Abstract:

Electrocatalytic carbon dioxide reduction to fuels remains an important area of study relevant to climate change mitigation. Transition metal hydrides are key intermediates in electrocatalytic CO2 reduction, prompting study of metal hydrides in a variety of reaction conditions. This dissertation describes thermochemical measurements of novel metal hydrides, development of electrocatalytic conditions that promote selective CO2 reduction, and ligand design strategies to make water-soluble transition metal complexes. Chapter 2 describes the measurement of a transition metal hydride bond dissociation free energy (BDFE) in water. This quantitation was achieved by synthesizing a highly cationic nickel hydride complex that is remarkably stable in water. Knowledge gained in this study can contribute to further design of water-soluble molecular catalysts. Chapter 3 reveals a strategy to promote selective CO2 reduction to formate using platinum catalysts in an organic solvent. Selectivity was achieved by employing a sterically bulky proton source, which kinetically slows the competing HER reaction, favoring the CO2 reduction reaction. This concept was probed by comparing reaction rate data with a series of proton sources with different steric profiles. In Chapter 4, the synthesis of novel water-soluble bidentate phosphine ligands and rhodium complexes are disclosed. These ligands fill a unique niche of bidentate phosphines because they are air stable, display pH dependent aqueous solubility, and do not contain sulfonate groups. Rhodium complexes are readily formed with these ligands and the electrochemical properties were studied. The electrocatalytic CO2 reduction activity of the rhodium complexes in aqueous conditions were investigated in Appendix 1. No CO2 reduction products were present in electrolysis experiments; further work could be performed to obtain in-depth conclusions on the origin of inactivity.