Defect Engineering of MoS2 and Its Impacts on Electrocatalytic and Photocatalytic Behavior in Hydrogen Evolution Reactions

Molybdenum disulfide (MoS₂) has been regarded as a favorable photocatalytic co‐catalyst and efficient hydrogen evolution reaction (HER) electrocatalyst alternative to expensive noble‐metals catalysts, owing to earth‐abundance, proper band gap, high surface area, and fast electron transfer ability. In order to achieve a higher catalytic efficiency, defects strategies such as phase engineering and vacancy introduction are considered as promising methods for natural 2H‐MoS₂ to increase its active sites and promote electron transfer rate. In this study, we report a new two‐step defect engineering process to generate vacancies‐rich hybrid‐phase MoS₂ and to introduce Ru particles at the same time, which includes hydrothermal reaction and a subsequent hydrogen reduction. Compositional and structural properties of the synthesized defects‐rich MoS₂ are investigated by XRD, XPS, XAFS and Raman measurements, and the electrochemical hydrogen evolution reaction performance, as well as photocatalytic hydrogen evolution performance in the ammonia borane dehydrogenation are evaluated. Both catalytic activities are boosted with the increase of defects concentrations in MoS₂, which ascertains that the defects engineering is a promising route to promote catalytic performance of MoS₂.     

Rhenium and molybdenum poorly crystalline disulfides and their mesophases with hexadecylamine

Sulfides of molybdenum and rhenium poorly crystalline were prepared by solvothermal oxidative decarbonylation of the respective metal carbonyls with sulfur using p-xylene as solvent. The same reaction, but in presence of hexadecylamine (HDA), was used for preparing the nanocomposites MoS₂/HDA and ReS₂/HDA. The products were analyzed by X-ray diffraction analysis, scanning electron microscopy, atomic force microscopy, and Fourier-transform infrared spectroscopy. The products, MoS₂ and ReS₂, are structurally similar but morphologically different: small undefined particles (150–300 nm) and well-defined, almost perfect microspheres (0.4–2.8 μm), respectively. Preparations containing HDA lead to the corresponding layered nanocomposites. MoS₂/HDA is a dark solid easily separable from the reaction mixture, while ReS₂/HDA remains as a suspension in p-xylene, from which it is obtained by evaporating the solvent under vacuum. Both are layered species with basal spacing of 33.8?Å (Mo) and 30.4?Å (Re), respectively. The preparation of thin films of ReS₂/HDA from its suspension by evaporating the solvent in the air produces small cylindrical particles of about 0.4 × 1.0 μm in size. Differences in the behavior of Mo and Re derivatives are discussed considering the coordination of the metal and the electronic structures of both metal disulfides.     

Einstieg in die Chemie einfacher Rhenium-Schwefel-Komplexe und -Cluster. Darstellung und Kristall-Struktur von R[ReS4], R′[ReS9], (NH4)4[Re4S22]·2H2O,R′2[Cl2Fe(MoS4)FeCl2]x [Cl2Fe(ReS4)FeCl2]1-x′ R′2 [(ReS4)Cu3l4] und RR′2[(ReS4)Cu5Br7] (R  NEt4; R′  PPh4; x = 0,3, 0,5)

Entry to the Chemistry of Simple Rhenium Sulfur Complexes and Clusters. Preparation and Crystal Structures of R′[ReS₄], R′[ReS₉], (NH₄)₄[Re₄S₂₂]·2H₂O, R′₂[Cl₂Fe(MoS₄)FeCl₂]_1-x, R′₂[(ReS₄)Cu₃I₄] and RR′₂[(ReS₄)Cu₅Br₇] (R ? NEt₄; R′ ? PPh₄, x = 0.3, 0.5) The compounds R[ReS₄] ( 1 ), R′[ReS₉] ( 2 ), (NH₄)₄[Re₄S₂₂]·2 H₂O ( 3 ), R′₂[Cl₂Fe(MoS₄) FeCl₂]_x[Cl₂Fe(ReS₄)FeCl₂] _1-x (x = 0.3 ( 4 ), 0.5), R′₂[(ReS₄)Cu₃I₄] ( 5 ) and R′₂[(ReS₄)Cu₅Br₇] ( 6 ) (R ? NEt₄; R′ ? PPh₄) have been prepared by reaction of perrhenates or rhenium(VII)oxide with S_x^2? solutions (under different conditions) or by reactions of metal-halides with [ReS₄]^?-ions. All compounds have been characterized by complete X- ray structure analysis. For further details see Inhaltsübersicht.     

