Oxygen Diffusion Kinetics Research Articles

Enhancing the CO2 Adsorption of the Cobalt-Free Layered Perovskite Cathode for Solid-Oxide Electrolysis Cells Gains Excellent Stability under High Voltages via Oxygen-Defect Adjustment.

Solid-oxide electrolysis cells are a clean energy conversion device with the ability to directly electrolyze the conversion of CO2 to CO efficiently. However, their practical applications are limited due to insufficient CO2 adsorption performance of the cathode materials. To overcome this issue, the A-site cation deficiency strategy has been applied in a layered perovskite PrBaFe1.6Ni0.4O6-δ (PBFN) cathode for direct CO2 electrolysis. The introduction of 5% deficiency at the Pr/Ba site leads to a significant increase in the concentration of oxygen vacancies (nonstoichiometric number δ of oxygen vacancies increased from 0.093 to 0.132), which greatly accelerates the CO2 adsorption performance as well as the O2- transport capacity toward the CO2 reduction reaction (CO2RR). CO2 temperature-programmed desorption indicates that A-site cation-deficient (PrBa)0.95Fe1.6Ni0.4O6-δ (PB95FN) shows a larger desorption peak area and a higher desorption temperature. PB95FN also exhibits a greater presence of carbonate in Fourier transform infrared (FT-IR) spectroscopy. The electrical conductivity relaxation test shows that the introduction of the 5% A-site deficiency effectively improves the surface oxygen exchange and diffusion kinetics of PB95FN. The current density of the electrolysis cell with the (PrBa)0.95Fe1.6Ni0.4O6-δ (PB95FN) cathode reaches 0.876 A·cm-2 under 1.5 V at 800 °C, which is 41% higher than that of PB100FN. Moreover, the PB95FN cathode demonstrates excellent long-term stability over 100 h and better short-term stability than PB100FN under high voltages, which can be ascribed to the enhanced CO2 adsorption performance. The PB95FN cathode maintains a porous structure and tightly binds to the electrolyte after stability testing. This study highlights the potential of regulating oxygen defects in layered perovskite PrBaFe1.6Ni0.4O6-δ cathode materials via incorporation of cation deficiency toward high-temperature CO2 electrolysis.

Redox condition changes caused by impacts: Insights from Chang’e-5 lunar glass beads

Lunar materials are overall more reducing compared with their terrestrial counterparts, but the mechanism remains to be elucidated. In this study, we present a possible explanation for the changes in redox state of the lunar regolith caused by impact events, based on our investigations of the impact glass beads from Chang’e-5 mission. These glass beads contain iron metal grains and show concentration gradients of FeO and K2O (with or without Na2O) from their rims to centers. The compositional profiles exhibit error-function-like shapes, which indicates a diffusion-limited mechanism. Our numerical modeling results suggest that the iron metal grains on the surface of the glass beads were generated through the reduction of FeO by elemental K and (or) Na produced during the impact events. Meanwhile, the iron metal grains inside the bead may have formed due to oxygen diffusion driven by redox potential gradients. Furthermore, our study suggests that impact processes intensify the local reducing conditions, as evidenced by the presence of calcium sulfide particles within troilite grains that coexist with iron metal grains on the surface of the glass beads. This study provides insights into the oxygen diffusion kinetics during the formation of iron metal spherules and sheds light on the changes in redox conditions of lunar materials caused by impact events.

Temperature-Dependent Electrochemical Performance of Ta-Substituted SrCoO3 Perovskite for Supercapacitors.

Developing new electrode materials with good temperature-dependent electrochemical performance has become a great issue for the deployment of hybrid supercapacitors with wide temperature tolerance. In this work, a series of Ta-substituted SrCo1-x Tax O3-δ (x=0.05, 0.10, 0.15, 0.20) perovskites have been studied as positive electrodes for hybrid supercapacitors in terms of their structures, elemental valence states and electrochemical performances. Incorporating Ta into SrCoO3-δ perovskite not only stabilizes the crystallite structure but also notably improves electrochemical activities. The SrCo0.95 Ta0.05 O3-δ @CC delivers the highest specific capacity (Qsp ) of 227.91 C g-1 at 1 A g-1 , which is attributed to the highest oxygen vacancy content and the fastest oxygen diffusion kinetics. The hybrid supercapacitor SrCo0.95 Ta0.05 O3-δ @CC//AC@CC exhibits a high energy density of 22.82 Wh kg-1 @775.09 W kg-1 and a stable long-term cycle life (5000 cycles) with 90.7 % capacity retention. As temperature increases from 25 to 85 °C, the capacitance properties are improved at elevated temperatures for both electrode and device due to the increased electrolyte conductivity. The outstanding electrochemical results present that SrCo1-x Tax O3-δ perovskite holds good prospects for hybrid supercapacitors with wide temperature tolerance.

