Diffusion Of Oxygen Molecules Research Articles

Multi-scale dynamic behaviors of oxygen entering carbon fiber/epoxy resin interfaces under thermal environment

Understanding the thermo-oxidative ageing behavior of carbon fiber/epoxy resin interfaces at multiple scales is crucial for structural optimization and durable design of composites. Here we report the effects of oxygen entering the interface on the 3D ageing crack evolutions, interface spatial structures, and multi-scale dynamic mechanisms for carbon fiber/epoxy composites under a thermal environment using experiments and molecular dynamics (MD) simulations. The dynamic behaviors under ambient temperature environments were studied for comparison. Ageing cracks first appear at the interface and then spread to the surrounding resin-rich region as the ageing time increases. Interface cracks provide channels for oxygen to enter the interior of the composite. The MD results show that interface systems with fewer oxygen molecules have serious interface cracks, weaker interaction energies and stronger diffusion capabilities than those with more oxygen molecules. The oxygen amounts entered the interface and the intermolecular interactions affect the interface dynamic behaviors. High temperature promotes the molecular movement, accelerates the interface cracking, weakens the interaction energy, and improves the diffusion capability. The diffusion of oxygen molecule from the interface to the epoxy matrix is a gradual process and is affected by the interface cracks.

Single Fe atoms anchored by short-range ordered nanographene boost oxygen reduction reaction in acidic media

The development of efficient and stable single-atom electrocatalysts with earth-abundant metals have emerged as a promising alternative to the costly Pt-based nanomaterials for oxygen reduction reaction (ORR). Herein, we synthesize a highly efficient electrocatalyst with single Fe atoms anchored by N-doped short-range ordered carbon loading on 2 D reduced graphene oxide (RGO). Unlike the highly graphitized carbon materials in previous ORR catalysts, in which the diffusion of oxygen molecules (∼3.46 Å) are blocked by long carbon chains and small interlayer spacing (∼3.4 Å), it is found that the Fe/N-doped nanographene possesses large interlayer spacing (>4 Å) and short carbon fragments in one layer. The unique nanographene structure in nanoscale can facilitate the transport of oxygen molecules to the active sites of atomically dispersed FeN4 and FeN5. In acidic media for ORR, as-prepared Fe1-N-NG/RGO catalyst exhibited half-wave potential (E1/2) of 0.84 V versus the reversible hydrogen electrode, and the loss of E1/2 is less than 5 mV during 15,000 potential cycles.

BaCo1‐xNbxO3−δ as a Promising Cathode for Intermediate Temperature Solid Oxide Fuel Cells

AbstractNb2O5 doped BaCoO3‐δ was synthesized using traditional solid‐state reaction method. The electrochemical performance, physical properties and rate‐determining step of BaCo1‐xNbxO3−δ as a cathode material for intermediate‐temperature solid oxide fuel cells (IT‐SOFCs) were investigated. The introduction of Nb in BaCo0.8Nb0.2O3‐δ(BCN20)brings a stable cubic phase and a relative lower TEC (∼16.94×10‐6 K−1) compared BCN20 with other Co‐based perovskites. The oxygen vacancy concentration (δ) for BCN20 symmetrical cell is 0.153. The area specific resistance (ASR) of BCN20 symmetrical cell is merely 0.0397 Ω⋅cm2 at 700 °C. Base on the above findings, BCN20 has a great electrochemical performance as a cathode material for IT‐SOFCs. Furthermore, we studies the reaction mechanism of BCN20 and concluded that desorption and diffusion of oxygen molecules is the oxygen reduction rate limiting step. Finally, full cell with BCN20 as cathode was tested and peak power density was measured to be 1042 mW⋅cm−2 at 800 °C.

