Regulating spin states of single transition metal atoms on N-doped graphene for efficient ammonia synthesis

Abstract

Ammonia, as one of the most important chemicals in the world, is mainly synthesized through the energy-intensive Haber–Bosch process. In recent years, researchers have been committed to exploring efficient catalysts for synthesizing ammonia under mild conditions, and a deeper understanding of the reaction mechanism is conducive to achieving this goal. Herein, we propose a strategy to regulate the spin states of single Mo atoms anchored on N-doped graphene (Mo–N/G) by applying strain, and use it to study the spin effect and improve the activity of the nitrogen reduction reaction (NRR). Through first-principles calculations, we found that applying strain can have a continuous effect on the magnetic moment of Mo without changing its charge distribution, which provides an ideal model for studying spin regulation. Further analysis of the interaction between Mo-4d and N-2p orbitals reveals that the spin splitting of the Mo-4d orbital has different effects on the two key intermediates (*N₂ and *NH₂) during the NRR, weakening the scaling relationship and greatly improving the performance to an ultra-low limiting potential of −0.19 V. More importantly, this strain-induced spin regulation can be extended to more catalysts to achieve a general improvement in NRR performance. Our work provides a new insight into the spin regulation and is of significance for the rational design of efficient catalysts.