A new proton conductor-derived cathode with high performance for protonic ceramic fuel cells

The proton conductor Sc-doped SrSnO3 is tuned with Fe and Co elements to provide a novel cathode for protonic ceramic fuel cells (PCFCs). The new SrFe0.4Co0.4Sn0.1Sc0.1O3-δ (SFCSS) material is successfully synthesized and demonstrated adequate chemical stability against CO2, which is preferable to traditional Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) cathodes. Although SFCSS's oxygen diffusion kinetics are inferior to those of BSCF, the proton-conductor-derived design allows SFCSS to retain good proton diffusion and surface exchange abilities, which are critical in PCFC cathode reactions. As a result, in terms of fuel cell performance, SFCSS-based cathode-based fuel cells outperform BSCF-based fuel cells. A further improvement of fuel cell performance with a high peak power density of 1538 mW cm−2 at 700 °C is obtained for the cell using the single-phase SFCSS cathode. The SFCSS cathode's suitability for PCFCs is also demonstrated by the long-term stability test, which demonstrates that the cell can operate continuously for approximately 200 h without degradation. This study not only provides an efficient cathode for PCFCs but also an intriguing method for fabricating novel cathodes from Sc-doped SrSnO3 proton conductors.

New Sr2FeMo0.5X0.5O6 (X=Ni, Co, Mn, Zn) cathodes for proton-conducting SOFCs

Transition metal elements were employed to customize the standard Sr2Fe1.5Mo0.5O6 (SFM) material, with the goal of improving the performance of the SFM cathode in proton-conducting solid oxide fuel cells (H–SOFCs). Sr2FeMo0.5X0.5O6 (X = Ni, Co, Mn, Zn) materials were prepared, but it was discovered that only the dopants Ni and Co can form a pure phase, whereas the dopants Mn and Zn produced an obvious secondary phase. When comparing oxygen vacancies and oxygen diffusion kinetics, utilizing the Co-dopant exhibited clear advantages. The Co-doped SFM had a higher oxygen vacancy content and faster oxygen diffusion kinetics than both the standard and Ni-doped SFM cathodes. The energy barrier for the oxygen reduction reaction (ORR) at the Co-doped SFM cathode was 0.76 eV, which was much lower than that for the SFM and Ni-doped SFM, which were 5.52 and 2.28 eV, respectively. As a result, the Co-doped SFM's cathode reaction was greatly accelerated, resulting in a high fuel cell performance of 1306 mW cm−2 at 700 °C. This finding suggests that using the appropriate dopant can alleviate the low-performance problem of the traditional SFM cathode, resulting in a promising cathode option for H–SOFCs.

Effect of water droplet growth dynamics on electrode current in fuel-cell catalyst layers

Fuel cells are a promising next-generation energy-conversion technology designed to replace internal combustion engines in transportation applications. However, much work remains to optimize them. Operation at high humidities causes liquid water droplet formation on Pt catalyst particles during oxygen reduction, potentially impeding reactant arrival to the reactive electrode. In this work, four different cases of water droplet growth in fuel-cell catalyst layers are considered: pinned or advancing droplets on a bare Pt surface, advancing droplets on a Nafion film, and water-layer growth in carbon nanopores. Transient drop growth is captured with a combination of mass, species mass, and momentum balances, and the subsequent limiting current is determined via oxygen diffusion and Tafel kinetics. Water droplets are found not to be mass-transfer limiting due to the relatively large liquid-gas area compared to the Pt nanoparticle. Mass-transfer-limited behavior is calculated in carbon nanopores.

Bioinspired Hydrophobicity Coupled with Single Fe-N4 Sites Promotes Oxygen Diffusion for Efficient Zinc-Air Batteries.

