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 occurring biocatalyst responsible for nitrogen conversion to ammonia under ambient conditions, is the most efficient catalyst for eNRR. The Iron-Molybdenum cofactor (FeMo-co) 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 eNRR on FeMo-co and decipher the key mechanisms at play.Most studies on FeMo-co tend to ignore the magnetic nature of transition metals (TMs) in the cofactor. Proper treatment of these TMs (Fe and Mo) is necessary to pinpoint the intermediates and potential limiting step along the eNRR pathway. We start with an iterative optimization of the Hubbard U parameter to capture the correct magnetic structure of the cofactor. We also explore the effect of local chemical environment including, H-coverage and various ligands attached to the cofactor, on its activity and selectivity. The potential limiting step is found to be sensitive to the magnetic orientation of the TMs in the cofactor and it is thus imperative to provide the U correction to capture the true bottleneck of eNRR. The cofactor also shows an affinity towards a medium H-coverage under eNRR operating conditions. These findings provide a comprehensive and elaborate view of nitrogen reduction on FeMo-co and insights from this study paves the path towards designing heterogeneous counterparts to the catalyst.Acknowledgments:This work was supported by the U.S. Department of Energy, via Grant DE-FOA-0002676 to the SUNCAT Center for Interface Science and Catalysis.