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

Abstract

Molybdenum disulfide (MoS2) monolayers with tertiary N atoms surrounding the single Mo-vacancy sites (MoS2_1VMo_3NS) 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_1VMo_3NS 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_1VMo_3NS sites, which are investigated using density functional theory (DFT). Compared with pure MoS2 (PMoS2), our DFT calculations reveal that the MoS2_1VMo_3NS 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 (ΔGa) of −0.27 eV; while H2O dissociates via two mechanisms: (1) into adsorbed OH* and H* species (ΔGa = 0.21 eV), and (2) into adsorbed O, H, H atoms (ΔGa = 0.10 eV). The computed ΔGa 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_1VMo_3NS in the sustainable production of fuels and chemicals via the highly efficient dissociation of inert CO2 and H2O.