Veyis Gunes | Universite du Maine (original) (raw)
Papers by Veyis Gunes
International Journal of Computational Materials Science and Engineering, Jun 1, 2013
In this paper, a method of electronic conductivity measurement is presented. It combines two well... more In this paper, a method of electronic conductivity measurement is presented. It combines two well known methods of electrochemistry: cyclic voltammetry and chronoamperometry. This DC technique uses the Hebb–Wagner approach to block ionic conduction (when steady state conditions are reached) and allows electronic conduction of solid electrolytes to be determined. In order to get short diffusion times, a micro contact is used as an ion blocking electrode. However, as the electronic conduction in electrolytes is and should be very low, the current is also very low, typically some tens of nanoamps. Thus, the heating system inevitably generates noise problems that are solved using a median filter. As opposed to other related work, our system allows the determination of the conductivities without any preliminary smoothing or fitting of the curves (since the noise is strongly reduced). Some results with oxygen ion conductors are also given.
Inorganic Materials, Oct 22, 2014
We report a study and comparative analysis of the medium temperature (850-1000°C) ionic and total... more We report a study and comparative analysis of the medium temperature (850-1000°C) ionic and total conductivities of zirconia stabilized by yttria and scandia based mixed oxides. Zirconia stabilized by combined yttria and scandia based dopants is shown to have low electronic conductivity in a wide range of oxygen activities. Our data suggest the possibility of using the synthesized materials as membranes in inter mediate temperature ceramic fuel cells.
Materials in engineering, Aug 1, 2010
Sensorial tests on silicones tackiness perception with naïve consumers show that the stickiness s... more Sensorial tests on silicones tackiness perception with naïve consumers show that the stickiness sensation can be disturbed by the sensation of finger penetration into the sample. Indeed a frequent report is that a non-expert people cannot perceive whether tackiness sensation is related to the material adhesion properties or whether it is related to the finger penetration. The samples are both elastomers silicones but some are gel-like elastomers and others are compact silicones. We use an experimental device to realize indentation tests in order to try to differentiate mechanically the two silicones. The apparatus developed in the laboratory allows to characterize and to study the adhesion properties of materials. The analysis of the results should allow to investigate which parameter can influence the sensorial analysis of tackiness.
HAL (Le Centre pour la Communication Scientifique Directe), 2009
Méthode, Rapport technique
HAL (Le Centre pour la Communication Scientifique Directe), 2009
Méthode, Rapport techniqu
Materials Chemistry and Physics, Aug 1, 2021
Abstract In this study, the synthesis of La0.75Sr0.25Cr0.4Mn0.5Ru0.1O3-δ a (LSC0.4MRu0.1) compoun... more Abstract In this study, the synthesis of La0.75Sr0.25Cr0.4Mn0.5Ru0.1O3-δ a (LSC0.4MRu0.1) compound is presented and its total conductivity is measured and compared with that of La0.75Sr0.25Cr0.5Mn0.5O3-δ (LSCM) and the Ni-substituted compound La0.75Sr0.25Cr0.5Mn0.3Ni0.2O3-δ (LSCM0.3Ni0.2). While the substitution of Ni decreased LSCM conductivity under a reducing atmosphere, an increase of the total conductivity of Ru substituted phase is evidenced. The reduction of Ni and Ru-substituted LSCM under Ar/H2 5% up to 800 °C or 1000 °C respectively leads to the exsolution of nanoparticles, but also to a slight decomposition for the Ru-substituted compound. However, the use of these reduced materials as anode for solid oxide fuel cell (SOFC) in symmetrical cells based on Ce0.9Gd0.1O1.95 (CGO) electrolyte implies not reducing the total system at a temperature higher than 600 °C to avoid ceria reduction. The solution consists of pre-reducing the electrode materials at their exsolution temperature before casting them on CGO thin disk. Under reductive atmospheres, Electrochemical impedance spectroscopy study of symmetrical cells suggests that the exsolution approach improves the adsorption of gaseous species compared to LSCM. LSC0.4MRu0.1 symmetrical cell exhibits the lowest polarization resistance, 0.087 Ω cm2 under Ar/H2 (5%) and 0.044 Ω cm2 under methane at 600 °C.
