Frequency Arc Research Articles

Short-Term Strong Cathodic Polarization of Ni/YSZ and Pt/YSZ

The initial stages of YSZ reduction and formation of intermetallic phases at Ni∣YSZ interfaces on strongly cathodically polarized electrodes were studied by a number of potential sweep and impedance techniques. The measurements were carried out in the potential range −1.0 V to −3.0 V vs E°(O2) in H2/H2O at 650 and 750 °C. Below −1.7 V the cathodic current increases almost exponentially, mainly due to electronic conductivity in the YSZ. Reduction and oxidation peaks develop below and above −1.9 V, respectively. The peaks reveal a simultaneous reduction of YSZ at the Ni∣YSZ interface and reoxidation of a Ni-Zr phase. Charges calculated from the reoxidation peaks indicate a thickness of 200 nm for the layer formed by conditioning the electrode for 300 s at −2.6 V vs E°(O2). Impedance measurements show a suppressed arc decreasing with increasing polarization. Below −2.3 V vs E°(O2) a capacitive high frequency arc segment and an inductive low frequency loop develop. Both are ascribed to electronic conductivity. SEM/EDS microscopy on cross sections of samples cooled with and without polarization showed the formation of uniform and homogeneous intermetallic reaction layers which after reoxidation resulted in a two-phased nanostructures.

Effect of welding parameters on microstructure and tensile properties of CA-TIG welded AMS-5596 grade thin high temperature alloy sheets for gas turbine engine applications

This paper presents the influence of Constricted Arc TIG (CA-TIG) welding parameters specifically Main Current (MC), Arc Constriction Current (ACC), ACC Frequency (ACCF) and Constricted Arc Traverse Speed (CATS) on weld bead, microstructure and tensile properties of Superalloy 718 joints. The mechanisms responsible for microstructural modification and consequential influence on tensile properties of joints are discussed in brief. The results showed that MC and CATS extend predominant influence on the weld bead geometrical features, growth of dendrites, volume % and morphology of laves precipitates in fusion zone (FZ) and tensile properties of Superalloy 718 joints than ACC and ACCF. The tensile properties of joints decrease at higher levels of MC (80 A), ACC (60 A) and ACCF (20 ​kHz) due to the high heat input which supresses the refinement of dendritic FZ microstructure. The tensile properties of joints increase at incremental levels of CATS due to the reduced heat input leading to the refinement of dendritic FZ microstructure. However, the joints exhibit poor tensile properties at higher level of CATS (80 ​mm/min) due to the insufficient heat input leading to partial penetration of joints. The joints made using MC of 65 A, ACC of 50 A, ACCF of 4 ​kHz and CATS of 60 ​mm/min yielded 99.20% joint efficiency and 27.93% ductility which is much higher than TIG welding process. It is attributed to the refinement of FZ dendritic structure and development of finer laves precipitates by virtue of constricted arc and high frequency pulsation of ACC.

Spectral properties of the dynamic state transition in metal halide perovskite-based memristor exhibiting negative capacitance

The evolution of device properties in memristor switching between high- and low-resistance states is critical for applications and is still highly subjected to significant ambiguity. Here, we present the dynamic state transition in a 2D Ruddlesden–Popper perovskite-based memristor device, measured via impedance spectroscopy. The spectral evolution of the transition exhibits a significant transformation of the low frequency arc to a negative capacitance arc, further decreasing the device resistance. The capacitance–frequency evolution of the device indicates that the appearance of the negative capacitance is intimately related to a slow kinetic phenomenon due to ionic migration and redistribution occurring at the perovskite/metal contact interface. In contrast, no negative capacitance arc is observed during the state transition of a memristor device where the contact is passivated by an undoped Spiro-OMeTAD interfacial layer. The switching mechanisms are entirely different, one due to interface transformation and the other due to filamentary formation.

Development of an experimental facility for the study of microparticle initiated radio frequency vacuum breakdown.

