Microstructural and compositional optimization of La0.5Ba0.5CoO3−δ—BaZr1−zYzO3−δ (z=0, 0.05 and 0.1) nanocomposite cathodes for protonic ceramic fuel cells

Abstract

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 La0.5Ba0.5CoO3−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°Cto 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 La0.5Ba0.5CoO3−δ—BaZr0.9Y0.1O2.95 cathode with an area specific resistance of 4.02 Ω·cm2 at 400 °Cand 0.21 Ω·cm2 at 600 °Cin 3%moist synthetic air. These results are among the best reported for cathodes of PCFCs as will be discussed.