Electron-blocking electrodes

Similar approaches are used for most steady-state measurement techniques developed for mixed ionic-electronic conductors (see -> conductors and -> conducting solids). These include the measurements of concentration-cell - electromotive force, experiments with ion- or electron-blocking electrodes, determination of - electrolytic permeability, and various combined techniques [ii-vii]. In all cases, the results may be affected by electrode polarization this influence should be avoided optimizing experimental procedures and/or taken into account via appropriate modeling. See also -> Wagner equation, -> Hebb-Wagner method, and -> ambipolar conductivity. 

Historically, this method was suggested by Wagner [i] following the work by Hebb [ii], who first proposed to use ion- or electron-blocking electrodes for the determination of partial conductivities in a 4-probe arrange-... 

The electronic current can be suppressed using electron-blocking electrodes, i.e., SEs. Alternatively, one can eliminate by short circuiting the MIEC imposing F= 0, hence = 0. This is the short-circuit method for determining... 

The electronic current can be eliminated as mentioned before using an electron-blocking electrode or by short circuiting. 

A seven-electrode arrangement also enables the simultaneous measurement of Oei and Oj in MIECs. The arrangement includes one reversible electrode, one ion-blocking and one electron-blocking electrode, one pair of ion-blocking probes, and one pair of electron-blocking probes. ... 

The defect distributions are independent of V. When electron-blocking electrodes are used Fji, is fixed by V V = V. 

Ion-Blocking Electrodes Electron-Blocking Electrodes Reference Electrodes... 

An exponential behaviom was obtained (see Section 7.3.4a) in the time domain for the switching-on measurements for long times in the case of selective ion or electron blocking electrodes (corresponding to pure stoichiometry polarization ) accordingly the diffusion impedance Z (Warburg impedance) for very small frequencies... 

Inhibition of Electron Transfer at Partially Blocked Electrodes... 

The major factors probably responsible for the acceleration effect of additives are (1) the charge density of the electron system of the additive and (2) the exchange of electrons between electrode, 7r-bonded additive molecule, and the complexed metal ions in the solution. Inhibition effect and cathodic passivation are explained in terms of blocking of the catalytic surface, which results in a decrease in the available surface area (45). 

We will consider these cells, primarily the oxygen cells, under open circuit conditions and under load (or even short-circuit condition). In the transient and in the steady state it is not necessary to treat them all in detail, since (as outlined below) cells with one selectively blocking electrode and those with two of the same kind show far-reaching similarities (compare cell 3 with cell 4 and cell 5 with cell 6). The same is true if we compare cells with electrodes that are selectively blocking for electrons with cells that are specifically blocking for ions (compare cell 3 with cell 5 and cell 4 with cell 6) it is easy to show that the relations are symmetrical as regards the indices e" and O2" (see below and Appendix l).21011... 

In the case of electron blocking the indices eon and ion have to be exchanged, but also the total equivalent circuit has to be complemented by circuit elements that take account of the bulk impedance of the blocking electrodes (e.g., YSZ). 

What has been ignored so far and will only be briefly mentioned is that a stoichiometric polarization is also caused by grain boundaries if the ratio of ionic and electronic conductivities differs from the bulk value, as it is usually the case.230 Figure 41 gives a clear example of this. In the general case of blocking electrodes and grain boundaries we expect even two stoichiometry polarization processes. 

Herefrom the electronic conductivity is precisely arrived at by differentiating the current with respect to the oxygen potential at the contact of the blocking electrode (x=L). As... 

Figure 5 illustrates an example of the schematic structure for an a-Si H target. On a glass substrate, a tin oxide transparent electrode layer is deposited by CVD. On this layer, a very thin Si02, as a hole-blocking layer, a photoconductive a-Si H layer, and an electron-blocking Sb2S3 layer are added, in that order. The thickness of the a-Si H layer is 2-4 pm. 

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