Proton transport properties at the grain boundary of barium zirconate based proton conductors for intermediate temperature operating SOFC

Abstract

Proton transport properties across the grain boundary of barium zirconate based proton conductors were studied in accordance with the space charge concept. The analysis is performed at temperatures lower than 200 C using a Mott-Schottky model. The barrier height of Y-and Gd-doped barium zirconate is in the range of 0.29 to 0.57 V, which higher than that of oxygen ionic conductors. The barrier height of the space charge layer shows a dependence on the dopant type and concentration. The dependence correlates with the enrichment of the dopant at the grain boundary. The results suggest that the enrichment of the dopant decreases the barrier height and is effective to improve proton transport properties across the grain boundary.

Theoretical modeling of defect segregation and space-charge formation in the BaZrO3 (210)[001] tilt grain boundary

“…Potential barriers around 0.65 V were obtained at temperatures below 900 K under wet conditions, which is consistent with experimental results [6,8,[11][12][13][14][15][16]. At these temperatures the excess core charge, and thereby the potential, is here found to be due only to protons.…”

“…6. The space-charge potential is about 0.65 V below 900 K under wet conditions which is consistent with experimental results [6,8,[11][12][13][14][15][16]. Under dry conditions the potential is slightly lower by a value of 0.05-0.1 V. A similar difference in the potential barrier height between dry and wet conditions was found experimentally by Shirpour et al [16].…”

“…However, sintered BaZrO 3 is polycrystalline and the conductivity of that material is orders of magnitude lower due to resistance at the grain boundaries (GBs) [1,3,4]. Grain boundaries in BaZrO 3 do not contain secondary phases [5][6][7][8] and the high resistance is therefore considered to be an intrinsic effect.…”

“…In turn, the potential depletes the surrounding regions of mobile charge carriers thus limiting the conductivity [9,10]. The spacecharge model has been applied to BaZrO 3 by several research groups where the space-charge potentials have been determined based on both experiments [6,8,[11][12][13][14][15][16] and theoretical modeling [17][18][19][20][21].…”

Oxygen vacancy segregation in grain boundaries of BaZrO3 using interatomic potentials

“…Polycrystalline samples do however display significantly lower conductivity which is caused by resistive grain boundaries (GBs) [1,3,4]. This has recently been interpreted in terms of the space-charge model by several research groups [5][6][7][8][9][10][11][12][13]. This model assumes that positively charged defects, such as oxygen vacancies, accumulate at the GB core and thereby give rise to an electrostatic potential.…”