Ceramic electrodes for SOFC's

The current trend in Solid Oxide Fuel Cell (SOFC) development is for a lowe ring of the operation temperature from similar to 1000 degrees C to tempera tures as low as 600 degrees C. This lowering of temperature is beneficial i n a number of ways. It relaxes the stringent materials requirements for cel l components, particularly, the interconnect, and for the balance of plant. One adverse consequence of the lower temperatures is a slowing. Of the ele ctrode kinetics, particularly, at the cathode (air electrode). It is thus n ecessary to have a thorough understanding of the processes occuring at the cathode to aid material selection and optimisation for low operating temper atures. The majority of the cathode materials use at present, are based on mixed co nducting, acceptor (A) doped, rare-earth (Ln) transition metal (T) perovski te oxides with the general formula. Ln(1x)A(x)TO(3+/-delta). Examples of th ese materials include La1-xSrxMnO3+/-delta La1-xSrxCoO3+/-delta etc. The pe rformance of these electrodes can be linked to their microsturcture, and to the kinetics of oxygen exchange and diffusion. In order to model the behav iour of such materials as cathodes. We have undertaken a systematic study o f the kinetics of the oxygen exchange process using the isotope exchange de pth profiling method (IEDP) employing Secondary Ion Mass Spectrometry (SIMS ). Oxygen self diffusion and surface exchange data are presented for a numb er of perovskite cathode compositions, in particular the effect of increasi ng the acceptor dopant level are explored together with the effect of chang ing the rare earth and transition metal cations.