Anchoring an Fe Dimer on Nitrogen-Doped Graphene toward Highly Efficient Electrocatalytic Ammonia Synthesis

Electrochemical reduction of N₂ to NH₃ based on sustainable energy is a green technique to produce decentralized and on-demand ammonia. In this work, taking graphene as a design platform, we explore the dual-atom catalysts (DACs) via embedding two homonuclear transition metal (TM) atoms into graphene decorated with four neighboring pyrrolic nitrogen atoms (TM₂N₄@graphene) to computationally screen the qualified nitrogen reduction reaction (NRR) catalysts. On the basis of the activity, selectivity, and stability of 15 homonuclear DACs of TM₂N₄@graphene, Fe₂N₄@graphene is identified as the most efficient NRR catalyst with a limiting potential of only -0.32 V. Electronic structure analysis demonstrates that the low oxidation state of Fe (+1) remarkably activates the molecular N₂, which contributes to its excellent NRR catalytic activity. Moreover, the kinetic studies reveal all of the NRR elementary steps exhibiting barriers smaller than that of the hydrogen evolution reaction (HER), showing that HER is effectively suppressed. In addition, we find that the integral crystal orbital Hamilton population (ICOHP) can be used as a descriptor to describe the Gibbs free energy of each step for its NRR performance. This work not only provides theoretical guidance for designing DACs for NRR but also promotes the understanding of DACs for N₂ fixation.