Due to the immediate energy shortage and the requirement of environment protection, the efficient, effective and environmental friendly use of current energy sources is urgent. Energy conversion and storage is thus an important focus both for industry and academia. As one of the hydrogen energy related materials, proton conducting ceramics can be applied in solid oxide fuel cells (SOFC) and steam electrolysers, as well as high temperature H2 separation membranes and H2 sensors. For most of the practical applications, both high proton conductivity and chemical stability are desirable. However,...