Effects of Side Chain Length on the Structure, Oxygen Transport and Thermal Conductivity for Perfluorosulfonic Acid Membrane: Molecular Dynamics Simulation

Many researches have indicated that the side chain length of perfluorosulfonic acid (PFSA) polymers had nonnegligible effects on PFSA membrane properties. However, the effects have not been completely revealed yet. This paper uses molecular dynamics simulation to explore the effects of side chain length on the structure, oxygen transport and thermal conductivity of PFSA membrane. In PFSA membrane with longer side chains, the maximum size of water clusters is larger, while the connectivity of water clusters is poorer and size distribution of water clusters is more heterogenous. And the structural characteristics have a strong effect on the diffusion and solubility coefficient of oxygen molecules. The diffusion of oxygen molecules may be hindered due to the existence of small pores in PFSA membrane with longer side chains even at high water content, leading to a lower diffusion coefficient. In addition, with the increment of water content λ, the solubility coefficient of oxygen molecules in PFSA membrane with shorter side chains decreases more quickly at λ < 12, resulting in a most obvious difference of solubility coefficients for different side chain lengths when λ is about 12. Moreover, the thermal conductivity of PFSA membrane with shorter side chains is higher.

Fatty Acid Composition of Erythrocyte Phospholipids in Rats Exposed to Stress (Prolonged Swimming)

The fatty acid composition of phospholipids was studied in rat erythrocytes after exhausting swimming. It was shown that this stressful exposure does not affect the fatty acid (FA) composition of erythrocyte phospholipids. However, differences in the variability of quantitatively dominant fatty acids were detected in stress-exposed animals compared to unstressed control. In saturated acids (C16:0, 18:0) and polyenoic arachidonic acid (C20:4ω6), the variability was close to its control values, while in unsaturated fatty acids (C18:1, C18:2ω6) it exceeded those 3–4 times. The obtained results indicate significant alterations in the unsaturated fatty acid composition of erythrocyte membrane phospholipids. Due to unsaturated fatty acids, a potential arises in the insulating layer between two surface charges of the erythrocyte plasma membrane. This additional internal potential, alongside with the potential difference between outer and inner surfaces of the erythrocyte plasma membrane, affects aqueous pores and Na+, K+-channels which jointly mediate diffusion of oxygen molecules. The revealed extraordinary variability of unsaturated fatty acids (C18:1, C18:2) with their mobile ω-electrons may relate to the mechanism of chemical interaction between phospholipid fatty acids in the hydrophobic zone of the erythrocyte plasma membrane due to phospholipid diffusion. Analogous mechanism of chemical interaction (via a proton jump from the hydronium ion to the water molecule) occurs in the hydrophilic (aqueous) zone.

A two-step growth route of ternary aluminium doped zirconium oxide film on silicon

Co-sputtering and post-sputter oxidation were incorporated as a two-step growth route for the formation of ternary aluminium doped zirconium oxide (AlxZryOz) films on silicon (Si) substrate using Al-Zr alloy film as the template film. Post-sputter oxidation at 400, 600, 800, and 1000 °C has transformed the amorphous as-deposited Al-Zr film to crystalline AlxZryOzfilms. A mixed monoclinic-tetragonal phase of AlxZryOz films was formed at 400 and 600 °C, while above which, tetragonal phase was obtained. The increase of oxidation temperature has also encouraged the formation of aluminium zirconium silicate (Al-Zr-Si-O) interfacial layer (IL), owing to an increase in the adsorption and diffusion of oxygen molecules from the ambient. The presence of excess oxygen in the film oxidized at the highest temperature (1000 °C) has translated into the formation of oxygen interstitials residing in the lattice, which have induced mid-gap states at the band gap of the film. As a result, a degradation in leakage current density-voltage (J-V) characteristic was obtained and the corresponding structural, optical, and capacitance-voltage characteristics were presented in comparison to the films oxidized at lower temperatures.

