T. S. Zyubina

Dissociation pathways of benzene trication

Abstract Density functional B3LYP calculations have been performed to investigate dissociation pathways of benzene trication in order to understand the mechanism of dissociative ionization of benzene after irradiation in intense laser fields. Numerous decomposition products can be formed: H 2 CCCH 2+ +C 3 H 3 + (with the activation barrier of 38.4 kcal/mol), cyclobutadiene dication C 4 H 4 2+ +C 2 H 2 + (53.0 kcal/mol), C 6 H 5 2+ +H + (64–65 kcal/mol), etc. The C 2 H 2 + detachment channels have the highest exothermicity (−131 to −138 kcal/mol), followed by C 3 H 3 + detachment (−125.7) and finally H + detachment (−83.7). The fragments are expected to be produced with high-translational energy due to high Coulomb repulsion energy barriers.

Silicon- and carbon-based anode materials: Quantum-chemical modeling

With the aim of searching for promising anode materials for lithium-ion batteries, we performed quantum-chemical modeling of the structure, stability, and electronic properties of silicon-coated carbon nanotubes, silicon rods, and silicon carbide fibers by the density functional theory method including gradient correction and periodic boundary conditions. It has been demonstrated that nanotubes poorly hold silicon, whereas silicon firmly adheres to the SiC surface. Silicon rods are more favorable than clusters and have the stability close to that of the crystal. The band gap in the rods is close to zero. Silicon carbide can be transformed into a conductor by doping with nitrogen.

Modeling of processes in fuel cells based on sulfonic acid membranes and platinum clusters

The density functional theory with account for gradient correction (DFT/PBE) and periodical boundary conditions was used to model the main stages of processes occurring in hydrogen low-temperature fuel cells. Modeling was carried out at the example of calculation of catalytic anodic and cathodic processes occurring on the surface of the Pt19 catalyst supported on a SnO2 and water adsorption processes on the surface of a membrane represented by a crystal of metisylene sulfonic acid dihydrate [(CH3)3C6H2SO3− · H5O2+]. It was shown that the most energy-efficient process in the membrane is formation of crystals, in which two stoichiometric water molecules correspond to a single SO3H group. Superstoichiometric water is adsorbed on the crystal surface with the adsorption energy of 0.3–0.6 eV; its transition inside the crystal is energy-consuming (2 eV). Barriers of surface proton conductivity are 0.2–0.3 eV.

Interaction of platinum nanoparticles with different types of tin dioxide surface: Quantum-chemical modeling

The interaction of Pt29 nanoparticles with pristine and reduced (110), (100), (011), and (001) SnO2 surfaces has been modeled using the density functional theory method within the generalized gradient approximation (GGA). It has been demonstrated that, in some cases, the reduction of the surface leads to a considerable increase in the energy of interaction with platinum. The second oxidation of such structures should lead to the platinum fixation on the surface.

Quantum chemical modeling of the structure formation and proton transfer in 2-hydroxybenzenesulfonic, 4-hydroxy-1,3-benzenedisulfonic, and 1,3-benzenedisulfonic acids

Hydrate clusters of 2-hydroxybenzenesulfonic and 1,3-benzenedisulfonic acids were calculated in terms of the density functional theory (DFT) by the B3LYP/6-31G** method. The process of water adsorption on the crystal surface of 4-hydroxy-1,3-benzenedisulfonic acid dihydrate was simulated using the generalized gradient approximation (DFT/PBE) and periodic boundary conditions. For the model system (OHC6H4SO3−)·H5O2+, the activation barriers for the proton transfer were calculated depending on the distance between the O atoms and the deviation of the proton from the O...O bond line. The presence of one H2O molecule per SO3H group is energetically most favorable for the formation of clusters of 1,3-benzenedisulfonic acid containing a stoichiometric amount of water. The simulation of the hydration of 4-hydroxy-1,3-benzenedisulfonic acid dihydrate (OHC6H3(SO3H)2·2 H2O + n H2O, n = 1–3) showed that the superstoichiometric H2O molecule is adsorbed on the crystal surface of this dihydrate with energy release of 0.75–0.95 eV. The position of this water molecule is less favorable in the bulk than on the surface.

