Oxygen Ion Diffusion Coefficients Research Articles

High Performance Protonic Ceramic Electrochemical Cells Operating at

Protonic ceramic electrochemical cells (PCECs) can operate in both fuel cell and steam electrolysis modes for efficient power generation and green hydrogen production. Thanks to the low activation energy of proton conduction, PCECs are uniquely capable of operating at temperatures below 600°C. Although some intriguing demonstrations of intermediate-temperature (500-600°C) PCECs (IT-PCECs) have been made in the last decade, the operating temperature of PCECs is still too high to revolutionize ceramic electrochemical cell technology, which is ascribed to the high ohmic resistance and positive electrode polarization resistance. It has been also recognized the electrode polarization resistance dominates the total resistance at <500°C. These challenges suggest both the electrolyte and positive electrode should be redesigned to lower the PCEC operating temperature.In this work, we present two main approaches to reducing electrolyte ohmic resistance, electrolyte-positive electrode contact resistance, and electrode polarization resistance, which enables PCECs operation at <500°C. First, by using the ultrasonic spray coating system to coat the electrolyte layer on a negative electrode substrate with low Ba-deficiency, a bamboo-structured, ultrathin, and chemically homogeneous electrolyte can be fabricated. Second, a newly in-situ formed composite positive electrode was developed, which enhances the interfacial bonding between the positive electrode and electrolyte, further reducing ASRo , while improving both bulk oxygen-ion diffusion coefficient and surface oxygen exchange coefficientat <500°C.The newly developed LT-PCECs attain outstanding power densities in fuel cell mode (as high as 0.77 W cm-2 at 450°C), and exceptional current densities in electrolysis mode (over -1.28 A cm-2 at 1.4 V and 450°C). Furthermore, reducing the temperature does not sacrifice the fuel flexibility of these ceramic fuel cells. We demonstrated that the PCECs can directly utilize ammonia and methane for power generation at <500°C. Exceptional durability has been also demonstrated in both fuel cell and electrolysis modes at <500°C.These results further emphasize that through the PCEC scalable manufacturing processes and novel positive electrode materials presented here, PCECs can be employed for power generation and H2 production at <500°C, thereby transforming the architectures and removing previous operational constraints of ceramic electrochemical cells for scaled operation. PCECs can therefore be considered as one part of the growing hydrogen economy, while leveraging the existing fossil fuel infrastructure and achieving higher energy efficiency and lower CO2 emissions.

Oxygen Ion Conduction Property of Solid Oxide Membrane Based on Multi-scale Analysis