Structural Control of Carbon-Free Catalyst Layer Using Connected Platinum-Iron Nanoparticle Catalyst for Improved Mass-Transport in Polymer Electrolyte Fuel Cells

We have developed the connected platinum-iron (PtFe) nanoparticle catalyst with a porous hollow capsule structure as a carbon-free catalyst-layer material for polymer electrolyte fuel cells (PEFCs). [1,2] As shown in Fig. 1A, this catalyst consists of a nanosized beaded network by the fusion of PtFe nanoparticles with a crystallite size of 6~7 nm and an L10type chemically-ordered (face centered tetragonal) structure. The beaded metal network is electrically conductive, enabling the removal of carbon supports form a catalyst layer. The carbon-free cathode catalyst layer using a connected PtFe catalyst exhibits high durability against start-stop cycles, because of elimination of carbon corrosion problems. In addition, the specific activity of a connected PtFe catalyst for oxygen-reduction-reaction (ORR) is about 9 times enhanced, compared with that of a commercial Pt-nanoparticle catalyst supported on carbon black (Pt/C). On the other hand, inside a cathode catalyst layer, complex phenomena occur during a fuel-cell operation, such as ORR on catalyst surface, diffusion of oxygen molecules, proton conduction via ionomers, etc. Thus, a high performance of PEFC requires not only high ORR activity and stability but also lower resistance of oxygen mass transport. In this study, the following structural effects on fuel-cell performances for the carbon-free catalyst layers using connected PtFe catalysts were investigated; (i) inner-space in hollow capsule, and (ii) inter-space between capsules (Fig. 1B). The effect of inner-space in hollow capsule was discussed by the comparison of the connected PtFe catalysts with hollow structure or on solid (silica) support. The inter-space between capsules was controlled by the use of different capsule sizes (capsule size = 300 nm, or 500 nm in diameter). The electrochemical analyses of the prepared catalyst layers revealed that the hollow structure and the enlargement of inter-space between capsules improved the IV performance, especially at the high current density region, implying an improved oxygen mass-transport due to a sufficient space for oxygen diffusion in the catalyst layer and/or effective removal of liquid water from the catalyst layer. Moreover, in this study, the structural effect of gas-diffusion layer on fuel-cell performances was also investigated. It was found that the gas diffusion layer with higher gas permeability would facilitate the removal of liquid water from the capsule catalyst layer, resulting in a lower oxygen-transport resistance. In this presentation, by means of structural and electrochemical analyses of the capsule catalyst layers, the relationship between the catalyst-layer nanostructures and the fuel-cell performances will be discussed in details. The knowledge obtained in this study will provide new insights into the design of a carbon-free catalyst layer to achieve an enhanced PEFC performance. [1] T. Tamaki, H. Kuroki, S. Ogura, T. Fuchigami, Y. Kitamoto, and T. Yamaguchi, Energy Environ. Sci., 8, 3545-3549 (2015). [2] H. Kuroki, T. Tamaki, and T. Yamaguchi, J. Electrochem. Soc., 163(8), F927-F932 (2016). Figure 1

Investigation of structural conversion and size effect from stretched bundle of electrospun polyacrylonitrile copolymer nanofibers during oxidative stabilization

The ultimate goal of this research is to develop continuous carbon nanofibers with superior mechanical strength. The hypothesis is that aligned and stretched polyacrylonitrile (PAN) copolymer nanofibers may be an innovative type of precursor, because the nanofibers possess high degrees of morphological and structural perfections; and due to size effect (i.e., the nanofibers are ~20 times thinner than the conventional microfibers), the formation of structural heterogeneities (e.g., sheath/core structure) can be effectively prevented/mitigated. In this study, a bundle consisting of aligned PAN copolymer nanofibers was first prepared by electrospinning (with nanofibers collected by a flowing water system) followed by 3 times stretching; the oxidative stabilization of precursor nanofiber bundle was then investigated. Compared to conventional microfibers, electrospun nanofibers had smoother surface, higher density, and higher degrees of crystallinity and macromolecular orientation. As a result, the activation energy for cyclization of nitrile groups was higher; nevertheless, the diffusion of oxygen molecules was easier and the distribution of oxygen was more uniform particularly when the stabilization temperature was 240°C or higher. Such a situation led to the reduction of activation energy for oxidative dehydrogenation, facilitated the structural conversion into aromatic and supra-molecular structures, and also prevented the formation of sheath/core structure.

