Processing of high performance composite cathodes for protonic ceramic fuel cells by exsolution†
Abstract
La0.5Ba0.5CoO3−δ–BaZrO3 (LB–BZ)-based composite materials were prepared by a modified Pechini sol–gel method combined with exsolution. Two different LB–BZ composites were prepared through two alternative thermal treatments of the precursor gel. A metastable single phase with a perovskite crystal structure was first obtained upon annealing the precursor in an inert atmosphere, and it was further transformed into a two-phase composite by in situ exsolution in air. Comparatively, direct calcination of the LB–BZ gel in air resulted in a two-phase composite with different microstructures and compositions of the two phases. The composite cathode formed by exsolution consisted of a matrix of BZ-phase with ∼45 nm grain size embedding ∼20 nm grains of LB-phase, while the composite cathode obtained by direct calcination consisted of a mixture of both phases with 50–60 nm grain size. Electrodes of symmetric half-cells were spray-coated on the BaZr0.9Y0.1O2.95 electrolyte to examine the electrochemical performance by impedance spectroscopy. The lowest area specific resistance (ASR) was obtained for the composite cathode produced by exsolution with an excellent ASR of 1.54 Ω cm2 at 600 °C and 18 Ω cm2 at 400 °C and an activation energy (Ea) of 0.60 eV in 3% moist synthetic air. This work demonstrates the potential of fabricating high performance nanocomposite cathodes with tailored chemical composition by a novel exsolution method.