Composite electrolytes for fuel cells: Long-term stability under variable atmosphere

• Highly favorable long-term stability of CGO and ceria-based composites in CO2.
• Impedance spectroscopy can be used to monitor the CGO matrix ageing.
• Degradation of ceria-based composite electrolytes higher in the case of CGO.
• Long-term stability in the absence of CO2 seems questionable in all cases.

Ceria-based composites (50 vol% of the ceramic phase) including one mixture of Li and Na carbonates (1:1 molar ratio), were prepared using either pure ceria (modest conductor) or Gd-doped ceria (excellent oxide–ion conductor) as ceramic matrix. These materials were aged for periods of up to 1000 h at 550 °C, under pure CO2, in air and in H2 diluted in N2, to test their stability and electrical performance. Impedance spectroscopy measurements performed between 300 and 600 °C were complemented by structural and microstructural characterization. The excellent long-term stability in CO2 drops slightly when moving to air and in a pronounced manner when moving to diluted H2. In all cases and in all conditions the best performance is observed for pure ceria-based composites. Electrode (Au) and electrolyte degradation were found interrelated.