Mixed Conducting Membranes

Synonyms

Electronic and ionic conductivity

A mixed conducting membrane can transport both electrons and ions as shown in the scheme below (Fig. 1); in most cases the ionic conductivity is based on oxygen ions or protons, but in principle also other ions like halogenide or chalcogenide anions are mobile and can be transported. Perovskites with the crystallographic structure ABO₃ (derived from the mineral perovskite CaTiO₃) are a prominent example for a materials class with mixed conductivity: Oxygen ions can be transported via vacancies in the oxygen lattice (denoted as oxygen deficiency δ in the perovskite structure ABO_3-δ ), and electrons can be transported via redox cycles of the cations if they can occur in different oxidation states (e.g., Feⁿ⁺, Coⁿ⁺, Tiⁿ⁺). The concentration of vacancies in the oxygen lattice can be engineered by bringing cations with a low valency on the position of high-valency cations (Sunarso et al. 2008).

Fig. 1

Schema of oxygen transport through a perovskite...