Single-atom catalysts (SACs) have been proved to be effective catalysts for electrochemical nitrogen fixation. However, most SACs face poor activity and low selectivity due to the inert $\text{N}\equiv \text{N}$ and the competing hydrogen evolution reaction (HER). Graphitic C₃N₅, a recently reported carbon nitride, is a promising substrate for SACs. In this work, a series of transition metal SACs based on g-C₃N₅ nanosheets are constructed (TM-g-C₃N₅), and V-g-C₃N₅ with high activity and selectivity is screened out. The onset potential for nitrogen reduction reaction (NRR) on V-g-C₃N₅ is −0.30 V, which is lower than most reported catalysts. An in-depth mechanism study reveals that the V atom as active site can tune the electron transfers between TM and nitrogen. The coupling between V and N₂ is not too strong or weak, which is beneficial for nitrogen adsorption and ammonia desorption. Furthermore, the $\Delta {\text{G}}_{\text{∗N}2\text{H}}$ < $\Delta {\text{G}}_{\text{∗H}}$ showing that HER can be effectively suppressed on V-g-C₃N₅. D-band center (D_F) as a function of $\Delta {\text{G}}_{\text{∗N}2\text{H}}$ and $\Delta {\text{G}}_{\text{∗H}}$ suggests that the 3d orbit of V play an important role in interacting with N₂ and minor role with H. This work finds a possible catalyst for NRR and improves the understanding of activity and selectivity of transition metal single-atom catalysis.

单原子催化剂（SACs）已被证明是电化学固氮的有效催化剂。然而，由于惰性，大多数 SACs 面临活性差和选择性低的问题。$\text{ñ}\equiv \text{ñ}$和竞争性析氢反应（HER）。最近报道的一种氮化碳石墨C ₃ N ₅是一种很有前途的SAC基材。本工作构建了一系列基于gC ₃ N ₅纳米片的过渡金属SACs（TM-gC ₃ N ₅），并筛选出具有高活性和选择性的VgC ₃ N _{5 。}VgC ₃ N _{5上氮还原反应 (NRR) 的起始电位}为-0.30 V，低于大多数报道的催化剂。深入的机理研究表明，V 原子作为活性位点可以调节 TM 和氮之间的电子转移。V与N ₂的耦合不太强也不太弱，有利于氮的吸附和氨的解吸。此外，该$\Delta {\text{G}}_{\text{*N}2\text{H}}$<$\Delta {\text{G}}_{\text{*H}}$表明HER可以在VgC ₃ N ₅上得到有效抑制。D波段中心（_DF）作为函数$\Delta {\text{G}}_{\text{*N}2\text{H}}$和$\Delta {\text{G}}_{\text{*H}}$表明 V 的 3d 轨道在与 N ₂相互作用中起重要作用，而与 H 相互作用中起次要作用。这项工作为 NRR 找到了可能的催化剂，并提高了对过渡金属单原子催化的活性和选择性的理解。