Electrodeposition of nanometer-thick ceria films by oxidation of cerium(III)–acetate

Thin films of ceria were electrodeposited onto Hastelloy substrates by the electrochemical oxidation of Ce(III) acetate complexes. The mode of deposition was dependent on the applied potential. At a potential of + 0.5 V vs. Ag/AgCl, the deposition proceeded by a direct oxidation of Ce(III) to ceria. Films deposited at this potential were smooth and crack-free as observed by SEM. Film thicknesses were determined by X-ray reflectivity and ellipsometry. For a deposition time of 1000 s, the ceria deposited to a thickness of approximately 40 nm and a density of 65%. The deposition exhibited self-limiting growth, with growth rates rapidly decreasing with deposition time. At a higher potential of + 1.1 V vs. Ag/AgCl, the films appear to grow by an indirect mechanism, in which the electrochemical oxidation of water forms O2 which then reacts with Ce(III) to form ceria nanoparticles in the growth solution. It was also shown that nanometer-scale ceria powder could be produced by bubbling the solution with molecular oxygen.