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

BaHf 0.8 Ln 0.2 O 3-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 H 2 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 BaHfO 3 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 BaHf 0.8 Y 0.2 O 3-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 H 2 O steam, pure H 2 and CO 2 , 200 ppm H 2 S/Ar and boiling water. The Pt/BaHf 0.8 Y 0.2 O 3-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 BaHf 0.8 Y 0.2 O 3-δ is a promising electrolyte candidate for proton-conducting fuel cells.