Key trends in the proton conductivity of Ln6-xMoO12-δ (Ln = La, Nd, Sm, Gd -Yb; x=0, 0.5, 0.6, 0.7, 1) rare-earth molybdates

We have studied the structure and proton conductivity of rhombohedral La6-xMoO12-delta (x = 0.5, 0.6, 0.7, 1) lanthanum molybdates prepared via mechanical activation of lanthanum and molybdenum oxides, followed by thermal annealing at 1650 degrees C. The La6-xMoO12-delta (x = 0.5, 0.6) materials were phase-pure and had a complex rhombohedral structure (R1). An increase in the molybdenum concentration leads to a decrease in the degree of rhombohedral distortion and proton conductivity in the La6-xMoO12-delta (x = 0.5, 0.6, 0.7, 1) series. The proton conductivity at the optimal composition La6-xMoO12-delta (x = 0.5) is similar to 4.0 x 10(-5) S/cm at 500 degrees C in wet air. A comparative analysis shows that, in the Ln(6-x)MoO(12-delta) (Ln = La, Nd, Sm, Gd, Dy, Ho, Er, Tm, Yb; x = 0-1) series, proton conductivity decreases with the Ln ionic radii decreasing regardless of the structural type. Because of this, the high proton conductivity is demostrated by the stable La6-xMoO12-delta (x = 0.5, 0.6) materials, with an inherently deficient oxygen sublattice, which crystallize in a large-volume, complex rhombohedral cell (R1). (C) 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Automated summary

The study focused on the structure and proton conductivity of rhombohedral La6-xMoO12-delta (x = 0.5, 0.6, 0.7, 1) lanthanum molybdates produced by mechanical activation and thermal annealing. It was found that an increase in molybdenum concentration in the La6-xMoO12-delta series led to a decrease in both rhombohedral distortion and proton conductivity. The optimal composition of La6-xMoO12-delta (x = 0.5) exhibited a proton conductivity of approximately 4.0 x 10(-5) S/cm at 500 degrees C in wet air.