Stability and compatibility of fuel cells based on proton conducting materials
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Stability and compatibility of the proton conducting electrolyte material La6WO12 with the potential cathode materials LaCoO3 and La2NiO4 were investigated by means of solid-solid diffusion couples. Reactivity studies were carried out at 1450 °C for various times. Reaction products were analysed by SEM and EDS. The study suggests a high reactivity between the electrolyte and the electrodes, which is detrimental for the fuel cell system.In the case of LaCoO3 as a cathode material a secondary phase of LaCo1-xWxO3 were formed at the interface and as precipitates in La6WO12. Theoretical models for both diffusion or interface controlled reactions failed to fit the experimental data. This failure is probably related to the reaction going towards equilibrium after a certain time, or poor connectivity between the materials. The solid- state reaction between La6WO12 and La2NiO4 showed formation of a composite layer of La2O3 and La6WO12 at the interface. The reaction kinetics of this product layer was diffusion controlled. In addition to the interface reaction, precipitates of La2O3 and La6WO12 were formed in the La2NiO4 phase.