Oxygen, chemical potential

The variation in quasireference electrode in presence of reactive gas mixtures. This is due to its high catalytic activity for H2 oxidation. Nevertheless the agreement with Eq. (7.11) is noteworthy, as is also the fact that, due to the faster catalytic reaction of H2 on Pt than on Ag and thus due to the lower oxygen chemical potential on Pt than on Ag,35 the work function of the Pt catalyst electrode is lower than that of the Ag catalyst-electrode over the entire UWr range (Fig. 7.8b), although on bare surfaces O0 is much higher for Pt than for Ag (Fig. 7.8b). 

Driven by the difference in oxygen chemical potential between fuel and air compartments of the cell, oxygen anions migrate through the electrolyte to the anode where they are consumed by oxidation of the fuel according to eq 2. 

Figure 7.4 shows the vacancy concentrations computed in this way for three different O2 pressures. Because of the dependence of the oxygen chemical potential on pressure [see Eq. (7.6)], increasing the oxygen pressure dramatically reduces the vacancy concentration. The results in Fig. 7.4 justify two approximations that were made in our calculations above. First, the vacancy concentrations under physically relevant conditions are always very small, so determining the properties of a vacancy in a DFT calculation representing... 

Fig. 7 Surface phase diagram indicating the most stable surface structures for Cu-Ag bimetallic surface as a function of the Cu surface content and oxygen chemical potential. Reprinted figure with permission from Piccinin et al. Physical Review B, 2008, 77, 075426. American Physical Society.

Figure 7.18. Plot of surface energy vs. oxygen chemical potential for different terminations of the a-Fe203 (0001) from ab initio thermodynamic calculations, (from [85]).

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... 

Due to the very low dependence of the total conductivity a on the oxygen chemical potential, one may write... 

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 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...

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