Efficient photocatalytic nitrogen reduction by MoS2 doped with transition metal and containing sulfur vacancies: enhanced nitrogen activation and inhibition of water decomposition

Abstract

Effectively enhancing nitrogen activation and inhibiting water splitting reactions are key factors in photocatalytic nitrogen reduction. This work integrated defect engineering and metal doping, doping transition metals Sc, Cu, and V into molybdenum sulfide (MoS₂) containing sulfur vacancies (V_S), to prepare TM@V_S-MoS₂ (TM = Sc, Cu, V) and applied it for the photocatalytic nitrogen reduction (pNRR). High angle annular dark field scanning transmission electron microscopy (HAADF-STEM) confirms the existence of S vacancies. The pNRR activity values of Sc@V_S-MoS₂, Cu@V_S-MoS₂ and V@V_S-MoS₂ are 124.26 μmol g⁻¹ h⁻¹, 101.32 μmol g⁻¹ h⁻¹, and 88.64 μmol g⁻¹ h⁻¹, respectively, which are much higher than those of MoS₂, V_S-MoS₂, and TM@MoS₂. This fully demonstrates that the comprehensive use of S vacancies and metal doping can significantly enhance the photocatalytic performance of MoS₂ (with a maximum activity improvement of nearly 5 times). DFT calculations show that transition metal doping of MoS₂ with sulfur vacancies can further promote the activation of N₂ and inhibit the production of H₂ from water decomposition. The above promotion and inhibition effects are consistent with the following order of activity and photoelectronic properties: Sc@V_S-MoS₂ > Cu@V_S-MoS₂ > V@V_S-MoS₂. In situ infrared spectroscopy revealed the generation of –N₂H_y (1 ≤ y ≤ 4) active species during the pNRR process, which is consistent with the most potential pathway (enzymatic mechanism) calculated by DFT.