An ongoing objective in the ion cyclotron range of frequencies (ICRF) systems is the improvement of power coupling to the plasma. During the last decade, this goal has been mainly pursued through the study of the coupling resistance, either by optimizing the antenna layout or by tailoring the scrape-off layer profile with gas puffing. Another approach is to increase the voltage handling capability of the ICRF system, limited by breakdown in the launchers or in the transmission lines. This paper describes the design of the ICRF Breakdown EXperiment (IBEX), a device to investigate fundamental aspects of radio frequency arcs under ICRF-relevant conditions. IBEX can achieve a peak voltage of 48 kV at 54MHz with a 5 kW input power.

The impact of spiro-OMeTAD photodoping on the reversible light-induced transients of perovskite solar cells

Hole transporting materials (HTMs) play essential roles in facilitating hole extraction and suppressing recombination in lead halide perovskite solar cells (PSCs). High levels of p-doping in HTMs is necessary for achieving high device performance, attributed to an increased electrical conductivity. In this work, we provide evidences that the poor performance of PSCs with low levels of doping (i.e., 4 mol% spiro-OMeTAD+) in spiro-OMeTAD is mainly caused by the presence of a Schottky barrier at the perovskite/spiro-OMeTAD interface, hampering hole injection. Under continuous illumination at open-circuit condition, the barrier gradually diminishes, increasing the PSC power conversion efficiency by 70-fold after 7 h. This process is completely reversible, returning to the initial poor performance after dark storage. We attribute this improvement in performance to a gradual photodoping of spiro-OMeTAD, triggered by the transfer of photogenerated holes and mediated by the slow migration of halide anions from perovskite to compensate the newly formed spiro-OMeTAD+. In-situ parallel analyses with impedance spectroscopy (IS) and photoluminescence are employed to gain insights into the charge dynamics along with light soaking. We find that the Schottky barrier resistance overlays with the recombination signal at the high frequency arc of IS, having important implications for the IS data analysis for PSCs. The work elucidates a major mechanism causing the slow efficiency variations during light/dark cycling, commonly observed in PSCs, which complicates the determination of long-term stability.

Research on the process of arc deionization under explosive high-speed airflow in semienclosed space

To study the process by which an explosive high-speed airflow extinguishes an arc and the characteristics of arc dielectric recovery in a semienclosed space, this study investigates the principles and processes of the formation, development, and extinction of an arc under the action of a high-speed airflow. When the impact arc occurs in a semienclosed arc-extinguishing chamber, the high-speed air suppresses arc development. Due to the high-speed airflow, the arc cools at an accelerated rate; the arc energy weakens, breakpoints occur, and the continuity of the arc energy channel is broken, preventing the arc from forming in the arc-extinguishing chamber and extinguishing it. This article employs AUTODYN software to establish a model for high-speed airflow arc extinguishing in a semienclosed space and then reveals a process by which a high-speed airflow extinguishes an arc in such a space. To verify whether a high-speed airflow can extinguish an arc, we conduct experiments in which high-speed airflow extinguishes a large impact arc and a power frequency arc. We recorded the arc extinguishing process with high-speed and ordinary cameras. The time taken to extinguish the arc is approximately 7 ms, and the arc does not regenerate.

Protective effect study of solid-phase arc-quenching device on superimposed lightning strike

Presently, the success rate of lightning protection is about 50% and one of the main reasons is the lack of effective protection against multiple superimposed lightning strikes. Superimposed lightning event is very likely to occur during lightning strikes. This paper reflects the research and practice on the protection of superimposed lightning, based on the solid-phase arc-extinguishing principle, using a lightning arc to trigger a strong jet electronegative gas-flow. And then a power frequency arc is extinguished through an empty cavity effect. It can be used to suppress one or more arc processes of working frequency. The protective effect and effectiveness of solid-phase arc-extinguishing device on μs-level lightning return stroke and ms-level repeated lightning strikes have been shown through engineering practices and simulations in FLUENT software.

