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.
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