Understanding gas adsorption on defect-engineered two-dimensional (2D) materials is essential for advancing applications in energy storage, catalysis, and sensing. In this work, first-principles calculations are employed to systematically investigate the adsorption behaviors of ${\mathrm{H}}_2,{\mathrm{O}}_2,{\mathrm{H}}_2\mathrm{O},\mathrm{CO}$, and ${\mathrm{CO}}_2$ at sulfur vacancy $V_{\text{S}}$ sites in both single-component transition metal dichalcogenides ${M\mathrm{S}}_2$ (M = W, Mo, Ta, Nb, and V) and high-entropy ${\left(\mathrm{WMoTaNbV}\right)}_{\mathrm{S}2}$ monolayers. In ${M\mathrm{S}}_2$ systems, $V_{\text{S}}$ introduces localized defect states that enhance surface reactivity, leading to diverse adsorption modes including physisorption, chemisorption, and dissociative adsorption. Notably, ${\mathrm{H}}_2$ dissociation is kinetically favorable on $V_{\text{S}}/{\mathrm{TaS}}_2$ and $V_{\text{S}}/{\mathrm{NbS}}_2$, while ${\mathrm{CO}}_2$ remains weakly physiosorbed across all single-metal systems. In contrast, high-entropy ${\left(\mathrm{WMoTaNbV}\right)}_{\mathrm{S}2}$ exhibits a continuous distribution of adsorption energies due to its diverse local coordination environments and synergistic multimetal interactions. This results in significantly reduced activation barriers for ${\mathrm{H}}_2$ dissociation, enhanced adsorption strength for ${\mathrm{O}}_2,{\mathrm{H}}_2\mathrm{O}$, and CO, and a transition of ${\mathrm{CO}}_2$ adsorption from physisorption to chemisorption. Electronic structure analyses reveal that these improvements originate from multicenter $d\text{−}p$ orbital hybridization and enhanced charge transfer at vacancy sites. Overall, the high-entropy design effectively tailors the adsorption landscape of 2D transition metal dichalcogenides, offering a promising strategy for developing advanced materials for hydrogen storage, ${\mathrm{CO}}_2$ activation, and gas-sensing applications.

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• Defects
• Density of states
• Electronic structure
• Energy materials
• Structural properties
• 2-dimensional systems
• High-entropy alloys
• Transition metal dichalcogenides
• Density functional theory
• First-principles calculations