Atomic layer deposition of epitaxial CeO2 thin layers for faster surface hydrogen oxidation and faster bulk ceria reduction/reoxidation

Abstract

Thin ceria layers of 120 nm were processed by atomic layer deposition on both YSZ(100) single crystal substrates and polycrystalline YSZ ones. The CeO₂ layer deposited on the oriented substrate proved to be epitaxial after low temperature annealing used to remove some crystallisation defects. The quality of the film was characterized by scanning electron microscopy and High Resolution X-ray diffraction. An electrochemical characterization under nitrogen and hydrogen atmospheres was carried out by electrochemical impedance spectroscopy (EIS). EIS measurements clearly show enhanced ceria reduction when the layer was epitaxial compared with the non-oriented CeO₂ layer. Moreover, the reoxidation process of the CeO₂ layer appears to be faster for the fully oriented sample. All those results are very promising to process orientation-controlled ceria surfaces for the catalysis of hydrogen oxidation inside SOFC devices but also for specific applications which need a high rate of ceria reduction/reoxidation over several cycles.