Elucidating reaction mechanisms in water oxidation catalysis by molecular simulation

With the anticipated growth in global energy consumption, there is an urgent need to develop sustainable energy sources. Among these, hydrogen production via sunlight-driven water splitting is a promising route, in which water oxidation catalysts play a critical role.
This thesis presents a computational investigation of water oxidation catalysis using first-principles molecular dynamics simulations based on density functional theory. Focusing on transition metal-based molecular catalysts, including ruthenium, copper, and iron systems, key mechanistic pathways for O–O bond formation in aqueous environments are elucidated.
For ruthenium complexes, simulations show that carboxylic acid ligands act as proton acceptors in the water nucleophilic attack (WNA) mechanism, while explicit solvent molecules facilitate proton transfer via hydrogen-bonded networks. pKa calculations explain the preference for ligand-based proton transfer.
In copper-based systems, catalysis is initiated by ligand oxidation, followed by water coordination and a proton-coupled electron transfer step, forming a Cu–OH intermediate. The mechanism exhibits strong pH dependence, governing selectivity between H₂O₂ and O₂.
Comparative analysis of WNA and interaction of two metal–oxo units (I2M) mechanisms highlights the role of solvent dynamics in stabilizing intermediates and lowering reaction barriers.
For an iron-based catalyst, conformational flexibility enables dynamic switching between active states, promoting both O–O bond formation and O₂ release.
Overall, this work emphasizes the importance of solvation, ligand properties, and structural flexibility in catalyst design.