Exploring the N₂ Adsorption and Activation Mechanisms over the 2H/1T Mixed-Phase Ultrathin Mo_1–xW_xS₂ Nanosheets for Boosting N₂ Photosynthesis

Solar-driven conversion of nitrogen (N₂) to ammonia (NH₃) is highly appealing, yet in its infancy, the low photocatalytic efficiency and unclear adsorption and activation mechanisms of N₂ are still issues to be addressed. In this study, ultrathin alloyed Mo_1–xW_xS₂ nanosheets with tunable hexagonal (2H)/trigonal (1T) phase ratios were proposed to boost photoreduction N₂ efficiency, while the mechanisms of N₂ adsorption and activation were explored simultaneously. The alloyed Mo_1–xW_xS₂ nanosheets for the 1T phase concentration of 33.6% and Mo/W = 0.68:0.32 were proven to reach about 111 μmol g_cat^–1 h^–1 under visible light, which is 3.7 (or 3)-fold higher than that of pristine MoS₂ (or WS₂). With the aid of density functional theory calculations and in situ N₂ adsorption X-ray absorption near-edge fine structure techniques, the adsorption and activation behaviors of N₂ over the interface of Mo_1–xW_xS₂ nanosheets were investigated during the N₂ reduction process. The results show that the W doping causes a higher electron density state in W 5d orbitals, which can further polarize the adsorbed N₂ molecules for adsorption and activation. This work provides a new insight into the adsorption and activation mechanisms for the NH₃ synthesis.