Phase and microstructure stability of BaZr0.1Ce0.7Y0.1Yb0.1O3−δ electrolyte under reducing environment of protonic ceramic cells

Abstract

The chemical and microstructural stability of proton-conducting electrolyte is crucial for durable operation of protonic ceramic cells (PCCs). In this study, the reduction stability of BaZr 0.1 Ce 0.7 Y 0.1 Yb 0.1 O 3−δ (BZCYYb) was systematically investigated. At 400-800 °C, wet H 2 caused more severe surface precipitation on BZCYYb than dry H 2 . Exposed to humidified H 2 at 800 °C, Ba depletion and Ce 4+ reduction promoted surface segregation of Zr, Y, Ce, and Yb and the formation of a 15-20 nm oxide layer on the surface of BZCYYb. Compared to the fresh BZCYYb, the conductivity of BZCYYb reduced in dry and wet H 2 at 800 °C decreased, while the conductivity of BZCYYb reduced in wet H 2 at 400-600 °C tended to increase. The segregation of multiple oxides from BZCYYb complicated the conductivity change trend. Tested at 200 °C in moist air, the total conductivities of BZCYYb reduced in moist H 2 for 50h at 400 °C, 600 °C, and 800 °C were respectively 6.5E-5, 6.3E-5, and 1.8E-6 S cm −1 , while those were 4.9E-5, 2.9E-5, and 1.9E-5 S cm −1 reduced in dry H 2 . These findings disclose the origins inducing the instability of the electrolyte in reducing atmosphere, provide insight into degradation mechanisms of proton-conducting electrolytes, and lay the foundation for design of stable electrolyte under practical operation conditions.