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 (ceMoS(2)) and ceWS(2) 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 ceWS(2), from 25 to 52% coverage per WS2. However, at every potential, the methyl coverage on ceWS(2) was similar to 20% lower than that on ceMoS(2). 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.