Review: Measurement of partial electrical conductivities and transport numbers of mixed ionic-electronic conducting oxides

Mixed ionic-electronic conducting (MIEC) oxides play crucial roles in energy and environmental applications such as fuel cells, electrolysis cells, batteries, gas separation membranes, and membrane reactors for chemical synthesis. The application of MIEC oxides is primarily determined by their electrical conduction properties. Correctly measuring the electrical conduction properties of MIEC oxides, including the partial conductivity and corresponding transport numbers, is fundamental for the development of MIEC oxides. In this review, the theoretical principles and experimental techniques of the five most widely used methods for determining electrical conduction properties of MIEC oxides, namely the total conductivity measurement (section 2), the electromotive force method (section 3), the Faradaic efficiency method (section 4), the Hebb-Wagner method (section 5), and the gas permeation method (section 6), are summarized. The modifications of these methods by considering the electrode polarization and operation conditions (under a certain voltage and current) are discussed. Application of these methods to assess the conduction properties of triple ionic-electronic conducting (TIEC) oxides is highlighted. Most importantly, the reliability and applicability of these methods are elaborated and compared (Section 7). This review is expected to provide an updated and informative summary concerning determination of the partial conductivities and transport numbers of MIEC oxides.