MECHANISTIC AND KINETIC EVALUATION OF COBALT HYDRIDE FORMATION FOR IMPROVED CATALYSIS

The environmental, health, and economic impacts of the increasing concentrations of atmospheric CO2 has urged society to transition to renewable energy technologies. However, many renewable resources, like solar and wind, are intermittent by nature, and we cannot power our world using these resources when the sun is not shining or when the wind is not blowing. One way to overcome this intermittency is to discover ways to store energy from renewable sources for off-peak hours. A promising approach involves converting renewable feedstocks (CO2, water) into energy-rich fuels (hydrogen, formate, carbon monoxide, methanol, ethanol, etc.), simultaneously sequestering one of our largest pollutants and recycling it into a sustainable fuel. While carbon sequestration and utilization show incredible promise, transforming CO2 into higher-value products is an uphill reaction that requires energy-intensive proton coupled electron transfer (PCET) reactions. Catalysts can lower the energetic barriers involved in these reactions, and in some cases, direct reactivity through pathways with low energy intermediates. This work aims to understand the reaction mechanisms and kinetics of elementary reaction steps common to energy-relevant catalytic cycles and to translate that information to design criteria for improved catalysts. The first chapter explores the factors that impact the proton transfer kinetics of reactions involving transition metal hydride complexes, which are key intermediates in CO2 reduction and H2 evolution. Chapter 2 highlights how acid-base functionality in the catalyst’s ligand backbone helps circumvent high energy barriers associated with metal-based proton transfer to generate metal hydride complexes, which has great implications on catalyst efficiency and selectivity. This work inspired the structure-reactivity work in Chapter 3, which correlates the changes to the acid-base functionality in the ligand scaffold to changes in metal hydride formation pathways and the associated kinetics. These understandings provide a blueprint for improved catalyst design. Finally, Chapter 4 employs a strategy to combine the benefits of homogeneous and heterogeneous catalysis through surface immobilization of a molecular catalyst onto a metallic electrode. Quantification of the rate constant for a PCET reaction involving a surface-bound species is demonstrated for the first time, which is a critical advance for realizing integrated catalyst systems.