Structural and Electronic Study of an Amorphous MoS3 Hydrogen-Generation Catalyst on a Quantum-Controlled Photosensitizer

Sulfurization-induced partially amorphous palladium sulfide nanosheets for highly efficient electrochemical hydrogen evolution

Partially amorphous PdS was synthesized by sulfurizing crystalline palladium nanosheets via a facile method, displaying excellent activity and stability towards hydrogen evolution in alkaline media.

Self-assembled hybrid organic-MoS3-nanoparticle catalyst for light energy conversion

We present photocatalytically active, stable polymer-amorphous-MoS3-nanoparticle hybrid structures in aqueous solution. Below 10 nm MoS3 particles in the polymer exhibit an up to 7.5-fold increased photocatalytic activity compared to the neat nanoparticles without any additional photosensitizer. Supramolecular interactions are key in directing the structure formation of the hybrid assembly. The hybrid structures bear potential as novel affordable photocatalysts for solar energy conversion.

The Origin of High Activity of Amorphous MoS2 in the Hydrogen Evolution Reaction

Molybdenum disulfide (MoS₂ ) and related transition metal chalcogenides can replace expensive precious metal catalysts such as Pt for the hydrogen evolution reaction (HER). The relations between the nanoscale properties and HER activity of well-controlled 2H and Li-promoted 1T phases of MoS₂ , as well as an amorphous MoS₂ phase, have been investigated and a detailed comparison is made on Mo-S and Mo-Mo bond analysis under operando HER conditions, which reveals a similar bond structure in 1T and amorphous MoS₂ phases as a key feature in explaining their increased HER activity. Whereas the distinct bond structure in 1T phase MoS₂ is caused by Li⁺ intercalation and disappears under harsh HER conditions, amorphous MoS₂ maintains its intrinsic short Mo-Mo bond feature and, with that, its high HER activity. Quantum-chemical calculations indicate similar electronic structures of small MoS₂ clusters serving as models for amorphous MoS₂ and the 1T phase MoS₂ , showing similar Gibbs free energies for hydrogen adsorption (ΔG_H* ) and metallic character.

Electrodeposition of MoSx Hydrogen Evolution Catalysts from Sulfur-Rich Precursors

Amorphous molybdenum sulfides (a-MoS_x) are known to be active electrocatalysts for the hydrogen evolution reaction (HER), but the role stoichiometry of the sulfur atoms plays in the HER activity remains unclear. In this work, we deposited thin films of a-MoS_x from two thiomolybdate deposition baths with different sulfur ratios (MoS₄^2- and Mo₂S₁₂^2-) and showed that the sulfur stoichiometry, as determined by X-ray photoelectron spectroscopy, is controlled by the precursor of choice and the electrochemical method used to deposit the thin films. Using the Mo₂S₁₂^2- precursor allows access to a MoS₆ thin film, with a higher S/Mo ratio compared with that of any previously reported electrodeposited films. We also examined the effect of electrochemistry on the resulting S/Mo ratio in the as-prepared a-MoS_x thin films. Samples with S/Mo ratios ranging from 2 to 6 were electrodeposited on glassy carbon (GC) substrates by using anodic, cathodic, or cyclic voltammetry deposition. The a-MoS_x thin films deposited on GC substrates were tested as HER catalysts in acidic electrolytes. The overpotentials needed to drive current densities of 10 mA/cm² ranged from 160 mV for MoS₆ samples to 216 mV for MoS₂ samples, signifying the important role sulfur content plays in HER activity of the prepared films. Furthermore, we characterized the deactivation of the a-MoS_x films and found that the sulfur content is gradually depleted over time, leading to a slow deactivation of the a-MoS_x thin-film catalysts. We showed a facile procedure that affords a-MoS_x films with high sulfur content by using S-rich precursors and highlighted the role of sulfur in the prepared films for HER.

Recent advances in metal sulfides: from controlled fabrication to electrocatalytic, photocatalytic and photoelectrochemical water splitting and beyond

This review describes an in-depth overview and knowledge on the variety of synthetic strategies for forming metal sulfides and their potential use to achieve effective hydrogen generation and beyond.

Faster Electron Injection and More Active Sites for Efficient Photocatalytic H2 Evolution in g-C3 N4 /MoS2 Hybrid

Herein, the structural effect of MoS₂ as a cocatalyst of photocatalytic H₂ generation activity of g-C₃ N₄ under visible light irradiation is studied. By using single-particle photoluminescence (PL) and femtosecond time-resolved transient absorption spectroscopies, charge transfer kinetics between g-C₃ N₄ and two kinds of nanostructured MoS₂ (nanodot and monolayer) are systematically investigated. Single-particle PL results show the emission of g-C₃ N₄ is quenched by MoS₂ nanodots more effectively than MoS₂ monolayers. Electron injection rate and efficiency of g-C₃ N₄ /MoS₂ -nanodot hybrid are calculated to be 5.96 × 10⁹ s^-1 and 73.3%, respectively, from transient absorption spectral measurement, which are 4.8 times faster and 2.0 times higher than those of g-C₃ N₄ /MoS₂ -monolayer hybrid. Stronger intimate junction between MoS₂ nanodots and g-C₃ N₄ is suggested to be responsible for faster and more efficient electron injection. In addition, more unsaturated terminal sulfur atoms can serve as the active site in MoS₂ nanodot compared with MoS₂ monolayer. Therefore, g-C₃ N₄ /MoS₂ nanodot exhibits a 7.9 times higher photocatalytic activity for H₂ evolution (660 µmol g-¹ h^-1 ) than g-C₃ N₄ /MoS₂ monolayer (83.8 µmol g^-1 h^-1 ). This work provides deep insight into charge transfer between g-C₃ N₄ and nanostructured MoS₂ cocatalysts, which can open a new avenue for more rationally designing MoS₂ -based catalysts for H₂ evolution.