In recent years, various environmental problems such as rising temperature, droughts, and extreme weather events have become more serious in many parts of the world because of global warming. One of the causes of the global warming is an increase in emissions of greenhouse gases such as CO2, CH4, and N2O, those are emitted during a combustion of fossil fuels such as coal, oil, and natural gas in thermal power generation. As energy consumption accelerates year by year, the depletion of fossil fuels is also becoming an issue. Therefore, hydrogen energy is attracting attention. Hydrogen is known as a clean energy because it reacts with oxygen to produce only water and chemical energy.Fuel cells are attracting attention as a new power generation device that produces electricity from hydrogen energy. Fuel cells generate electricity directly through chemical reactions, resulting in minimal power generation loss from energy conversion. Solid oxide fuel cells (SOFC), in which solid oxide electrolyte membrane (SOEM) is used as the electrolyte membrane, have particularly high-power generation efficiency. On the other hand, the operating temperature of SOFCs is extremely high (over 1000 K), which accelerates degradation of SOEM. Therefore, it is necessary to lower the operating temperature from high to medium (about 700 K) while maintaining high power generation efficiency.To solve this problem, we focus on dual-phasing and nano-structuring of SOEMs. Previous studies of SOEM have shown that dual-phase membranes have better ion transport performance than a single-phase membrane. For example, a dual-phase SOEM is composed of SSC (SrSc0.1Co0.9O3-d) with perovskite structure and SDC (Sm0.2Ce0.8O2-d) with fluorite structure. One the other hand, nano-structuring are nano-thin film and nano-crystalline. Nano-thin film is a method of forming an electrolyte film of several μm by layering nano-films of several nm in size. Nano-crystalline is a method to reduce a crystal size to several tens of nanometers. By these nano structures, the resistance of ion conduction is reduced, and ion conductivity is improved.However, the number of interfaces in dual-phase SOEM and nano structured membrane is expected to increase. Previous studies have reported a decrease in ion conductivity near the interface between different structures of membrane. This decrease in ion conductivity at the interface is caused by an increase in the energy barrier as the conduction path passes through the interface. The correlation between the reduction of ion conductivity and nano structures in membrane has not been clarified clearly.In this study, we analyze the mechanism of oxygen ion conductivity reduction near the interface by numerical simulations. Molecular simulations are performed to build up information by multi-scale analysis. Specifically, density functional theory (DFT), molecular dynamics (MD), and kinetic Monte Carlo (kMC) are performed in a bottom-up manner. First, MD simulations were performed using a potential model constructed from the energy states in the atomic arrangement at the interface obtained by DFT. We analyzed the ion conductivity at the interface and its crystal size dependence. We also create a hopping model of oxygen ions moving from site to site for kMC simulations. Next, kMC simulations are performed to analyze the oxygen ion conductivity in the dual-phase SOEM including interface, on a time and spatial scale similar to that of a real SOEMs.In this presentation, we report on the results of MD simulation. A dual-phase SOEM model consisting of SSC and SDC was used as the simulation model (Fig.1(a)). The diffusion coefficient of oxygen ions was obtained as an indicator of ionic conductivity. Because the ionic conductivity is determined by the balance between the energy barrier of the conduction path and the kinetic energy of the ions involved in ionic conduction. In this study, the activation energy for the diffusion was calculated as the energy barrier. The activation energy was estimated from Arrhenius relation of diffusion coefficient. The number of unit cells in the dual-phase SOEM model was varied to change the crystal size. As a result, both the diffusion coefficient and activation energy increase as the crystal size of SSC increases. On the other hand, as the crystal size of SDC increases, although the diffusion coefficient decreases, the activation energy increases (Fig.1(b)). These results show the dependence of the diffusion coefficient and activation energy on the crystal size in a dual-phase SOEM. Figure 1

A comprehensive random pore model kinetic study of hematite to iron reduction by hydrogen

The consistent growth of industrialization has intensified the need for Iron and steel. Thus, it is essential to improve the efficiency of iron manufacturing plants. This work studies the inherent kinetics of hematite reduction to Iron with H2 via a random pore model (RPM) as the most sophisticated non-catalytic gas–solid reaction model. In this regard, reduction tests were performed on a pure hematite pellet by changing the reduction temperature and H2 concentration. Then, kinetic parameters were calculated via an RPM based on the pellet's pore size distribution. Validations of the calculated kinetic parameters using other pure hematite pellets with different characteristics besides an industrial pellet proved the robustness of this inclusive approach. The activation energy for the H2 reduction was obtained at 40.87 kJ/mol. Also, the diffusion coefficient of oxygen ions through the iron product layer for the industrial pellet was measured at 2.83 × 10-17 m2/s.

High-Temperature Oxidation Behavior of Ni/Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; Composites with Various Ni Content

Al2O3 composites dispersed with 1, 5, 10, and 15 vol% nickel particles were prepared using a pulsed electric current sintering technique. High-temperature oxidation was conducted at temperatures ranging from 1200°C to 1350°C for 6–24 h in air. After oxidation, the sample surface mainly consisted of NiAl2O4 oxide. The growth of the oxidized zone in all sample groups followed a parabolic pattern. The influence of the Ni content on the high-temperature oxidation behavior of Ni/Al2O3 is discussed. A kinetic model was proposed to explain the growth of the oxidized zone. The diffusion coefficient of oxygen ions through the grain boundaries of the Al2O3 matrix can be obtained using the proposed model, which is in agreement with those in the literature.

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.

