Electrochemical mechanisms of the reduction of N2 to NH3 catalyzed by TM anchored on Nvs-g-C3N4/graphene van der Waals heterostructure: Insights from a first-principles study

Nitrogen fixation is one of the most critical issues in chemical science and technology. However, developing efficient and stable electro(photo)catalysts remains a comprehensive challenge. Here, we constructed 21 single-atom heterostructures consisting of g-C3N4 with nitrogen vacancies and graphene (TM@Nvs-g-C3N4/graphene, TM=Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Ag, Pd, Cd and Pt) and systematically investigated their stabilities and catalytic activities for the conversion from N2 to NH3. The calculations indicate that all heterostructures are thermodynamically stable. Among of them, 15 TM@Nvs-g-C3N4/graphene heterojunctions can activate N2, and effectively reduce N2 into NH3 by a distal or alternating mechanism. The Cr, Mo and Nb atoms anchored in Nvs-g-C3N4/graphene heterojunctions have higher activities and selectivities for nitrogen reduction reaction (NRR). In particular, Mo@Nvs-g-C3N4/graphene has the highest NRR performance. The Bader charge and PDOS analysis elucidate that the d-π* feedback bonds formed by 4d orbitals of Mo atom and π* orbitals of N2 plays a dominant role in the activation of N2. Altogether, the results obtained in this study could provide new avenues for the development of electrochemical catalyst for the reduction of N2 to NH3.