Effect of Copper Dopant Ions on the Redox Properties of Electrochemically Prepared Cerium Dioxide Thin Films

We successfully synthesised ceria and Cu-doped ceria thin films on fluorine-doped tin oxide (FTO) glass using electrochemical deposition methods. Although X-ray diffraction characterisation did not confirm the presence of pure CeO₂ phase, XPS and high-resolution fluorescence detection method to collect XANES data at Ce L3 edge confirmed the presence of only Ce⁴⁺ and the spectral features resembled that of CeO₂ in all the as-synthesised samples. In situ reactivity studies in the H₂ atmosphere of these samples employing XANES data, recorded during the heating and cooling cycle, revealed the extent of Ce⁴⁺ conversion to Ce³⁺. Most importantly the stability of converted Ce³⁺ appears to depend on the presence of reducible transition metal, where the presence of copper ions indeed decreased the reduction temperature of Ce⁴⁺ and upon cooling the formed Ce³⁺ appears to be stable in a reducing atmosphere. In the absence of copper, not only is the extent of reduction to Ce³⁺ much less compared with the copper-containing samples but also, the reduced Ce³⁺ ions appear to reoxidise to Ce⁴⁺ upon cooling to room temperature. These results are in line with observed results of powder CeO₂ samples typically used as catalyst supports.