(697e) First-Principles Design of Nitrogen Reduction Catalysts: Taking Inspiration from Nature

Electrochemical nitrogen reduction reaction (eNRR), one of the most studied problems in catalysis, has the potential to replace the century-old Haber-Bosch process for ammonia synthesis. However, a low-cost, highly selective and efficient catalyst for eNRR is yet to be discovered. Nitrogenase, a naturally occuring biocatalyst responsible for nitrogen conversion to ammonia, is the most efficient at eNRR. The Iron-Molybdenum cofactor (FeMo-cofactor) in the enzyme is identified as the catalytic part with bridging irons being active sites. Despite decades of work the exact mechanism of its operation and various intermediates along the pathway are still debated. We revisit the nitrogenase FeMo-cofactor and decipher the key mechanism at play. Proper treatment of the transition metals in the cofactor is necessary to identify the intermediates along various steps of eNRR. We explore the role of various ligands attached to the cofactor and the effect of the local chemical environment on its activity. We also study the role of H-coverage on the activity and selectivity of the catalyst.

2D boron-based electrocatalysts for nitrogen reduction are also explored the effect of carbon substitution on their activity. We demonstrate that pristine and carbon (C) substituted 𝛼 borophene catalyze eNRR at exceptionally low limiting potentials of -0.33 V and -0.25 V, respectively. These 𝛼 borophene based catalysts also show high selectivity towards eNRR over the competing hydrogen evolution reaction (HER). Our results show that C-substituted 𝛼 borophene exhibits outstanding catalytic activity towards eNRR via the distal pathway with a small activation barrier of 0.56 eV, almost half the value reported for Ru (0001). Finally, we identify two novel descriptors, adsorption energy of *NNH and charge transfer to *N₂, which can be used in high-throughput screening of catalysts for eNRR. These findings provide a more comprehensive and elaborate view of ammonia synthesis for N₂ reduction reaction space.