Solid Electrolyte Fugacity Sensors

It is also possible to measure oxygen and other gas fugacities with electrochemical sensors. These methods use the same theoretical principles that apply to measurement of Eh. The design and operation of such sensors is described in detail by Sato (1971) and Huebner (1987). We will illustrate the technique briefly, by describing an oxygen fugacity sensor. 

In this case 5red = ox so that fwhoie ceii = 0 V. This just means that if pure oxygen at the same T and P is on both sides of the electrolyte, no voltage wiU be obtained. The cell develops a voltage from the difference in pressure of oxygen on the two sides. Therefore 

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Fig. 18.7. Schematic solid electrolyte oxygen fugacity sensor, where /02 (standard) > /02 (unknown).

LT is the standard cell potential difference, which is determined only by the reactants in definited standard states. This quantity results as the difference of standard electrode potentials. The power term Ila contains the corrected composition quantities a, (fugacities and activities) with the stoichiometric coefficients v, of the gases and condensed substances taking part in the cell reaction [10,12]. If a sensor at equilibrium delivers signals in agreement with Equation (25-7) then we have a reaction celt. In this case at solid electrolytes with oxide ion vacancies Vo> two reactions can be found besides... 

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