Engineering of Molybdenum Sulfide Nanobunches on MWCNTs: Modulation of Active Sites and Electronic Conductivity via Controllable Solvothermal Deposition

Amorphous, mixed-valency, molybdenum sulfide (MoSx) with a proposed formula, [Mo(IV)4Mo(V)2(S22–)3(S2–)5](SO4)5, was grown through a one-pot, solvothermal synthesis on multi-walled carbon nanotubes (MWCNTs) in a gram-scale setup. Optimizing the loading of the active catalyst relative to the conductive support resulted in optimized catalytic performance in hydrogen evolution reaction, reaching down to one of the lowest reported overpotentials, η10 = 140 mV and η100 = 198 mV with a Tafel slope of 62 mV/dec, for the 6.5 wt % of MoSx@MWCNTs. Engineering this amorphous MoSx catalyst was made possible through control of the oxidation state of Mo to avoid the fully reduced MoS2 phases. We also demonstrate that engineering defects in the MoSx catalyst does not require sophisticated techniques (e.g., UHV deposition, ion beam sputtering, and pulsed laser ablation) but can rather be induced simply through controlling the reductive synthesis conditions