Electrochemical Behavior of Cerium at an Indium Tin-Doped Oxide Electrode in Acidic Media

The redox behavior and speciation of cerium at mesoporous thin films composed of nanoparticles of indium tin-doped oxide (nITO) electrodes were characterized in pH 4.8, 0.1 M acetate buffer and both 0.1 and 1 M HNO3 using electrochemical techniques and X-ray photoelectron spectroscopy. Anodic deposition of ceria species from Ce(III) to the nITO electrode was achieved under all solvent conditions via spontaneous condensation of electrochemically generated ceric hydroxide species. In 1 M nitric acid, the rate of CeO2 dissolution is on the same order as CeO2 deposition, resulting in negligible amounts of CeO2 electrodeposited at the nITO surface. The cathodic stripping of CeO2 from the nITO substrate deposited in 0.1 M nitric acid or pH 4.8 acetate buffer follows a 2-step process where Ce(IV)-oxide is initially reduced to an unstable Ce(III)-oxide species that rapidly undergoes acid catalyzed dissolution to yield soluble Ce(III)(aq). These findings provide a foundation for the pH and anodic potential controlled deposition of CeO2 thin films to ITO substrates, which can aid in the development of materials composed of ceria. They can also be used to infer likely analogous actinide redox behavior and speciation at these electrodes.