Tailoring oxide thin films for fuel cells
Lowering the operating temperature of solid oxide fuel cells (SOFCs) would limit materials' degradation and lower overall costs. The challenge is to find materials that perform well at lower temperatures i.e. better electrodes and electrolytes. Among the most promising cathode materials are those that conduct both ions and conventional electrons — mixed ionic and electronic conductors (MIECs). A new EU-funded study of candidate MIEC ceramics combined novel experimental techniques for the first time to probe structure and function. The project 'Design of new engineered oxide thin films with tailored properties' (ENGINEERED OXIDES) led to the pioneering discovery of oxygen diffusion and exchange properties. Studies on MIEC ceramics revealed spatially non-uniform ionic transport properties. Scientists investigated single crystals and epitaxial films to gain insight into their inherent anisotropies. Novel measurement techniques revealed the anisotropy of oxygen diffusion experimentally in some promising cathode materials (double perovskites) for the first time. In unprecedented work, researchers probed the temperature dependence of atomic surface structure and reconstruction/relaxation of single crystals. The structural models were correlated with experimental data regarding the outermost surface layer and near-surface depth profiles obtained with other advanced techniques. Researchers conducted ground-breaking measurements of oxygen surface exchange and diffusion properties in combinatorial thin films consisting of films of spatially-resolved differing composition. The results not only provide important insight but demonstrate the power of scanning a wide range of material compositions in a single thin film deposition experiment. Many additional in-depth studies of the surface science of a number of cathode materials, both thin films and single crystals, constitute the first of their kind. Knowledge gained and methodologies demonstrated within the scope of the ENGINEERED OXIDES project lay the foundation for development of tomorrow’s high-performance, low-cost SOFCs. Outcomes are expected to improve performance of a wealth of other electrochemical energy conversion devices as well. All said scientists have made a major contribution to the evolution of the EU’s green energy plan.
Keywords
Oxide thin film, green energy, SOFCs, MIEC, ceramics, oxygen diffusion, single crystals