Lightning Protection of 10-kV Distribution Lines by Multiple Breakpoints Arc-Extinguishing Lightning Protection Gap

This article introduces a 10-kV multiple breakpoints arc-extinguishing lightning protection gap, which can solve the lightning protection problem of 10-kV distribution lines. In order to investigate the arc-extinguishing characteristics of the device, ANSYS' Fluent software was used to simulate and analyze the high-speed airflow-coupled arc process. A magnetohydrodynamic (MHD) model has been developed to analyze the temperature distribution of the arc plasma in the arc-extinguishing chamber. The experiment modeling the lightning discharge effect and the lightning impulse combined frequency coupling experiment are performed to validate the effectiveness of the device. The test results indicate that the power frequency arc was extinguished by the device within 0.3 ms and did not rekindle with the effect of the power frequency voltage.

Investigation on characteristics of arc extinguishing time of a new lighting protection gap for transmission lines

The present research envisages the development of a novel arc extinguishing lightning protection gap in pursuit of reducing the lightning trip-out rate and accident rate. In the developed setup, the jetting stream arc extinction lightning protection gap device was used for transmission line. When this transmission line was struck by lightning and the lightning surge was going to break down the gap, the arc extinguishing lightning protection gap immediately jetted out sufficient electronegative gas flow that quickly cut off the arc and effectively prevented the insulator from being damaged by the arc. Furthermore, when the line was attacked by lightning, the generated overvoltage instantaneously broke the gap that was parallel to the insulator string, so that the lightning current was oriented to the earth from the gap. Simultaneously, it triggered the gas generator and generated a high speed stream, then extinguished the frequency continuous current arc rapidly, thus effectively reducing the rate of line trip to ensure the reliability of power supply. We used a high-speed camera and ordinary camera that automatically captured the process of the jetting stream arc in the extinction lightning protection gap device, while extinguishing the 1kA power frequency arc. The image of the high-speed camera indicated that the power frequency arc of 1kA was quenched in 10 ms before the relay protection action of the test loop, which made that the overhead line lightning flashover but the circuit breaker did not trip. Thus, a reduction in the rate of lightning trip was observed by the developed setup, and it has an immense potential for application at the transmission lines of China.

Electrochemical performance of La0.8Sr0.2MnO3 oxygen electrode promoted by Ruddlesden‐Popper structured La2NiO4

AbstractThe effects of introducing La2NiO4 nanocatalyst on the electrochemical performance of La0.8Sr0.2MnO3 are investigated under solid oxide electrolysis cell and fuel cell modes, as well as open circuit voltage. Extracted data from impedance spectroscopy are interpreted with the analysis of distribution of relaxation times. La2NiO4 infiltration effectively reduces the activation energy of the oxygen reactions from 1.35 to 0.99 eV. It also changes the rate controlling process of the overall reaction. Polarization behavior of La2NiO4‐infiltrated La0.8Sr0.2MnO3 electrode shows superior performance under electrolysis mode compared to the fuel cell mode. Drastic increase in the size of low frequency arc during anodic current passage in the non‐infiltrated La0.8Sr0.2MnO3 electrode is hampered by infiltration of La2NiO4 nanocatalyst. By applying anodic current on infiltrated La0.8Sr0.2MnO3, no displacement is observed in the position of high frequency peaks in the distribution of relaxation time graphs and only a small increase in height occurs for the low frequency arc. Additionally, La2NiO4‐infiltrated electrode impressively decreases overpotential by 74% compared to the non‐infiltrated one under electrolysis mode at 800°C.

