Kinetic parameters influencing the performance of IT-SOFC composite electrodes

Composite electrodes have made important contributions to the development o f intermediate temperature solid oxide fuel cells (IT-SOFC). At a macroscop ic level the separate electronic and ionic components can usefully be consi dered as a combined mixed conductor. This allows available kinetic data for oxygen self-diffusion (D* cm(2) s(-1)) and surface exchange (k cm s(-1)) c oefficients to be evaluated so that possible rate-determining processes can be identified. For LSM/YSZ and LSCF/CGO composite electrodes it appears th at the k values for YSZ and CGO have to be enhanced by at least two orders of magnitude to account for observed cathode ASR values. It is suggested th at 'spillover' reactions involving the electronic component could be respon sible for the increased rate of O2- injection into YSZ and CGO. Additional strategies to further enhance the surface exchange rate for CGO at 500 degr eesC, such as doping with redox cations (e.g. Tb4+/Tb3+, Nb5+/Nb4+), changi ng the reduction enthalpy for Ce4+ double right arrow Ce3+, and promotion w ith noble metal catalysts, are also discussed. (C) 2000 Elsevier Science B. V. All rights reserved.