The poor oxygen diffusion and sluggish oxygen reduction reaction (ORR) kinetics at multiphase interfaces in the cathode suppress the practical application of zinc-air batteries. Developing effective strategies to tackle the issue is of great significance for overcoming the performance bottleneck but remains challenging. Here, a multiscale hydrophobic surface is designed on the iron single-atom catalyst via a gas-phase fluorination-assisted method inspired by the structure of gas-trapping mastoids on lotus leaves. The hydrophobic Fe-FNC attains a higher peak power density of up to 226mW cm-2 , a long durability of up close to 140h, and better cyclic durability of up to 300 cycles compared to the corresponding Pt/C-based Zn-air battery. Experiments and theoretical calculations indicate that the formed more triple-phase interfaces and exposed isolated Fe-N4 sites are proposed as the governing factors in boosting electrocatalytic ORR activity and remarkable cycling durability for Zn-air batteries.

Oxygen diffusion kinetics during SiO2/SiC plasma oxidation

SiO2 as the gate dielectric is important for SiC MOSFETs. For the process to obtain SiO2, plasma oxidation as an alternative to conventional thermal oxidation has made some progress. However, the oxygen diffusion kinetics in plasma oxidation have not been systematically studied yet. In this work, the oxygen diffusion behavior in plasma oxidation is investigated by 18O isotope tracing technique and compared with that in thermal oxidation. Two kinetic models are proposed, which consider oxygen exchange between ambient and SiO2, and direct oxygen diffusion in SiO2 in terms of atoms and/or molecules. Moreover, for plasma oxidation, two types of oxygen diffusion have been studied quantitatively. This work unveils the oxygen diffusion mechanism, which would be meaningful for further research of plasma oxidation, such as optimizing conditions, understanding reactions, etc.

Radio-frequency magnetron sputtered thin-film La0.5Sr0.5Co0.95Nb0.05O3-δ perovskite electrodes for intermediate temperature symmetric solid oxide fuel cell (IT-SSOFC)

The present work explores the application of La0.5Sr0.5Co0.95Nb0.05O3-δ (LSCNO) perovskite as electrode material for the symmetric solid oxide fuel cell. Symmetric solid oxide fuel cells of thin-film LSCNO electrodes were prepared to study the oxygen reduction reaction at intermediate temperature. The Rietveld refinement of synthesized material shows a hexagonal structure with the R-3c space group of the prepared perovskite material. Lattice parameter and fractional coordinates were utilized to calculate the oxygen ion diffusion coefficient for molecular dynamic simulation. At 973 K, the oxygen ion diffusion of LSCNO was 1.407 × 10−8 cm2 s−1 higher by order of one magnitude than that of the La0.5Sr0.5CoO3-δ (7.751 × 10−9 cm2 s−1). The results suggest that the Nb doping provide the structural stability which improves oxygen anion diffusion. The enhanced structural stability was analysed by the thermal expansion coefficient calculated experimentally and from molecular dynamics simulations. Furthermore, the density functional theory calculation revealed the role of Nb dopant for oxygen vacancy formation energy at Sr–O and La–O planes is lower than the undoped structure. To understand the rate-limiting process for sluggish oxygen diffusion kinetics, 80 nm and 40 nm thin films were fabricated using radio frequency magnetron sputtering on gadolinium doped ceria electrolyte substrate. The impedance was observed to increase with an increasing thickness, suggesting the bulk diffusion as a rate-limiting step for oxygen ion diffusion. The electrochemical performance was analysed for the thin-film symmetric solid oxide fuel cell, which achieved a peak power density of 390 mW cm−2 at 1.02 V in the presence of H2 fuel on the anode side and air on the cathode side.

Inhibiting in situ phase transition in Ruddlesden-Popper perovskite via tailoring bond hybridization and its application in oxygen permeation

Inhibiting in situ phase transition in Ruddlesden-Popper perovskite via tailoring bond hybridization and its application in oxygen permeation

Efficient reversible CO/CO2 conversion in solid oxide cells with a phase-transformed fuel electrode