Understanding Oxygen Anion Transport in Nb-Doped La0.7Sr0.3CoO3 Perovskite Materials

Simple perovskite structured electrode materials of the series (LaxSr1-xCoO3- δ) are commonly utilised for high-temperature solid-state electrochemical cells and Li-air batteries with some limitations observed on prolong operations due to the structural instability associated with the segregation of strontium ions. In order to overcome this structural incompatibility, doping of heterovalent dopant at the B-site is proposed which could possibly improve upon the stability by controlling the segregation of surface cations. In addition, the doped structure is likely to provide faster oxygen anion transport through the vacancies in the structure, thereby improving its electrochemical performance. Herein, oxygen anion diffusion in pure La0.7Sr0.3CoO3-- δ (LSC) and Nb-doped La0.7Sr0.3Co0.95Nb0.05O3- δ (LCSN) perovskite structure is calculated using molecular dynamics (MD) simulations. Self diffusion coefficient of oxygen ions in the LSCN structure is observed to increase by an order of magnitude (1.356×10-8 cm2/s) on Nb doping as compared to the undoped LSC structure (6.499×10-9 cm2/s) at 1073 K. On varying the Nb concentration from 0.05 to 0.15 and optimum Nb concentration is estimated to be 0.05 corresponding to a maximum oxygen anion diffusivity in the structure (1.356×10-8 cm2/s) at 1073 K.

Binary-dopant promoted lattice oxygen participation in OER on cobaltate electrocatalyst

• A Fe/Mn doped cobaltate catalyst was studied experimentally and theoretically. • Binary-dopant intensifies the involvement of lattice oxygen for OER. • The configurational entropy effect may determine the unique property of material. Lattice oxygen-mediated mechanism (LOM) on perovskite oxides for oxygen evolution reaction (OER) process has revealed kinetic superiority over conventional adsorbate evolution mechanism (AEM). However, feasibly enhancing the participation of lattice oxygen is still challenging. Here we designed a perovskite cobaltate (La 0.6 Sr 0.4 Co 0.8 Fe 0.1 Mn 0.1 O 3-δ , LSCFM) nanofiber, and discovered that the co-incorporation of Fe/Mn elements significantly intensifies the involvement of lattice oxygen for OER. Compared with its mono-dopant (Fe or Mn only) counterparts, the LSCFM gives rise to higher surface oxygen vacancies (V o ) concentration and faster oxygen ion diffusion coefficient, endowing a small overpotential of 343 mV at 10 mA cm −2 and low Tafel slope of 63 mV dec −1 . The strongest pH-dependent activity and metal–oxygen covalency are further unveiled on LSCFM by experimental and theoretical approaches, evidencing that the promoted OER kinetics on LSCFM predominantly stems from the formation of reactive lattice oxygen site.

The effect of atomic polarization on the diffusion coefficient of oxygen ions in cubic zirconia

We study single crystal zirconia using molecular dynamics method. We calculate the diffusion coefficient of oxygen ions in the temperature range from the occurrence of diffusion at our calculation parameters to the loss of stability of the crystal. In the potential of interatomic interactions, in addition to conventional terms, we introduce into our model the interaction due to the polarization of atoms. These interactions turned out to be crucial for the correspondence between the calculations and available experimental data.

Localization model description of diffusion and structural relaxation in superionic crystalline UO2.

We test the Localization Model (LM) prediction of a parameter-free relationship between the α-structural relaxation time τα and the oxygen ion diffusion coefficient DO with the Debye-Waller factor ⟨u2⟩ for crystalline UO2 under superionic conditions where large anharmonic interactions lead to non-Arrhenius relaxation and high ion mobility. As in a previous study of structural relaxation in Cu-Zr metallic glass materials having a range of compositions, we find that the LM relationship between the picosecond atomic dynamics ("fast" beta relaxation) and the long-time structural relaxation time and oxygen ion diffusion coefficient holds to an excellent approximation without any free parameters over the full range of temperatures and pressures investigated in our simulations.