Temperature dependency of activity of nano-catalysts on La0.6Sr0.4Co0.2Fe0.8O3−δ cathode of solid oxide fuel cells

In this study, Ag-ceria, Co-ceria, and Ba0.5Sr0.5Co0.8Fe0.2O3 nano-catalysts were introduced onto the structure of La0.6Sr0.4Co0.2Fe0.8O3−δ cathode of solid oxide fuel cells through infiltration technique and the electrochemical features of the infiltrated cathodes were examined by electrochemical impedance spectroscopy and analysis of distribution of relaxation times in the temperature range of 500–800 °C. The results revealed that Ba0.5Sr0.5Co0.8Fe0.2O3 exhibits considerable promoting behavior in the upper portion of the studied temperature range, while Co-ceria demonstrates significant catalytic activity for the oxygen reduction reaction at lower temperatures probably due to the active valence exchange of cobalt species in the spinel structure of cobalt oxide. Analysis of distribution of relaxation times revealed that low frequency arc of the impedance spectra is effectively hampered as a result of Ag-ceria and Co-ceria infiltration. Cathodic polarization of the infiltrated cells showed stable performance of the infiltrated electrodes over 50 h at 700 °C.

Use and Misuse of Electrochemical Impedance Spectroscopy (EIS) in Fuel Cell Research

Electrochemical impedance spectroscopy (EIS) is a powerful method to analyze the sources of performance loss mechanisms in fuel cells and other electrochemical devices. Its major advantage is the reasonable experimental effort necessary to perform EIS measurements. However, the results of EIS measurements can easily be misinterpreted: in particular, two major mistakes can regularly be found in the fuel cell literature. The first of these mistakes consists in using a set of interpretation tools developed for electrochemical reactions near equilibrium. The charge transfer resistance (RCT) obtained from EIS is equivalent to a linearization of the Butler-Volmer equation around the operation point. While there is a linear relation between RCT and the corresponding charge transfer overpotential ηCT when the system is near equilibrium, these two values become fully uncorrelated for irreversible reactions such as the oxygen reduction reaction (ORR) of PEFCs (see Figure 1a). This is a direct and simply calculable consequence of being in the region where the Tafel approximation of the Butler-Volmer equation is valid. Thus, the value of RCT can by no means be considered a measure – or even an indication – of the magnitude of the activation losses related to the ORR. Despite this easily demonstrable fact (as developed for example in equation 10.37 of the reference book by Orazem and Tribollet (1)), values of RCT are often compared and discussed in terms of ORR activity. The second recurrent error is the comparison of measurements performed on highly inhomogeneous experimental cells with equivalent circuits assuming a homogeneous distribution of parameters, in particular along the flow channels. A common related misinterpretation is the attribution of the low frequency arc to only the oxygen diffusion across the gas diffusion layer (GDL). In their pioneering work, Brett et al. (2), Schneider et al. (3, 4) and Kramer et al. (5) identified the origin of this low frequency arc as being an oscillation of O2 concentration induced by the sinusoidal current, which propagates along the gas flow channels. A full model taking into account these oscillations was shown to reproduce the experimentally measured spectra. Moreover, measurements on segmented cells comparing the local impedance obtained by applying the sinusoidal perturbation either to the entire cell or to one specific segment confirmed without doubt the proposed explanation (4). This effect was later confirmed by other researchers (e.g. (6, 7)). The models presented in the literature take into account both the diffusion across the GDL and the oxygen concentration oscillation in the gas channels. However, it can easily be calculated (see result in Figure 1b) that a cell which with no diffusion limitations at all would also exhibit the low frequency loop characteristic of the concentration oscillation in the gas channels. Despite the strong evidence supporting the importance of this oscillation, it remains largely ignored when analyzing EIS data of fuel cells. In this critical review presentation, we will analyze the use of EIS in PEFC research and the frequency of the two interpretation mistakes described above – both in recent publications and on a historical perspective. We will present simple rules to assess EIS results interpretation critically, as well as our view on the correct procedures to extract useful information out of EIS results. References M. E. Orazem and B. Tribollet, Electrochemical Impedance Spectroscopy (2nd Edition), John Wiley & Sons, Inc., Hoboken, New Jersey (2017), ISBN 9781119341222.D. J. L. Brett, S. Atkins, N. P. Brandon, V. Vesovic, N. Vasileiadis and A. Kucernak, Electrochemical and Solid-State Letters, 6, A63 (2003).I. A. Schneider, S. A. Freunberger, D. Kramer, A. Wokaun and G. G. Scherer, Journal of The Electrochemical Society, 154, B383 (2007).I. A. Schneider, D. Kramer, A. Wokaun and G. G. Scherer, Journal of The Electrochemical Society, 154, B770 (2007).D. Kramer, I. A. Schneider, A. Wokaun and G. G. Scherer, ECS Transactions, 3, 1249 (2006).G. Maranzana, J. Mainka, O. Lottin, J. Dillet, A. Lamibrac, A. Thomas and S. Didierjean, Electrochimica Acta, 83, 13 (2012).A. A. Kulikovsky, Journal of The Electrochemical Society, 159, F294 (2012). Figure 1

