Explore the underlying mechanism of graphitic C3N5-hosted single-atom catalyst for electrocatalytic nitrogen fixation

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 N≡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 ΔG∗N2H < ΔG∗H showing that HER can be effectively suppressed on V-g-C3N5. D-band center (DF) as a function of ΔG∗N2H and ΔG∗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.