Protonated BaZr0.8Y0.2O3-δ: Impact of Hydration on Electrochemical Conductivity and Local Crystal Structure

Acceptor-doped BaZrO3 is a promising electrolyte candidate in fuel cells and electrolysis cells due to its high proton conductivity and excellent chemical stability. However, it turns to be partially hole-conductive in an oxidizing atmosphere, resulting in the degraded performance of these electrochemical devices. Based on the knowledge of defect chemistry on BaZrO3, its electrochemical properties can be tuned by simply controlling the partial pressure of oxygen (p(O2)) and water vapor (p(H2O)) in the atmosphere. In this work, we investigated the hydration behavior of BaZrO3 doped with Y or Yb under p(H2O) varying from 0.03 to 0.51 atm and found that both the proton concentration and lattice constants increased for BaZr0.8Yb0.2O3-delta (BZY20) and BaZr0.8Yb0.2O3-delta (BZYb20) with increasing p(H2O). Also, the chemical expansion coefficients of (0.882 +/- 0.036) x 10(-2) and (1.44 +/- 0.067) x 10(-2) per one proton per unit cell were estimated for BZY20 and BZYb20, respectively. The change in the local crystal structure due to such chemical expansion induced by water incorporation was probed by EXAFS analysis, and the result coincides with the reported insight that the oxide ions and protons are more favorable to reside in the vicinity to Y cations. Furthermore, it is effective to suppress the hole conduction by elevating p(H2O) and lowering p(O2); for example, the ionic transport number (t(ion)) at 600 degrees C can be increased to be higher than 0.9 by elevating p(H2O) over 0.20 atm, suggesting an effective and feasible strategy to improve the performance of the electrochemical devices with the BZY20 electrolyte.

Automated summary

This study investigates the hydration behavior of acceptor-doped BaZrO3 under varying water vapor pressure and reveals that hydration process increases proton concentration and lattice constants. The chemical expansion due to water incorporation influences the local crystal structure and can effectively suppress hole conduction in BaZrO3, showing a feasible strategy to enhance the performance of electrochemical devices.