Oxygen surface exchange and diffusion in Ca
12
Al
14
O
33±
δ
single crystal were studied by a unique
in situ
method based on isotope equilibration in the gas phase. Although the interphase exchange ...rate and oxygen diffusion coefficient demonstrate good agreement with available data, only the employed method is efficient to isolate the contributions of various types of exchange; thus, for the first time, it is possible to estimate the surface heterogeneity of mayenite. The obtained results disprove conclusions previously developed in the literature; the temperature region of 750 °C to 850 °C is not the intermediate region where two types of oxygen diffusion coexist. Complex discussion of the accumulated information on the temperature-dependent properties of mayenite allowed us to represent a model describing the observed dependencies based on the near-surface layer stability in the studied temperature range.
Oxygen surface exchange and diffusion in Ca
12
Al
14
O
33±
δ
single crystal were studied by a unique
in situ
method based on isotope equilibration in the gas phase.
Oxygen surface exchange kinetics of La
0.7
A
0.3
MnO
3±δ
has been studied by the isotope exchange method with gas phase equilibration using a static circulation experimental rig at the temperature of ...850 °C and oxygen pressure of 1 kPa. Oxides of La
0.7
A
0.3
MnO
3±δ
with different dopant at one level of doping were considered. Rates of elementary acts of the oxygen exchange were found to change differently. So, the oxygen dissociative adsorption rate increased, the oxygen incorporation rate decreased, and the increase in the cation radius did not influence the interphase exchange rate. These trends are associated with the AO segregation processes at the surface and the appropriate mechanism of oxygen reduction is considered.
Graphical Abstract
The oxygen dissociative adsorption rate increased, the incorporation rate decreased, and the increase in the cation radius did not influence the interphase exchange rate. These trends are associated with the AO segregation processes at the surface.
The paper presents the results of an investigation into thin single- and triple-layer ZrO2-Sc2O3-based electrolytes prepared using the tape-casting technique in combination with promising electrodes ...based on La2NiO4+δ and Ni-Ce0.8Sm0.2O2-δ materials. It is shown that pressing and joint sintering of single electrolyte layers allows multilayer structures to be obtained that are free of defects at the layer interface. Electrical conductivity measurements of a triple-layer electrolyte carried out in longitudinal and transverse directions with both direct and alternating current showed resistance of the interface between the layers on the total resistance of the electrolyte to be minimal. Long-term tests have shown that the greatest degradation in resistance over time occurs in the case of an electrolyte with a tetragonal structure. Symmetrical electrochemical cells with electrodes fabricated using a screen-printing method were examined by means of electrochemical impedance spectroscopy. The polarization resistance of the electrodes was 0.45 and 0.16 Ohm∙cm2 at 800 °C for the fuel and oxygen electrodes, respectively. The distribution of relaxation times method was applied for impedance data analysis. During tests of a single solid oxide fuel cell comprising a supporting triple-layer electrolyte having a thickness of 300 microns, a power density of about 160 mW/cm2 at 850 °C was obtained using wet hydrogen as fuel and air as an oxidizing gas.
In order to overcome different tasks related to the thermal and chemical compatibility of functional solid oxide electrochemical cell materials, including those based on proton-conducting ...electrolytes, the search for new potential oxygen/steam electrodes is of great interest. In the present work, the Lа2Ni1–хCuxO4+δ (LNCx, x = 0. 0.1, 0.2 and 0.3) compounds, which constitute a class of Co-free and alkaline-earth elements (AEE)-free layered materials, were successfully synthesised and then studied as possible oxygen electrodes for protonic ceramic fuel cells. A complex of methods was used to comprehensively analyse the individual characteristics of LNCx (structural parameters, oxygen overstoichiometry, thermal expansion, total conductivity) as well as their properties in symmetrical and fuel cell architectures (polarisation resistance, performance). According to the obtained results, a slight degree of Ni with Cu substitution can be used for optimising the functional properties of LNCx, such as low sintering temperatures of cathode formation, low thermal expansion coefficients, good electronic conductivity and sufficient electrochemical activity (including under conditions of moisturised atmospheres). Therefore, the LNCx cathodes can be considered as one of the possible Co- and AEE-free candidates for intermediate-temperature protonic ceramic electrochemical cells.
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•The La2Ni1–xCuxO4+δ (LNCx, x = 0–0.4) oxides were successfully synthesised.•LNCx were evaluated as Co-, Fe-, Ca-, Sr- and Ba-free cathodes for H+-SOFCs.•Cu-doping differently affects the functional properties of LNCx cathodes.•A medium Cu-concentration (x = 0.2) can be considered as an optimal choice.