Filtration process combined with mechanical action, as a method for efficient extraction of endohedral metallofullerenes from carbon soot

The paper presents results of fullerenes and endohedral metallofullerenes extracts studies, isolated from the graphite rods carbon soot spray, and containing Y2O3 in a high frequency arc discharge. Two ways of extraction were applied and compared – (1) the classic method of Soxhlet extraction, and (2) the one developed by our team – extraction based on mechanical action combined with filtration. To implement the method, we used a laboratory version of installation, embodying technical solutions for rapid extraction. Chromatographic and mass spectrometry studies of fullerene extracts obtained by these methods revealed that by combining mechanical action with simultaneous filtration, we can significantly intensify and reduce the process of extracting fullerenes and endohedral metallofullerenes compared to the Soxhlet extraction method. This is especially evident in the release of endohedral metallofullerenes. Our method allows to reduce the release time of fullerenes from 10 g of carbon soot on laboratory installation up to 15 minutes, against the Soxhlet extraction method taking 18 hours. Whilst, the total number of fullerenes extracted by both methods almost coincides (the extraction method using mechanical action allowed us to extract 0.2-0.4 wt. % more), the composition of the isolated fullerene mixtures is different. The relative content of higher fullerenes and endohedral metallofullerenes exceeds when the mechanical action-based extraction method applied.

Study on impulse quenching based multichamber arc quenching structure

In order to reduce the lightning trip-out rate of grid power lines, a kind of impulse quenching based multichamber arc quenching structure (IQBMAS) is developed by the authors. This kind of MAS can attract the lightning impulse arc into its arc quenching channel and truncate the impulse arc into multiple parts rapidly. In this case, the impulse arc will not develop into steady power frequency current, so the lightning trip-out can be avoided. In this paper, simulations and experiments are conducted to verify the arc-quenching effect of IQBMAS on the basis of expounding the operating principle of IQBMAS, establishing the arc model in the channel as well as deriving the relevant numerical equations. The test result shows that IQBMAS can extinguish the power frequency arc of 10 kV lines within 1.5 ms with no reignition.

Influence of a Hole-Transport Layer on Light-Induced Degradation of Mixed Organic–Inorganic Halide Perovskite Solar Cells

Organic–inorganic halide perovskites (OIHPs) have been intensively studied in recent years for use in solar cells. Many studies have reported the light-induced phenomena of OIHP materials and their solar cells. In this study, we investigated the influence of a hole-transport layer (HTL) on light-induced degradation (LID) of mixed OIHP solar cells, especially at the OIHP/HTL interface, by hard X-ray photoelectron spectroscopy (HAXPES) and impedance spectroscopy. HAXPES shows accumulation of iodine and metallic lead in the vicinity of the OIHP/HTL and electron-transport layer/OIHP interfaces, respectively, after LID. Under light illumination and in the dark after LID, characteristic impedance responses are observed for a sample with a highly damaged OIHP/HTL interface as an intermediate frequency arc and negative capacitance, respectively, because of the electrochemical reaction in the vicinity of the OIHP/HTL interface. Overall, the results indicate that light-induced iodide diffusion to the OIHP/HTL inter...