The measurement of the diffusion coefficient of oxygen ions in the YBa2Cu3O7-x layer of the electro-resistance memory

The measurement of the diffusion coefficient of oxygen ions in the YBa2Cu3O7-x layer of the electro-resistance memory

Diffusion mechanism of oxygen ions in La2Zr2O7/YSZ composite ceramics

In this paper, the diffusion mechanism of oxygen ions in La2Zr2O7/YSZ (LZ/YSZ) composites was investigated experimentally and numerically. LZ/YSZ composite samples with multiple amounts of LZ were successfully synthesized via a two-step sintering process. The so-obtained samples preserved most of the tetragonal phase (82.2 mol%) in YSZ. Moreover, an adhesive grain boundary and good chemical compatibility between YSZ and LZ grains were verified in the composite samples. The measured impedance spectra revealed that pure YSZ is an excellent oxygen ionic conductor, whereas the LZ can serve as an effective oxygen ionic isolator at high temperatures as further confirmed via the molecular dynamics simulation. For LZ/YSZ composites, the measured ionic conductivity decreases nonlinearly with the increase of the volume fraction of LZ, indicating that the addition of LZ can significantly reduce the oxygen ionic conductivity of these composites. More specifically, the simulation results showed that pores and LZ crystals would reduce the diffusion coefficient of oxygen ions, especially for the oxygen ions near the LZ/YSZ interfaces or the pore surfaces. Furthermore, we demonstrated that the bulk diffusion coefficient in YSZ increases as a direct consequence of the application of tensile stress induced by the lattice distortion between LZ and YSZ. However, the ionic conductivity in the LZ/YSZ composite was not enhanced due to the dominant ‘blocking effect’ from pores and interfaces. Indeed, we experimentally proved that both LZ grains and closed pores would reduce the ionic conductivity as a result of the ‘blocking effect’.

Oxygen reduction at the three-phase boundary of PrBaCo2O5+δ-Sm0.2Ce0.8O1.9 composite

Oxygen reduction at PrBaCo2O5+δ-Sm0.2Ce0.8O1.9 (PBC-SDC) composite might take place at the PBC-gas two-phase interface (2PB) as well as the PBC-SDC-gas three-phase boundary (3PB). This work investigates oxygen reduction process at the 3PB of PBC-SDC composite using electrical conductivity relaxation technique. The obtained results indicate the reaction at 3PB is much more facile than that at 2PB, which contributes up to 80% of the total oxygen incorporated to the composite when 60% wt. % SDC is introduced. The reaction rate constant at 3PB shows non-linear dependence on 3PB length, suggesting that the oxygen incorporation reaction is not confined at 3PB. It is possible that the oxygen species adsorbed on PBC transfer to the surface of SDC via a spillover phenomenon to combine with the oxygen vacancies from SDC. The introduction of SDC results in increased chemical oxygen ion diffusion coefficient by a factor up to 3.37, and chemical oxygen surface exchange coefficient by a factor up to 3.06 when 60wt. % SDC is used. The enhanced oxygen transport properties are also demonstrated with symmetrical cells using electrochemical impedance spectroscopy. The interfacial polarization resistance is reduced from 0.281Ωcm2 for a bare PBC electrode to 0.107Ωcm2 at 700°C for a PBC-SDC composite electrode with 60wt. % SDC.

Kinetic analysis of the interactions between calcium ferrite and coal char for chemical looping gasification applications: Identifying reduction routes and modes of oxygen transfer

Chemical Looping Gasification (CLG) is an emerging technology that shows promise for efficient coal gasification by eliminating the need for energy intensive gas separations to achieve a non-nitrogen diluted syngas stream. Oxygen from oxygen carriers, such as CaFe2O4, are used for coal gasification in place of conventionally produced gaseous oxygen from cryogenic separation of air. These oxygen carriers are unique for their ability to selectively oxidize coal to form syngas and show limited reactivity with syngas components (H2, CO). This study was carried out to determine the kinetic model representation and parameters associated with the selective oxidation of coal derived char (Wyodak and Illinois #6) with a metal ferrite (CaFe2O4) of which are needed for advancement of the process concept. Using thermogravimetric analysis (TGA) coupled with mass spectrometry, the selective oxygen release from metal ferrite in the presence of char by proximal contact was examined. The application of model fitting approaches was used to describe controlling resistances during oxygen release. A combination of the modified shrinking core model (SCM) with planar oxygen ion diffusion control and reaction order based models were applied for kinetic parameter determination. CaFe2O4 particle size plays a major role in the prevailing mode of oxygen release. Particle sizes on the range of 40–50µm tend to favor first order kinetically controlled regimes independent of geometric and diffusion controls. The probability for oxygen ion diffusion controlling regimes increased when the particle size range of the oxygen carrier was increased up to 350µm. Char type also impacted the prevalence of the controlling regime. Higher ranked chars react in a slower manner, limiting the gradient for oxygen ion release from the oxygen carrier. Activation energies determined for this process range from 120 to 200kJ/mol and oxygen ion diffusion coefficients are on the order of 10−8cm2/s. It is suggested that oxygen ion movement is regulated by lattice diffusion out of partially reduced phases (Ca2Fe2O5) and through reduced outer layers composed of CaO and Fe. The controlled movement of oxygen ions influences the rate of carbon oxidation in the char and therefore the selectivity towards partial oxidation products, which are desirable in CLG applications.

