Experimental and Theoretical Comparison of Potential-dependent Methylation on Chemically Exfoliated WS₂ and MoS₂

Reductant-activated functionalization is shown to enhance the methylation of chemically exfoliated MoS₂ (ceMoS₂) and ceWS₂ by introducing excess negative charge to facilitate a nucleophilic attack reaction. Relative to methylation in the absence of a reductant, the reaction produces a twofold increase in coverage of ceWS₂, from 25 to 52% coverage per WS₂. However, at every potential, the methyl coverage on ceWS₂ was ∼20% lower than that on ceMoS₂. We applied grand canonical density functional theory to show that at constant potential, more negative charge is present on 1T′-MoS₂ than on 1T′-WS₂, making methylation both thermodynamically and kinetically more favorable for 1T′-MoS₂ than 1T′-WS₂. This effect was moderated when the reactions were compared at constant charge, emphasizing the importance of comparing the reactivity of materials at nominally identical electrode potentials.