Engineering of Molybdenum Sulfide Nanobunches on MWCNTs: Modulation of Active Sites and Electronic Conductivity via...

Amorphous, mixed-valency, molybdenum sulfide (MoS_x) with a proposed formula [Mo^(IV) ₄Mo^(V) ₂(S₂ ^2-)₃(S^2-)₅](SO₄)₅, was grown through 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 (HER), 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% MoS_x@MWCNTs. Engineering this amorphous MoS_x 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 MoS_x catalyst does not require sophisticated techniques (e.g. UHV deposition, ion beam sputtering, pulsed laser ablation), but can rather be induced simply through controlling the reductive synthesis conditions.