Solid electrolytes work function probes

The implications of Equation (4.30) for solid state electrochemistry and electrochemical promotion in particular can hardly be overemphasized It shows that solid electrolyte cells are both work function probes and work function controllers for their gas-exposed electrode surfaces. 

Equation (5.19) shows that the emf eUV of solid electrolyte cells provides a direct measure of the difference in work function of the two gas-exposed, i.e., catalytically active, electrode surfaces. Thus, solid electrolyte cells are work function probes for their gas exposed electrode surfaces. This was shown in Figures 5.15 and 5.16. 

One of the first key steps in understanding the origin of electrochemical promotion was the realization that solid electrolyte cells with metal electrodes are both work function probes and work function controllers for the gas-exposed surfaces of their electrodes (Figure 18) ... 

It therefore follows that solid electrolyte cells may be used as work function probes. Comparing this experimental relationship with Eqs. (11) and (12), one may conclude that the Volta potential at the catalyst surface remains invariant provided that the electric double layer has been built up at the catalyst/gas interface. Based on electrodynamic arguments it was also concluded, that in an overall neutral electrochemical cell this invariant Volta potential equals zero, since the double layer formed via ion backspillover is overall neutral. 

Equation (13.40) is always valid provided the ealalyst and reference electrodes are made of the same material.It is also valid when other types of solid electrolytes are used, e.g., P"-Al203, aNa+ conductor. Equation (13.40) is mnch more general and fundamental than Equation (13.35), as it does not require the establishment of ai r specific electrochemical equilibrium. It shows that solid electrolyte cells are work function probes for their gas-exposed electrode surfaces. It also shows that SEP is essentially a work function measuring technique and that several aspects of the SEP literature reviewed in References 92,97-99 must be reexamined in the light of these findings. One can still use SEP to extract information about surface activities, provided the nature of the electrocataly tic reaction at the tpb is well known, but, even when this is not the case, the cell emf still provides a direct measure of the work function difference between the two gas-exposed electrode surfaces. Equation (13.40) also holds under closed-circuit conditions, as is further discussed in Section III.B. 

Solid electrolyte cells are work-function probes for the gas-ex-posed, catalytically active catalyst-electrode surfaces that is, the change A(e0) in catalyst surface average work function e0 is equal to eAVwR-The catalyst potential Vwr with respect to a reference electrode can be varied both by changing the gaseous composition and/or by polarizing the catalyst/solid electrolyte interface. 

Before discussing how Equation (13.35) has been used in the past to analyze SEP data, it is important to discuss first some recent findings. It was recently found both theoretically and experimentally by means of a Kelvin probe . that the emf of solid electrolyte cells provides a direct measure of the difference in the work function eO of the gas-exposed surfaces of the working and reference electrodes ... 

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