CAS: Developing Homogeneous Mn Catalyst Systems for the Oxygen Reduction Reaction

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With the support of the Chemical Catalysis program in the Division of Chemistry, Dr. Charles W. Machan of the University of Virginia is studying the catalytic reduction of dioxygen by molecular manganese compounds. The reduction of dioxygen is important for producing energy from chemical bonds. Fuel cells, for example, often employ the reduction of dioxygen to water to generate clean energy. The current best catalysts for this reaction are based on platinum metal, which is rare and expensive. In the search for earth-abundant alternatives, systems containing iron and cobalt have been studied extensively, however, manganese versions of these systems are more poorly understood. Manganese generally interacts strongly with dioxygen and has the potential to rival or exceed the catalytic activity of iron or cobalt. These studies will achieve this by developing design principles for dioxygen reduction by manganese complexes, thus enabling optimized systems with improved performance. Integrated into these efforts is a research-focused educational outreach program, which will develop a scientific communication training program and a research-based lab experience. The integrated research and educational components will address fundamental challenges for the field and priorities of the current NSF Strategic Plan, with the goal of maximizing the health, environmental and economic benefits of renewable energy technologies.With the support of the Chemical Catalysis program in the Division of Chemistry, Dr. Charles W. Machan of the University of Virginia is studying the catalytic reduction of dioxygen by molecular manganese compounds. When paired with the oxidation of energy rich molecules, dioxygen reduction is a convenient way to drive oxidation reactions or to convert chemical energy to electrical energy. Manganese metal centers, while underrepresented as molecular catalyst active sites, have strong interactions with dioxygen and could demonstrate catalytic activity that rivals or exceeds the activity of more well-understood iron and cobalt species. A coordination chemistry-based approach will be used to enhance the binding and activation of dioxygen by tuning electronic properties at the Mn center, with the ultimate goal of improving catalytic performance. In initial studies, conditions for the selective generation of hydrogen peroxide or water as the reaction product have been developed: hydrogen peroxide is a valuable chemical oxidant and water is the desired half-reaction for fuel cells. Understanding how to achieve high selectivity and activity for each of these products has implications for renewable energy utilization. To address the ongoing need for fundamental understanding of the reduction of dioxygen by manganese complexes, the role of axial ligands in dioxygen binding and activation will be quantified, the catalytic response will be improved by synthetically modifying the ligand framework, and conditions for selective hydrogen peroxide and water production will be sought using redox mediators.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.