The depletion of current petrochemical reserves and the geographic and strategic importance of securing adequate energy production prioritize the development of alternative fuel sources. A favorable approach involves utilizing carbon dioxide (CO2) as a carbon feedstock for fuels and fuel precursors in the hopes of developing a carbon neutral energy cycle. This process can be driven electrochemically to produce the more synthetically useful products of carbon monoxide and formic acid. However, the thermodynamic stability of the C=O double bonds of CO2, presents a continuing challenge to the field for developing molecular electrocatalysts capable of reducing this small molecule with high selectivity and efficiency. Our initial approach involved the use of polydentate ligands with platforms that can successfully accommodate redox-induced structural changes. The polypyridyl ligand framework - N, N, N’ ,N’’ -tetrakis(2-pyridylmethyl) ethylenediamine (TPEN) was employed in developing a Ni-based molecular complex capable of mediating the two-electron reduction of CO2 to CO and H2O with phenol as an added proton donor. However, results found it prone to rapid degradation as Ni(CO)4. Attempts to mitigate this deleterious pathway by the inclusion of a CO scavenger, required stoichiometric amounts for each catalyst turn over. Building on this knowledge and the previous success observed with N4 macrocyclic complexes such as porphyrins and cyclam derivatives, our goal is to modify macrocyclic ligand frameworks to incorporate both steric bulk and a pendent proton source for CO2 reduction with first row transition metals. The incorporation of a pendent proton will allow for secondary sphere interactions that can drive the C–O bond cleavage forward with concerted electron transfer from the metal center, which is commonly the rate determining step in this class of catalytic process. Furthermore, the addition of Brønsted acids will be examined to enhance the relay effect of the pendent proton sources.

Development of molecular electrocatalyst for CO2 reduction based on polypyridyl and nitrogen-based macrocyclic ligands

2019 Fall National Meeting

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.