MoS2 Nanosheets Supported on 3D Graphene Aerogel as a Highly Efficient Catalyst for Hydrogen Evolution

The development of efficient catalysts for electrochemical hydrogen evolution is essential for energy conversion technologies. Molybdenum disulfide (MoS₂) has emerged as a promising electrocatalyst for hydrogen evolution reaction, and its performance greatly depends on its exposed edge sites and conductivity. Layered MoS₂ nanosheets supported on a 3D graphene aerogel network (GA‐MoS₂) exhibit significant catalytic activity in hydrogen evolution. The GA‐MoS₂ composite displays a unique 3D architecture with large active surface areas, leading to high catalytic performance with low overpotential, high current density, and good stability.     

Tuning the Intrinsic Activity and Electrochemical Surface Area of MoS2 via Tiny Zn Doping: Toward an Efficient Hydrogen Evolution Reaction (HER) Catalyst

Molybdenum sulfide (MoS₂) is considered as an alternative material for commercial platinum catalysts for electrocatalytic hydrogen evolution reaction (HER). Improving the apparent HER activity of MoS₂ to a level comparable to that of Pt is an essential premise for the commercial use of MoS₂. In this work, a Zn-doping strategy is proposed to enhance the HER performance of MoS₂. It is shown that tiny Zn doping into MoS₂ leads to the enhancement of the electrochemical surface area, increases in proportion of HER active 1T phase in the material and formation of catalytic sites of higher intrinsic activity. These benefits result in a high-performance HER electrocatalyst with a low overpotential of 190 mV(@10 mA cm⁻²) and a low Tafel slope of 58 mV dec⁻¹. The origin for the excellent electrochemical performance of the doped MoS₂ is rationalized with both experimental and theoretical investigations.     

Patternable Large‐Scale Molybdenium Disulfide Atomic Layers Grown by Gold‐Assisted Chemical Vapor Deposition

A novel way to grow MoS₂ on a large scale with uniformity and in desired patterns is developed. We use Au film as a catalyst on which [Mo(CO)₆] vapor decomposes to form a Mo‐Au surface alloy that is an ideal Mo reservoir for the growth of atomic layers of MoS₂. Upon exposure to H₂S, this surface alloy transforms into a few layers of MoS₂, which can be isolated and transferred on an arbitrary substrate. By simply patterning Au catalyst film by conventional lithographic techniques, MoS₂ atomic layers in desired patterns can be fabricated.     

Monolayer 1T and 1T′ MoSO as Promising Electrocatalyst for Hydrogen Evolution based on First Principle Calculations

Molybdenum disulfide (MoS₂) has been regarded as one of the most promising candidates for replacing Pt group noble metals as an efficient electrocatalyst to enhance the hydrogen evolution reaction (HER) in consideration of its relatively high earth abundance. Recent studies show that the catalytic efficiency of MoS₂ for HER can be promoted by the presence of 1T-phase MoS₂. It is hard to precisely control the formation of 1T-MoS₂, however, due to its metastability relative to 2H-MoS₂. Elevating the stability of 1T phase allotrope is therefore of great importance and could be realized by replacing divalent S with monovalent elements or groups according to crystal field theory, which has been demonstrated through our first-principles density functional theory (DFT) calculation results. Differential Gibbs free energy analysis for hydrogen adsorption (ΔG_H*) suggest that 1T and 1T′ MoSO (O doped MoS₂) might be taken as potential candidate catalysts for HER process with better performance than 1T and 1T′ MoS₂. We also propose a probable approach to synthesize 1T and 1T′ MoSO under oxidation circumstance environment of graphene oxide.     

