Conductivity measurements on ceria at high oxygen pressures

Baker, E. H.; Iqbal, M. Zafar; Knox, Bruce E.

doi:10.1007/bf00566271

Cited by 11 publications

(6 citation statements)

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“…A potentially highly attractive feature in utilizing bias to access higher and lower oxygen activities than those existing in the surrounding gas phase is the possibility of reaching oxygen acitivities otherwise very difficult to achieve experimentally. Specifically, in this study one observes in Figures and , that values of pO 2 , eff as high as 280 atm were reached by application of a positive bias of 100 mV without need for more complex high pressure apparatus, as used in previous studies . Interestingly, the data collected for pO 2, eff values above 1 atm continue to fit the predicted model quite well, even though, at these high oxygen activities, one would expect to have to replace defect concentrations with activities.…”

Section: Discussionsupporting

confidence: 62%

“…As we demonstrate, the δ values, at a given oxygen activity within the film, achieved with and without DC bias, agree well under all measurement conditions and fit the predictions of the defect chemical model well. This confirms the suitability of this technique for controlling the δ of oxide thin films, even under conditions difficult or impossible to achieve by conventional means, e.g., up to oxygen pressures equivalent to 280 atm …”

Section: Introductionsupporting

confidence: 73%

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Voltage‐Controlled Nonstoichiometry in Oxide Thin Films: Pr_0.1Ce_0.9O_2−δ Case Study

Chen

Tuller

2014

Adv Funct Materials

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While the properties of functional oxide thin films often depend strongly on oxygen stoichiometry, there have been few means available for its control in a reliable and in situ fashion. This work describes the use of DC bias as a means of systematically controlling the stoichiometry of oxide thin films deposited onto yttria‐stabilized zirconia substrates. Impedance spectroscopy is performed on the electrochemical cell Pr0.1Ce0.9O2−δ (PCO)/YSZ/Ag for conditions: T = 550 to 700 °C, pO 2 = 10−4 to 1 atm, and ΔE = ‐100 to 100 mV. The DC bias ΔE is used to control the effective pO 2 or oxygen activity at the PCO/YSZ interface. The non‐stoichiometry (δ) of the PCO films is calculated from the measured chemical capacitance (Cchem ). These δ values, when plotted isothermally as a function of effective pO 2, established, either by the surrounding gas composition alone, or in combination with applied bias, agree well with each other and to predictions based on a previously determined defect model. These results confirm the suitability of using bias to precisely control δ of thin films in an in situ fashion and simultaneously monitor these changes by measurement of Cchem . Of further interest is the ability to reach effective pO 2s as high as 280 atm.

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Section: Discussionsupporting

confidence: 62%

Section: Introductionsupporting

confidence: 73%

Voltage‐Controlled Nonstoichiometry in Oxide Thin Films: Pr_0.1Ce_0.9O_2−δ Case Study

Chen

Tuller

2014

Adv Funct Materials

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“…CeO 2 is a mixed conductor, and both electronic and ionic conductivities have been investigated in several studies. [3][4][5][6][7][8][9][10] It is generally agreed 11 that the electronic conductivity of undoped CeO 2 is of the n-type. Since the ionic conductivity in this material is directly related to oxygen diffusion, it is important to understand the diffusion characteristics.…”

mentioning

confidence: 99%

Intrinsic and Extrinsic Oxygen Diffusion and Surface Exchange Reaction in Cerium Oxide

