As a route to earth-abundant electrocatalysts for CO2 reduction, we have used quantum mechanical calculations including solvation to uncover relationships between the composition of known catalysts and their attributes (i.e. rate, product selectivity, onset potential.) Among these are Milstein’s (PNP)Fe(CO)H2 and Meyer and Brookhart’s (PoCoP)Ir(MeCN)H2 (demonstrated to electrochemically reduce CO2 selectively to formate in water.) Modeling (PNP)Fe(CO)H2 (a demonstrated CO2 hydrogenation catalyst) in an prospective electrochemical cycle generating formate, we find that an impractical potential would be required for the two-electron reduction regenerating the dihydride, and that both hydrides would be prone to hydrogen evolution during such a cycle. A space of earth-abundant metal hydrides characterized by (L3)ML2H was explored for free energy surfaces supporting selective, low-overpotential CO2 reduction. Replacing the PNP ligand with a redox-active pincer ligand effectively raises the computed potential required to reduce Fe(II) by 2-electrons over a volt, into an attractive range. Replacing a hydride in the “H-Fe-H” core with a lesser sigma donor erodes the driving force for hydride transfer, but this can be restored upon substitution of a more nucleophilic metal. We will discuss the influence of compositional degrees of freedom on free energy surfaces and make comparisons to the successful template provided by the iridium catalyst.

Navigating structure-activity relationships in molecular electrocatalysts for CO2 reduction

249th National Meeting (2015)

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