TiO2 nanorods based self-supported electrode of 1T/2H MoS2 nanosheets decorated by Ag nano-particles for efficient hydrogen evolution reaction

Molybdenum disulfide (MoS₂) has shown significant promise as an economic hydrogen evolution reaction (HER) catalyst for hydrogen generation, but its catalytic performance is still lower than noble metal-based catalysists. Herein, a silver nanoparticles (Ag NPs)-decorated 1T/2H phase layered MoS₂ electrocatalyst grown on titanium dioxide nanorod arrays (Ag NPs/1T(2H) MoS₂/TNRs) was prepared through acid-tunable ammonium ion intercalation. Taking advantage of MoS₂ layered structure and crystal phase controllability, as-prepared Ag NPs/1T(2H) MoS₂/TNRs exhibited ultrahigh HER activity. As-proposed strategy combines facile hydrogen desorption (Ag NPs) with efficient hydrogen adsorption (1T/2H MoS₂) effectively circumventes the kinetic limitation of hydrogen desorption by 1T/2H MoS₂. The as-prepared Ag NPs/1T(2H) MoS₂/TNRs electrocatalyst exhibited excellent HER activity in 0.5 mol/L H₂SO₄ with low overpotential (118 mV vs. reversible hydrogen electrode (RHE)) and small Tafel slope (38.61 mV/dec). The overpotential exhibts no obvious attenuation after 10 h of constant current flow. First-principles calculation demonstrates that as-prepared 1T/2H MoS₂ exhibit a large capacity to store protons. These protons can be subsequently transferred to Ag NPs, which significantly increases the hydrogen coverage on the surface of Ag NPs in HER process and thus change the rate-determining step of HER on Ag NPs from water dissociation to hydrogen recombination. This study provides a unique strategy to improve the catalytic activity and stability for MoS₂-based electrocatalyst.     

Hexagram-like CoS-MoS<Subscript>2</Subscript> composites with enhanced activity for hydrogen evolution reaction

Hexagram-like CoS-MoS₂ composites were prepared on indium tin oxide (ITO) conductive glasses via cyclic voltammetry electrodeposition using Co(NO₃)₂ and (NH₄)₂MoS₂ as precursors and tested for application in hydrogen evolution reaction (HER). The structure of CoS-MoS₂ composites was characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and X-ray photoelectron spectrum (XPS). Electrochemical characterizations indicate that CoS-MoS₂ composites exhibit more excellent catalytic activity and stability than MoS₂. Compared with pure MoS₂, the hexagram-like CoS-MoS₂ composites with increased specific surface area improved the density of exposed active sites, and the Co binding S edges in CoS-MoS₂ composites promote the number of highly catalytic edge sites and decreased the binding energy △G _H. Moreover, the effects of different substrates on the CoS-MoS₂ composites were also investigated. Our further understanding of this highly active hydrogen evolution catalyst can facilitate the development of economical electrochemical hydrogen production systems.     

Bifunctional Electrocatalyst with 0D/2D Heterostructure for Highly Efficient Hydrogen and Oxygen Generation

A novel MoS₂ quantum dots/CoSe₂ nanosheet (MoS₂ QDs/CoSe₂) hybrid with 0D/2D heterostructure has been developed. The CoSe₂ nanosheets (NSs) enable an excellent oxygen evolution reaction (OER) activity with increasing vacancy configuration on one hand, while the MoS₂ QDs serve as an eminent hydrogen evolution reaction (HER) catalyst on the other. By integrating MoS₂ QDs and CoSe₂ NSs, the hybrid exhibits excellent electrocatalytic performances in HER and OER. The unique 0D/2D hetero‐interface increases the exposed active sites and facilitates electron transfer, thereby boosting the electrocatalytic activity. Relatively low overpotentials of 82 mV and 280 mV are required to drive the current density of 10 mA/cm² for HER and OER, with corresponding Tafel slopes of 69 and 75 mV/dec, respectively. As such, this work provides an efficient yet simple approach to construct bifunctional electrocatalysts with enhanced activity and stability.     