The reversible solid oxide cell (RSOC) is an attractive technology to mutually convert power and chemicals at elevated temperatures. However, its development has been hindered mainly due to the absence of a highly active and durable fuel electrode. Here, we report a phase-transformed CoFe-Sr3Fe1.25Mo0.75O7−δ (CoFe-SFM) fuel electrode consisting of CoFe nanoparticles and Ruddlesden-Popper-layered Sr3Fe1.25Mo0.75O7−δ (SFM) from a Sr2Fe7/6Mo0.5Co1/3O6−δ (SFMCo) perovskite oxide after annealing in hydrogen and apply it to reversible CO/CO2 conversion in RSOC. The CoFe-SFM fuel electrode shows improved catalytic activity by accelerating oxygen diffusion and surface kinetics towards the CO/CO2 conversion as demonstrated by the distribution of relaxation time (DRT) study and equivalent circuit model fitting analysis. Furthermore, an electrolyte-supported single cell is evaluated in the 2:1 CO-CO2 atmosphere at 800°C, which shows a peak power density of 259 mW cm−2 for CO oxidation and a current density of −0.453 A cm−2 at 1.3 V for CO2 reduction, which correspond to 3.079 and 3.155 mL min−1 cm−2 for the CO and CO2 conversion rates, respectively. More importantly, the reversible conversion is successfully demonstrated over 20 cyclic electrolysis and fuel cell switching test modes at 1.3 and 0.6 V. This work provides a useful guideline for designing a fuel electrode through a surface/interface exsolution process for RSOC towards efficient CO-CO2 reversible conversion.

Tuning Memristivity by Varying the Oxygen Content in a Mixed Ionic–Electronic Conductor

AbstractThe rising interest shown for adaptable electronics and brain‐inspired neuromorphic hardware increases the need for new device architectures and functional materials to build such devices. The rational design of these memory components also benefits the comprehension and thus the control over the microscopic mechanisms at the origin of memristivity. In oxide‐based valence‐change memories, the control of the oxygen drift and diffusion kinetics is a key aspect in obtaining the gradual analog‐type change in resistance required for artificial synapse applications. However, only a few devices are designed with this in mind, as they are commonly built around ionic insulating active materials. This shortcoming is addressed by using a mixed ionic–electronic conductor as functional memristive material. This work demonstrates how the oxygen content in La2NiO4+δ (L2NO4), tuned through post‐annealing treatments, has a critical influence on the memory characteristics of L2NO4‐based memristive devices. The presence of interstitial oxygen point defects in L2NO4 affects both its structure and electrical properties. High oxygen stoichiometry in the pristine state leads to an increased electrical conductivity, ultimately resulting in an improved memory window with highly multilevel, analog‐type memory programing capabilities, desirable for analog computing and synaptic applications in particular.

Revealing Strain Effects on the Chemical Composition of Perovskite Oxide Thin Films Surface, Bulk, and Interfaces

AbstractUnderstanding the effects of lattice strain on oxygen surface and diffusion kinetics in oxides is a controversial subject that is critical for developing efficient energy storage and conversion materials. In this work, high‐quality epitaxial thin films of the model perovskite La0.5Sr0.5Mn0.5Co0.5O3−δ (LSMC), under compressive or tensile strain, are characterized with a combination of in situ and ex situ bulk and surface‐sensitive techniques. The results demonstrate a nonlinear correlation of mechanical and chemical properties as a function of the operation conditions. It is observed that the effect of strain on reducibility is dependent on the “effective strain” induced on the chemical bonds. In‐plain strain, and in particular the relative BO length bond, is the key factor controlling which of the B‐site cation can be reduced preferentially. Furthermore, the need to use a set of complimentary techniques to isolate different chemically induced strain effects is proven. With this, it is confirmed that tensile strain favors the stabilization of a more reduced lattice, accompanied by greater segregation of strontium secondary phases and a decrease of oxygen exchange kinetics on LSMC thin films.

A Novel Analysis of Transient Isothermal 18O Isotopic Exchange on Commercial CexZr1−xO2-Based OSC Materials

A novel methodology for the analysis of 18O2-transient isothermal isotopic exchange (TIIE) response curves obtained over commercial mixed metal oxides upon the gas switch 16O2/Ar (30 min) → 18O2/Kr/Ar (t) at constant T in a flow CSTR micro-reactor in the absence of external and internal mass transport resistances and grain boundary effects, is presented for the first time. The specific aim of this analysis was to derive quantitative descriptors of the16O/18O exchange under pseudo-equilibrium conditions for the transfer rates of oxygen between the gas and solid phases, enabling the assessment of differences in the kinetics of bulk oxygen diffusion over a series of commercial OSC materials used in various catalytic applications (e.g. TWC), without the need of performing any mathematical and kinetic modelling of the surface/bulk oxygen diffusion processes. Based on these descriptors, commercial OSC mixed metal oxides prepared by the same chemical synthesis route but varying the value of one of the synthesis parameters, and having the same at.% composition, were proved to possess largely different transient kinetic rates and other features of the transient response curves of 16O/18O exchange strongly related to the bulk oxygen diffusion in the solids. This novel 18O2-TIIE analysis is quick and provides a reliable means for proving or disproving likely infringement of patented commercial mixed metal oxides OSC materials.

