Application of solid electrolytes. II. Coulometric titration

As mentioned in Section 1.4.7, the EMF for the electrolyte cell depicted in Fig. 1.47(a) is given by eqn (1.172). On the application of a voltage from an external battery, as shown in Fig. 1.47(b), on the other hand, we can forcibly transfer oxygen molecules from room (I) to room (II) by the following process as in eqn (1.170), oxygen gas, O2, in room (I) in the vicinity of the electrode is ionized to O, which migrates towards room (II). At the surface of the electrode in room (II), O is oxidized to O2 as in eqn (1.171). The quantity of oxygen gas transferred from room (I) to (II) by this process, Amoi, is described as 

In this experiment the non-stoichiometric nickel oxide is expressed as NiOj + y. Since y 10 the concentration of nickel vacancies [Vn ] (this denotes the total concentration nickel vacancies having different electronic states, such as V i, V i, and VnD can be described as 

If NiOi+y, and NiOi +, j are the compositions before and after titration, respectively, then we get 

the results are in good agreement with those mentioned in Section 

NiOi + y could be measured precisely by use of the solid electrolyte, without chemical analysis. This result is shown in Fig. 1.51, as log Po. versus T curves, in which the dotted lines indicate the iso-y values. This figure shows that in order to get stoichiometric NiO, the sample has to be prepared at low temperature and low oxygen partial pressure in the NiO phase region. 

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