Various dopants were added to BaZrO 3 and the conductivities, the proton concentrations, the site occupancy of the dopants and the change in lattice volume as a result of chemical expansion were investigated. Lanthanide group dopants occupied both the Ba and Zr sites, but the amount of these dopants in the Ba site was too limited to significantly influence the conductivity. The samples doped with Yb, Tm, Er, Y and Ho showed both high proton concentrations and high conductivities, together with a relatively large lattice expansion as a result of hydration. We therefore suggest that, in most instances, the proton concentration, proton conductivity and lattice change as a result of chemical expansion were all correlated in proton conductive acceptor-doped BaZrO 3 . However, Scdoped BaZrO 3 seemed to be different. Its proton concentration was high, but the conductivity and lattice change as a result of chemical expansion were relatively small. This indicates that the conductivity was strongly related to the lattice expansion resulting from hydration rather than simply the proton concentration.

Y-doped BaZrO (BZY) is currently the most promising proton-conductive ceramic-type electrolyte for application in electrochemical devices, including fuel cells and electrolyzer cells. However, owing to its refractory nature, sintering additives, such as NiO, CuO, or ZnO are commonly added to reduce its high sintering temperature from 1600 °C to approximately 1400 °C. Even without deliberately adding a sintering additive, the NiO anode substrate provides another source of the sintering additive; during the co-sintering process, NiO diffuses from the anode into the BZY electrolyte layer. In this work, a systematic study of the effect of NiO, CuO, and ZnO on the electroconductive properties of BaZr Y O (BZY20) is conducted. The results revealed that the addition of NiO, CuO, or ZnO into BZY20 not only degraded the electrical conductivity but also resulted in enhancement of the hole conduction. Removal of these sintering additives can be realized by post-annealing in hydrogen at a mild temperature of 700 °C, but it is kinetically very slow. Therefore, the addition of NiO, CuO, and ZnO is detrimental to the electroconductive properties of BZY20, and significantly restrict its application as an electrolyte. The development of new sintering additives, new anode catalysts, or new methods for preparing BZY electrolyte-based cells is urgently needed.

Nickel (Ni) is expected to be an attractive anode material for protonic ceramic fuel cells using Y-doped BaZrO 3 (BZY) as an electrolyte, since Ni shows good catalytic properties for the anode reaction, and NiO is a sintering aid for BZY. In this work, a systematic investigation has been performed to reveal the influence of Ni incorporation on structural and electrochemical properties of BZY. Then, some new knowledge was obtained; the important point is that Ni cations occupy the interstitial position of (1/2, 0, 0) in the lattice of BZY, with a greatly Ba-deficient environment. As a result, Ba cations were possibly driven to the grain boundary and induced the formation of a liquid phase, which promoted the sintering process. However, the occupation of Ni on this (1/2, 0, 0) position also resulted in a negative influence on conductivity. A careful processing is required to apply Ni as the electrode in BZY based fuel cells.

Knowledge of thermal behavior of electrolyte is important for fuel cell fabrication. In this study, using high‐temperature X‐ray diffraction analysis (HT‐XRD) and thermo‐mechanical analysis (TMA), a systematic investigation of lattice constants was performed on Y‐doped BaZrO3, which is a promising candidate for electrolyte in protonic ceramic fuel cells. The results revealed that a chemical expansion was observed between 300°C and 450°C during the heating process in HT‐XRD, and was attributed to the dehydration of BZY. Furthermore, it was found that the lattice constants of the samples doped with Y, Sm, Eu, and Dy were larger for the ones finally heat‐treated at 1600°C for sintering than those heat‐treated at 1300°C for synthesizing. The similar behavior was not observed in Sc‐doped samples.