Collaborative Research: CAS-SC: Electrochemical Approaches to Sustainable Dinitrogen Fixation

With the support of the Chemical Catalysis program in the Division of Chemistry, Professors Alan Goldman of Rutgers University, Patrick Holland of Yale University, and Alexander Miller of the University of North Carolina at Chapel Hill are studying the principles of electrochemical conversion of atmospheric nitrogen (N2) to ammonia (NH3) using molecular catalysts. The research will establish a foundation for efforts to discover sustainable alternatives to replace current fossil fuel-based routes to ammonia. A low-temperature electrochemical N2 fixation process for NH3 production using only renewable energy could transform global agriculture by eliminating dependence on natural gas and decentralizing fertilizer production, thus substantially mitigating CO2 emissions. Beyond fertilizer, electrochemical N2 fixation could also enable carbon-free production of ammonia for the storage and transportation of renewably produced energy, for direct use as fuel for electric utilities or transportation or for conversion to hydrogen. Connecting the fundamental chemistry and catalysis research with possible future application is aided by collaboration with Professor Gal Hochman of Rutgers University, an agroeconomist and sustainability expert. The three research groups have established a collaborative environment ideal for training future leaders in science. In addition to research, the students and PIs are further developing the NitrogenFixers.org outreach program, which includes live in-person, virtual remote, and do-it-yourself experiments on electrochemistry and sustainable energy. It inspires middle and high school students by demonstrating the importance and excitement of chemical research, including the importance of N2 fixation and sustainability. In this collaborative project, the research groups of Professors Alan Goldman of Rutgers University, Patrick Holland of Yale University, and Alexander Miller of the University of North Carolina at Chapel Hill are working on a grand challenge in chemistry that relates to providing electrochemical alternatives to the Haber-Bosch procedure for conversion of atmospheric nitrogen (N2) to ammonia (NH3) using molecular catalysts. The guiding mechanistic hypothesis behind the research approach is that bimetallic splitting of dinitrogen to form metal nitride complexes can give high activity, high selectivity for NH3 (over H2), and low overpotential for electrochemical nitrogen reduction. The collaborative team seeks detailed mechanistic understanding of electrochemical N2 binding and splitting, and subsequent proton-coupled electron transfer (PCET) to nitride, which can be leveraged to discover new catalysts for ammonia synthesis. One highlight is the use of a parallel experimentation workflow for refinement of reaction conditions. Mechanistic studies will focus on the two key steps enabling catalysis (N2 cleavage and nitride complex reduction). Electrochemically induced N2 binding and the mechanism of formation of nitride complexes are being addressed using computational studies integrated with experimental electrochemical studies. The reduction of the nitrides in the following step is relevant to other mechanisms of N2 reduction as well, and therefore has broad relevance. Molecular electrocatalysis of N2 reduction remains far behind other reactions such as CO2 reduction and H2 evolution, but the combination of parallel electrolysis methodology and molecular-level mechanistic detail in this project promises to lead to effective electrocatalytic systems that are well-defined and amenable to continued development.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.