Investigation of Oxygen Diffusion in Irradiated UO2 with MD Simulation

AbstractIn this study, irradiated UO2 is analyzed by atomistic simulation method to obtain diffusion coefficient of oxygen ions. For this purpose, a couple of molecular dynamics (MD) supercells containing Frenkel, Schottky, vacancy and interstitial types for both anion and cation defects is constructed individually. Each of their contribution is used to calculate the total oxygen diffusion for both intrinsic and extrinsic ranges. The results display that irradiation-induced defects contribute the most to the overall oxygen diffusion at temperatures below 800–1,200 K. This result is quite sensible because experimental data shows that, from room temperature to about 1,500 K, irradiation-induced swelling decreases and irradiated UO2 lattice parameter is gradually recovered because defects annihilate each other. Another point is that, concentration of defects enhances the irradiation-induced oxygen diffusion. Irradiation type also has the similar effect, namely oxygen diffusion in crystals irradiated with α-particles is more than the crystals irradiated with neutrons. Dynamic Frenkel defects dominate the oxygen diffusion data above 1,500—1,800 K. In all these temperature ranges, thermally induced Frenkel defects make no significant contribution to overall oxygen diffusion.

Determination of Oxygen Diffusion Coefficient in Oxidation Films of the AISI 439 Ferritic Stainless Steel

In order to investigate the role of oxygen diffusion in the oxidation process of the AISI 439 ferritic stainless steel, oxygen ion diffusion coefficients were determined, for the first time, in oxide films formed by the oxidation of this steel. Steel samples were firstly oxidized from 750o C to 900o C, in synthetic air, in order to grow oxide films mainly made up of chrome oxide; the oxygen diffusion experiments were then performed using the stable isotope 18O as oxygen tracer. The introduction of the 18O in the oxide film was performed by means of the gas-solid isotopic exchange method, in the temperature range of 750-900o C, in Ar+21%18O2 atmosphere. The 18O diffusion profiles were established by secondary ion mass spectrometry (SIMS). Parabolic oxidation constants calculated by means of Wagner´s theory, using the oxygen ion diffusion coefficient determined by our experimental process, are greater than oxidation constants previously determined in oxidation experiments from 850 to 950º C, in air, which indicates that the oxygen ion diffusion is large enough to assure the growth rate of the oxide film formed by the oxidation of the AISI 439 steel in these temperatures.

Oxygen Diffusion Study in Oxidation Films of the AISI 304 Austenitic Stainless Steel

Oxygen ion diffusion coefficient was measured, for the first time, in oxide films grown by the high temperature oxidation of the AISI 304 austenitic stainless steel. The steel samples were polished and then oxidized in synthetic air in order to grow the chromia oxide (Cr2O3) film. The oxygen diffusion experiments in the oxide films were performed by using the18O isotope as oxygen tracer. The isotope diffusion studies were performed from 750 to 900o C, in Ar +21%18O2 atmosphere and the oxygen ion diffusion profiles were established by secondary ion mass spectrometry (SIMS) analysis. From the18O diffusion profiles, the bulk, effective and grain boundary diffusivities were determined. Using Wagner´s theory, it is shown that, under the used experimental conditions, the oxygen ion diffusion is large enough to assure the growth rate of the chrome oxide films formed by the oxidation of the AISI 304 stainless steel.