Solid State Ionics, Oct 1, 2012
ABSTRACT The effect of the addition of a small amount of iron oxide (3 mol%) in Y-stabilized ZrO2... more ABSTRACT The effect of the addition of a small amount of iron oxide (3 mol%) in Y-stabilized ZrO2 has been investigated. The aging of the obtained compound has been studied and the sintering temperature has been determined. The bulk and total conductivities of (ZrO2)0.90–(Y2O3)0.07–(Fe2O3)0.03 have been studied by means of impedance spectroscopy in the temperature range from 425 K to 775 K. The electronic conductivity has been studied by the Hebb-Wagner technique using a blocking Pt microelectrode. The investigation has been carried out in a wide range of oxygen activity, 10− 25 < aO2 < 103, and from 770 K to 1020 K. These data have been compared to the compound without iron oxide, YSZ (ZrO2)0.90–(Y2O3)0.10. This study demonstrates that the addition of a small amount of Fe2O3 decreases the sintering temperature and increases the stability of the compound without increasing the electronic conductivity.
Effect of deposition temperature, post-deposition annealing and substrate crystallinity on the mi... more Effect of deposition temperature, post-deposition annealing and substrate crystallinity on the microstructure and gas sensitivity of tellurium thin films has been investigated. As the substrate temperature during deposition is increased, due to increased mobility of adatoms, microstructure of films gradually changes from a smooth amorphous nature at low temperatures to polycrystalline films showing dendritic growth at high temperatures. It is also seen that improvement in crystalline nature of substrate leads to enhancement in grain size of the deposited films. Post-deposition annealing is found to have much less influence on the film morphology compared to films deposited on heated substrates. For films deposited at same temperature (on different substrates), gas sensitivity improves with reduction in the grain size. This has been attributed to increase in effective surface area for gas-film interaction. On the contrary, for films deposited at different temperatures, increase in grain size (higher deposition temperature) leads to better sensitivity. This has been understood to arise from reduced intragrain defect density. Small grain size and reduced defect density are seen to be conducive to better gas sensitivity of the films.
IEEE Transactions on Instrumentation and Measurement, 2021
Mobility/Diffusion of ions can occur mainly in two situations. The first one when a potential dif... more Mobility/Diffusion of ions can occur mainly in two situations. The first one when a potential difference is applied to electrodes of an electrochemical device as in batteries for instance (i.e., charge/discharge). In the second one, the diffusion process is driven by the thermal gradient existing within the material. This paper deals with the design of a controlled Thermal Gradient Generator (TGG) which opens the way to thoroughly study the effect of temperature difference on the chemical diffusion and mechanical resistance of shaped samples (e.g., a pellet, a rod). This TGG uses a combination of two susceptors involving the control of their respective temperatures. One is controlled by adjusting the power of a high frequency generator which supplies an induction heating coil. The other is controlled, mainly, by the displacement of the sample/susceptors set through this same coil, with a motorized stage. The operation and control parameters are defined within a dedicated user-friendly software application. During the whole experiment, the two temperatures can be varied while the inner thermal gradient of the sample is kept constant, as long as these temperatures are high enough.
HAL (Le Centre pour la Communication Scientifique Directe), 2008
Neorganičeskie materialy, 2014
Проведено изучение и сравнительный анализ ионной и общей проводимости оксида циркония, стабилизир... more Проведено изучение и сравнительный анализ ионной и общей проводимости оксида циркония, стабилизированного сложными оксидами иттрия, скандия в области средних температур (8501000 K). Установлено, что оксид циркония, стабилизированный комплексными добавками на основе оксидов иттрия и скандия, характеризуется низким значением электронной проводимости в широком интервале активности кислорода. Полученные данные показывают возможность использования синтезированных материалов в качестве мембран в среднетемпературных керамических топливных элементах.
Chemistry of Materials, Dec 13, 2012
ABSTRACT In this work, we have used nickel nanoparticles to improve proton conductivity of the el... more ABSTRACT In this work, we have used nickel nanoparticles to improve proton conductivity of the electrolyte BaCe0.9Y0.1O3−δ (BCY). Ni nanoparticles were dissolved into the compounds as their oxidized form (BaCe0.9–xY0.1NixO3−δ) and precipitated upon heating under a reducing atmosphere. Below 700 °C, proton conductivity is enhanced under a reducing atmosphere. An increase of 1 order of magnitude, with respect to BCY, was observed for BaCe0.7Y0.1Ni0.2O3−δ (1.7 × 10–2 S/cm at 500 °C). This phenomenon is more pronounced for the compounds containing more nickel on the surface, which can facilitate the dissociation of hydrogen and the incorporation of protons in the structure. Under reducing atmosphere, nickel doping enhances both bulk and grain boundaries conductivities and the blocking effect appear at lower temperature.
