Oxygen chemical potential gradients

With an open system to which electrodes are attached, we can study the stability of interface morphology in an external electric field. A particularly simple case is met if the crystals involved are chemically homogeneous. In this case, Vfij = 0, and the ions are essentially driven by the electric field. Also, this is easy to handle experimentally. The counterpart of our basic stability experiment (Fig. 11-7) in which the AO crystal was exposed to an oxygen chemical potential gradient is now the exposure of AX to an electric field from the attached electrodes. In order to define the thermodynamic state of AX, it is necessary to apply electrodes with a predetermined... 

Oxygen anions travel from the source side through the solid electrolyte to the sink side (anode) under the combination of the influence of an applied dc electric field and an oxygen chemical potential gradient. At the sink side (the anode of the SOFC), the oxygen anions react electrochemically with both zirconium and yttrium reactants from the sink vapor phase to form the desired product, yttria doped zirconia, and release electrons to the metallic anode. Electrons travel through the external electrical circuit back to the source side for further cathodic reaction. 

Figure 9.12 Temperature dependence of the oxygen permeation fluxes through various mixed-conducting membranes, made of perovskite-related compounds with predominant electronic conductivity, under fixed oxygen chemical potential gradients...

Vedula, K., Modeling of transient and steady-state demixing of oxide solid solutions in an oxygen chemical potential gradients, Oxid. Met., 1987, 28, 99-108. 

When a mixed ionic-electronic conductor (i.e. Lai xSrxB03.5) is subjected to an oxygen chemical potential gradient, there arises a chemical diffusion of oxygen ions down the gradient (or the diffusion of oxygen vacancies in the opposite direction) and redistribution of electronic carriers. At typical values of x (0.1 < x < 0.5), the charge neutrality condition stipulates that... 

Figure 6 Function of a bilayer membrane subjected to a large gradient of oxygen chemical potential. The protective coating diminishes the gradient across the delicate MIEC substrate, which would decompose below lM02)cnt...

If the oxygen partial pressures at the opposite membrane sides are different (in other words, the gradient of oxygen chemical potential is created), the mass and charge flows should arise as illustrated by Figure 3.9. When the membrane is dense enough to avoid transport in the pores, the following equation for the flow ofj-species is valid ... 

The molecular oxygen flux through a perovskite OTM is related to the chemical potential gradient Vp(02) ... 

In the past two decades there has been considerable interest in C02-selective liquid membranes (1-9). Over fifteen years ago prototypes thousands of times more permeable to carbon dioxide than to oxygen were reported (10). Systems have been explored more recently which employ an electrical field to pump CO2, in the form of bicarbonate ion, up its chemical potential gradient (11). Still, no commercial applications are known to the authors. 

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