P-052

Olena Siamuk

o.siamuk2@uw.edu.pl

Anna Chmielnicka, Beata Rytelewska, Claudia Janiszewska, Jingxia Yang, Günther Rupprechter, Iwona A. Rutkowska, Pawel J. Kulesza

Faculty of Chemistry, University of Warsaw, Poland

Application of Co3O4-CeO2 nanocomposites as catalysts and cocatalysts in oxygen electrochemistry

Catalytic systems based on nanostructures of carbon-supported platinum, Pt/C (catalytic centers), and metal oxides, namely nanocomposites of cobalt(III,II)-oxide and cerium(IV,III)-oxide (cocatalytic sites), admixed in different proportions have been investigated under electrochemical conditions toward both the reduction of oxygen as well as the oxidation of water (water splitting to oxygen). Evidence has been provided that specific interactions between the oxide and noble metal (Pt) nanoparticles should improve the stability and activity of the metal catalytic sites due to modification of the Pt electronic structure and diminishing adsorption of oxo (OH) species on Pt surface, thus promoting centers for the adsorptive activation of oxygen and the cleavage of O=O bonds. There is a need of better utilization of catalytic sites and significant lowering of the noble metal loadings, particularly when it comes potential applications in low-temperature fuel cells. The activating interactions mentioned above would also facilitate dispersion of Pt catalytic centers, inhibit their detachment and further aggregation, and, consequently, prevent or decrease their degradation during the practical operation. In the present study, we have demonstrate that Co3O4-modified CeO2 additive (to Pt/C) synthesized in a form of intermixed oxides with homogenously dispersed cobalt ionic sites enhance activity of Pt centers during oxygen reduction in acid medium. Conventional cyclic voltammetry and rotating ring-disk electrode voltammetry were considered as diagnostic techniques permitting to comment on the dynamic of oxygen reduction and formation of the undesirable hydrogen peroxide intermediate. Finally, the Co3O4-CeO2 nanocomposites have occurred to exhibit high stability and promising activity under anodic conditions, namely during electrooxidation of water (water splitting) in acid medium. Among important issues is the stabilization effect of the ceria component on the cobalt oxide catalytic sites. In addition to promising results in 0.5 mol dm-3 H2SO4, the relatively highest activities toward water oxidation have been observed in strongly acidic polytungstate solutions, presumably due to the formation of the highly active electrocatalytic interface formed by the oxidized CoOx/CeOy catalytic nanocomposites activated and stabilized by tungsten-oxo-species. The CoOx/CeOy additives can also act as potent cocatalysts together with Pt during water oxidation.