Mechanism of interaction of molecular hydrogen with adsorbed oxygen on platinum electrodes under open circuit conditions

Transients of open-circuit potential observed at the reaction of hydrogen molecules with oxygen preliminarily adsorbed (O_ads) on the smooth polycrystalline (pc Pt) and platinized platinum (Pt/Pt) electrodes are measured under conditions of controlled stirring of solution (0.5 M H₂ SO₄). The dependence of the surface coverage with O_ads(θ_O) on the potential in the cause of the potential decay on pc Pt are determined. It is found that for Pt/Pt, the reaction kinetics is largely determined by diffusion of H₂. For pc Pt in the range of high θ_O, the Eley-Ridiel mechanism is realized. For medium θ_O, the regions where the reaction obeys the mechanisms of Eley-Ridiel, “conjugated reactions”, and diffusion control are observed to overlap (even at the most intense stirring possible). The rate of H₂ reaction with O_ads is substantially higher compared with analogous reactions of CO, HCOOH, and CH₃OH.     

Quantum chemical modeling of the interaction of hydrogen atoms with the (111) surface of silicon

The interaction of a hydrogen atom with the (111) face of silicon was studied by the MNDO method in a cluster approximation. The energy of adsorption of a hydrogen atom as well as the values of the barriers for its incorporation and desorption from the surface layer of silicon were calculated taking into account its structure relaxation. It was found that the hydrogen atom can penetrate into the crystal through its surface cavities.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 28, No. 3, pp. 253–257, May–June, 1992.The authors wish to express their gratitude to P. A. Aleksandrova for fostering interest in the investigation and for her helpful suggestions.     

Special features of methanol interaction with adsorbed oxygen at platinized platinum electrode: Transients of the open-circuit potential

Open-circuit potential transients are measured under the conditions of methanol interaction with the pre-adsorbed oxygen at platinized platinum electrode. The time necessary for complete removal of the adsorbed oxygen monolayer appeared being shorter by a factor of ～1.5 as compared with smooth polycrystalline platinum. The dependence of platinum surface coverage with adsorbed oxygen on the potential during its decay is found. It was shown that the reaction of methanol with the adsorbed oxygen is most slow at a high coverage (1–0.8). It is suggested that at these coverages, like the case of polycrystalline platinum, the adsorbed oxygen directly interacts with the methanol molecules from the solution. At moderate coverages (0.8–0.2), the reaction of the adsorbed oxygen with methanol at the platinized platinum is better described by the “conjugated reactions” mechanism. The specific rates of the methanol dissociative adsorption at the platinized platinum turned out to be close to those observed earlier for the polycrystalline platinum.     

Quantum chemical calculation of vibrational spectra of large molecules--Raman and IR spectra for Buckminsterfullerene

In this work we demonstrate how different modern quantum chemical methods can be efficiently combined and applied for the calculation of the vibrational modes and spectra of large molecules. We are aiming at harmonic force fields, and infrared as well as Raman intensities within the double harmonic approximation, because consideration of higher order terms is only feasible for small molecules. In particular, density functional methods have evolved to a powerful quantum chemical tool for the determination of the electronic structure of molecules in the last decade. Underlying theoretical concepts for the calculation of intensities are reviewed, emphasizing necessary approximations and formal aspects of the introduced quantities, which are often not explicated in detail in elementary treatments of this topic. It is shown how complex quantum chemistry program packages can be interfaced to new programs in order to calculate IR and Raman spectra. The advantages of numerical differentiation of analytical gradients, dipole moments, and static, as well as dynamic polarizabilities, are pointed out. We carefully investigate the influence of the basis set size on polarizabilities and their spatial derivatives. This leads us to the construction of a hybrid basis set, which is equally well suited for the calculation of vibrational frequencies and Raman intensities. The efficiency is demonstrated for the highly symmetric C(60), for which we present the first all-electron density functional calculation of its Raman spectrum.     

Structure and electronic spectra of 2-phenylbenzimidazoles. Quantum chemical analysis of the intramolecular hydrogen bond

Institute of High-Molecular-Weight Compounds, Russian Academy of Sciences. Leningrad State University Translated from Zhurnal Strukturnoi Khimii, Vol. 33, No. 5, pp. 20–27, September–October, 1992.     

