Electrochemical routes provide an attractive alternative to the Haber-Bosch process for cheaper and more efficient ammonia (NH3) synthesis from N2 while avoiding the onerous environmental impact of the Haber-Bosch process. We prototype a strategy based on a eutectic mixture of phosphate molten salt. Using quantum-mechanics (QM)-based reactive molecular dynamics, we demonstrate that lithium nitride (Li3N) produced from the reduction of nitrogen gas (N2) by a lithium electrode can react with the phosphate molten salt to form ammonia. We extract reaction kinetics of the various steps from QM to identify conditions with favorable reaction rates for N2 reduction by a porous lithium electrode to form Li3N followed by protonation from phosphate molten salt (Li2HPO4-LiH2PO4 mixture) to selectively form NH3.