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

Abstract

Amorphous, mixed-valency, molybdenum sulfide (MoS x ) with a proposed formula, [Mo(IV) 4Mo(V) 2(S2 2–)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 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, and pulsed laser ablation) but can rather be induced simply through controlling the reductive synthesis conditions.

A Comprehensive Review of MoSx for Improved Photo(electro)catalytic Performance

“…So far, papers in the literature have primarily used Raman and X‐ray photoelectron spectroscopy (XPS) to demonstrate the presence of MoS x . Particularly, XPS can detect distinct valence states (+4, +5, +6) of Mo in MoS x and the various bonding interactions of S. [ 73–81 ] Niu et al designed the synthesis of amorphous MoS x displaying high overpotential under both acidic conditions (0.5 mol L −1 H 2 SO 4 , 156 mV) and basic conditions (1.0 mol L −1 KOH, 232 mV). [ 5 ] Figure a exhibits an example of the high‐magnification XPS spectra of Mo 3 d , from which it can be seen that Mo shows three different valence states, namely Mo 6+ (235.6 eV), Mo 5+ (233.3 and 230.1 eV), and Mo 4+ (232.6 and 229.6 eV).…”

“…So far, papers in the literature have primarily used Raman and X-ray photoelectron spectroscopy (XPS) to demonstrate the presence of MoS x . Particularly, XPS can detect distinct valence states (þ4, þ5, þ6) of Mo in MoS x and the various bonding interactions of S. [73][74][75][76][77][78][79][80][81] Niu et al designed the synthesis of amorphous MoS x displaying high overpotential under both acidic conditions (0.5 mol L À1 H 2 SO 4 , 156 mV) and basic conditions (1.0 mol L À1 KOH, 232 mV). [5] on Mo plates by hydrothermal method and showed excellent hydrogen precipitation properties.…”

Introduction of MoS2–FeS2 with an S-Vacancy Defect as an Efficient Bifunctional Electrocatalyst for Hydrogen Evolution Reaction and Ferrocyanide and Iodide Oxidation Reactions

“…To address these challenges, a cost-effective and energy-saving approach has been proposed, involving the oxidation of chemical substrates like hydrazine, urea, iodide, amines, and alcohols at the anode instead of water oxidation. − Among these alternative oxidation reactions, the iodide oxidation reaction (IOR) and ferrocyanide oxidation reaction (FOR) offer promising avenues for hydrogen production and value-added products. Utilizing such substrate oxidation reactions not only reduces energy consumption but also eliminates the production of reactive oxygen species (ROS) and extends the electrolyzer’s lifetime. , However, both HER and IOR exhibit sluggish kinetics at conventional electrodes, necessitating effective electrocatalysts to operate at lower overpotentials. ,, Transition metal dichalcogenides (TMDs), like molybdenum disulfide (MoS 2 ), have emerged as desirable alternatives to expensive Pt-based electrocatalysts due to their high chemical reactivity, stability, and performance under harsh conditions. − While MoS 2 presents electroactive sites at its sulfur vacancies (S-vacancies) and edges, ,− its practical application is hindered by limitations such as low-density active sites, inert basal plane, poor electrical conductivity, and severe aggregation. To enhance catalytic activity, various strategies have been explored, ,− including the synthesis of MoS 2 -based composites rich in sulfur atoms and edges using different metal sulfides such as iron disulfide (FeS 2 ) and the incorporation of materials like carbon nanotubes (CNTs) , and rGO …”