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SSCI-VIDE+CARE+PVE:ACV; International audience; Ethylene oxide (EO) is nowadays a chemical intermediate of paramount importance. As one of the highest volume petrochemicals, it serves as a precursor for the further production of added value molecules, including plastics, polyester and ethylene glycol. EO is industrially produced by the partial oxidation (epoxidation) of ethylene with air (or oxygen) on Ag/α-Al2O3 catalysts at low reaction temperatures (around 220 oC) and high pressures (10-30 bar). Silver is the only one known active heterogeneous catalyst for the epoxidation of ethylene. The epoxidation is in competition with the combustion side reactions of both ethylene and EO, leading to the production of CO2 and H2O. The mechanism of the epoxidation and, in particular the nature of the involved oxygen species are under debate. We have designed by reactive magnetron sputtering a solid oxide electrochemical cell based on nanostructured Ag/Gadolinia-Doped Ceria (a well-known O2- conductor) catalyst. We found an unprecedent linear increase of the selectivity towards EO (Fig. 1) and of the ethylene conversion. These results demonstrate that EO can be electrocatalytically produced in a solid oxide electrochemical cell between 220 °C and 300 °C on a nanostructured Ag/GDC electrocatalyst prepared by reactive magnetron sputtering. Despite low values of Faradaic efficiencies, the EO selectivity and the ethylene conversion can be increased at 220 °C with the application of small positive currents (< 1 mA) that correspond to an energy consumption of around ~ 1 mW/cm². This proof-of-concept opens the way for a new environmentally-friendly route (without utilization of chlorinated hydrocarbons) for the epoxidation of ethylene in a solid oxide cell via direct electrooxidation of ethylene. These results also underline the key role of O2- species in the mechanism of ethylene epoxidation on Ag.

In this work, we report the self-assembled growth of vertically aligned columnar Cu2O + Cu4O3 nanocomposite thin films on glass and silicon substrates by reactive sputtering at room temperature. Microstructure analyses show that each phase in nanocomposite films has the columnar growth along the whole thickness, while each column exhibits the single phase characteristics. The local epitaxial growth behavior of Cu2O is thought to be responsible for such an unusual microstructure. The intermediate oxygen flow rate between those required to synthesize single phase Cu2O and Cu4O3 films produces some Cu2O nuclei, and then the local epitaxial growth provides a strong driving force to promote Cu2O nuclei to grow sequentially, giving rise to Cu2O columns along the whole thickness. Lower resistivity has been observed in such kind of nanocomposite thin films than that in single phase thin films, which may be due to the interface coupling between Cu2O and Cu4O3 columns.

International audience; Transparent nanoscale-film heterojunctions based on Cu2O and ZnO were fabricated by atomic layer deposition and reactive magnetron sputtering. The constitutive layers exhibit high crystalline quality and a local epitaxial relation between Cu2O and ZnO was achieved with [110] Cu2O || [001] ZnO and [001] Cu2O || [010] ZnO as evidenced by high resolution transmission electron microscopy and. Cu2O films show very low resistivity and high mobility values of 9–150 Ω cm and 19 cm2/V s, respectively. The Cu2O/ZnO heterojunctions exhibit a nonlinear rectifying behavior characteristic of a p–n junction, self-powered photoresponse under 1 Sun illumination and an average transmittance of 73% in the visible region of the electromagnetic spectrum. These results are promising for all-oxide transparent electronics, photodetection and photovoltaic applications.

MICROSCOPIE+CARE+TCV:IKL:ABO:LBU:FGA:LRE:ACV:PVE; National audience; Des tests catalytiques et electrocatalytiques ont été menés sur des membranes denses conductrices ionique pour la combustion du propène en utilisant une couche catalytique d'argent synthétysée via PVD ou sérigraphie déposée sur une membrane dense de Zircone stabilisée avec 8% d'yttrium (YSZ), un conducteur ionique de O2-. Une adsorption compétitive entre le propène et l'oxygène a été observée à 300°C. Les performances catalyques des films d'argents ont pu être modifiées via une polarisation et ce, de manière non-faradique (effet EPOC) à 300°C. L'impact de la polarisation depend principalement du taux de recouvrement du propène sur l'argent : pour des taux de recouvrement faible comme dans des conditions d'oxydation, des effets de promotions ont été observés lors de polarisation positive alors que pour un fort taux de recouvrement, obtenu dans des conditions stoechiomètrique, seulement des effets d'inhibition ont pu être observé lors de polarisations négatives.