Experimental and Theoretical Comparison of Potential-dependent Methylation on Chemically Exfoliated WS 2 and MoS 2 .

Reductant-activated functionalization is shown to enhance the methylation of chemically exfoliated MoS 2 ( ce MoS 2 ) and ce WS 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 ce WS 2 , from 25 to 52% coverage per WS 2 . However, at every potential, the methyl coverage on ce WS 2 was ∼20% lower than that on ce MoS 2 . We applied grand canonical density functional theory to show that at constant potential, more negative charge is present on 1T'-MoS 2 than on 1T'-WS 2 , making methylation both thermodynamically and kinetically more favorable for 1T'-MoS 2 than 1T'-WS 2 . 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.