Insights into the effects of single Mo vacancy sites on the adsorption and dissociation of CO₂ and H₂O over the tertiary N-doped MoS₂ monolayers

Molybdenum disulfide (MoS₂) monolayers with tertiary N atoms surrounding the single Mo-vacancy sites (MoS₂_1V_Mo_3N_S) sites have been found to exhibit outstanding adsorption activity and stability. While previous literature suggested the enhanced physical adsorption nature of CO₂, N₂ and H₂O molecules on MoS₂_1V_Mo_3N_S sites due to promotional effects of tertiary nitrogen doping of 1 Mo-vacancy, this work highlights the adsorption and dissociation of CO₂ and H₂O on MoS₂_1V_Mo_3N_S sites, which are investigated using density functional theory (DFT). Compared with pure MoS₂ (PMoS₂), our DFT calculations reveal that the MoS₂_1V_Mo_3N_S are the most catalytically active sites. The interactions with CO₂ and H₂O are enhanced by the larger electron distribution with N dopants and neighboring S atoms. Climbing image nudged elastic band (Cl-NEB) and ab initio molecular dynamics (AIMD) analyses indicate that the interactions are exothermic and result in spontaneous molecular dissociation. Here, CO₂ dissociates into CO* and O* on two N atoms with free energy barrier (ΔG_a) of −0.27 eV; while H₂O dissociates via two mechanisms: (1) into adsorbed OH* and H* species (ΔG_a = 0.21 eV), and (2) into adsorbed O, H, H atoms (ΔG_a = 0.10 eV). The computed ΔG_a values are significantly lower than the threshold energy barrier for chemical reactions at room temperature (0.8 eV), which also indicates that CO₂ and H₂O dissociation is spontaneous at ambient temperature. This study shows the immense potential of MoS₂_1V_Mo_3N_S in the sustainable production of fuels and chemicals via the highly efficient dissociation of inert CO₂ and H₂O.