C3: Watching a Catalyst Function

This project is part of the CATALIGHT consortium, devoted to utilize solar energy to obtain oxygen and hydrogen from water. Water splitting is a fundamental challenge for sustainable energy technologies. Inspired by natural photosynthesis, a wide range of molecular chromophore-catalyst systems have been developed. However, progress in molecular catalyst design has so far not been translated into technological solar energy conversion systems, due to unsolved fundamental issues such as long-term stability, suitable material integration routes, or selective repair mechanisms. CATALIGHT proposes the integration of light-driven catalysts into functional soft matter matrices, as a new concept for energy conversion technologies. The specific goal of this project (C3) is the theoretical simulation of the photoinduced water oxidation process including the design of catalyst-photosensitizer assemblies embedded in functionalized polymer matrices. Molecular catalysts will be based on manganese-vanadium oxide (Mn-V) clusters, which have shown promising water oxidation activity by our experimental partners. Different organic and inorganic photosensitizers are planned to be studied, as well as different soft polymer matrixes. The optimization of the water oxidation process requires mechanistic knowledge of all steps involved. This will be gained by means of stationary and dynamical computational methods, partially performed on highly efficient graphics-processor-units (GPUs). The simulation of the electronic ground- and excited-state events on different time scales will be performed by combining electrostatic quantum mechanics/molecular mechanics (QM/MM) calculations, non-adiabatic surface-hopping QM/MM molecular dynamics (MD), wavefunction analysis, Born-Oppenheimer classical MD, enhanced-sampling classical MD, and automated pathways search.

This project employed computational methods to investigate the function of several photocatalysts and associated photosensitizers able to promote efficient photoinduced water oxidation. In particular, we comprehensively studied the Mn-V cluster [Mn4V4O17(OAc)3]n ---a catalyst that had experimentally shown promising water-oxidation activity. We obtained mechanistic knowledge of all steps involved in the water oxidation, which is the most challenging step in the process of water splitting. We characterized the catalyst in its pristine form, determined its entire catalytic cycle consisting of activation, water oxidation, and regeneration, and explored degradation pathways. All these studies were performed in implicit solution, in a mixture of water and acetonitrile, where the catalysis was shown to perform best in the laboratory. We also parametrized oxidation state-specific force fields to enable classical molecular dynamic simulations of this catalyst embedded in a functionalized polymer matrix. Additionally, we studied the photophysical properties of several Ru-based photocatalysts and photosensitizers, as well as the catalytic cycle of one of them. Most of these studies were performed in close cooperation with the experimental partners. These findings are essential to improve the design of better photocatalysts for water splitting and thus advance renewable energy technologies, reducing environmental impact.