Le Centre pour la Communication Scientifique Directe - HAL - memSIC, Feb 1, 2000
Méthode, Rapport techniqu
IEEE Transactions on Instrumentation and Measurement, 2021
We present a deterministic distributed algorithm to compute all-pairs shortest paths(APSP) in an ... more We present a deterministic distributed algorithm to compute all-pairs shortest paths(APSP) in an edge-weighted directed or undirected graph. Our algorithm runs inÕ(n 3/2) rounds in the Congest model, where n is the number of nodes in the graph. This is the first o(n 2) rounds deterministic distributed algorithm for the weighted APSP problem. Our algorithm is fairly simple and incorporates a deterministic distributed algorithm we develop for computing a 'blocker set' [14], which has been used earlier in sequential dynamic computation of APSP.
The successful preparation of organized porous inorganic fluorides (OPIFs) with a high specific s... more The successful preparation of organized porous inorganic fluorides (OPIFs) with a high specific surface area is demonstrated for MgF 2. For the first time, macroporous MgF 2 OPIFs with a surface area of above 200 m 2 g −1 and mesoporous MgF 2 powder were prepared through the assembly of preformed MgF 2 nanoparticles and homemade polymer templates with a tunable size. These OPIF materials have been fully examined at different synthesis stages by means of powder X-ray diffraction, N 2 sorption, scanning electron microscopy, and transmission electron microscopy analyses and 19 F and 1 H solid-state nuclear magnetic resonance. The relation between the nature, the size, and the amount of polymer template on the porous structure was deeply investigated. The MgF 2 OPIFs present a higher thermal stability under air and F 2 calcination than MgF 2 NPs as the structuration of the OPIF composite considerably slows down the crystallite growth during thermal treatment under air. OPIF materials were evaluated for the first time as heterogeneous catalysts for the fluorination of 2-chloropyridine under HF gas as a fluorinating agent at 350°C. This study evidences catalytic sites with two Lewis acidity strengths (medium and low).
Metal fluorides with 3D open structures, pyrochlore (pyr) or hexagonal tungsten bronze (HTB), are... more Metal fluorides with 3D open structures, pyrochlore (pyr) or hexagonal tungsten bronze (HTB), are promising materials as positive electrodes for rechargeable batteries or catalysts. Herein, we have...
Materials Chemistry and Physics, 2021
Abstract In this study, the synthesis of La0.75Sr0.25Cr0.4Mn0.5Ru0.1O3-δ a (LSC0.4MRu0.1) compoun... more Abstract In this study, the synthesis of La0.75Sr0.25Cr0.4Mn0.5Ru0.1O3-δ a (LSC0.4MRu0.1) compound is presented and its total conductivity is measured and compared with that of La0.75Sr0.25Cr0.5Mn0.5O3-δ (LSCM) and the Ni-substituted compound La0.75Sr0.25Cr0.5Mn0.3Ni0.2O3-δ (LSCM0.3Ni0.2). While the substitution of Ni decreased LSCM conductivity under a reducing atmosphere, an increase of the total conductivity of Ru substituted phase is evidenced. The reduction of Ni and Ru-substituted LSCM under Ar/H2 5% up to 800 °C or 1000 °C respectively leads to the exsolution of nanoparticles, but also to a slight decomposition for the Ru-substituted compound. However, the use of these reduced materials as anode for solid oxide fuel cell (SOFC) in symmetrical cells based on Ce0.9Gd0.1O1.95 (CGO) electrolyte implies not reducing the total system at a temperature higher than 600 °C to avoid ceria reduction. The solution consists of pre-reducing the electrode materials at their exsolution temperature before casting them on CGO thin disk. Under reductive atmospheres, Electrochemical impedance spectroscopy study of symmetrical cells suggests that the exsolution approach improves the adsorption of gaseous species compared to LSCM. LSC0.4MRu0.1 symmetrical cell exhibits the lowest polarization resistance, 0.087 Ω cm2 under Ar/H2 (5%) and 0.044 Ω cm2 under methane at 600 °C.