Study on mass transfer property of oxygen molecules and kinetic regimes of pressured pulverized coal combustion

The effects of pressure on diffusion of oxygen molecules during the coal combustion could not be ignored. The compressibility factor of real oxygen is investigated to evaluate the deviation between real and ideal oxygen, and obtain the mean free path of real oxygen. Comparing the Knudsen pore diameter with the minimum pore diameter, it is found that with the increase of pressure, Knudsen diffusion cannot exist at low pressure and may delay to occur at higher temperature. When pressure exceeds 3.5 MPa, no Knudsen diffusion occurs within the whole temperature range of our research. Comparing the diffusion rate at 1 MPa with the burning rate, one can conclude that the combustion mainly take place on the internal and external surfaces, and the reaction is controlled by the chemical kinetics below 1400 K. When themperature is between 1400 K and 1600 K, the reaction is controlled by both the diffusion and the chemical kinetics. When the temperature is more than 1600 K, the combustion primarily happens on the external surfaces and is controlled by the diffusion.

Nitrogen‐Doped Carbon with Mesopore Confinement Efficiently Enhances the Tolerance, Sensitivity, and Stability of a Pt Catalyst for the Oxygen Reduction Reaction

Electrocatalysts for the oxygen reduction reaction (ORR) present some of the most challenging vulnerability issues reducing ORR performance and shortening their practical lifetime. Fuel crossover resistance, selective activity, and catalytic stability of ORR catalysts are still to be addressed. Here, a facile and in situ template‐free synthesis of Pt‐containing mesoporous nitrogen‐doped carbon composites (Pt‐m‐N‐C) is designed and specifically developed to overcome its drawback as an electrocatalyst for ORR, while its high activity is sustained. The as‐prepared Pt‐m‐N‐C catalyst exhibits high electrocatalytic activity, dominant four‐electron oxygen reduction pathway, superior stability, fuel crossover resistance, and selective activity to a commercial Pt/C catalyst in 0.1 m KOH aqueous solution. Such excellent performance benefits from in situ covalent incorporation of Pt nanoparticles with optimal size into N‐doped carbon support, dense active catalytic sites on surface, excellent electrical contacts between the catalytic sites and the electron‐conducting host, and a favorable mesoporous structure for the stabilization of the Pt nanoparticles by pore confinement and diffusion of oxygen molecules.

Diffusion of oxygen molecules in fluorine-doped amorphous SiO2

Abstract Effects of fluorine doping on the diffusion of interstitial oxygen molecules (O2) in amorphous SiO2 (a-SiO2) were compared to those obtained from a-SiO2 containing SiOH groups. Incorporation of moderate concentration ( ∼ 1 0 19 cm−3) of SiF groups gives rise to minor changes in diffusion parameters between 800 and 1100 ° C: only a slight decrease in solubility and an increase in the activation energy for diffusion can be detected. Incorporation of SiOH groups has similar weak effects on the solubility and activation energy for diffusion. These minor changes are most likely due to the enhancement of the flexibility of local Si–O network as a result of the dissociation of the network by SiOH and SiF groups. However, in contrast to the SiF doping, SiOH doping leads to a notable decrease in the diffusion coefficient. The heat of solution changes by ∼ 0.1 –0.2 eV at ∼ 1000 ° C and it is attributed to the glass transition of a-SiO2.

