La0.5Ba0.5CoO3−δ–BaZrO3 (LB–BZ)-based composite materials were prepared by a modified Pechini sol–gel method combined with exsolution.

The effect of A-site cation ordering on the cathode performance and chemical stability of A-site cation ordered LaBaCo2O5+δ and disordered La0.5Ba0.5CoO3−δ materials are reported. Symmetric half-cells with a proton-conducting BaZr0.9Y0.1O3−δ electrolyte were prepared by ceramic processing, and good chemical compatibility of the materials was demonstrated. Both A-site ordered LaBaCo2O5+δ and A-site disordered La0.5Ba0.5CoO3−δ yield excellent cathode performance with Area Specific Resistances as low as 7.4 and 11.5 Ω·cm2 at 400 °C and 0.16 and 0.32 Ω·cm2 at 600 °C in 3% humidified synthetic air respectively. The oxygen vacancy concentration, electrical conductivity, basicity of cations and crystal structure were evaluated to rationalize the electrochemical performance of the two materials. The combination of high-basicity elements and high electrical conductivity as well as sufficient oxygen vacancy concentration explains the excellent performance of both LaBaCo2O5+δ and La0.5Ba0.5CoO3−δ materials at high temperatures. At lower temperatures, oxygen-deficiency in both materials is greatly reduced, leading to decreased performance despite the high basicity and electrical conductivity. A-site cation ordering leads to a higher oxygen vacancy concentration, which explains the better performance of LaBaCo2O5+δ. Finally, the more pronounced oxygen deficiency of the cation ordered polymorph and the lower chemical stability at reducing conditions were confirmed by coulometric titration.

A novel exsolution process was used to fabricate complex all-oxide nanocomposite cathodes for Protonic Ceramic Fuel Cells (PCFCs).The nanocomposite cathodes with La 0.5 Ba 0.−δ nominal composition were prepared from a single-phase precursor via an oxidation-driven exsolution mechanism. The exsolution process results in a highly nanostructured and intimately interconnected percolating network of the two final phases, one proton conducting (BaZr 1−z Y z O 3−δ ) and one mixed oxygen ion and electron conducting (La 0.5 Ba 0.5 Co 1/3 Mn 1/3 Fe 1/3 O 3−δ ), yielding excellent cathode performance. The cathode powder is synthesized as a single-phase cubic precursor by a modified Pechini route followed by annealing at 700 • C in N 2 . The precursor phase is exsolved into two cubic perovskite phases by further heat treatment in air. The phase composition and chemical composition of the two phases were confirmed by Rietveld refinement. The electrical conductivity of the composites was measured and the electrochemical performance was determined by impedance spectroscopy of symmetrical cells using BaZr 0.9 Y 0.1 O 2.95 as electrolyte. Our results establish the potential of this exsolution method where a large number of different cations can be used to design composite cathodes. The La 0.5 Ba 0.5 Co 1/3 Mn 1/3 Fe 1/3 O 3−δ -BaZr 0.9 Y 0.1 O 2.95 composite cathode shows the best performance of 0.44 Ω·cm 2 at 600 • C in 3% moist synthetic air.

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 0.5 Ba 0.5 CoO 3−δ -BaZrO 3 -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 BaZrO 3 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 0.5 Ba 0.5 CoO 3−δ -BaZr 0.9 Y 0.1 O 2.95 cathode with an area specific resistance of 4.02 Ω·cm 2 at 400°C and 0.21 Ω·cm 2 at 600°C in 3% moist synthetic air. These results are among the best reported for cathodes of PCFCs as will be discussed.