Proton uptake in the H+-SOFC cathode material Ba0.5Sr0.5Fe0.8Zn0.2O3−δ: transition from hydration to hydrogenation with increasing oxygen partial pressure

2015 ◽  
Vol 182 ◽  
pp. 129-143 ◽  
Author(s):  
Daniel Poetzsch ◽  
Rotraut Merkle ◽  
Joachim Maier
Keyword(s):  
Diffusion Coefficient ◽  
Oxygen Partial Pressure ◽  
Partial Pressure ◽  
Effective Diffusion ◽  
Hydrogen Uptake ◽  
Protonic Conductivity ◽  
Acid Base ◽  
Sofc Cathode ◽  
Proton Uptake ◽  
Thermogravimetric Investigations

Thermogravimetric investigations on the perovskite Ba0.5Sr0.5Fe0.8Zn0.2O3−δ (BSFZ, with mixed hole, oxygen vacancy and proton conductivity) from water vapor can occur by acid–base reaction (hydration) or redox reaction (hydrogen uptake), depending on the oxygen partial pressure, i.e. on the material's defect concentrations. In parallel, the effective diffusion coefficient of the stoichiometry relaxation kinetics also changes. These striking observations can be rationalized in terms of a defect chemical model and transport equations for materials with three mobile carriers. Implications for the search of cathode materials with mixed electronic and protonic conductivity for application on proton conducting oxide electrolytes are discussed.

Acid-base equilibrium during acute long-lasting experiments in artificially ventilated cats

1979 ◽  
Vol 236 (1) ◽  
pp. R126-R131
Author(s):  
C. Galletti ◽  
M. G. Maioli ◽  
E. R. Sanseverino
Keyword(s):  
Carbon Dioxide ◽  
Oxygen Partial Pressure ◽  
Partial Pressure ◽  
Artificial Ventilation ◽  
Venous Blood ◽  
Co2 Concentration ◽  
Acid Base ◽  
Base Equilibrium ◽  
Acid Base Equilibrium ◽  
Expired Air

Experiments were carried out to study blood acid-base equilibrium in the cat during experiments with artificial ventilation. Blood acid-base equilibrium was examined in the arterial and venous blood by analyzing pH, carbon dioxide and oxygen partial pressure, and plasma bicarbonates. Artificial ventilation was regulated on the basis of this analysis; CO2 concentration in expired air was monitored throughout the experiment. An attempt was made to verify if artificial ventilation could be regulated indirectly only on the basis of CO2 concentration in expired air. The most appropriate acid-base equilibrium was maintained when CO2 concentration in expired air was kept within the range of 3.9-4.1%.

Oxygen Transport Kinetics in La0.5Sro0.5Fe0.8Ga0.2O3−δ Membranes Under Both Small and Large Oxygen Partial Pressure Gradients

1998 ◽  
Vol 548 ◽  
Author(s):  
Sangtae Kim ◽  
Allan J. Jacobson ◽  
Benjamin Abeles
Keyword(s):  
Diffusion Coefficient ◽  
Oxygen Partial Pressure ◽  
Partial Pressure ◽  
Oxygen Transport ◽  
Oxygen Flow Rate ◽  
Pressure Gradients ◽  
Exchange Coefficient ◽  
Maximum Enhancement ◽  
Surface Exchange ◽  
Surface Exchange Coefficient

ABSTRACTOxygen permeation through a new perovskite La0.5Sr0.5Fe0.8Ga0.2O3−δ membrane has been measured both under small (air/He) and large (air/CO, CO2) oxygen partial pressure gradients. In both cases oxygen transport is close to surface limited. By modeling the pressure dependence of the oxygen flow rate under small pressure gradient an ambipolar diffusion coefficient 9.65 × 10−7cm2/s and a surface exchange coefficient 7.15 × 10−6 cm/s at 974 °C were determined. With air/CO, CO2 on the permeate side, the permeability increases linearly with the partial pressure of CO. The observed increase is greater than the maximum enhancement predicted by our model.

Properties of Species Profiles during Oxygen Chemical Diffusion in Oxides

2018 ◽  
Vol 383 ◽  
pp. 153-158
Author(s):  
Misha Sinder
Keyword(s):  
Diffusion Coefficient ◽  
Diffusion Equation ◽  
Oxygen Partial Pressure ◽  
Partial Pressure ◽  
Chemical Diffusion ◽  
Ambipolar Diffusion ◽  
Chemical Diffusion Coefficient ◽  
Diffusion Front ◽  
Oxide Crystal ◽  
Ambient Oxygen

This is a theoretical study of species profiles during the oxygen chemical diffusion in an acceptor doped oxide crystal driven by large changes in the ambient oxygen partial pressure. The oxide crystal containing three species: mobile oxygen vacancy, mobile electron, immobile dopant ion, is considered. Our analysis is based on the expression of the chemical diffusion coefficient obtained in the framework of the concept of conservative ensembles (Maier J., 1993). It is shown that the dependence of chemical diffusion coefficient on ambient oxygen partial pressure in double-logarithmic coordinates is divided into distinct intervals. For each pressure interval the chemical diffusion equation is reduced to the diffusion equation with a diffusion coefficient which exhibits a power dependence on concentration. First, we analyzed the chemical diffusion under pressure inside each interval. As a result two singularities on the species diffusion profiles can be found: an internal reaction diffusion front, and an ambipolar diffusion front. This ambipolar diffusion front is characterized by a step of the electron concentration, moving inside a specimen. Afterwards, we consider a crystal in which the range of partial pressure spans all considered pressure intervals.

Oxygen diffusion in La2−x Srx CuO4−y

1988 ◽  
Vol 3 (1) ◽  
pp. 116-121 ◽  
Author(s):  
J. L. Routbort ◽  
S. J. Rothman ◽  
B. K. Flandermeyer ◽  
L. J. Nowicki ◽  
J. E. Baker
Keyword(s):  
Activation Energy ◽  
Diffusion Coefficient ◽  
Oxygen Partial Pressure ◽  
Partial Pressure ◽  
Mass Spectrometer ◽  
Oxygen Diffusion ◽  
Oxygen Vacancies ◽  
Vacancy Concentration ◽  
Concentration Profiles ◽  
Secondary Ion

Diffusion of 18O in the superconductor La2−x Srx CuO4−y has been measured as a function of x (0 to 0.20) between 300 and 500°C at an oxygen partial pressure of ≍ 1 atm. Concentration profiles were obtained using a secondary ion mass spectrometer. The diffusion coefficient decreases with increasing Sr additions from 0.1 to 0.2, primarily because of an increase in activation energy. This result, which is contradictory to the expectation that the diffusion coefficient should increase with increasing vacancy concentration caused by the added Sr, can be explained if oxygen vacancies are bound to Sr clusters. Measurements on samples with x = 0 or 0.05 were unsuccessful, probably because of porosity.

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