Membrane dehydration with increasing current density at high inlet gas relative humidity in polymer electrolyte membrane fuel cells

The membrane hydration state of a polymer electrolyte membrane fuel cell is investigated in operando at high current densities (>1.5 A cm−2) for various inlet gas relative humidities (RH). The ohmic resistance, an indicator for membrane hydration, is found to have a non-monotonic dependence on current densities between 0 and 3.0 A cm−2, and the current density corresponding to the local minimum ohmic resistance is defined as the optimal hydration current density. While the relative thickness of the membrane increases with increasing inlet RH, an interesting observation was made whereby elevating the catalyst-coated membrane (CCM) temperature at current densities above the optimal hydration current density leads to membrane dehydration. Surprisingly, at high inlet gas RH values (70% and 100%) and high current densities, membrane dehydration results in membrane shrinkage (relative to its thickness at 0 A cm−2). We attribute the membrane dehydration and associated shrinkage to the reduced local RH at the CCM, even though the net water flux from the cathode to anode increases. The relative membrane thicknesses as a function of inlet RH conditions are determined from the low frequency arc time constants obtained via electrochemical impedance spectroscopy measurements.

Physical modeling of the electrochemical impedance spectra for the O2 reduction reaction in HTPEM fuel cells’ cathodic electrochemical interface

In this study we propose a microkinetic transition state pathway for the oxygen reduction reaction, (ORR), for the high temperature polymer electrolyte (HTPEM) fuel cell cathodic electrode, focusing on the importance of the cathodic impedance spectrum features, in the kinetic low current density, (lcd), regime of operation when ORR activation power losses are dominant. The ORR impedance spectrum involves a linear high frequency part feature and two arcs depending on the double layer capacitance, (Cdl), value. The high frequency linear part of the spectrum stems from the finite ionic, (H+), resistance in the catalyst layer. Our simulations revealed two arcs: all charge transfer reaction steps appear under the same high frequency arc directly related to the Cdl of the electrochemical interface, (EI), while the low frequency, (LF), arc originates from the relaxation of the adsorbed surface reaction intermediates on the catalyst surface, which is caused by the depletion of OHad on the surface. The kinetic model provides two Tafel slopes in the low and high current density (hcd) regime equal to 60 (mV/dec) and 180 (mV/dec) respectively.

Study of the n=3 Ruddlesden-Popper phases LnSr3Fe1.5Co1.5O10−δ (Ln = La, Pr, Nd) as oxygen reduction electrodes by impedance spectroscopy

The polarization resistance (Rp) of the n = 3 Ruddlesden-Popper phases LnSr3Fe1.5Co1.5O10−δ with Ln = La, Nd and Pr has been studied by Electrochemical Impedance Spectroscopy as a function of both temperature and oxygen partial pressure. The three electrodes show Rp values comparable to other Perovskite-related materials considered as candidates for cathode of solid oxide fuel cells. The lowest polarization resistance for oxygen reduction was found for PrSr3Fe1.5Co1.5O10−δ. The impedance spectra of the three electrodes reveal the presence of two contributions which has been preliminarily identified based on the dependence of the polarization resistance of these contributions on oxygen partial pressure (pO2) and temperature. For the intermediate frequency contribution, the rate limiting processes would be a mixture of oxygen adsorption plus charge transfer at the electrode surface with oxide ion diffusion whereas the low frequency arc would correspond to the oxygen molecule adsorption and dissociation and oxygen gas diffusion.

Reducing Porosity and Refining Grains for Arc Additive Manufacturing Aluminum Alloy by Adjusting Arc Pulse Frequency and Current.