Kamiya

Shimada

Ikuma

et al. 2000

J. Electrochem. Soc.

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Fluorite structure oxides have a property of deviating from stoichiometry as a function of temperature and/or pressure. CeO 2 has a fluorite structure and a wide range of nonstoichiometry. 1 The material deviates from stoichiometry with increasing temperature and decreasing oxygen partial pressure, leading to a high concentration of defects. The concentration of defects can also be controlled by doping the oxide with impurities. Since CeO 2 exhibits a wide range of solubility 2 for rare earth elements, the concentration of defects may be controlled by dopant concentration. CeO 2 is a mixed conductor, and both electronic and ionic conductivities have been investigated in several studies. 3-10 It is generally agreed 11 that the electronic conductivity of undoped CeO 2 is of the n-type. Since the ionic conductivity in this material is directly related to oxygen diffusion, it is important to understand the diffusion characteristics. However, the characteristics of oxygen diffusion in CeO 2 remain unclear. In particular, the oxygen diffusion in undoped CeO 2 must be studied in detail, because it is useful in understanding the behavior of oxygen diffusion and electrical conductivity for doped CeO 2 .The oxygen self-diffusion coefficients in oxides having fluorite structure are summarized by Ando et al. 12 and Kamiya et al. 13 The characteristic in fluorite structure is that the absolute value of the oxygen diffusion coefficients in stoichiometric oxides, i.e., UO 2 , 14,15 PuO 2 , 16 ThO 2 , 17,18 and CeO 2 , 19 are lower than those of nonstoichiometric oxides, i.e., UO 2ϩx and CeO 2 doped with Y. In addition, the activation energy for oxygen diffusion in stoichiometric oxides is large (202 kJ mol Ϫ1 for PuO 2 and 248-273 kJ mol Ϫ1 for UO 2 ). However, the absolute values of the oxygen diffusion coefficients of nonstoichiometric oxides are higher than those of stoichiometric oxides, and the activation energy for oxygen diffusion in nonstoichiometric oxides is small (77-89 kJ mol Ϫ1 for CeO 2 doped with Y).In the literature, two results, one by Floyd 19 and the other by Kamiya et al., 13 have been presented for oxygen diffusion coefficients in undoped CeO 2 . The activation energy reported by Floyd for undoped CeO 2 was 104 kJ mol Ϫ1 and was close to the value for nonstoichiometric UO 2 and for CeO 2 doped with Y. In contrast, the activation energy indicated by the data by Kamiya et al. (322 kJ mol Ϫ1 ) was close to the value of stoichiometric UO 2 , ThO 2 , and PuO 2 and the absolute value of the oxygen diffusion coefficient of CeO 2.00 was found to be similar to the value of other stoichiometric oxides having fluorite structure. Consequently, Kamiya et al. concluded that their result corresponds to stoichiometric CeO 2 (Ce-1). In their study, the oxygen self-diffusion coefficient for stoichiometric cerium oxide was obtained using gas-phase analysis. Direct measurement of the diffusion coefficient can be performed via secondary ion mass spectroscopy (SIMS). One of the objectives of the present study was to investigate ...

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“…7 For example, Barnett et al 8 showed that the addition of doped ceria to the Ni-YSZ anode resulted in a good SOFC performance with no deleterious coke formation at 600…”

