Computational Scaling Relationships Predict Experimental Activity and Rate Limiting Behavior in Homogenous Water Oxidation

While computational screening with first-principles density functional theory (DFT) is essential for evaluating mechanisms of candidate catalysts, limitations in accuracy typically prevent prediction of experimentally relevant activities. Exemplary of these challenges are homogeneous water oxidation catalysts (WOCs) where differences in experimental conditions along with small changes in ligand structure can alter rate constants by over an order of magnitude. To leverage computational screening for homogeneous WOC design, a distinct approach is needed. Here, we compute mechanistically-relevant electronic and energetic properties for 19 mononuclear Ru transition metal complexes (TMCs) from three experimental water oxidation catalysis studies. We discover that 15 of these TMCs have experimental activities that can be correlated to a single property, the ionization potential of the Ru(II)-O2 catalytic intermediate. This scaling parameter is well correlated with experimentally-reported rate constants, allowing quantitative understanding activity trends and insight into rate-limiting behavior. We use this approach to rationalize differences in activity with differing experimental conditions, and we qualitatively analyze the source of distinct behavior for differing electronic states in the other four catalysts. Comparison to closely related single-atom catalysts and modified WOCs enables rationalization of the source of rate enhancement in these experimental WOC catalysts.