International Journal of Computational Materials Science and Engineering, Jun 1, 2013
In this paper, a method of electronic conductivity measurement is presented. It combines two well... more In this paper, a method of electronic conductivity measurement is presented. It combines two well known methods of electrochemistry: cyclic voltammetry and chronoamperometry. This DC technique uses the Hebb–Wagner approach to block ionic conduction (when steady state conditions are reached) and allows electronic conduction of solid electrolytes to be determined. In order to get short diffusion times, a micro contact is used as an ion blocking electrode. However, as the electronic conduction in electrolytes is and should be very low, the current is also very low, typically some tens of nanoamps. Thus, the heating system inevitably generates noise problems that are solved using a median filter. As opposed to other related work, our system allows the determination of the conductivities without any preliminary smoothing or fitting of the curves (since the noise is strongly reduced). Some results with oxygen ion conductors are also given.
Inorganic Materials, Oct 22, 2014
We report a study and comparative analysis of the medium temperature (850-1000°C) ionic and total... more We report a study and comparative analysis of the medium temperature (850-1000°C) ionic and total conductivities of zirconia stabilized by yttria and scandia based mixed oxides. Zirconia stabilized by combined yttria and scandia based dopants is shown to have low electronic conductivity in a wide range of oxygen activities. Our data suggest the possibility of using the synthesized materials as membranes in inter mediate temperature ceramic fuel cells.
Materials in engineering, Aug 1, 2010
Sensorial tests on silicones tackiness perception with naïve consumers show that the stickiness s... more Sensorial tests on silicones tackiness perception with naïve consumers show that the stickiness sensation can be disturbed by the sensation of finger penetration into the sample. Indeed a frequent report is that a non-expert people cannot perceive whether tackiness sensation is related to the material adhesion properties or whether it is related to the finger penetration. The samples are both elastomers silicones but some are gel-like elastomers and others are compact silicones. We use an experimental device to realize indentation tests in order to try to differentiate mechanically the two silicones. The apparatus developed in the laboratory allows to characterize and to study the adhesion properties of materials. The analysis of the results should allow to investigate which parameter can influence the sensorial analysis of tackiness.
HAL (Le Centre pour la Communication Scientifique Directe), 2009
Méthode, Rapport technique
HAL (Le Centre pour la Communication Scientifique Directe), 2009
Méthode, Rapport techniqu
Materials Chemistry and Physics, Aug 1, 2021
Abstract In this study, the synthesis of La0.75Sr0.25Cr0.4Mn0.5Ru0.1O3-δ a (LSC0.4MRu0.1) compoun... more Abstract In this study, the synthesis of La0.75Sr0.25Cr0.4Mn0.5Ru0.1O3-δ a (LSC0.4MRu0.1) compound is presented and its total conductivity is measured and compared with that of La0.75Sr0.25Cr0.5Mn0.5O3-δ (LSCM) and the Ni-substituted compound La0.75Sr0.25Cr0.5Mn0.3Ni0.2O3-δ (LSCM0.3Ni0.2). While the substitution of Ni decreased LSCM conductivity under a reducing atmosphere, an increase of the total conductivity of Ru substituted phase is evidenced. The reduction of Ni and Ru-substituted LSCM under Ar/H2 5% up to 800 °C or 1000 °C respectively leads to the exsolution of nanoparticles, but also to a slight decomposition for the Ru-substituted compound. However, the use of these reduced materials as anode for solid oxide fuel cell (SOFC) in symmetrical cells based on Ce0.9Gd0.1O1.95 (CGO) electrolyte implies not reducing the total system at a temperature higher than 600 °C to avoid ceria reduction. The solution consists of pre-reducing the electrode materials at their exsolution temperature before casting them on CGO thin disk. Under reductive atmospheres, Electrochemical impedance spectroscopy study of symmetrical cells suggests that the exsolution approach improves the adsorption of gaseous species compared to LSCM. LSC0.4MRu0.1 symmetrical cell exhibits the lowest polarization resistance, 0.087 Ω cm2 under Ar/H2 (5%) and 0.044 Ω cm2 under methane at 600 °C.