Transport and Electrochemical Properties of SrFe(Al,Mo)O3–δ

In this work, effects of molybdenum doping on the crystal structure, stability, electrical conductivity, oxygen permeability and thermomechanical properties of Sr(Fe,Al)O3–δ-based perovskites, were studied. The electrochemical performance of model anodes of solid oxide fuel cells (SOFCs), made of SrFe0.7Mo0.3O3–δ, was assessed. Whilst the introduction of Mo cations improves structural stability with respect to the oxygen vacancy ordering processes, excessive molybdenum content leads to a worse phase and mechanical stability under oxidizing conditions. Mo-doping was shown to decrease the thermal and chemical expansivity, to reduce p-type electronic conductivity and to increase n-type electronic conduction. The oxygen permeation fluxes through gas-tight Sr0.97Fe0.75Al0.2Mo0.05O3–δ membranes are determined by both the bulk oxygen diffusion and surface exchange kinetics. The role of the latter factor increases on decreasing temperature and reducing oxygen partial pressure. Due to a relatively high electrical conductivity and moderate thermal expansion coefficients in reducing conditions, SrFe0.7Mo0.3O3–δ-based anodes show a substantially high electrochemical activity.

Oxygen diffusion kinetics of an advanced three step heat treatment for zirconium alloy ZrNb7

ZrNb7 was exposed to a very specific three step heat treatment. The alloy is first oxidized in ambient air. The second step is a solid state reduction in vacuum, during which the oxide scale is dissolved and the oxygen diffuses into the substrate. Within a third step, the alloy is oxidized again to generate the desired ceramic coating on the outside followed by an oxygen hardened diffusion zone, that gradually reduces the hardness of the material from the outer surface to the inside. The high oxygen solubility of up to 29 at.% is distinctive in zirconium. Only titanium and hafnium show similar properties. Therefore, this rare phenomenon is further investigated with the main focus on the oxygen diffusion mechanisms through the oxide scale and the substrate. The reaction kinetics are evaluated and activation energies, parabolic oxidation constants and diffusion coefficients are determined for the two diffusion controlled processes: the oxidation and deoxidation of zirconium. This article reveals why the diffusion hardened zone does not appear in the desired thickness within a simple oxidation step and ideal process parameters are given concerning oxide thickness, cracks in the oxide scale and oxygen diffusion depth.

Oxygen diffusion and surface exchange kinetics for the mixed-conducting oxide La0.6Sr0.4Co0.8Fe0.2O3-δ

Studies of oxygen surface exchange kinetics for La0.6Sr0.4Co0.8Fe0.2O3-δ oxide were performed using the technique of isotopic exchange of molecular oxygen with analysis of gas phase isotopic composition in a static circulation system at the temperatures of 600-800 °С in the oxygen pressure range of 0.27-2.13 kPa. The values of interphase exchange rate and oxygen diffusion coefficient were determined. The effective activation energies for oxygen exchange and diffusion processes as well as the exponents in the dependence of these values versus oxygen pressure in the double logarithmic coordinates were calculated. The process of oxygen dissociative adsorption at the surface of La0.6Sr0.4Co0.8Fe0.2O3-δ oxide was found to be the rate-determining stage.

Use of gas cluster ion source depth profiling to study the oxidation of fullerene thin films by XPS

The analysis of organic materials such as phenyl-C61-butyric acid methyl ester (PC61BM) by depth profiling is typically fraught with difficulty due to the fragile nature of the sample. In this work we utilise a gas cluster ion source for the controlled depth profiling of organic materials that would historically have been too fragile to analyse and obtain quantitative compositional data through the whole thickness of the film. In particular we examine the oxygen diffusion and photo-oxidation kinetics of one of the most commonly used electron acceptor materials for many organic optoelectronic applications, namely PC61BM, in both neat films and in blends with polystyrene. Exposure to AM1.5G light and air under ambient conditions, results in a higher level of surface oxidation of blended PC61BM:polystyrene than is observed for either pure control film. Gas cluster ion source depth profiling further confirms that this oxidation is strongest at the extreme surface, but that over time elevated oxygen levels associated with oxidised organic species are observed to penetrate through the whole blended film. The results presented herein provide further insights on the environmental stability of fullerene based organic optoelectronic devices.

