Dissociation Of Oxygen Molecules Research Articles

Development of a Novel Manganese Dioxide/Nickel Oxyhydroxide Fibrous Positive Electrode for Fuel Cell/Battery (FCB) Systems

A novel MnO2/NiOOH fibrous positive electrode for Fuel Cell/Battery (FCB) systems has been proposed. FCB systems containing manganese dioxide and metal hydride (MH) as active materials for the positive and negative electrodes, respectively, have been found to be attractive energy storage and power generation systems because they can function as both fuel cells and secondary batteries with high energy and power density. Moreover, they can also be chemically charged by gaseous hydrogen and oxygen supply. However, the chemical charging rate of the positive electrode of the FCB systems is relatively low compared to the negative electrode. In our previous study, highly dissolved oxygen in an electrolyte was used in order to improve the chemical reaction rate of oxygen charging on a manganese dioxide electrode. The study showed that the charge rate will be 3.45 mAh/(g･min) if the oxygen is supplied with the limiting pressure. This result implies that the proton diffusion in the crystalline structure of the manganese dioxide or the dissociation of oxygen molecule on the manganese dioxide surface is the rate determining step in the oxygen charging. In the current study, therefore, we suggest two approaches for the fabrication of FCB positive electrodes to improve the oxygen charging rate: i) enlargement of active surface area by an electrodeposition method of active materials on carbon fibers, and ii) introduction of small amount of nickel oxyhydroxide to fibrous manganese dioxide electrodes in order to enhance the electrical conductivity of the positive electrode. Nickel oxyhydroxide is a well known positive electrode material of Ni-MH batteries and has higher electrical conductivity than manganese dioxide. Thus, the combination of nickel oxyhydroxide with manganese dioxide is expected to lead to a higher electrical conductivity of the FCB positive electrode. In the present paper, the characteristics of the proposed fibrous electrode will be studied by using galvanostatic measurement, electrochemical impedance spectroscopy, scanning electron microscopy analysis, and X-ray diffraction measurement.

Role of oxygen vacancy in dissociation of oxygen molecule on SOFC cathode: Ab initio molecular dynamics simulation

The oxygen reduction reaction (ORR) at the cathode of the solid oxide fuel cell (SOFC) is investigated by the ab initio MD simulation, focusing on the role of the oxygen vacancy on the oxygen dissociation and reduction reaction. The oxygen molecule easily adsorbs on the nickel atom at the NiO surface as the monodentate superoxide ion (O2−(ad)), which turns quickly to the bidentate peroxide ion (O22−(ad)) regardless of the existence of vacancies at surface. The bidentate O22−(ad) in the vicinity of the oxygen vacancy dissociates easily, while that on the surface without vacancy is kept undissociated. Nickel atoms next to the oxygen vacancy have more electrons compared with those in the bulk NiO, and therefore, are able to donate more electrons to the adsorbed oxygen molecules, which results in the dissociation of the oxygen molecule. Detailed Mulliken charge analyses in term of bond overlap population on the dissociation process have revealed that dissociation undergoes with two series steps of O22−(ad) via O− state either in the form of V••O or O−(ad) into O2− state in the form of V×O or O2−(ad). Moreover, the NEB analyses reveal that the energy decreases monotonically along the reaction path of oxygen dissociation on the NiO surface with vacancies, while there exists the activation energy of about 0.6eV in the case without vacancies. Since the dissociation of O22−(ad) takes place quickly upon encounter with oxygen vacancy at the surface, it is expected that the probability of meeting O22− and V••O per time and area determines the reaction rate of ORR.

