Proton-conducting ceramics based on barium hafnate and cerate doped with zirconium, yttrium and ytterbium oxides for fuel cell electrolytes

Nanopowders of the compositions BaHf1 – xYbxO3 – δ (x = 0.04; 0.08; 0.10) and BaCe0.9 – xZrxY0.1O3 – δ (x = 0; 0.5; 0.6; 0.7 and 0.8) were synthesized by the combined crystallization and nitric acid salts using the citrate-nitrate method. Those nanopowders were used to produce ceramic materials with a cubic crystal structure of the perovskite type, with a grain size of ~ 20 – 70 nm. The study of electrophysical properties revealed that they have a proton type of conductivity in the temperature range of 500 – 700 °C; σ = 10–2 – 10–5 Cm/cm. Type and mechanism of electrical conductivity of ceramics of the composition BaHf1 – xYbxO3 – δ (x = 0.04; 0.08; 0.10) have been studied both experimentally and using theoretical calculations-by computer modeling using the electron density functional method; the results are in good agreement. The research shows the prospects of using the obtained ceramic materials as proton-conducting electrolytes of solid-oxide fuel cells.

Cooperative origin of proton pair diffusivity in yttrium substituted barium zirconate

Proton conduction is an important property for fuel cell electrolytes. The search for molecular details on proton transport is an ongoing quest. Here, we show that in hydrated yttrium doped barium zirconate using X-ray and neutron diffraction that protons tend to localize near the dopant yttrium as a conjugated superstructure. The proton jump time measured using quasi-elastic neutron scattering follows the Holstein-Samgin polaron model, revealing that proton hopping is weakly coupled to the high-frequency O-H stretching motion, but strongly coupled to low-frequency lattice phonons. The ratio of the proton polaron effective mass, m*, and the proton mass is m*/m = 2, when coupled to the Zr-O stretching mode, giving experimental evidence of proton pairing in perovskites, as a result of proton-phonon coupling. Possible pathways of a proton pair are provided through Nudge Elastic Band calculations. The pairing of protons, when jumping, is discussed in context of a cooperative protonic charge transport process.