Ab-initio modeling of cobalt based water reduction catalysts in aqueous solution and on surface

The common use of hydrogen as a renewable energy source has been one of today's challenges that, if resolved, could replace dependence on fossil fuels. One of the sustainable ways of H2 production is the photocatalytic water reduction reaction catalyzed by molecules with transition metals as reaction centers. Studies have shown that cobalt-based catalysts have an active and efficient effect in photocatalytic water reduction reactions and can be used instead of expensive transition metals such as ruthenium and platinum. In this study, we investigate Co-based water reduction catalysts in aqueous solution as well as on the TiO2 surface by means of Ab-initio Molecular Dynamics (AIMD), Metadynamics (MTD), Density Functional Theory (DFT) as well as Free Energy Perturbation Theory. Regarding homogeneous catalysis, we model the first and second electron injection intermediate steps of the EECC water reduction reaction mechanism. We analyze the solvent response following the electron injections as well as the behavior of the planar structure of the catalyst in the water solvent. The first and the second reduction free energies are calculated, AIMD trajectories are analyzed, and electronic structures of the selected snapshots are further evaluated using more sophisticated methods. For the heterogeneous catalysis, we compare the optimized geometries as well as adsorption energies of several cobalt-based catalysts on the rutile(110) surface. Electronic structures of the selected catalysts/TiO2 systems are further investigated by calculating electron density difference maps.