Abstract: Rare-earth niobates are a promising group of materials due to the complexity of their structure and properties which qualify them as candidates for a variety of applications. LaNbO4 has been studied as a perspective type of proton conductor even though its conductivity is somewhat low. Many attempts have been made to improve the conductivity by single- or multi-element doping. In general, good mechanical properties, high stability in H2O- and CO2-containing atmospheres and compatibility with transition metals (Cu, Ni, Cu-Ni alloys) and their oxides [1, 2] make these compounds attractive for design of nanocomposite hydrogen separation membranes. In our work lanthanum niobates LaNbO4, La0.99Ca0.01NbO4, LaNb1-xMoxOx and LaNb3O9 were synthesized using a modified Pechini route and mechanochemistry by high-energy milling. Structural and transport properties of sintered niobates were characterized by X-ray, Raman and IR- spectroscopy and 93NbNMR nuclear magnetic resonance, SEM, TEM, thermogravimetry and conductivity measurements. Besides, hydrated niobates have been investigated by using 1H-NMR. Oxide-oxide (La0.99Ca0.01NbO4+LaNb3O9) and metal-oxide (Cu0.5Ni0.5+La0.99Ca0.01NbO4 and Cu0.5Ni0.5 + LaNb1-xMoxOx ) nanocomposites were prepared by treating the mixture of either complex oxides calcined at 700ºC or oxide + Cu0.5Ni0.5 powders in weight ratio 35:65. 5 wt. % by their ultrasonic dispersion in isopropanol. The powders of nanocomposites were pressed into pellets (d = 13 mm) and sintered using conventional thermal sintering as well as hot pressing under 50 MPa at 1100 °C. All obtained nanocomposite materials were characterized using XRD, SEM, TEM, impedance spectroscopy, oxygen 16O/18O (with C18O2) isotope heteroexchange. A wide range of methods were used to examine hydrated niobates and nanocomposites in order to ascertain the nature of H+-containing species and to get understanding of the mechanism of proton transport. Typical proton conductivity values are ~10 5 S/cm at 550 °C. OH migration appears to be more favorable way of migration than H+ jumps between O2 . H2O desorption experiments revealed the working temperature range being 300 – 450 °C.

Cite: Bespalko Y.N. , Sadykov V.A. , Skriabin P.I. , Eremeev N.F. , Krieger T.A. , Khabibulin D.F. , Krasnov A. , Uvarov N.F.
Preparation and Characterization of Proton-Conducting Materials Based on Lanthanum Niobates for Hydrogen Separation Membranes
XVI Conference of the European Ceramic Society 16-20 Jun 2019