Sc-Doped Sulfur Vacancy MoS2 Photocatalytic Nitrogen Reduction to Ammonia: Experimental and Theoretical Investigation

This paper combines defect engineering and metal doping to prepare transition metal Sc-doped molybdenum sulfide-containing sulfur vacancies (Sc@VS–MoS2), which is used for photocatalytic nitrogen reduction to synthesize ammonia (pNRR). The activity of Sc@VS–MoS2 for pNRR is as high as 124.26 μmol g–1 h–1, which is 6.16, 2.23, and 2.69 times for MoS2, VS-MoS2, and Sc@MoS2, respectively. This indicates that the combination of S vacancies and Sc doping can significantly improve the photocatalytic performance of MoS2 materials. Theoretical calculations show that the energy barrier UL of the potential determining step (PDS) is only −0.393 V, much lower than VS–MoS2, making Sc@VS–MoS2 exhibit excellent nitrogen reduction activity for ammonia synthesis. Computational results demonstrate that Sc@VS–MoS2 exhibits outstanding N2 adsorption and activation properties, with 0.533 e charge transfer to N2 that significantly reduces the free energy barrier for the first hydrogenation step. Moreover, its hydrogen adsorption free energy is substantially lower than that of VS-MoS2, effectively suppressing the competing hydrogen evolution reaction and enhancing N2 reduction selectivity. In situ infrared spectroscopy showed the formation of −N2Hy species on the catalyst surface, indicating that the enzyme pathway is the most likely reaction pathway, consistent with the calculated results.