Adherence of Air-Steam Electrodes to Proton-Conducting Ceramic Electrolytes

Protonic-ceramic performance degradation remains an active area of study. As with oxygen-ion-conducting ceramics, the interface between the electrolyte and the positrode (air-stream electrode) is an area of concern, where materials instability, thermal-expansion mismatch, and poor adherence can compromise cell performance over time. This work examines positrode-electrolyte adherence through pull-testing on 168 protonic-ceramic membrane-electrode assemblies. Cell materials include a porous BaCo 0.4 Fe 0.4 Zr 0.1 Y 0.1 O 3-d positrode, a dense BaCe 0.4 Zr 0.4 Y 0.1 Yb 0.1 O 3-d electrolyte, and a Ce 0.9 Gd 0.1 O 1.95 (GDC) interlayer placed at their interface. Positrode adherence to a GDC pellet is also measured. Cells are exposed to humidified air for 72 h at 620 °C at humidities varying from 1 to 50 mol-% H 2 O. Two hypotheses are tested: (1) a GDC interlayer improves positrode-electrolyte adherence; and (2) adherence is compromised by long-term exposure to high concentrations of water vapor at elevated temperature. Morphological and statistical analyses provide insight on results. The GDC interlayer increases positrode-electrolyte adherence, while cell exposure to H 2 O is not found to compromise adherence. Through transmission electron microscopy, energy-dispersive X-ray spectroscopy, and atomic force microscopy, the improvement in positrode-electrolyte adherence is attributed to an enhanced nano-scale morphology that provides an increased bonding-surface area, effectively anchoring the positrode to the electrolyte.