Design of Ordered Mesoporous CeO 2 -YSZ Nanocomposite Thin Films with Mixed Ionic/Electronic Conductivity via Surface Engineering.

Mixed ionic and electronic conductors represent a technologically relevant materials system for electrochemical device applications in the field of energy storage and conversion. Here, we report about the design of mixed-conducting nanocomposites by facile surface modification using atomic layer deposition (ALD). ALD is the method of choice, as it allows coating of even complex surfaces. Thermally stable mesoporous thin films of 8 mol-% yttria-stabilized zirconia (YSZ) with different pore sizes of 17, 24, and 40 nm were prepared through an evaporation-induced self-assembly process. The free surface of the YSZ films was uniformly coated via ALD with a ceria layer of either 3 or 7 nm thickness. Electrochemical impedance spectroscopy was utilized to probe the influence of the coating on the charge-transport properties. Interestingly, the porosity is found to have no effect at all. In contrast, the thickness of the ceria surface layer plays an important role. While the nanocomposites with a 7 nm coating only show ionic conductivity, those with a 3 nm coating exhibit mixed conductivity. The results highlight the possibility of tailoring the electrical transport properties by varying the coating thickness, thereby providing innovative design principles for the next-generation electrochemical devices.