Coarse grains and gas pores are two main problems that limit the application of additive manufacturing aluminum alloys. To reduce porosity and refine grains, this paper presents a quantitative investigation into the effect of pulse frequency and arc current on the porosity and grains of arc additive manufacturing Al–5Si alloy. The experiment results show that pulse frequency and arc current have a significant impact on the macrostructure, microstructure, porosity, and tensile properties of the samples. Fine grains and a uniform microstructure can be obtained with low pulse frequency and low arc current as a result of the rapid cooling of the molten pool. With the increase of pulse frequency, density shows a trend that firstly escalates and attains the maximum value at 50 Hz, but later declines as a result of the relation between pores formation and gas escape. Moreover, better tensile properties can be obtained at low pulse frequency and low arc current because of the finer grains.

Simultaneous Optical Transmission Relaxation and Impedance Spectroscopy Measurements of Thin Film Oxygen Surface Exchange Kinetics

The rate of oxygen exchange across mixed conducting oxide surfaces, often described via measurements of the surface exchange coefficient k, is a key metric impacting high temperature electrochemical device efficiency. Continuous measurement over time of native surface k values in realistic operating conditions can be accomplished by the contact-free optical transmission relaxation (OTR) approach, which relies on changes in oxygen stoichiometry being proportional to changes in optical absorption that can be detected by in situ optical transmission measurements. Conventional approaches to measuring k may suffer from being non-continuous (e.g., tracer exchange with ex situ secondary ion mass spectrometry), and therefore unable to observe changes in k over time, or require metal current collectors (e.g., ac-impedance spectroscopy measurements of area-specific resistance, or electrical conductivity relaxation), which could modify the surface reaction mechanisms and/or kinetics being probed. It is therefore of interest to compare k values obtained by ac-impedance spectroscopy (AC-IS) using metal current collectors and those obtained by OTR on native surfaces to examine the impact of current collectors and different measurement approaches. While k values obtained by various methods are already available in the literature, comparisons of such values measured on different samples may not provide much insight, as k can vary orders of magnitude depending on surface chemical composition, which is influenced by measurement conditions, processing, and thermal history. Therefore, in the present study, the two techniques were compared simultaneously on the same sample. A thin film of the mixed conductor SrTi0.65Fe0.35O3-x (STF35) was prepared by pulsed laser deposition on a transparent, ionically conducting (Zr,Y)O2-δ single crystal substrate. Its k values were measured by AC-IS on one region and by OTR on another region of the film, at 600 °C as a function of oxygen activity, controlled by gas partial pressure and/or dc bias applied across the substrate. Upon changing the oxygen activity, optical transmission relaxations resulted, corresponding to changes in the film oxygen stoichiometry and corresponding concentration of optically absorbing oxidized Fe (~Fe4+) species; such relaxation profiles were successfully described by the equation for surface exchange-limited kinetics appropriate for the film geometry, to obtain kchem values. From AC-IS, the fitted resistance and capacitance of the low frequency arc were used to determine both kchem (from the time constant) and kq (from the resistance), and additionally kchem values were estimated by multiplying kq by the thermodynamic factor (γ). Thin film γ values, determined from the film’s apparent volumetric chemical capacitance, were typically higher than the bulk values, determined from thermogravimetric measurements of non-stoichiometry, and varied with current collector material used (porous Au vs. porous Pt), suggesting a possible interfacial capacitance contribution. The AC-IS-derived kchem values and kq values multiplied by the thermodynamic factor (both bulk and thin film) were consistently orders of magnitude higher than the kchem values obtained by OTR, regardless of current collector material (Au or Pt). The results suggest a possible enhancement in k by the metal current collectors, which has similarly been observed previously for films of the mixed conductor (Pr,Ce)O2-δ. Additionally, long-term degradation in kchem and kq values obtained by AC-IS was also attributed to deterioration of the current collector, while hardly any degradation was observed in that time period in the optically-derived kchem values. The results suggest that, while the current collector could modify surface exchange coefficient evaluation by AC-IS, the contact-free OTR method offers a continuous, in situ approach to evaluate native surface exchange behavior.