Compatibility of La26O27(BO3)8 electrolyte with standard cathode materials for use in proton conducting solid oxide fuel cells

The chemical and mechanical compatibility of proton conducting La26O27(BO3)8 (LBO) electrolyte with standard cathode materials La0.7Sr0.3MnO3 (LSM), La0.75Sr0.25Cr0.5Mn0.5O3 (LSCM), La2NiO4 and Ba0.5Sr0.5Co0.8Fe0.2O3 (BSCF) was investigated. The results show that LSM, LSCM and La2NiO4 cathodes are chemically and mechanically stable with the LBO electrolyte, and BSCF reacts with LBO after heat-treatment of their mechanical ground mixtures at T = 1150 °C. Symmetrical cell tests based on LBO demonstrated that the values of the cathode ASR (area specific resistance) are much lower in the case of the LSM and La2NiO4 cathodes than in the case of the LSCM cathode (in humidified air at 700 °C: ASRLSM = 15 Ω·cm2; ASRLSCM= 60 Ω·cm2; ASRLa2NiO4 = 1 Ω·cm2). The large value obtained for LSCM cathode may be related to the low level of its oxygen ion conductivity. Finally, a composite cathode (CER-CER) approach was used in order to optimize the polarization resistance of the LSM cathode. Several CER-CER cathodes with different cathode/electrolyte weight ratios were prepared. The lowest value of ASR for LSM-based composite cathode was obtained by adding 50 wt% of LBO to LSM cathode (ASRLSM/LBO = 3.4 Ω·cm2 in humidified air at 700 °C).