Positrons as probes of Si(100) surface with adsorbed hydrogen and oxygen

Positron annihilation induced Auger spectra from the Si(100) surface exposed to hydrogen and oxygen are analyzed by performing calculations of positron surface states and annihilation characteristics of surface trapped positrons. Positron binding energies and work functions are also computed. It is found that the adsorption of hydrogen and oxygen on the Si(100) surface leads to a displacement of the positron surface state wave function away from the substrate Si atoms. As a result of this displacement, the overlap of the positron wave function with Si core electrons and, consequently, the annihilation probability of Si core electrons reduce, in agreement with experimental data.     

光催化制氢中助催化剂表面氢氧复合反应的抑制

在光催化分解水产氢的过程中,Pt等助催化剂在催化产生氢的同时也会诱导催化氢气和氧气重新复合为水的逆反应,严重降低了悬浮体系光催化全分解水产氢的效率。本文综述了近年来在逆反应抑制方面的研究进展,总结和对比分析了各种抑制逆反应策略的特点,并对这些方法的应用于悬浮体系光催化全分解水制氢的前景进行了展望。     

Short‐Range Interactions in Na Coadsorption with CO and O on Ni(111)

The coadsorption of Na with CO and O on Ni(111) is studied by high‐resolution electron energy loss spectroscopy. Experimental evidence for a very short‐range interaction between Na and coadsorbates is reported, in contrast with recent theoretical predictions overestimating nonlocal alkali‐induced effects. Loss spectra show distinct features, as a consequence of different local [CO]:[Na] and [O]:[Na] stoichiometries.     

The READY program: Building a global potential energy surface and reactive dynamic simulations for the hydrogen combustion

READY (REActive DYnamics) is a program for studying reactive dynamic systems using a global potential energy surface (PES) built from previously existing PESs corresponding to each of the most important elementary reactions present in the system. We present an application to the combustion dynamics of a mixture of hydrogen and oxygen using accurate PESs for all the systems involving up to four oxygen and hydrogen atoms. Results at the temperature of 4000 K and pressure of 2 atm are presented and compared with model based on rate constants. Drawbacks and advantages of this approach are discussed and future directions of research are pointed out. © 2014 Wiley Periodicals, Inc.     

Effect of ionic composition of solutions on the methanol reaction with adsorbed oxygen on smooth polycrystalline platinum electrodes: Transients of the open-circuit potential

Transients of the open-circuit potential observed in the reaction of methanol with oxygen (O_ads) preliminarily adsorbed on smooth polycrystalline platinum (pcPt) are measured in 0.05 M HClO₄, 0.5 M HClO₄, 0.05 M H₂SO₄, 0.05 M H₂SO₄ + 0.45 M Na₂SO₄, and 0.05 M H₂SO₄ + 0.45 M Cs₂SO₄. It is shown that the solution pH has a weak effect on the transient characteristics (when the reversible hydrogen electrode potential scale is used). This confirms the chemical nature of rate-controlling stages in the reaction mechanism. The changes in the reaction rate, observed upon going from one electrolyte to another, are preferentially associated with the involvement of solution ions in the formation of activated surface complexes that include CH₃OH, O_ads, and supporting-electrolyte components.     

Kinetics and mechanism of interaction between methanol and adsorbed oxygen on a smooth polycrystalline platinum electrode: Transients of the open-circuit potential

The method of transients of the open-circuit potential, combined with cathodic potentiodynamic pulses, is used for studying the methanol interaction with preliminarily adsorbed oxygen (O_ads) in 0.5 M H₂SO₄. It is established that, for the larger part of the time period required for a full reduction of a monolayer of O_ads in solutions of methanol on polycrystalline platinum, the process occurs at large coverages of the surface by O_ads (?_O). In the region of medium coverages, transients of the open-circuit potential are accurately described by the equation that corresponds to the mechanism of “conjugated reactions.” The mechanism of the methanol interaction with O_ads happens to be close to that for formic acid, which is explained by a dissociative character of these HCO compounds. Kinetic parameters characterizing the methanol reaction with O_ads in the region of large and medium coverages are determined and analyzed.     

Chemisorption of hydrogen and oxygen atoms on a cobalt surface: A quantum chemical cluster model study

The chemisorption of atomic hydrogen and oxygen on a cobalt surface has been studied on a five-atom cluster model using one-electron effective core potential (1e⁻ECP) and all-electron calculations at the ab initio SCF and MCPF levels. Also, density functional calculations have been carried out. The different approaches are evaluated. The 1e⁻ECP has been compared to similar ECPS for nickel and copper. Our results indicate that this approach is valid also for cobalt. Different contributions to the cluster-adsorbate bonding energy are discussed. © 1996 John Wiley & Sons, Inc.     

