Influence of rare-earth doping on the phase composition, sinterability, chemical stability and conductivity of BaHf0.8Ln0.2O3-δ (Ln = Yb, Y, Dy, Gd) proton conductors

Abstract

BaHf0.8Ln0.2O3-δ doped with rare earth elements with different ionic radii (Ln = Yb, Y, Dy and Gd) as candidate materials for solid oxide fuel cells and H2 separation membrane have been prepared. Their phase composition, sinterability, chemical stability and conductivity were studied systematically. The rare earth elements are successfully incorporated into the main phase crystal lattice of barium hafnate to generate a single perovskite phase. The relative density of all samples sintered at 1600 °C reaches above 90%, and Y-doped BaHfO3 has the highest relative density (94.7%) and the biggest grain size (about 1 μm) among all samples. The conductivities of the samples firstly increase and then decrease with the increase of the doped ion radius. Among all samples the conductivity of BaHf0.8Y0.2O3-δ is the highest and reaches 6.02 × 10−3 S cm−1 in wet air at 700 °C, which is attributed to the good sinterability and suitable crystal structure (tolerance factor and free volume). All samples also show excellent chemical stability in the test atmospheres, including saturated H2O steam, pure H2 and CO2, 200 ppm H2S/Ar and boiling water. The Pt/BaHf0.8Y0.2O3-δ electrolyte/Pt single cell was fabricated with a 530 μm-thick disk and its electrochemical properties were tested. The peak power density reaches 10.21 mW cm−2 at 700 °C, which is comparable to similar fuel cells reported. These results suggest that BaHf0.8Y0.2O3-δ is a promising electrolyte candidate for proton-conducting fuel cells.