Synthesis of new polyporphines by replacing central ion in magnesium polyporphine

It is shown that the derivatives of the source electroactive polymer, magnesium polyporphine (pMgP), can be synthesized by successive treatment of electropolymerized pMgP film on the electrode surface with trifluoroacetic acid and zinc acetate solutions in the organic solvents. Based on the electrochemical and spectral characteristics of the modifying layers, it is concluded that the central magnesium ion in the porphine monomeric blocks is replaced with the formation of polyporphine in the form of free base (pH2P) and zinc polyporphine, respectively. The oxidative transformation of thus obtained new polyporphines pH2P and pZnP (which are the polymers of type I) is realized. It leads to a change in the molecular structure of polymer films (the transition to the type II); as a result, the potential range of their electroactivity is extended significantly.

Chemical and electrochemical processes in low-temperature superionic hydrogen sulfide sensors

Effect the morphology of the surface of the working electrode (PbS) exerts on the sensitivity of a low-temperature potentiometric hydrogen sulfide sensor is studied. The sensor, which is based on electrochemical cell NaxWO3/NASICON/PbS, may be used for fast selective detection of hydrogen sulfide in air in natural conditions. It is demonstrated that the sensors with PbS that are deposited out of solution have a faster response than the pressed-to ones. The dependence of EMF on the hydrogen sulfide concentration for the former is linear in semilogarithmic coordinates. Thus difference is explained by the microstructure of the lead sulfide layer. It is shown that the lead sulfide interaction with hydrogen sulfide involves a reversible partial reduction of sulfur and lead at the surface. The species that form in so doing contain sulfur atoms in lower oxidation degrees (poly-and oligo sulfides, sulfite). A mechanism of the sensor operation is proposed on the basis of data yielded by experiment and quantum-chemical simulation. The mechanism includes reversible transport of hydrogen from sulfur atoms to oxygen atoms.

Platinum nanoparticles on different types of titanium dioxide surface: A quantum-chemical modeling

The interaction of a Pt29 nanoparticle with pristine and reduced TiO2 (110), (100), (101), and (100) surfaces in the rutile and anatase modifications has been modeled by the density functional theory method within the generalized gradient approximation (GGA). It has been demonstrated that the interaction energy of platinum particles with stoichiometric surfaces of titanium dioxide crystals is noticeably lower than for tin dioxide crystals. Like for SnO2, the reduction of the surface leads in some cases to a significant increase in the energy of interaction with platinum. The reoxidation of such structures should result in platinum fixation on the surface.

Interaction of oxygen with the platinum surface: A quantum-chemical modeling

The interaction of oxygen with the (111), (110), and (100) platinum crystal surfaces has been modeled by the density functional theory method within the generalized gradient approximation (GGA). It has been demonstrated that the dissociative adsorption of a dioxygen molecule to all three types of surfaces is energetically favorable. The peroxide species are less stable than the dissociated ones, but they are also energetically favorable. There have been considered the relative stability of different structures involving one and several oxygen atoms, the mutual influence of the atoms on the surface, the adsorption energy as a function of the surface coverage, and adsorption onto the intrinsic surface defects.

Behavior of molecular hydrogen on the platinum crystal surface: Quantum-chemical modeling

The interaction of molecular hydrogen with the (111), (110), and (100) surfaces of the platinum crystal has been modeled by the density functional theory method within the generalized gradient approximation (GGA). The (100) surface is the least energetically favorable one, while the (111) and (110) surfaces are close in energy. The hydrogen molecule is attached to all three types of surfaces without a barrier. The largest decrease in energy is realized for the (100) surface. The bidentate coordination of hydrogen atoms is typical of the (100) and (110) surfaces, and the tridentate coordination is characteristic of the (111) surface. The H atoms can migrate over the crystal surface, overcoming moderate potential barriers of ∼0.1–0.2 eV; however, over the (110) surface, migration is possible only along the ridges. The maximal number of attached atoms per surface atom is close to unity for the (111) or (110) surface and to 1.67 for the (100) surface.