Synthesis and Crystal structure of Novel Proton-conductor, RbMg(PO3)3•3(H2O)

Proton conductors have been studied for applications in electrochemical devices such as fuel cells. Phosphate and sulfate based materials are one of the categories of proton conductors suitable for medium temperature range. Among these materials, proton-conductive solid acid salts, CsH2PO4 and CsHSO4, are well known as high proton conductors. The ionic conductivity exceeds 10 Scm at 200°C. However, the temperature range where the material shows high proton conduction is rather narrow, and the search for new proton conductors is still necessary. In the present study, novel proton conduction materials were synthesized in the solid acid salt systems. The structure of RbxMg1-x(PO3)3 were examined by x-ray and neutron diffraction measurements. The proton conductivities were also determined by ac impedance methods. The relationship between the structure and proton conductivity mechanism will be discussed.