Hydrogen titanates as potential proton conducting fuel cell electrolytes

This work examines the possibility of using hydrogen titanate materials, which may exhibit appreciable protonic conductivity at low temperatures (100–500°C), as electrolytes in the next generation of solid oxide fuel cells. The ramsdellite lithium titanate phase, Li2Ti3O7 was used as a basis for H+ exchange to form H2Ti3O7. The ramsdellite structure of this compound was confirmed by X-ray diffraction and its composition confirmed by thermogravimetric analysis. Magic angle spinning solid state NMR showed that the protons occupied at least two sites in the ramsdellite structure, in accord with the proposed H2Ti3O7 formula. The conductivity of compressed compacts of this compound was measured and the bulk value extracted. The measured conductivity of H2Ti3O7 was 2.66×10−6 S cm−1 at 200°C, about one order of magnitude lower than the Li analogue Li2Ti3O7, and two orders of magnitude lower than the best perovskite ceramic proton conductors at this temperature.