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

Amorphous, mixed-valency, molybdenum sulfide (MoS x ) with a proposed formula, [Mo (IV) 4 Mo (V) 2 (S 2 2– ) 3 (S 2– ) 5 ](SO 4 ) 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, η 10 = 140 mV and η 100 = 198 mV with a Tafel slope of 62 mV/dec, for the 6.5 wt % of 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 MoS 2 phases. We also demonstrate that engineering defects in the MoS x 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.