KINETIC MODELING STUDY OF A VOLOXIDATION FOR THE PRODUCTION OF U3O8POWDER FROM A UO2PELLET

A kinetic model for the oxidation of a UO₂ pellet to U₃O? powder has been suggested by considering the mass transfer and the diffusion of oxygen molecules. The kinetic parameters were estimated by a fitting of the experimental data. The activation energies for the chemical reaction and the product layer diffusion were calculated from the kinetic model. The oxidation conversion of a UO₂ pellet was simulated at various operating conditions. The suggested model explains the oxidation behavior of UO₂ well.

Inefficient Crystal Packing in Chiral [Ru(phen)3](PF6)2Enables Oxygen Molecule Quenching of the Solid-State MLCT Emission

The molecular oxygen quenching of the solid-state emission from pure crystals of Delta-Ru(phen)(3)(PF(6))(2), Lambda-Ru(phen)(3)(PF(6))(2), and racemic Ru(phen)(3)(PF(6))(2) (phen = 1,10-phenanthroline) was studied by emission spectroscopy. Crystals of the pure enantiomers exhibit significant and nearly identical emission-intensity quenching [0.36(2) and 0.33(2), respectively] in the presence of air [where the fraction quenched is (I(nitrogen) - I(air))/I(nitrogen)]; in comparison, the racemic compound shows a much lower value [0.05(2)]. The large difference in the quenching behavior is a result of major structural differences between the two chiral salts and the racemic salt. The chiral compounds crystallize in the space groups P4(1) and P4(3), respectively, with toluene and acetonitrile molecules in the lattice that can be partially removed to create void-space channels. These open channels allow the diffusion of oxygen molecules within the crystals and enable efficient emission quenching that is not possible in the closely packed racemic salt. Lifetime measurements, thermal gravimetric analysis, and single-crystal X-ray structure determinations support these conclusions.

Porous Crystalline Ruthenium Complexes Are Oxygen Sensors

Several highly emissive, crystalline salts (ClO4-, PF6-, BF4-, B(C6F5)4-, and tfpb-; B(C6F5)4- = tetrakis(pentafluorophenyl)borate; tfpb- = tetrakis(bis-3,5-trifluoromethylphenylborate) of the Ru(pp)32+ (pp = bpy (2,2‘-bipyridine), phen (1,10-phenanthroline) or 4,7-Me2phen (4,7-dimethyl-1,10-phenanthroline) lumophore have been tested as oxygen sensors. Oxygen detection by luminescence quenching correlates with the void space in the crystalline lattice, particularly in the case of [Ru(phen)3](tfpb)2 which has channels occupying approximately 136 Å3 per Ru in the crystals. The emission intensity and lifetime quenching of [Ru(phen)3](tfpb)2 displayed strictly linear (R2 = 0.9996) Stern−Volmer behavior (plots of I0/I and τ0/τ vs mole fraction of oxygen) with a slope of 2.43. A single exponential (τ = 640 nsec, pure nitrogen; 190 nsec, pure oxygen) is observed for the emission intensity decay for all oxygen concentrations. The time dependence of the emission caused by a step function air pressure drop is significantly affected by changing the light penetration depth when different excitation wavelengths are used (at 400 nm, t1/2 = 120 ms; at 518 nm, t1/2 = 2200 ms). These experiments are consistent with the diffusion of oxygen molecules in and out of [Ru(phen)3](tfpb)2 crystals with a diffusion coefficient on the order of 10-7−10-8 cm2/s. The technological significance of these crystalline oxygen sensors was demonstrated by long-term stability studies and by the successful calibration of a ballprobe sensor coated with crystalline [Ru(phen)3](tfpb)2 against a dissolved oxygen Clark electrode using a partial least-squares (PLS) model with a single principle component.

Effect of the temperature on the kinetics of the chemisorption of atmospheric oxygen by a sodium dithionite solution

Properties of a 0.0316 mol/l sodium hydroxide solution and the reactivity of reactants involved in the reaction of aerobic oxidation of sodium dithionite are studied over a temperature range of 283–353 K, and changes in motive forces of the rate-limiting, multistage interphase transfer of atmospheric oxygen are estimated. It is established that heating accelerates the adsorption of the gas by the liquid surface by a factor of 18, decreases the solubility of oxygen by a factor of 2, increases the rate of diffusion of oxygen molecules by a factor of 5, and, as a result, increases the absorption of the oxidizer from the air by a factor of 8.

