Applicability of emf measurements under external load resistance conditions for ion transport number determination

In order to evaluate the applicability of concentration cells for the ion transference number measurements with external load, the cell response was simulated with variable transport properties of the cell material, external load resistance, geometrical factors such as ion-conducting membrane thickness, and electrode kinetics. This technique is expected to be pertinent when ηF/RT<0.2, except possibly for conditions when the electrode kinetics is dependent on a relatively small limiting current density. In each particular case, the method validity can be verified by testing if the overpotential sum grows faster than current on decreasing the external load resistance. A pyrochlore-type material Gd_1.9Ca_0.1Ti₂O_7-δ with dominant oxygen ionic conductivity is used as a study case to demonstrate the criteria proposed to assess the applicability of emf measurements under short-circuit conditions.