Mechanisms of Photocatalytic H₂ Evolution on Co-Catalyst Loaded Semiconductors in the UHV

Despite of intense research efforts in the last decade, photocatalytic processes for the generation of renewable fuels are still lacking the requirements for successful application on industrial scale. Research strategies have so far been focused on material screening due to the complexity of the underlying processes. However, a deep fundamental understanding will ultimately allow us to implement knowledge-based improvements towards enhanced photocatalytic efficiencies, selectivities and stabilities.
In this work, we examine the reaction mechanism of photocatalytic alcohol reforming on a model system (co-catalyst loaded rutile TiO₂(110)). By judicious choice of surface preparation and catalyst loading, we are able to fully assign all reaction sites to unravel the photochemical mechanism on an atomic scale. By changing the reaction conditions e.g. temperature, photochemical reaction steps of the isotopically labeled reactant can clearly be disentangled from chemical thermal reaction steps in the mechanisms. A detailed kinetic analysis reveals, that the photocatalytic reaction rate depends linearly on the photon flux, indicating that only one charge transfer of this two-step process is facilitated photochemically.