Solid State Ionics, Oct 1, 2012
ABSTRACT The effect of the addition of a small amount of iron oxide (3 mol%) in Y-stabilized ZrO2... more ABSTRACT The effect of the addition of a small amount of iron oxide (3 mol%) in Y-stabilized ZrO2 has been investigated. The aging of the obtained compound has been studied and the sintering temperature has been determined. The bulk and total conductivities of (ZrO2)0.90–(Y2O3)0.07–(Fe2O3)0.03 have been studied by means of impedance spectroscopy in the temperature range from 425 K to 775 K. The electronic conductivity has been studied by the Hebb-Wagner technique using a blocking Pt microelectrode. The investigation has been carried out in a wide range of oxygen activity, 10− 25 < aO2 < 103, and from 770 K to 1020 K. These data have been compared to the compound without iron oxide, YSZ (ZrO2)0.90–(Y2O3)0.10. This study demonstrates that the addition of a small amount of Fe2O3 decreases the sintering temperature and increases the stability of the compound without increasing the electronic conductivity.
Effect of deposition temperature, post-deposition annealing and substrate crystallinity on the mi... more Effect of deposition temperature, post-deposition annealing and substrate crystallinity on the microstructure and gas sensitivity of tellurium thin films has been investigated. As the substrate temperature during deposition is increased, due to increased mobility of adatoms, microstructure of films gradually changes from a smooth amorphous nature at low temperatures to polycrystalline films showing dendritic growth at high temperatures. It is also seen that improvement in crystalline nature of substrate leads to enhancement in grain size of the deposited films. Post-deposition annealing is found to have much less influence on the film morphology compared to films deposited on heated substrates. For films deposited at same temperature (on different substrates), gas sensitivity improves with reduction in the grain size. This has been attributed to increase in effective surface area for gas-film interaction. On the contrary, for films deposited at different temperatures, increase in grain size (higher deposition temperature) leads to better sensitivity. This has been understood to arise from reduced intragrain defect density. Small grain size and reduced defect density are seen to be conducive to better gas sensitivity of the films.
IEEE Transactions on Instrumentation and Measurement, 2021
Mobility/Diffusion of ions can occur mainly in two situations. The first one when a potential dif... more Mobility/Diffusion of ions can occur mainly in two situations. The first one when a potential difference is applied to electrodes of an electrochemical device as in batteries for instance (i.e., charge/discharge). In the second one, the diffusion process is driven by the thermal gradient existing within the material. This paper deals with the design of a controlled Thermal Gradient Generator (TGG) which opens the way to thoroughly study the effect of temperature difference on the chemical diffusion and mechanical resistance of shaped samples (e.g., a pellet, a rod). This TGG uses a combination of two susceptors involving the control of their respective temperatures. One is controlled by adjusting the power of a high frequency generator which supplies an induction heating coil. The other is controlled, mainly, by the displacement of the sample/susceptors set through this same coil, with a motorized stage. The operation and control parameters are defined within a dedicated user-friendly software application. During the whole experiment, the two temperatures can be varied while the inner thermal gradient of the sample is kept constant, as long as these temperatures are high enough.
HAL (Le Centre pour la Communication Scientifique Directe), 2008
Neorganičeskie materialy, 2014
Проведено изучение и сравнительный анализ ионной и общей проводимости оксида циркония, стабилизир... more Проведено изучение и сравнительный анализ ионной и общей проводимости оксида циркония, стабилизированного сложными оксидами иттрия, скандия в области средних температур (8501000 K). Установлено, что оксид циркония, стабилизированный комплексными добавками на основе оксидов иттрия и скандия, характеризуется низким значением электронной проводимости в широком интервале активности кислорода. Полученные данные показывают возможность использования синтезированных материалов в качестве мембран в среднетемпературных керамических топливных элементах.
Chemistry of Materials, Dec 13, 2012
ABSTRACT In this work, we have used nickel nanoparticles to improve proton conductivity of the el... more ABSTRACT In this work, we have used nickel nanoparticles to improve proton conductivity of the electrolyte BaCe0.9Y0.1O3−δ (BCY). Ni nanoparticles were dissolved into the compounds as their oxidized form (BaCe0.9–xY0.1NixO3−δ) and precipitated upon heating under a reducing atmosphere. Below 700 °C, proton conductivity is enhanced under a reducing atmosphere. An increase of 1 order of magnitude, with respect to BCY, was observed for BaCe0.7Y0.1Ni0.2O3−δ (1.7 × 10–2 S/cm at 500 °C). This phenomenon is more pronounced for the compounds containing more nickel on the surface, which can facilitate the dissociation of hydrogen and the incorporation of protons in the structure. Under reducing atmosphere, nickel doping enhances both bulk and grain boundaries conductivities and the blocking effect appear at lower temperature.
