ accompanied with fast fluctuation of coordination number and rearrangement of coordination structure. It was concluded that 6-fold coordination structure dominated the coordination structure of U³⁺ in the molten LiCl–KCl–UCl₃ mixture and a high temperature was conducive to the formation of low coordinated structure

Highly Active Carbon Supported Pd–Ag Nanofacets Catalysts for Hydrogen Production from HCOOH

Hydrogen is regarded as a future sustainable and clean energy carrier. Formic acid is a safe and sustainable hydrogen storage medium with many advantages, including high hydrogen content, nontoxicity, and low cost. In this work, a series of highly active catalysts for hydrogen production from formic acid are successfully synthesized by controllably depositing Pd onto Ag nanoplates with different Ag nanofacets, such as Ag{111}, Ag{100}, and the nanofacet on hexagonal close packing Ag crystal (Ag­{hcp}). Then, the Pd–Ag nanoplate catalysts are supported on Vulcan XC-72 carbon black to prevent the aggregation of the catalysts. The research reveals that the high activity is attributed to the formation of Pd–Ag alloy nanofacets, such as Pd–Ag{111}, Pd–Ag{100}, and Pd–Ag­{hcp}. The activity order of these Pd-decorated Ag nanofacets is Pd–Ag­{hcp} > Pd–Ag{111} > Pd–Ag{100}. Particularly, the activity of Pd–Ag­{hcp} is up to an extremely high value, i.e., TOF_{hcp} = 19 000 ± 1630 h^–1 at 90 °C (lower limit value), which is more than 800 times higher than our previous quasi-spherical Pd–Ag alloy nanocatalyst. The initial activity of Pd–Ag­{hcp} even reaches (3.13 ± 0.19) × 10⁶ h^–1 at 90 °C. This research not only presents highly active catalysts for hydrogen generation but also shows that the facet on the hcp Ag crystal can act as a potentially highly active catalyst

Nucleophile-Dependent Regioselective Reaction of (<i>S</i>)‑4-Benzyl-2-Fluoroalkyl-1,3-Oxazolines

Nucleophile-dependent regioselectivities in the nucleophilic reaction of (<i>S</i>)-4-benzyl-2-fluoroalkyl-1,3-oxazoline to different types of fluorinated compounds were investigated experimentally and theoretically. The ring opening of (<i>S</i>)-4-benzyl-2-bromodifluoromethyl-1,3-oxazoline by arenethiolates exclusively occurred at the C5 position of the 1,3-oxazoline ring, whereas completely different regioselectivity was observed for a unimolecular radical nucleophilic substitution (S_RN1) at the terminal bromine atom of the CF₂Br group when arenolates were employed as the nucleophiles. The reaction of (<i>S</i>)-4-benzyl-2-trifluoromethyl-1,3-oxazoline with nucleophiles such as arenethiols, arenols, and TMSCl underwent nucleophilic ring opening in a regiospecific way, while the use of TMSCF₃ was determined to proceed through nucleophilic addition to the CN bond