Experimental and Theoretical Comparison of Potential-dependent Methylation on Chemically Exfoliated WS and MoS.

Reductant-activated functionalization is shown to enhance the methylation of chemically exfoliated MoS (MoS) and WS 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 WS, from 25 to 52% coverage per WS. However, at every potential, the methyl coverage on WS was ∼20% lower than that on MoS. We applied grand canonical density functional theory to show that at constant potential, more negative charge is present on 1T'-MoS than on 1T'-WS, making methylation both thermodynamically and kinetically more favorable for 1T'-MoS than 1T'-WS. 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.