Intermediate temperature proton conducting salt-oxide composites

Compared with high temperature proton conducting oxides, proton conducting salts and salt-oxide composites (SOCs) may be called intermediate temperature (300 to 700 degrees 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. (C) 1999 Elsevier Science B.V. All rights reserved.