GDC-Infiltrated La0.3Ca0.7Fe0.7Cr0.3O3-δ Symmetrical Oxygen Electrodes for Reversible SOFCs

There is great interest in the development of reversible fuel cells, particularly reversible solid oxide fuel cells (RSOFCs). RSOFCs can run in both the electrolysis mode (SOEC) to electrolyze H₂O to H₂ or co-electrolyze CO₂ and H₂O to syngas when excess electricity is available, and then run in the fuel cell mode (SOFC) to convert H₂ or syngas to electricity and heat when energy is needed. The primary goal of this work has been to develop new materials for highly efficient electrolyte-supported RSOFCs, based on La_0.3M_0.7Fe_0.7Cr_0.3O_3-δ (M = Sr, Ca) mixed ionic-electronic conducting perovskite electrodes, with a particular forcus on La0.3Sr0.7Cr0.3Fe0.7O3-δ (LSFCr) and La0.3Ca0.7Cr0.3Fe0.7O3-δ (LCFCr) operating in air at 600-800 ^oC. The specific goal of this work is to employ LSFCr and LCFCr as both the air and fuel electrodes in both the SOFC and SOEC modes, thus significantly lowering cost and simplifying the manufacturing process.

Because of the excellent performance of LSFC [1] as an air electrode, efforts are now focussed on further improving its performance in air and also in fuel environments. For this reason, the A-site of the perovskite was doped with Ca in place of Sr, primarily to decrease the thermal expansion coefficient of the perovskite to more closely match that of the most commonly used electrolytes [2]. Although relatively low electrode polarization resistances were obtained with porous LSFCr [1] and LCFCr [2] electrodes, further improvement of the electrochemical performance would still be possible through microstructural modifications. Since the electrochemical performance of these mixed electronic and ionic conductors (MIECs) depends on the double phase boundary (DPB) area of the MIEC/electrolyte interface, in this study, an attempt was made to further enhance the DPB area by infiltrating the porous MIEC electrode with the electrolyte material (Gadolinia doped Ceria, GDC).  To achieve this goal, a polymeric GDC solution precursor, which has the ability to form an interconnected film [3], was infiltrated into a previously sintered porous La_0.3M_0.7Fe_0.7Cr_0.3O_3-δ scaffold structure.

Two types of electrolyte supported symmetrical cells were used in this study. In Type 1, LSFCr and LCFCr were screen-printed on both sides of a 250 µm thick GDC electrolyte-support, followed by firing at 1100 ^oC in air. A second set of cells was then infiltrated with a polymeric GDC precursor (Type 2).The performance of these half cells, operated at 600-800 ^oC in air, was then investigated. The initial impedance spectroscopy results showed that GDC infiltration resulted in a ca. 3 fold decrease in the polarization resistance of the MIEC electrodes in air at 800 °C. The 0.06 Ω.cm² polarization resistance obtained for these electrodes at this temperature is a strong indication that polymeric GDC precursor infiltration into MIEC electrodes is a promising approach for the fabrication of very high performance RSOFC electrodes.  

 

Acknowledgements:  We are very grateful to the SOFC Canada NSERC Strategic Research Network, as well as Carbon Management Canada, for the support of this work.  .

References:

[1] M. Chen, S. Paulson, V. Thangadurai and V. Birss, J. Power Sources, 236 (2013) 68.

[2] B. Molero-Sanchez, J. Prado-Gonjal, , D. Ávila-Brande, M. Chen, E. Morán, E. and V. Birss, International Journal of Hydrogen Energy-Accepted, (2014).

[3] A. Buyukaksoy, V. Petrovsky and F. Dogan, J. Electrochem. Soc., 160 (2013) F482.