Intermediate temperature proton conducting salt–oxide composites

Abstract

Compared with high temperature proton conducting oxides, proton conducting salts and salt–oxide composites (SOCs) may be called intermediate temperature (300 to 700°C) proton conductors. SOCs can be solid or solid-like with a soft plastic or molten salt phase (MSOCs). Three types of SOCs (MSOCs) are discussed in this paper, oxyacid-based SOCs, chloride- and fluoride-based SOCs and hydroxide- or nitrate-based MSOCs. The MSOC is a new concept for materials science, which is based on the typical character of superionic conductors. Chlorides, fluorides and relevant SOCs have opened a new promising area for the investigation of proton conducting materials, since all previously studied proton conductors are always oxygen containing materials. It is a highly interesting academic subject why and how proton conduction occurs in chlorides, fluorides and relevant SOCs. Some proton conducting mechanisms in these new materials are under discussion.