Samarium as a Catalytic Electron-Transfer Mediator in Electrocatalytic Nitrogen Reduction to Ammonia

Abstract

Samarium diiodide (SmI₂) exhibits high selectivity for N₂R catalyzed by molybdenum complexes; however, it has so far been employed only as a stoichiometric reagent (0.3 equiv of NH₃ per Sm) combined with coordinating proton sources (e.g., H₂O, ROH). The latter inhibit catalytic turnover of Sm^III owing to buildup of stable hydroxide/alkoxide sinks. Here, we report a tandem Sm/Mo-catalyzed eN₂R system that achieves the lowest overpotential and highest Faradaic efficiency (82%) reported to date for nonaqueous eN₂R at ambient pressure. Up to 8.4 equiv of NH₃ is produced per Sm, representing a 25-fold increase over N₂R with stoichiometric SmI₂. A noncoordinating proton source enables electrochemical SmI₃/SmI₂ cycling at the applied potential of −1.45 V vs Fc^+/0.