ADSORPTION AND DISSOCIATION OF O2 ON Ti3Al (0001) STUDIED BY FIRST-PRINCIPLES

The adsorption and dissociation of oxygen molecule on Ti 3 Al (0001) surface have been investigated by density functional theory (DFT) with the generalized gradient approximation (GGA). All possible adsorption sites including nine vertical and fifteen parallel sites of O 2 are considered on Ti 3 Al (0001) surface. It is found that all oxygen molecules dissociate except for three vertical adsorption sites after structure optimization. This indicates that oxygen molecules prefer to dissociate on the junction site between Ti and Al atoms. Oxygen atoms coming from dissociation of oxygen molecule tend to occupy the most stable adsorption sites of the Ti 3 Al (0001) surface. The distance of O – O is related to the surface dissociation distance of Ti 3 Al (0001) surface. The valence electron localization function (ELF) and projected density of states (DOS) show that the bonds of O – O are breakaway at parallel adsorption end structures.

Ab Initio Molecular Dynamics Simulation of Oxygen Adsorption and Electron Transfer on SOFC Cathode

Absorption and subsequent dissociation of oxygen molecules on the cathode surface of the solid oxide fuel cell (SOFC) with various types of vacancy are investigated by the ab initio MD simulation. The oxygen molecule adsorbed on the nickelous oxide (NiO) surface with an oxygen vacancy at the surface layer and that on the surface with a nickel vacancy at the subsurface layer are dissociated. On the other hand, the oxygen molecule adsorbed on the NiO surface with a nickel vacancy at the surface layer and that on the surface with an oxygen vacancy at the subsurface are not dissociated. The change in Mulliken charge of oxygen atoms and connecting nickel atoms during the dissociation is larger during the adsorption.

First-principles molecular dynamics study of water dissociation on the γ-U(1 0 0) surface

Based on first-principles molecular dynamics simulations at finite temperatures, we systematically study the adsorption and dissociation of water molecules on the γ-U(1 0 0) surface. We predict that water molecules spontaneously dissociate upon approaching the native γ-U(1 0 0) surface. The dissociation results from electronic interactions between surface uranium 6d states and 1b2, 3a1, and 1b1 molecular orbitals of water. With segregated Nb atoms existing on the surface, adsorbing water molecules also dissociate spontaneously because Nb 3d electronic states can also interact with the molecular orbitals similarly. After dissociation, the isolated hydrogen atoms are found to diffuse fast on both the γ-U surface and that with a surface substitutional Nb atom, which is very similar to the ‘Hot-Atom’ dissociation of oxygen molecules on the Al(1 1 1) surface. From a series of consecutive molecular dynamics simulations, we further reveal that on both the γ-U surface and that with a surface substitutional Nb atom, one surface U atom will be pulled out to form the U–O–U structure after dissociative adsorption of 0.44 ML water molecules. This result indicates that oxide nucleus can form at low coverage of water adsorption on the two surfaces.

The Role of Atomic Structures on the Oxygen Corrosion of Polycrystalline Copper Surface

The mechanical property of materials for pressure vessel, like steel, Ti, Cu and their alloys always turns out to be poor in the severely corrosive environment. The knowledge of oxygen corrosion on metal surface at atomic level is still lack. Using reactive molecular dynamic simulation, the oxygen corrosion behavior on polycrystalline copper is studied at the early stage of oxidation. Results indicate a higher reactivity at the grain boundary. The preferential dissociation of oxygen molecules at grain boundary is ascribed to the diffusion-related trapping effect and dissociation barriers. In addition, the difference of oxygen corrosion between grain boundary and grain on copper surface is elucidated in terms of the atomic-structure-related radial distribution functions. This study directly shows us the origin of intergranular oxygen corrosion and provides us useful information for the corrosion prevention, especially in the situation that the atomic structure changes under the thermal or mechanical loadings.

On the use of pulsed Dielectric Barrier Discharges to control the gas-phase composition of atmospheric pressure air plasmas

We presents results obtained from the numerical simulation of the gas-phase chemical kinetics in atmospheric pressure air non-equilibrium plasmas. In particular we have addressed the effect of pulsed operation mode of a plane dielectric barrier discharge. It was conjectured that the large difference in the time scales involved in the fast dissociation of oxygen molecules in plasma and their subsequent reactions to produce ozone and nitrogen oxides, makes the presence of a continuously repeated plasma production unnecessary and a waste of electrical power and thus efficiency. In order to test such suggestion we have performed a numerical study of the composition and the temporal evolution of the gas-phase of atmospheric pressure air non-equilibrium plasmas. Comparison with experimental findings in a dielectric barrier discharge with an electrode configuration symmetrical and almost ideally plane is briefly addressed too, using plasma diagnostics to extract the properties of the single micro-discharges and a sensor to measure the concentration of ozone produced by the plasma.