Le Centre pour la Communication Scientifique Directe - HAL - memSIC, Feb 1, 2000
Méthode, Rapport techniqu
IEEE Transactions on Instrumentation and Measurement, 2021
We present a deterministic distributed algorithm to compute all-pairs shortest paths(APSP) in an ... more We present a deterministic distributed algorithm to compute all-pairs shortest paths(APSP) in an edge-weighted directed or undirected graph. Our algorithm runs inÕ(n 3/2) rounds in the Congest model, where n is the number of nodes in the graph. This is the first o(n 2) rounds deterministic distributed algorithm for the weighted APSP problem. Our algorithm is fairly simple and incorporates a deterministic distributed algorithm we develop for computing a 'blocker set' [14], which has been used earlier in sequential dynamic computation of APSP.
The successful preparation of organized porous inorganic fluorides (OPIFs) with a high specific s... more The successful preparation of organized porous inorganic fluorides (OPIFs) with a high specific surface area is demonstrated for MgF 2. For the first time, macroporous MgF 2 OPIFs with a surface area of above 200 m 2 g −1 and mesoporous MgF 2 powder were prepared through the assembly of preformed MgF 2 nanoparticles and homemade polymer templates with a tunable size. These OPIF materials have been fully examined at different synthesis stages by means of powder X-ray diffraction, N 2 sorption, scanning electron microscopy, and transmission electron microscopy analyses and 19 F and 1 H solid-state nuclear magnetic resonance. The relation between the nature, the size, and the amount of polymer template on the porous structure was deeply investigated. The MgF 2 OPIFs present a higher thermal stability under air and F 2 calcination than MgF 2 NPs as the structuration of the OPIF composite considerably slows down the crystallite growth during thermal treatment under air. OPIF materials were evaluated for the first time as heterogeneous catalysts for the fluorination of 2-chloropyridine under HF gas as a fluorinating agent at 350°C. This study evidences catalytic sites with two Lewis acidity strengths (medium and low).
Metal fluorides with 3D open structures, pyrochlore (pyr) or hexagonal tungsten bronze (HTB), are... more Metal fluorides with 3D open structures, pyrochlore (pyr) or hexagonal tungsten bronze (HTB), are promising materials as positive electrodes for rechargeable batteries or catalysts. Herein, we have...
Materials Chemistry and Physics, 2021
Abstract In this study, the synthesis of La0.75Sr0.25Cr0.4Mn0.5Ru0.1O3-δ a (LSC0.4MRu0.1) compoun... more Abstract In this study, the synthesis of La0.75Sr0.25Cr0.4Mn0.5Ru0.1O3-δ a (LSC0.4MRu0.1) compound is presented and its total conductivity is measured and compared with that of La0.75Sr0.25Cr0.5Mn0.5O3-δ (LSCM) and the Ni-substituted compound La0.75Sr0.25Cr0.5Mn0.3Ni0.2O3-δ (LSCM0.3Ni0.2). While the substitution of Ni decreased LSCM conductivity under a reducing atmosphere, an increase of the total conductivity of Ru substituted phase is evidenced. The reduction of Ni and Ru-substituted LSCM under Ar/H2 5% up to 800 °C or 1000 °C respectively leads to the exsolution of nanoparticles, but also to a slight decomposition for the Ru-substituted compound. However, the use of these reduced materials as anode for solid oxide fuel cell (SOFC) in symmetrical cells based on Ce0.9Gd0.1O1.95 (CGO) electrolyte implies not reducing the total system at a temperature higher than 600 °C to avoid ceria reduction. The solution consists of pre-reducing the electrode materials at their exsolution temperature before casting them on CGO thin disk. Under reductive atmospheres, Electrochemical impedance spectroscopy study of symmetrical cells suggests that the exsolution approach improves the adsorption of gaseous species compared to LSCM. LSC0.4MRu0.1 symmetrical cell exhibits the lowest polarization resistance, 0.087 Ω cm2 under Ar/H2 (5%) and 0.044 Ω cm2 under methane at 600 °C.