Water splitting catalysts for artificial photosynthesis

Abstract

Artificial photosynthesis is one of the most promising methods for the direct conversion of solar energy into renewable chemical fuels. The process involves splitting water by first creating spatially separated electron-hole pairs, which then drive the redox semi-reactions leading to the evolution of molecular hydrogen and oxygen. This project aims at providing an atomistic understanding of the mechanism of water oxidation, the bottleneck of the overall process. To this end, we will use state-of-the-art first-principles numerical modeling based on density functional theory. In particular, we will focus on inorganic ruthenium-containing polyoxometalate homogeneous catalysts that have been recently synthesized and that display unprecedented reactivity and stability in solution. Given the complexity of this four-electron process, to date it has not been possible to determine experimentally a reliable mechanistic model for this reaction. Here we will employ large scale metadynamics simulations to explore the free energy surface as a function of a few key collective variables, to determine the most likely reaction path, the associated activation energies and the key properties of the catalyst affecting its performance. The necessity to employ hybrid functionals to describe the oxidation and reduction of the metal centers makes the project extremely demanding from a computational point of view, requiring the exceptional DEISA infrastructure to be carried out. The activity will be linked to the EU FP7-PEOPLE-IRG-2008 grant awarded on the same topic.