New insights into the oxygen dissociation and migration on Pt(1 1 1) surface from the Car–Parrinello molecular dynamics study

Car–Parrinello molecular dynamics simulations were performed to study the dissociation of oxygen molecule on the Pt(111) surface at 350K. The results show oxygen dissociation is a step-by-step process. The dissociated oxygen atoms can form fcc–fcc or fcc–hcp adsorption structure on the Pt(111) surface, which is consistent with the results of previous experiments. The Kohn–Sham energy evolutions indicate that the hcp–hcp adsorption structure possesses relatively high energy, and would transform into an fcc–hcp adsorption structure with low energy barrier. This study provides important information in understanding the oxygen dissociation dynamics at the atomic level.

Room-temperature hydrogen sensor based on grain-boundary controlled Pt decorated In2O3 nanocubes

New, highly sensitive room temperature (RT) hydrogen gas sensors were fabricated by coating Pt-decorated-cube-like-In2O3 on Au electrodes. In2O3, with diameters between 200 and 300nm, was obtained by a hydrothermal method and coated with Pt by a simple solution based on chemical technique. The morphological and elemental studies of the material were carried out using SEM, TEM and EDAX analysis. The loading of the Pt nanoparticles (NPs) enhanced the catalytic dissociation of oxygen molecules, adsorbed a substantial quantity of hydrogen, and the sensor exhibited a dramatic decrease in working temperatures to 25°C. Responding to 1.5vol% hydrogen, the sensor achieved response and recovery times of approximately 33s and 66s, respectively. The sensor also achieved excellent stability and high sensitivity to hydrogen at RT. In addition, it also showed a slow response to CO. The gas response to 1.5vol% CO was 10 times lower than that to hydrogen. For other organic compounds in the gaseous state, such as ethanol, acetone and isopropanol, the response could be neglected. Such a large discrepancy reveals the sensor's outstanding selectivity to H2. Grain boundary theory and spillover theory are applied to explain the gas sensing effect of the Pt-coated In2O3 nanocubes sensor.

A Model for Extracting Fundamental Kinetic Rates of SOFC Cathode Materials from Oxygen Isotope Exchange Experiments

