PEROVSKITE SOLID ELECTROLYTES - STRUCTURE, TRANSPORT-PROPERTIES AND FUEL-CELL APPLICATIONS

Doped barium cerate perovskites, first investigated by Iwahara and co- workers, have ionic conductivities of the order of 20 mS/cm at 800 deg rees C making them attractive as fuel cell electrolytes for this tempe rature region. They have been used to construct laboratory scale fuel cells, which, in addition to performance data, have provided an unexpe cted insight into the transport processes operating in these materials . In the temperature range of 600-1000 degrees C, the dominant transpo rt process varies from protonic to oxide-ion dominated. This transitio n has been confirmed by measurement of water vapour transfer in a cell in which the perovskite is exposed to wet hydrogen on both sides. The evolution of transport properties with temperature is discussed in re lation to structure. Neutron diffraction studies of doped and undoped barium cerate are reported, revealing a series of phase transitions be tween ambient temperature and 1000 degrees C. The available literature on chemical stability of cerate perovskites to reduction and attack b y carbon dioxide is reviewed in brief.