MOLECULAR DYNAMICS SIMULATION OF UO2: AN ALTERNATIVE RIGID ION MODEL POTENTIAL

A semi-empirical effective interionic potential model has been parameterized to investigate UO 2 by molecular dynamics simulation technique. The simulations were performed in the constant pressure–temperature ensemble between 300 K–3200 K at 100 K intervals. The pair distribution functions and coordination numbers signal the onset of structural changes at temperatures in accord with the Bredig transition and melting. The oxygen ion diffusion coefficients calculated from the mean square displacements markedly increase the liquid like value at T &gt; 2100 K . The transition to the superionic state and melting are well reproduced within the limitations of a rigid ion potential.

Effect of Oxygen Ions Diffusion on Steel Corrosion in Concrete

Oxygen ions are the necessary condition for steel corrosion which occurs when the steel’s passive film is destroyed. Oxygen ions diffusion directly influences steel corrosion rate. The paper, starting from the steel corrosion mechanism, summarized the testing technology and the research progress of oxygen ions diffusion coefficient, analyzed the influencing factors and studied further the effect of oxygen ions diffusion on steel corrosion in concrete. The testing technology of oxygen ion diffusion coefficient is combined with the testing method of steel corrosion rate, and the relationship between oxygen ions diffusion coefficient and steel corrosion rate are established.

Surface exchange and bulk diffusion properties of Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3− δ mixed conductor

Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3− δ (BSCF) is a mixed conducting oxide that shows high oxygen permeability to perform as a ceramic membrane and high electrochemical activity for oxygen reduction to perform as a cathode of solid oxide fuel cells. Both performances are closely related to the bulk and surface properties of the BSCF oxide. In this study, the chemical bulk diffusion coefficient ( D chem) and chemical surface exchange coefficient ( k chem) of BSCF at various temperatures and oxygen partial pressures are determined by an electrical conductivity relaxation (ECR) method. Both D chem and k chem are found to be dependent on p O 2 with positive effect. Ea of D chem and k chem are respectively 111 ± 5 and 110 ± 6 kJ mol −1 between 600 and 800 °C. Oxygen-ion diffusion and tracer diffusion coefficients are estimated from D chem and compared with the literature results. Ionic conductivities are further derived according to the Nernst–Einstein relation. The poisoning effect of CO 2 on the performances of BSCF is further investigated by the ECR method in combination with oxygen temperature-programmed desorption technique. The presence of CO 2 causes a substantial decrease in k chem, however, the surface kinetics can be recovered by performing re-calcination in an oxidative atmosphere at 900 °C, agreeing well with literature reports.

Effect of Cr 2O 3 on the 18O tracer incorporation in SOFC materials

Investigations of the impact of Cr 2O 3 overlayers on the oxygen self diffusion in two SOFC materials were conducted to gain insight into the Cr poisoning mechanism at the cathode side of solid oxide fuel cells (SOFCs) with stainless steel interconnects. High density Y 0.15Zr 0.85O 2 (YSZ) and La 0.6Sr 0.4Co 0.2Fe 0.8O 3 (LSCF) sintered pellets were covered with 3 to 30 nm Cr overlayers that were subsequently oxidized, forming Cr 2O 3. Standard 18O tracer diffusion experiments at 800 °C were performed and ToF-SIMS profiling revealed that the oxygen ion diffusion coefficients were unaffected by the thin Cr 2O 3 overlayers, which is predictable since they are a bulk property, but the extracted effective surface exchange coefficients varied with Cr 2O 3 overlayer thickness. Solid-state reaction measurements and electronic structure considerations concerning the surface exchange, led to the conclusion that the observed oxygen uptake hindrance for Cr 2O 3 capped LSCF and the slight increase of the surface exchange coefficient for Cr 2O 3 capped YSZ can be attributed to the electronic properties of Cr 2O 3. A critical thickness for Cr 2O 3 was determined to be 12 nm where the transition from decreasing cathode-performance to a Cr 2O 3-property-governed regime occurs.