Kinetic and mechanistic studies on model systems have bridged the materials gap between surface science and heterogeneous catalysis, thus contributing to our fundamental understanding of catalytic processes. Such model catalysts, made by surface science methods, allow for simulating the complexity of real catalysts step-by-step, keeping atomic level control at any stage. In this contribution, we show that a similar model approach can be applied to study reactions at electrified interfaces. We prepare atomically-defined model interfaces by surface science methods in ultrahigh vacuum (UHV) and show that such systems can be brought into the electrochemical environment while maintaining their atomic surface structure. This allows us to study catalytic reactions on identical model interfaces both in ultrahigh vacuum and under electrochemical conditions. Specifically, we investigated model catalysts consisting of Pt nanoparticles grown on well-ordered Co3O4(111) films on Ir(100). In a first step, these model systems are characterized using a broad range of surface science methods under UHV conditions. We explore the interaction with water and CO and demonstrate that electronic metal support interactions lead to size-dependent partial oxidation of the Pt nanoparticles. This process facilitates the reverse spillover of lattice oxygen during CO oxidation and leads to reduction of the Co3O4(111) film. In a second step, the same model catalysts are studied under electrochemical conditions. To this end, the samples are transferred from UHV into the electrochemical environment without exposure to ambient conditions. We show that the atomic surface structure of the model systems is preserved upon transfer in a well-defined pH and potential window (phosphate buffer). Noteworthy, very similar surface processes can be observed in UHV and in the electrolyte. We follow the potential-dependent hydroxylation of the Co3O4(111) surface and observe pronounced size-dependent changes in the site-occupation of CO adsorbed on the supported Pt nanoparticles. The same metal-support interactions that were identified in the UHV experiments also lead to modification of the CO adsorption and reaction behavior at the electrified interface.

Electrifying model catalysis: Complex model catalysts studied in ultrahigh vacuum and under electrochemical conditions

255th National Meeting (2018)

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