mentioning

confidence: 99%

Evaluation of MIEC Ce_0.8Y_0.1Mn_0.1O_2-δAnode in Electrolyte-Supported SOFC

Handal

Addo

Büyükaksoy

et al. 2016

J. Electrochem. Soc.

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In this study, the electrochemical performance of a single phase, mixed ion and electron conducting (MIEC) Ce 0.8 Y 0.1 Mn 0.1 O 2-δ (10CYMO) anode was evaluated using symmetrical half-cell and full-cell configurations under humidified H 2 , 10 ppm H 2 S/H 2 , and CH 4 . An yttria-stabilized zirconia (YSZ) electrolyte support layer was used in this work, as ac impedance spectroscopy revealed that the 10CYMO/YSZ/10CYMO cell gave the lowest area specific polarization resistance (ASR) of 0.23 cm 2 at 800 • C in wet H 2 , compared to La 0.8 Sr 0.2 Ga 0.8 Mg 0.2 O 3-δ (LSGM) and Zr 0.89 Sc 0.1 Ce 0.01 O 2-δ (ScSZ). Exposure of the 10CYMO anodes to 10 ppm H 2 S/H 2 , either in a half-cell or full cell configuration, showed slight enhancement on the electrochemical performance, which was explained using a concept describing the sulfur and ceria interaction. Nickel and yttria-stabilized zirconia (Ni-YSZ) composite materials are used as anodes in solid oxide fuel cells (SOFCs) because they meet most of the key requirements, such as a high electrical conductivity of ∼10 3 Scm −1 , high catalytic activity for the hydrogen oxidation reaction (HOR), and thermal and chemical stability with YSZ at 700-1000• C. 1 Although the Ni-YSZ anode demonstrates good performance when H 2 is used as a fuel, this anode suffers from some drawbacks. These include a rapid deactivation of the Ni catalyst due to carbon deposition under hydrocarbon fuels.2 Also, adsorption of sulfur species that are present in hydrocarbon fuels on the Ni surface results in its poisoning due to a decrease in the electrochemically active area for the HOR.3 Furthermore, Ni coarsening 4 and redox instability 5 remain long-term issues in Ni-YSZ based SOFCs; therefore, immense work is in progress to find alternative anodes for advanced SOFCs. Perovskite and fluorite-type metal oxides have shown several interesting functional properties toward sulfur tolerance and coking that make them promising anodes for SOFCs.6 Acceptor-doped ceria exhibits mixed ion and electronic conduction (MIEC) in reducing conditions, which makes it suitable to be employed in anodes in intermediate temperature (IT) (500-750• C) SOFCs. 7 For example, Barnett et al. 8 showed that the addition of doped ceria to the Ni-YSZ anode resulted in a good SOFC performance with no deleterious coke formation at 600 • C in wet CH 4 . Nevertheless, the SOFC performance of doped ceria-based anodes in CH 4 was still significantly lower than in H 2 . 9,10 It is known that sulfur is present as H 2 S in many common fuels and is added as an odorant in commercial fuels, such as natural gas. Thus, the stability of SOFC anodes toward sulfur poisoning is an important parameter, especially for the commercialization of SOFCs, operating on a variety of fuels.3 Therefore, we have investigated the sulfur tolerance of ceria-based anodes, reporting that Ni infiltration into porous GDC yielded an anode that was stable in 10 ppm H 2 S. Also, B-site ordered double perovskite type tranisiton metals-doped Ba 3 CaNb 2 O 9 proved...

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Conductivity measurements on ceria at high oxygen pressures

Cited by 11 publications

References 5 publications

Voltage‐Controlled Nonstoichiometry in Oxide Thin Films: Pr_0.1Ce_0.9O_2−δ Case Study

Voltage‐Controlled Nonstoichiometry in Oxide Thin Films: Pr_0.1Ce_0.9O_2−δ Case Study

Intrinsic and Extrinsic Oxygen Diffusion and Surface Exchange Reaction in Cerium Oxide

Evaluation of MIEC Ce_0.8Y_0.1Mn_0.1O_2-δAnode in Electrolyte-Supported SOFC

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Conductivity measurements on ceria at high oxygen pressures

Cited by 11 publications

References 5 publications

Voltage‐Controlled Nonstoichiometry in Oxide Thin Films: Pr0.1Ce0.9O2−δ Case Study

Voltage‐Controlled Nonstoichiometry in Oxide Thin Films: Pr0.1Ce0.9O2−δ Case Study

Intrinsic and Extrinsic Oxygen Diffusion and Surface Exchange Reaction in Cerium Oxide

Evaluation of MIEC Ce0.8Y0.1Mn0.1O2-δAnode in Electrolyte-Supported SOFC

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Voltage‐Controlled Nonstoichiometry in Oxide Thin Films: Pr_0.1Ce_0.9O_2−δ Case Study

Voltage‐Controlled Nonstoichiometry in Oxide Thin Films: Pr_0.1Ce_0.9O_2−δ Case Study

Evaluation of MIEC Ce_0.8Y_0.1Mn_0.1O_2-δAnode in Electrolyte-Supported SOFC