Computational Investigation of the Rate Determining Step in a Water Oxidation Process involving Mononuclear Ruthenium
Authors:
Kevin Joerger, Juan MelendezMentor:
Emily Jarvis, Assistant Professor of Chemistry, Loyola Marymount UniversityMononuclear ruthenium catalysts are currently a focus in studies investigating catalysts employed for water oxidation – splitting H2O into H2 and O2. The oxidation mimics the photosynthetic process of photosystem II with the goal of serving as a solar fuel source. Although significant progess has been made experimentally mapping the water oxidation mechanism for these catalysts, some detailed features remain incompletely understood. This study focuses on characterizing the ruthenium bond with molecular oxygen and the mechanistic step involving the replacement of this bound oxygen with water, which has been implicated as the rate determining step in the water oxidation cycle. The potential energies throughout this exchange were calculated using first principles density functional theory (DFT). The reaction barrier was calculated for several distinct mononuclear Ru catalysts in gas and aqueous phase. It was determined that the process can be described as a one-step or two-step process; the identity of the ligands attached to the Ru center alters the characterization of the bond-breaking/bond-forming step and the energetics of these depend on the detailed nature of that step.