A kinetic study of the oxidation of uranium dioxide

A kinetic model for the oxidation of a UO2 pellet is suggested by considering the mass transfer and the diffusion of oxygen molecules. The kinetic parameters were estimated by a fitting of the experimental data. The activation energies for the chemical reaction and the product layer diffusion were calculated from the kinetic model. The suggested model explains well the oxidation behavior of UO2.

Kinetics of the reduction of molecular oxygen from water by ultrafine copper in an ion-exchange matrix

The rate of the reduction of molecular oxygen from water with a low-capacity copper-containing electron-ion exchanger at various initial ionic forms, grain radii, and sizes of metal particles dispersed into pores. The applicability of the mixed-diffusion and diffusional-kinetic models incorporating a first-order irreversible reaction to describing the system under study was examined. The kinetic parameters of the system were determined within the framework of these models. It was found that the limiting stage of the process in the stationary mode is the internal diffusion of oxygen molecules to the redox sorbent particle. The increase in the rate of the absorption of oxygen by samples containing copper of higher dispersity was observed at the initial stage of the process and was likely associated with an increase in the surface area of the reactive interface.

Vapor-Phase Deposition for Dense CeO2 Film Growth on Porous Substrates

Pure and Sm-doped thin films were deposited on porous substrates by vapor-phase deposition, which is similar to the well-known electrochemical vapor deposition (EVD). By supplying metal chlorides (, ; Ce and Sm) vapor and oxygen to a disk-shaped porous substrate from opposite directions, a dense oxide film was grown on the chloride side of the substrate with high homogeneity. The films deposited are suitable for the electrolytes in the ceria-based intermediate temperature solid oxide fuel cells (SOFCs). The growth kinetics of these films was also discussed along with an observed growth rate and theoretical analysis based on oxygen flux and oxygen potential gradient over the film and the substrate. It was found that the film growth was governed by rates of each competitive process: diffusion of oxygen molecules through substrate pores, oxygen reduction at the film/substrate interface, and transport of electrochemical species ( and ) through the growing dense film.

Diffusion of Oxygen Molecules in Aqueous Saccharide Solution Measured by Fluorescence Correlation Spectroscopy(Papers presented at the 52nd Annual Meeting)

Diffusion of Oxygen Molecules in Aqueous Saccharide Solution Measured by Fluorescence Correlation Spectroscopy(Papers presented at the 52nd Annual Meeting)

Preparation and Characterization of Hybrid Organic-Inorganic Composite Material: Polymerization of m-Aminobenzoic Acid-Intercalated Into Zn/Al-Layered Double Hydroxides

Layered double hydroxides of aluminum and zinc (Zn/Al-LDH’s) were synthesized directly by hydrolysis at room temperature as reported elsewhere. After characterization, the material was reacted with m-aminobenzoat anion (m-NH2C6H4COO-) which undergoes polymerization in the interlayer space; resulting in the formation of a matrix with polymeric organic macromolecule. The resulting material along with the host LDH’s compound of Zn/Al-Cl was characterized by X-Ray Powder Diffraction (PXRD), Thermal Analysis (TG), Differential Thermal Analysis (DTA), and Fourier Transform Infrared Spectroscopy (FTIR). The study confirms the intercalation of m-aminobenzoat anion. Diffusion of oxygen molecules between the contact region of two anions in the interlayer space and oxidation of the anion lead to the formation of a polymer macromolecule. This intercalation compound result in a gallery height of 15.8 A, indicating that the guest anion stack to form a monolayer with the benzene rings perpendicular to the host layers, giving a suitable orientation for polymerization.