Losses from cathode polarization in solid oxide fuel cells (SOFC) limit their performance at intermediate temperatures. A fundamental understanding of the oxygen reduction mechanisms on SOFC cathodes is essential for the development of lower temperature SOFCs with high performance. In order to separate the various contributions to cathode polarization, different techniques and experiments have been carried out to gain an understanding of the kinetics occurring at the gas-solid interface. Isotope exchange is a powerful tool for analyzing the oxygen exchange process (1, 2, 3, 4, 5), however, most isotope tracer experiments are limited in their scope. Experiments typically take one of two approaches, a focus on the kinetics of oxygen adsorption on the surface (SSIKTA), or the diffusion of oxygen through the lattice (SIMS). For SOFC cathodes, we are concerned with both the dissociation of oxygen on the surface and the ability of oxygen atoms to incorporate into and diffuse through the lattice. In this study, we attempt to determine the ORR mechanism and extract fundamental kinetics rates for La0.6Sr0.4Co0.2Fe0.8O3-x (LSCF) and (La0.8Sr0.2)0.95MnO3-x (LSM) using isothermal isotope exchange (IIE) (6,7). Studies of isotope exchange can greatly contribute to the elucidation of the interactions between molecular oxygen and the cathode surface. Isotope exchange can help characterize the dissociation of oxygen molecules at the oxide surface as well as the conduction of oxygen ions within the oxide. IIE experiments will be conducted at various temperatures and oxygen partial pressures.To extract fundamental kinetic rates from in-situ isotope exchange experiments on LSM and LSCF, a model has been developed based on a two-step reaction mechanism across the heterogeneous gas-solid interface. The coupled reactions can be shown in two elementary steps: dissociative adsorption and incorporation. The relation between the fundamental kinetics rates and surface exchange coefficient (kex) (8, 9) will also be linked. Acknowledgments This work was supported by the Department of Energy under contract DEFE0009084. The authors would like to thank Dr. Dongxia Liu for reviewing our model.ReferencesM.W. den Otter, B.A. Boukamp, H.J.M. Bouwmeester, Solid State Ionics 139 (2001) 89–94Henny J. M. Bouwmeester,* Chunlin Song, Jianjun Zhu, Jianxin Yi, Martin van Sint Annaland and Bernard A. Boukamp, Phys. Chem. Chem. Phys., 2009, 11, 9640–9643S. Lacombe, H. Zanthoff, and C. Mirodatos, Jounal of Catalysis, 155, 106-116(1995)M.W. den Otter, B.A. Boukamp, H.J.M. Bouwmeester, Solid State Ionics 139 (2001) 89–94Schohn L. Shannon and James G. Goodwin, Jr.*, Chem. Rev. 1995, 677-695C.C. Kan, E.D. Wachsman, Solid State Ionics 181 (2010) 338–347C.C. Kan, H. H. Kan, F. M. Van Assche IV, E. N. Armstrong, and E. D. Wachsman, Journal of The Electrochemical Society, 155 (10) B985-B993 (2008E. N. Armstrong, K. L. Duncan, D. J. Oh, J. F. Weaver, and E. D. Wachsman, Journal of The Electrochemical Society, 158 (5) B492-B499 (2011)S. Wang, P.A.W. van der Heide, C. Chavez, A.J. Jacobson, S.B. Adler, Solid State Ionics 156 (2003) 201–208

Catalytic behavior and synergistic effect of nanostructured mesoporous CuO-MnOx-CeO2 catalysts for chlorobenzene destruction

Mesoporous CuO-MnOx-CeO2 composite metal oxides with different copper and manganese loadings were prepared by a urea-assistant hydrothermal method, and were further adopted for the complete catalytic combustion of chlorobenzene. The effects of reaction conditions such as inlet reagent concentration and water feed concentration on chlorobenzene combustion were also studied. The structure and textural properties of the synthesized catalysts were characterized via the XRD, N2 adsorption/desorption, FE-SEM, TEM, H2-TPR, O2-TPD, and XPS techniques. The characterization results reveal that the presence of a small amount of Mn species can facilitate the incorporation of Cu and Mn ions into ceria lattice to form Cu-Mn-Ce-O solid solution. The synergistic effect of Cu and Mn species can reduce the redox potential of the composite catalysts, and produce large amounts of oxygen vacancies in the interface of CuOx, MnOx, and CeO2 oxides. The catalyst with Cu/Mn atomic ratio of 1/1 exhibits the best chlorobenzene elimination capability, oxidizing about 95% of the inlet chlorobenzene at 264°C with CO2 selectivity higher than 99.5%. The concentration and mobility of the chemically adsorbed oxygen are vital for the effective removal of surface Cl species, which inhibits the dissociation of oxygen molecules and decreases the reducibility of the copper and manganese species. It can be rationally concluded that the superior catalytic performance and durability of the mesoporous CuO-MnOx-CeO2 composite oxides are primarily attributed to the higher surface oxygen concentration and better active oxygen mobility.

Oxide diffusion in innovative SOFC cathode materials.