2D/2D h‐BN/N‐doped MoS2 Heterostructure Catalyst with Enhanced Peroxidase‐like Performance for Visual Colorimetric Determination of H2O2

Recently, nanozymes have attracted extensive attention because of their advantages of combining nanomaterials with enzymes. Herein, hexagonal boron nitride (h‐BN) and nitride‐doped molybdenum disulfide (N?MoS₂) nano‐composites (h‐BN/N?MoS₂) were synthesized by facile and cost‐effective liquid exfoliation with a solvothermal method in nontoxic ethanol solution. The results show that h‐BN, as a co‐catalyst, can not only dope into the lattice of MoS₂ but also form a heterogeneous structure with MoS₂NSs. It expanded the layer spacing and specific surface area of MoS₂NSs, which was beneficial to the contact between the catalyst and the substrate, and resulted in a synergistic enhancement of the catalytic activity of hydrogen peroxide (H₂O₂) with MoS₂. A colorimetric determination platform of h‐BN/N?MoS₂‐TMB‐H₂O₂ was constructed. It exhibited a wide linear range of 1–1000 μM with a low limit of detection (LOD) of 0.4 μM under optimal conditions, high sensitivity and stability, as well as good reliability (99.4–110.0%) in practice, making the measurement system more widely applicable.1. Introduction     

二硫化钼纳米片/碳纳米纤维杂化材料的制备及其析氢性能

以碳纳米纤维(CNFs)作为负载基体和反应器采用静电纺丝技术和碳化工艺生长和调控二硫化钼(MoS_2)纳米片。通过改变前驱体溶液浓度来调控纳米片的形貌和结构,利用MoS_2纳米片的高催化活性和CNFs高比表面积、良好的稳定性以及高电导率的协同作用,研究不同形貌和结构的杂化纳米材料在电催化析氢方面的应用,探索杂化材料形貌与性能之间的潜在规律。运用多种分析测试技术对制备得到的纳米杂化材料进行表征,并对所制备的MoS_2/CNFs杂化材料的电催化析氢性能(HER)进行研究,研究表明近似皮芯结构的MoS_2/CNFs-10杂化材料的电催化析氢性能最好,初始析氢过电位在220 mV,Tafel斜率为110m V·dec~(-1)。     

二硫化钼纳米片/碳纳米纤维杂化材料的制备及其析氢性能

以碳纳米纤维（CNFs）作为负载基体和反应器采用静电纺丝技术和碳化工艺生长和调控二硫化钼（MoS₂）纳米片。通过改变前驱体溶液浓度来调控纳米片的形貌和结构,利用MoS₂纳米片的高催化活性和CNFs高比表面积、良好的稳定性以及高电导率的协同作用,研究不同形貌和结构的杂化纳米材料在电催化析氢方面的应用,探索杂化材料形貌与性能之间的潜在规律。运用多种分析测试技术对制备得到的纳米杂化材料进行表征,并对所制备的MoS₂/CNFs杂化材料的电催化析氢性能（HER）进行研究,研究表明近似皮芯结构的MoS₂/CNFs-10杂化材料的电催化析氢性能最好,初始析氢过电位在220 mV,Tafel斜率为110 mV·dec^-1。     

Controlled Synthesis of Ni-Doped MoS2 Hybrid Electrode for Synergistically Enhanced Water-Splitting Process

The development of high-efficiency, low-cost, and earth-abundant electrocatalysts for overall water splitting remains a challenge. In this work, Ni-modified MoS₂ hybrid catalysts are grown on carbon cloth (Ni-Mo-S@CC) through a one-step hydrothermal treatment. The optimized Ni-Mo-S@CC catalyst shows excellent hydrogen evolution reaction (HER) activity with a low overpotential of 168 mV at a current density of 10 mA cm⁻² in 1.0 m KOH, which is lower than those of Ni-Mo-S@CC (1:1), Ni-Mo-S@CC (3:1), and pure MoS₂. Significantly, the Ni-Mo-S@CC hybrid catalyst also displays outstanding oxygen evolution reaction (OER) activity with a low overpotential of 320 mV at a current density of 10 mA cm⁻², and remarkable long-term stability for 30 h at a constant current density of 10 mA cm⁻². Experimental results and theoretical analysis based on density functional theory demonstrate that the excellent electrocatalytic performance can be attributed mainly to the remarkable conductivity, abundant active sites, and synergistic effect of the Ni-doped MoS₂. This work sheds light on a unique strategy for the design of high-performance and stable electrocatalysts for water-splitting electrolyzers.     

