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

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 degree C, under pure CO sub(2), in air and in H sub(2) diluted in N sub(2), to test their stability and electrical performance. Impedance spectroscopy measurements performed between 300 and 600 degree C were complemented by structural and microstructural characterization. The excellent long-term stability in CO sub(2) drops slightly when moving to air and in a pronounced manner when moving to diluted H sub(2). 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.