Theoretical study of the adsorption of oxygen on a Cu(100) surface and the coadsorption with alkali atoms

We performed a theoretical study of the adsorption of oxygen on a cluster model of the Cu(100) surface and also the surface coadsorbed with lithium and potassium atoms. The study showed that alkali coadsorption facilitates in a significant way the process of molecular adsorption, whereas the adsorption of atomic oxygen is only slightly modified. The alkali atoms on the copper surface produce an increase in the charge transfer toward the oxygen molecule, favoring the oxygen dissociation. The effect is greater for the potassium coadsorption. In addition, we found that the potassium coadsorption favored the dissociation and recombination processes by about 60 and 15%, respectively. In turn, the lithium coadsorption favored only the recombination process by about 50%. These results could be an important aspect for catalytic processes.From the Proceedings of the 28th Congreso de Quimicos Teóricos de Expression Latina (QUITEL 2002)     

Quantum chemical simulations of water adsorption on a diamond (100) surface with vacancy defects

Results from quantum chemical calculations of the structural, electronic, and energy characteristics of the chemisorption of water on a diamond C(100)-(2 × 1) surface with a vacancy defect are presented. The metastable state of the surface with an adsorbed H₂O molecule and possible configurations of the surface with adsorbed -H and -OH water dissociation fragments are described. It is shown that the presence of a vacancy on the surface decreases the activation energy of the dissociative adsorption of a water molecule.     

Structure and properties of Ni(110) surface coadsorbing chlorine and oxygen

The coadsorption of chlorine with oxygen on Ni(110) surface has been investigated by XPS, UPS, AES and work function measurements. The chlorine preadsorption drastically inhibits the further uptake of oxygen. On the contrary, precovered oxygen has hardly any influence on the additional adsorption of chlorine due to the incorporation of precovered oxygen into the subsurface driven by the chlorine coadsorption. ARXPS measurements provide the evidence for this coadsorption model. The thermal desorption of chlorine and oxygen from the coadsorption surface is very similar to that of both individual adsorbates under the same heating conditions, but the desorption temperature of both the adsorbates apparently decreases on the coadsorption surface. The coadsorption and thermodesorption mechanisms are also discussed in detail.     

Spectroscopic analysis and kinetics of intermolecular hydrogen bond formation in poly‐pyridobisimidazole (M5) fiber

Poly‐pyridobisimiazole (M5) single filaments subjected to varying degrees of heat treatment have been analyzed using Fourier Transform Infrared (FTIR) microspectroscopy in transmission mode to detect changes in the state of intermolecular hydrogen bonding as a function of fiber annealing conditions. The FTIR absorbance bands associated with hydrogen bonding in M5 fiber have been identified, and the integrated molar absorption coefficients for the bands of interest have been determined experimentally, which allows to quantify the concentration of N? H vibration groups hydrogen‐bonded (H‐bonded) to water molecules, and the concentration of N? H vibration groups H‐bonded to adjacent polymer chains in the fiber. A dual mechanism kinetic rate expression is used to describe intermolecular H‐bond formation in M5 fiber as a function of annealing conditions, from which an activation energy for H‐bond formation of 14.8 kJ/mol is obtained. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1809–1824, 2009     

Accurate ab initio potential energy surface and vibration‐rotation energy levels of hydrogen peroxide

The accurate ground‐state potential energy surface of hydrogen peroxide, H₂O₂, has been determined from ab initio calculations using the coupled‐cluster approach in conjunction with the correlation‐consistent basis sets up to septuple‐zeta quality. Results obtained with the conventional and explicitly correlated coupled‐cluster methods were compared. The core–electron correlation, scalar relativistic, and higher‐order valence–electron correlation effects were taken into account. The adiabatic effects were also discussed. The vibration–rotation energy levels of the H₂O₂, D₂O₂, and HOOD isotopologues were predicted, and the experimental vibrational fundamental wavenumbers were reproduced to 1 cm^?1 (“spectroscopic”) accuracy. © 2012 Wiley Periodicals, Inc.     

Effect of chemical potential on the computer simulation of hydrogen storage in single walled carbon nanotubes

Hydrogen is a kind of clean, sustainable and renewable energy carrier. Of the problems to be solved for the utilization of hydrogen energy, how to store and transport hydrogen has been given high priority on the research agenda. Recently, carbon nanotubes (CNTs) were reported to be very promising candidates for hydrogen uptake[1], which may have possibility to satisfy the benchmark set by the US Department of Energy (DOE) Hydrogen Plan for fuel cell powered vehicles: a gravimetric density …