Experimental Establishment of the Absolute Potential Scale

The constancy of 0R with changing potential is also remarkable, as expected for a reference electrode. The deviation from Eq. (7.11) for negative potentials is due to the removal of O2 and concomitant destruction of the effective double layer. 

The variation in DR(Ag) with UWr shows that Ag is not a good 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). 

Equation (7.12) has been reported since 199031 by several groups31 39,40,42 45 and has been confirmed using both the Kelvin probe technique and UPS, as already discussed in Chapter 5. Only one group46 has reported significant deviations from it, but the SEMs in that work show massive blocking nonporous electrodes which apparently do not allow for ion spillover. 

The implications of Equations (7.11) and (7.12) are quite significant. They allow for the establishment and straightforward measurement of a unique absolute electrode potential scale in solid state electrochemistry. 

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