Oxide diffusion was studied in two innovative SOFC cathode materials, Ba(2)Co(9)O(14) and Ca(3)Co(4)O(9)+δ derivatives. Although oxygen diffusion was confirmed in the promising material Ba(2)Co(9)O(14), it was not possible to derive accurate transport parameters because of an oxidation process at the sample surface which has still to be clarified. In contrast, oxygen diffusion in the well-known Ca(3)Co(4)O(9)+δ thermoelectric material was improved when calcium was partly substituted with strontium, likely due to an increase of the volume of the rock salt layers in which the conduction process takes place. Although the diffusion coefficient remains low, interestingly, fast kinetics towards the oxygen molecule dissociation reaction were shown with surface exchange coefficients higher than those reported for the best cathode materials in the field. They increased with the strontium content; the Sr atoms potentially play a key role in the mechanism of oxygen molecule dissociation at the solid surface.

Adsorption and dissociation of oxygen molecules on Si(111)-(7×7) surface

The adsorption and dissociation of O2 molecules on Si(111)-(7×7) surface have been studied by first-principles calculations. Our results show that all the O2 molecular species adsorbed on Si(111)-(7×7) surface are unstable and dissociate into atomic species with a small energy barrier about 0.1 eV. The single O2 molecule adsorption tends to form an ins×2 or a new metastable ins×2* structure on the Si adatom sites and the further coming O2 molecules adsorb on those structures to produce an ad-ins×3 structure. The ad-ins×3 structure is indeed highly stable and kinetically limited for diving into the subsurface layer to form the ins×3-tri structure by a large barrier of 1.3 eV. Unlike the previous views, we find that all the ad-ins, ins×2, and ad-ins×3 structures show bright images, while the ins×2*, ins×3, and ins×3-tri structures show dark images. The proposed oxidation pathways and simulated scanning tunneling microscope images account well for the experimental results and resolve the long-standing confusion and issue about the adsorption and reaction of O2 molecules on Si(111) surface.

First-Principles Studies of the Activation of Oxygen Molecule and Its Role in Partial Oxidation of Methane on Boron-Doped Single-Walled Carbon Nanotubes

The nanostructured carbon materials have been widely tested as catalyst in a number of chemical reactions. The oxygen functional groups on nanostructured carbon catalyst are believed to be the active sites, for example, in the oxidative dehydrogenation reaction of hydrocarbons. However, the doping is one of the effective ways to tune the properties of nanostructured carbon materials. It will be important to examine the effect of doping on the catalytic properties of oxygen molecule on nanostructured carbon materials. In current work, the dissociation of the oxygen molecule on the boron-doped single-walled carbon nanotube (BSWCNT) and their catalytic properties in the partial oxidation of methane to formaldehyde are investigated by using first-principles calculations. Both defect-free BSWCNT and defective BSWCNT with a monovacancy are studied, and the comparisons between them are made. BSWCNT demonstrates a good ability for the dissociation of oxygen molecule. The favorable binding sites for the dissociate...

Can Si-doped graphene activate or dissociate O2 molecule?

Recently, the adsorption and dissociation of oxygen molecule on a metal-free catalyst has attracted considerable attention due to the fundamental and industrial importance. In the present work, we have investigated the adsorption and dissociation of O2 molecule on pristine and silicon-doped graphene, using density functional theory calculations. We found that O2 is firstly adsorbed on Si-doped graphene by [2+1] or [2+2] cycloaddition, with adsorption energies of −1.439 and −0.856eV, respectively. Following this, the molecularly adsorbed O2 can be dissociated in different pathways. In the most favorable reaction path, the dissociation barrier of adsorbed O2 is significantly reduced from 3.180 to 0.206eV due to the doping of silicon into graphene. Our results may be useful to further develop effective metal-free catalysts for the oxygen reduction reactions (ORRs), thus greatly widening the potential applications of graphene.

Dissociation and reconstruction of O2 on Al (1 1 1) studied by First-principles

The dissociative adsorption and reconstruction of oxygen molecule on Al (111) surface have been investigated by Density Functional Theory (DFT) with the generalized gradient approximation using structure optimization and a supercell approach. Four vertical and eight parallel sites of O2 adsorption on Al (111) surface were calculated corresponding to oxygen coverages of 0.22, 0.5 and 1 ML (monolayer). It is found that different surface geometries are formed after oxygen molecule dissociation on different sites of Al (111) surface, which is determined by oxygen original adsorption sites as well as oxygen coverage. The oxygen atoms coming from oxygen molecule dissociation tend to occupy the most stable adsorption sites of the Al (111) surface. When oxygen coverage is 1 ML, the dissociation of oxygen molecule is related to both its original adsorption site and the interaction between oxygen molecules. The correlation of surface reconstruction of Al (111) surface, adsorption site, adsorption energy and oxygen coverage is discussed in detail. The steering effect plays an important role in the oxygen molecule dissociative process.