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•The La1–xBaxYbO3–δ (LBY) materials were successfully synthesized.•Ba-doping results in a deterioration of sintering behaviour of LBY.•Transport properties of LBY were studied by AC ...and DC conductivity measurements.•Bulk conductivity changes more sharply than the grain boundary one with x variation.•La0.97Ba0.03YbO3–δ exhibits the highest conductivity values.
The effective operation of protonic ceramic electrochemical cells requires the design of electrolytes having not only high ionic conductivity, but also excellent stability with respect to carbonisation. In the present work, the La-based oxides (La1–xBaxYbO3–δ, 0.03 ≤ x ≤ 0.10) are proposed as a possible alternative to the convenient Ba(Ce,Zr)O3-based electrolytes due to their high chemical stability. It was discovered that Ba-doping results in a deterioration of sintering behaviour; as a result, the relative density decreases and open porosity appears (for x = 0.10). A thorough analysis of transport properties by means of AC and DC measurement techniques enables a selection of the La0.97Ba0.03YbO3–δ sample, which demonstrates the highest conductivity compared with those samples where x = 0.5 and 0.10. Due to its excellent densification behaviour, stability and ionic conductivity, La0.97Ba0.03YbO3–δ can be considered as a promising proton-conducting electrolyte in the La-based family.
The La
2
Mo
2
O
9
and La
2
(MoO
4
)
3
powders were synthesized using a solid-state reaction method and used to prepare dense ceramics. X-ray photoelectron spectroscopy was used to study the chemical ...composition and charge numbers of the elements in the subsurface area of dense ceramics of lanthanum molybdates. The spectra were measured under an ultra-high vacuum of 7 × 10
−11
atm at 30 °C and 600 °C, and under an oxygen atmosphere at 2 × 10
−3
atm at 600 °C and 825 °C. High resolution spectra for La 3d, Mo 3d and O 1s states were obtained and analyzed. The kinetics of oxygen exchange were considered in the framework of a two-step model including the consecutive steps of dissociative adsorption and the incorporation of oxygen. The oxygen adsorption (
r
a
) and incorporation (
r
i
) rates were calculated. Correlations between the oxide surface defect chemistry and the rates of individual oxygen-exchange steps were discussed.
The chemical state of the near-surface La
2
Mo
2
O
9
and La
2
(MoO
4
)
3
ceramic layers differs from the bulk state, which has a significant influence on the interaction kinetics of the gas-phase oxygen and the surface of the oxide material.
The La 2 Mo 2 O 9 and La 2 (MoO 4 ) 3 powders were synthesized using a solid-state reaction method and used to prepare dense ceramics. X-ray photoelectron spectroscopy was used to study the chemical ...composition and charge numbers of the elements in the subsurface area of dense ceramics of lanthanum molybdates. The spectra were measured under an ultra-high vacuum of 7 × 10 −11 atm at 30 °C and 600 °C, and under an oxygen atmosphere at 2 × 10 −3 atm at 600 °C and 825 °C. High resolution spectra for La 3d, Mo 3d and O 1s states were obtained and analyzed. The kinetics of oxygen exchange were considered in the framework of a two-step model including the consecutive steps of dissociative adsorption and the incorporation of oxygen. The oxygen adsorption ( r a ) and incorporation ( r i ) rates were calculated. Correlations between the oxide surface defect chemistry and the rates of individual oxygen-exchange steps were discussed.
The La2Mo2O9 and La2(MoO4)3 powders were synthesized using a solid-state reaction method and used to prepare dense ceramics. X-ray photoelectron spectroscopy was used to study the chemical ...composition and charge numbers of the elements in the subsurface area of dense ceramics of lanthanum molybdates. The spectra were measured under an ultra-high vacuum of 7 × 10−11 atm at 30 °C and 600 °C, and under an oxygen atmosphere at 2 × 10−3 atm at 600 °C and 825 °C. High resolution spectra for La 3d, Mo 3d and O 1s states were obtained and analyzed. The kinetics of oxygen exchange were considered in the framework of a two-step model including the consecutive steps of dissociative adsorption and the incorporation of oxygen. The oxygen adsorption (ra) and incorporation (ri) rates were calculated. Correlations between the oxide surface defect chemistry and the rates of individual oxygen-exchange steps were discussed.
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