Laura Rioja-Monllor

Cathodes are one of the key components of protonic ceramic fuel cells (PCFCs) requiring further development to enhance the performance of PCFCs. This encompasses the optimization of material compositions and microstructures, as well as a further understanding of the electrode processes. Here, a compositional optimization of a La_0.5Ba_0.5CoO_3−δ —BaZrO₃-based nano-composite cathode prepared by exsolution of a single-phase material was performed by substituting 5 and 10 mol% Y at the B-site in the BaZrO₃ phase. Electrodes with different microstructures were prepared by two different deposition methods, spray coating and screen printing, and by varying the firing temperature from 600°C to 1100 °C. Further, composite electrodes were prepared by directly coating and firing the single-phase materials on the dense electrolyte to prepare symmetric cells. A good adhesion of the cathode to the electrolyte was observed in all cases. In general, a more homogeneous microstructure was observed for the cathodes prepared by screen printing. The single step method encompassing exsolution of the single phase and firing of the symmetric cells yielded significant improvement in the cathode performance compared to the other routes. The best electrochemical performance was observed for La_0.5Ba_0.5CoO_3−δ —BaZr_0.9Y_0.1O_2.95 cathode with an area specific resistance of 4.02 Ω · cm² at 400 °C and 0.21 Ω · cm² at 600 °C in 3% moist synthetic air. These results are among the best reported for cathodes of PCFCs as will be discussed.

Compositionally engineered a La_1-xBa_xCoO_3-δ-(1-a) BaZr_0.9Y_0.1O_2.95 (a = 0.6, 0.7, 0.8 and x = 0.5, 0.6, 0.7) (LBZ) nanocomposite cathodes were prepared by oxidation driven in situ exsolution of a single-phase material deposited on a BaZr_0.9Y_0.1O_2.95 electrolyte. The processing procedure of the cathode was optimized by reducing the number of thermal treatments as the single-phase precursor was deposited directly on the electrolyte. The exsolution and firing of the cathodes occurred in one step. The electrochemical performance of symmetrical cells with the compositionally engineered cathodes was investigated by impedance spectroscopy in controlled atmospheres. The optimized materials processing gave web-like nanostructured cathodes with superior electrochemical performance for all compositions. The area specific resistances obtained were all below 12 Ω·cm² at 400 °C and below 0.59 Ω·cm² at 600 °C in 3% moist synthetic air. The resistances of the nominal 0.6 La_0.5Ba_0.5CoO_3-δ-0.4 BaZr_0.9Y_0.1O_2.95 and 0.8 La_0.5Ba_0.5CoO_3-δ-0.2 BaZr_0.9Y_0.1O_2.95 composite cathodes were among the lowest reported for protonic ceramic fuel cells cathodes in symmetrical cell configuration with ASR equal to 4.04 and 4.84 Ω·cm² at 400 °C, and 0.21 and 0.27 Ω·cm² at 600 °C, respectively.

La_0.5Ba_0.5CoO_3−δ–BaZrO₃(LB–BZ)-based composite materials were prepared by a modified Pechini sol–gel method combined with exsolution.