사각형 유도 결합 플라즈마 시스템의 수치 모델링

Low pressure inductively coupled plasma characteristics of argon and oxygen are numerically simulated for a 400 mm rectangular type system with a plasma fluid model. The results showed lower power absorption profile at the corner than a circular one in a 13.56 MHz driven 1.5 turn antenna system with a drift-diffusion and quasi-neutrality assumption. Ions controlled by electric field are more non-uniform than metastables and the power absorption profile of oxygen plasma is affected by horizontal gas flow pattern to show 25% lower power absorption at the pumping flange side. Oxygen negative ions which are generated in electron collisional dissociation of oxygen molecules was calculated as 0.1% of oxygen atoms with similar spatial profile.

Ab initio modelling of UN grain boundary interfaces

The uranium mononitride (UN) is a material considered as a promising candidate for Generation-IV nuclear reactor fuels. Unfortunately, oxygen in air affects UN fuel performance and stability. Therefore, it is necessary to understand the mechanism of oxygen adsorption and further UN oxidation in the bulk and at surface. Recently, we performed a detailed study on oxygen interaction with UN surface using density functional theory (DFT) calculations. We were able to identify an atomistic mechanism of UN surface oxidation consisting of several important steps, starting with the oxygen molecule dissociation and finishing with oxygen atom incorporation into vacancies on the surface. However, in reality most of processes occur at the interfaces and on UN grain boundaries. In this study, we present the results of first DFT calculations on O behaviour inside UN grain boundaries performed using GGA exchange-correlation functional PW91 as implemented into the VASP computer code. We consider a simple interface (310)[001](36.8°) tilt grain boundary. The N vacancy formation energies and energies of O incorporation into pre-existing vacancies in the grain boundaries as well as O solution energies were compared with those obtained for the UN (001) and (110) surfaces

Electrochemical Oxygen Reduction on LaNi0.6Fe0.4O3-δ Film Electrode

Electrochemical oxygen reduction on an LaNi0.6Fe0.4O3-δ (LNF) dense film electrode was investigated by using AC impedance spectroscopy as functions of temperature (923~1073 K), oxygen partial pressure (10-3~1 bar), and DC bias (-50~+20 mV). It was found the oxygen reduction reaction on the LNF electrode is rate-controlled by the absorption and the dissociation of oxygen molecules at the surface, although other elementary reactions also might contribute to the total reaction rate. 18O isotope exchange and its depth profile measurements by using a secondary ion mass spectrometry (SIMS) were performed to give quantitative analysis for the rate determining step (RDS) on LNF. The conclusion derived from the SIMS measurements was in good agreement with that from the electrochemical measurements, showing that the surface reaction is a major cause of the resistance in the LNF electrode but the bulk diffusion also may contribute to the reaction rate.

Oxygen molecule dissociation on carbon nanostructures with different types of nitrogen doping

The energy barrier of oxygen molecule dissociation on carbon nanotubes or graphene with different types of nitrogen doping is investigated using density functional theory. The results show that the energy barriers can be reduced efficiently by all types of nitrogen doping in both carbon nanotubes and graphene. Graphite-like nitrogen and Stone-Wales defect nitrogen decrease the energy barrier more efficiently than pyridine-like nitrogen, and a dissociation barrier lower than 0.2 eV can be obtained. Higher nitrogen concentration reduces the energy barrier much more efficiently for graphite-like nitrogen. These observations are closely related to partial occupation of π* orbitals and change of work functions. Our results thus provide useful insights into the oxygen reduction reactions.