General Scheme for Oxidative Quenching of a Copper Bis-Phenanthroline Photosensitizer for Light-Driven Hydrogen Production

A new, general reaction scheme for photocatalytic hydrogen production is presented based on oxidative quenching of a homoleptic copper(I) bis-1,10-phenanthroline photosensitizer (PS) by 1-methyl-4-phenyl-pyridinium (MPP(+) ) as the electron relay and subsequent regeneration of the so formed copper(II) complex by a sacrificial electron donor. Electron transfer from the relay to various cobalt based water reduction catalysts and subsequent H2 production was shown to close the catalytic cycle. Transient absorption experiments unambiguously confirmed the proposed pathway, both the oxidative quenching and subsequent regeneration of oxidized PS. Photocatalytic test runs further confirmed the role of MPP(+) and up to 10 turnovers were achieved in the relay. The performance limiting factor of the system was shown to be the decomplexation of the copper PS. Quantum yields of the system were 0.03 for H2 production, but 0.6 for MPP(.) formation, clearly indicating that unproductive pathways still prevail.

A study on the origin of the active sites of HDN catalysts using alumina-supported MoS3 nanoparticles as a precursor

The origin of the active sites of the hydrodenitrogenation catalysts was comprehensively studied using alumina-supported MoS₃ nanoparticles (NPs) as a novel precursor.

Noble-Metal-Free Molybdenum Disulfide Cocatalyst for Photocatalytic Hydrogen Production

Photocatalytic water splitting using powered semiconductors as photocatalysts represents a promising strategy for clean, low-cost, and environmentally friendly production of H2 utilizing solar energy. The loading of noble-metal cocatalysts on semiconductors can significantly enhance the solar-to-H2 conversion efficiency. However, the high cost and scarcity of noble metals counter their extensive utilization. Therefore, the use of alternative cocatalysts based on non-precious metal materials is pursued. Nanosized MoS2 cocatalysts have attracted considerable attention in the last decade as a viable alternative to improve solar-to-H2 conversion efficiency because of its superb catalytic activity, excellent stability, low cost, availability, environmental friendliness, and chemical inertness. In this perspective, the design, structures, synthesis, and application of MoS2 -based composite photocatalysts for solar H2 generation are summarized, compared, and discussed. Finally, this Review concludes with a summary and remarks on some challenges and opportunities for the future development of MoS2 -based photocatalysts.

Water-soluble MoS3 nanoparticles for photocatalytic H2 evolution

Polyvinylpyrrolidone (PVP)-modified MoS3 nanoparticles with unusual water solubility up to 1.0 mg mL(-1) were synthesized through a facile hydrothermal method in the presence of thioacetic acid. The amorphous nanoparticles wrapped by PVP have sizes of around 2.5 nm, which represent the smallest MoS3 clusters reported. The photocatalytic performance of the MoS3 nanoparticles was evaluated under visible light for H2 evolution using xanthene dyes as photosensitizers. The quantum efficiency of the optimized system for H2 evolution under green light irradiation (520 nm) is up to 36.2 %, which is comparable with those of other excellent photocatalytic systems involving earth-abundant catalysts. The excellent photocatalytic activity can be attributed to its good dispersion in water, amorphous nature and limited layers with abundant surface active sites, and possibly higher conduction band potential for proton reduction and larger indirect band gap for a longer lifetime of the excited electrons.

Enhanced electrocatalytic activity of MoS(x) on TCNQ-treated electrode for hydrogen evolution reaction

Molybdenum sulfide has recently attracted much attention because of its low cost and excellent catalytical effects in the application of hydrogen evolution reaction (HER). To improve the HER efficiency, many researchers have extensively explored various avenues such as material modification, forming hybrid structures or modifying geometric morphology. In this work, we reported a significant enhancement in the electrocatalytic activity of the MoSx via growing on Tetracyanoquinodimethane (TCNQ) treated carbon cloth, where the MoSx was synthesized by thermolysis from the ammonium tetrathiomolybdate ((NH4)2MoS4) precursor at 170 °C. The pyridinic N- and graphitic N-like species on the surface of carbon cloth arising from the TCNQ treatment facilitate the formation of Mo(5+) and S2(2-) species in the MoSx, especially with S2(2-) serving as an active site for HER. In addition, the smaller particle size of the MoSx grown on TCNQ-treated carbon cloth reveals a high ratio of edge sites relative to basal plane sites, indicating the richer effective reaction sites and superior electrocatalytic characteristics. Hence, we reported a high hydrogen evolution rate for MoSx on TCNQ-treated carbon cloth of 6408 mL g(-1) cm(-2) h(-1) (286 mmol g(-1) cm(-2) h(-1)) at an overpotential of V = 0.2 V. This study provides the fundamental concepts useful in the design and preparation of transition metal dichalcogenide catalysts, beneficial in the development in clean energy.

Highly efficient electrocatalytic hydrogen production by MoS(x) grown on graphene-protected 3D Ni foams

A three-dimensional Ni foam deposited with graphene layers on surfaces is used as a conducting solid support to load MoS(x) catalysts for electrocatalytic hydrogen evolution. The graphene sheets grown on Ni foams provide robust protection and efficiently increase the stability in acid. The superior performance of hydrogen evolution is attributed to the relatively high catalyst loading weight as well as its relatively low resistance.