An Elementary Kinetic Model for the Electrochemical Reduction of Oxygen on LSM/YSZ Composite Cathodes

A detailed computational model of the oxygen reduction reaction in composite strontium-doped lanthanum manganite/yttria-stabilized zirconia (LSM/YSZ) SOFC cathodes is presented.  The coupled interactions of elementary heterogeneous chemistry, elementary electrochemistry (at two separate electrochemical double layers) and transport through the porous electrode are studied. Species diffusion and convection through the porous cathode are evaluated using the Dusty Gas Model while a distributed charge transfer model is used to study the ionic and electronic transport through the cathode. Charge-transfer reactions are modeled using a spillover mechanism with no a priori assumption of rate limiting steps unlike the frequently published Butler-Volmer approach. The model is validated against overall area-specific resistance (ASR) values previously reported by Barbucci et al. [Electrochemica Acta, 47 (2002)] over a temperature range of 950-1200 K. A sensitivity analysis reveals the impact of various kinetic parameters on the ASR and subsequently leads to the identification of rate-limiting steps. Preliminary results indicate that the ASR is sensitive to the rate of dissociative adsorption of O₂ on LSM and oxygen ion transfer from the YSZ surface to the YSZ bulk.