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.