(Invited) The Mechanisms By Which Graphene Nano-Pigments Inhibit Corrosion-Driven Organic Coating Delamination

There has been significant recent interest in the development of nano-pigments based on graphene (graphene nano-pigments or GNPs) as possible additives to corrosion-resistant organic coatings. It has been claimed that lyophilized graphene particles dispersed in organic polymer coatings can effectively inhibit under-coating corrosion and corrosion-driven coating delamination. It has been further proposed that the inhibitory effect of GNPs results from either a) their blocking the through-coating diffusion of reactive species such as oxygen or b) the displacement of electrochemical processes (specifically cathodic oxygen reduction) away from the metal-coating interface and onto the intra-coating graphene surface. In this study a commercially available surface-modified GNP based on exfoliated graphite is used to systematically study the effect of GNPs on electrochemical and mass-transport processes occurring in GNP pigmented polymer films both in a free-standing state and as applied to iron and zinc surfaces. The GNP used consists of small secondary particles with a typical planar diameter of 0.3-5 microns and a thickness < 50nm. These secondary particles are in turn composed of varying number of graphene nanoplatelets. The GNP supplied had been subject to plasma processing intended to improve dispersibility in oxygenated solvents and promote compatibility with organic polymers bearing oxygen functionality. The GNP pigmented coatings consist of 30 micron thick solution-cast polyvinylbutyral (PVB) composites films. The PVB/GNP ratio is systematically varied to produce a series of composites with GNP volume fractions between zero and 0.2. The O2 permeability of these composites is determined using a photochemical method based on the atmospheric re-oxidation of leucomethylene blue in conjunction with free-standing films to follow the kinetics of through-coating oxygen diffusion. It is thus shown that O2permeability decreases sharply (by 1-2 orders of magnitude) as the GNP volume fraction is increased from zero towards 0.15. An in-situ scanning Kelvin probe technique is used to study the effect of varying GNP pigment volume fractions on the development of metal-coating contact potentials and on the kinetics of corrosion-driven coating (cathodic) delamination. Under circumstances where the GNP volume fraction is sufficiently high as to allow charge percolation through a continuous network of GNP particles contact potentials are measurable between the metal substrate and PVB/GNP composite coating on both iron and zinc. In both cases these contact potentials are consistent with the work function difference between the relevant metal and graphene/graphite. In the case of zinc this contact potential is significant (>0.5V) and is consistent with the GNP network being the cathode in any galvanic couple involving zinc and the GNPs. In the case of iron the contact potential is relatively small. When a penetrative defect is created in the PVB/GNP coating and the substrate exposed to aqueous sodium chloride electrolyte in an atmosphere of 95% relative humidity for up to 100 hours. On both iron and zinc it is shown that the rate of cathodic delamination becomes reduced by > 90% relative to the unpigmented case as at a GNP volume fraction increases. Typical SKP-derived time-dependent potential (Ecorr) versus distance (from the penetrative defect edge) profiles for unpigmented PVB and PVB/GNP composite coatings are presented. Delamination kinetics are quantified by plotting the position of the delamination front as a function of time for coatings comprising various GNP volume fractions. Similar dependence of delamination kinetics on GNP volume fraction are observed for composite coatings adherent to both iron and zinc. Analysis of these kinetics suggests that addition of GNP at > 2.5% volume fraction changes the delamination rate law from parabolic (half order) to linear (zero order) with respect to time. This is consistent with the rate limiting step changing from under-film cation mass transport to an interfacial processes such as O2 reduction becoming rate limiting. The mechanism of GNP inhibition is discussed in relation to the electrochemical and mass transfer-blocking properties of graphene. It is concluded that, although a displacement of cathodic O2 reduction away from the metal coating interface is possible (and in fact predicted) the observed inhibition effects are immediately consistent with the measured reduction in O2 permeability at the relevant GNP volume fraction.

Determination of oxygen diffusion kinetics during thin film ruthenium oxidation

In situ X-ray reflectivity was used to reveal oxygen diffusion kinetics for thermal oxidation of polycrystalline ruthenium thin films and accurate determination of activation energies for this process. Diffusion rates in nanometer thin RuO2 films were found to show Arrhenius behaviour. However, a gradual decrease in diffusion rates was observed with oxide growth, with the activation energy increasing from about 2.1 to 2.4 eV. Further exploration of the Arrhenius pre-exponential factor for diffusion process revealed that oxidation of polycrystalline ruthenium joins the class of materials that obey the Meyer-Neldel rule.