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

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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 CeO 2 phase, XPS and high‐resolution fluorescence detection method to collect XANES data at Ce L3 edge confirmed the presence of only Ce 4+ and the spectral features resembled that of CeO 2 in all the as‐synthesised samples. In situ reactivity studies in the H 2 atmosphere of these samples employing XANES data, recorded during the heating and cooling cycle, revealed the extent of Ce 4+ conversion to Ce 3+ . Most importantly the stability of converted Ce 3+ appears to depend on the presence of reducible transition metal, where the presence of copper ions indeed decreased the reduction temperature of Ce 4+ and upon cooling the formed Ce 3+ appears to be stable in a reducing atmosphere. In the absence of copper, not only is the extent of reduction to Ce 3+ much less compared with the copper‐containing samples but also, the reduced Ce 3+ ions appear to reoxidise to Ce 4+ upon cooling to room temperature. These results are in line with observed results of powder CeO 2 samples typically used as catalyst supports.