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

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 (VS) to prepare TM@VS−MoS2(TM=Sc, Cu, V), applied for photocatalytic nitrogen reduction (pNRR). High angle annular dark field scanning transmission electron microscopy (HAADF-STEM) confirms the existence of S vacancies. The pNRR activity of Sc@VS−MoS2, Cu@VS−MoS2 and V@VS−MoS2 is 124.26 μmol g−1 h−1, 101.32 μmol g−1 h−1, 88.64 μmol g−1 h−1, respectively, which is much higher than that of MoS2, VS−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 can further promote the activation of N2 and inhibit the production of H2 from water decomposition for vacancy MoS2. The effect of the above promotion and inhibition is consistent with the order of activity and photoelectronic properties: Sc@VS−MoS2>Cu@VS−MoS2>V@VS−MoS2. In situ infrared spectroscopy revealed the generation of −N2Hy (1≤y≤4) active species during the pNRR process, which is consistent with the most potential pathway (enzymatic mechanism) calculated by DFT.