Proton conducting materials based on hydrofluorides

Hydrofluorides are novel proton conducting ceramic materials with the best proton conductivity for intermediate temperatures. Proton conduction dominates the hydrofluoride electrolyte fuel cell processes although i) the hydride ion, H^-, may make an opposite electrode reaction against proton electrode process and lower the fuel cell voltage; and ii) the side product of the interlayer may be formed at the electrolyte/cathode interface. However, this interlayer of the hydrofluorides with CaO may also be some kind of proton conductor, which can maintain a good fuel cell performance. In addition, oxygen ionic conduction may exist in some cases due to the defect structural nature.