Evolution of CeO2 and Ce2O3 Phases in CexOy High Surface Spherical Clusters Decorated with gold catalysts During the Ethanol Oxidation Reaction - research data

Au-Ce<sub>x</sub>O<sub>y</sub> high-surface spherical clusters (SCs) catalysts were synthesized by wet chemistry methods. Transmission Electron Microscopy (TEM) observations revealed, that 2 nm small, crystalline ceria nanospheres (NSs) self-assembled into high-surface spherical clusters. After decoration with Au nanoparticles (NPs), their catalytic activity towards ethanol oxidation reaction (EOR) was evaluated using cyclic voltammetry, while the short-term durability by <i>operando</i> IRRAS. <i>Operando</i> Raman and synchrotron measurement techniques, such as XANES and STXM, were used to assess the oxidation state of cerium supports. XANES spectra showed that the as synthesized Ce<sub>x</sub>O<sub>y</sub> SCs consist of mixed phases system comprising CeO<sub>2</sub> and Ce<sub>2</sub>O<sub>3</sub>. After decoration with Au NPs, the CeO<sub>2</sub> phase volume fraction increased and steadily continued to grow after EOR cycling. STXM mapping of individual ceria SCs, showed, that the Ce<sup>3+</sup> state is prevailing over Ce<sup>4+</sup> state on the surface. <i>Operando</i> Raman demonstrated that oxygen vacancies form dynamically within seconds of initiating the electrochemical reaction and that these vacancies persist throughout the reaction, stabilizing under operational conditions. This imbalance is driven by ceria, which is more reduced after reactions, because Au atoms induce oxygen release.