Manufacturing of intermediate-temperature solid oxide fuel cells using novel cathode compositions

Abstract

The development of intermediate temperatures solid oxide fuel cells (IT-SOFC) with YSZ electrolytes imposes a double requirement in their manufacturing. First, the electrolyte has to be kept as thin as possible to minimize ohmic polarization losses. Second, the cathode compositions used must exhibit an adequate catalytic activity at the operating temperature (600 – 800 ºC). Current methods to manufacture thin YSZ electrolytes require complex processes, and sometimes costly equipment. Cathode compositions traditionally used for high temperature solid oxide fuel cells, such as (La,Sr)MnO3 do not exhibit good catalytic properties at intermediate temperatures. These challenges present areas of opportunity in the development of original manufacturing techniques and new cathode compositions. This study presents a low-cost fabrication procedure for IT-SOFC using tape casting, co-firing and screen printing. The electrochemical performance of the cells is evaluated using a known cathode composition for IT-SOFC, such as La0.6Sr0.4CoO3-δ (LSC), novel perovskite oxides, such as Nd0.6Sr0.4CoO3-δ (NSC), and perovskite-related intergrowth oxides compositions, like Sr0.7La0.3Fe1.4Co0.6O7-δ (SLFCO7) and LaSr3Fe1.5Co1.5O10-δ (LSFCO10). The impact of conductivity is studied by substituting Fe for Co in the case of the perovskite oxides, with compositions such as La0.6Sr0.4Co0.5Fe0.5O3-δ (LSCF), and Nd0.6Sr0.4Co0.5Fe0.5O3-δ (NSCF) and by infiltration of NSCF with silver. The effect of the cathode sintering temperature is studied using LSC and LSCF cathodes. It is found that there is generally a correlation between cell performance and conductivity. However, the microstructure of the cathode is also important in determining cell performance by tailoring the cathode sintering temperature. IT-SOFC with SLFCO7 cathodes show a performance comparable to cells with LSFC cathode. In the case of LSFCO10, the performance loss associated with its lower conductivity compared to LSC can be more than offset by tailoring the microstructure.