Embedding Amorphous Molybdenum Sulfide within a Porous Poly(3,4‐ethylenedioxythiophene) Matrix to Enhance its H2‐evolving Catalytic Activity and Robustness

Amorphous molybdenum sulfide (MoS_x) is a promising alternative to Pt catalyst for the H₂ evolution in water. However, it is suffered of an electrochemical corrosion. In this report, we present a strategy to tack this issue by embedding the MoS_x catalyst within a porous poly(3,4‐ethylenedioxythiophene) (PEDOT) matrix. The PEDOT host is firstly grown onto a fluorine‐doped tin oxide (FTO) electrode by electrochemical polymerization of EDOT monomer in an acetonitrile solution to perform a porous structure. The MoS_x catalyst is subsequently deposited onto the PEDOT by an electrochemical oxidation of [MoS₄]^2? monomer. In a 0.5 M H₂SO₄ electrolyte solution, the MoS_x/PEDOT shows higher H₂‐evolving catalytic activities (current density of 34.2 mA/cm² at ?0.4 V vs RHE) in comparison to a pristine MoS_x grown on a planar FTO electrode having similar catalyst loading (24.2 mA/cm²). The PEDOT matrix contributes to enhance the stability of MoS_x catalyst by a significant manner. As such, the MoS_x/PEDOT retains 81 % of its best catalytic activity after 1000 potential scans from 0 to ?0.4 V vs. RHE, whereas a planar MoS_x catalyst is completely degraded after about 240 potential scans, due to its complete corrosion.     

Hierarchical Nanoboxes Composed of Co9S8−MoS2 Nanosheets as Efficient Electrocatalysts for the Hydrogen Evolution Reaction

The development of hydrogen evolution catalysts based on nonprecious metals is essential for the practical application of water‐splitting devices. Herein, the synthesis of Co₉S₈?MoS₂ hierarchical nanoboxes (HNBs) as efficient catalysts for the hydrogen evolution reaction (HER) is reported. The surface of the hollow cubic structure was organized by CoMoS₄ nanosheets formed through the reaction of MoS₄^2? and Co²⁺ released from the cobalt zeolite imidazole framework (ZIF‐67) templates under reflux in a mixture of water/ethanol. The formation process for the CoMoS₄ HNB structures was characterized by TEM images recorded at various reaction temperatures. The amorphous CoMoS₄ HNBs were converted through sequential heat treatments into CoS_x?MoS₂ and Co₉S₈?MoS₂ HNBs. Owing to their unique chemical compositions and structural features, Co₉S₈?MoS₂ HNBs have a high specific surface area (124.6 m² g^?1) and superior electrocatalytic performances for the HER. The Co₉S₈?MoS₂ HNBs exhibit a low overpotential (η₁₀) of 106 mV, a low Tafel slope of 51.8 mV dec^?1, and long‐term stability in an acidic medium. The electrocatalytic activity of Co₉S₈?MoS₂ HNBs is superior to that of recently reported values, and these HNBs prove to be promising candidates for the HER.     

Highly Efficient,Green, and Scalable β‐Cyclodextrin‐Assisted Aqueous Exfoliation of Transition‐Metal Dichalcogenides: MoS2 and ReS2 Nanoflakes

The β‐cyclodextrin‐assisted aqueous‐exfoliation method was used to prepare transition‐metal dichalcogenide (TMD) nanosheets, in a cheap, highly efficient, scalable and environmentally friendly manner. As study cases, MoS₂ and ReS₂ nanoflakes were prepared according to this method. Particularly, the effective exfoliation of ReS₂ crystals in an aqueous environment was observed for the first time. Moreover, exfoliated nanomaterials can be readily utilized in hydrogen evolution reactions (HERs) as noble‐metal‐free catalysts. This work provides new opportunities for highly efficient exfoliation of TMDs and other 2D nanomaterials into few‐layer nanosheets in aqueous media. Their production process showed high biocompatibility, broad applicability and excellent sustainability.     

Boosting CO2 Hydrogenation to Formate over Edge-Sulfur Vacancies of Molybdenum Disulfide

Synthesis of formate from hydrogenation of carbon dioxide (CO₂) is an atom-economic reaction but is confronted with challenges in developing high-performance non-precious metal catalysts for application of the process. Herein, we report a highly durable edge-rich molybdenum disulfide (MoS₂) catalyst for CO₂ hydrogenation to formate at 200 °C, which delivers a high selectivity of over 99 % with a superior turnover frequency of 780.7 h⁻¹ surpassing those of previously reported non-precious metal catalysts. Multiple experimental characterization techniques combined with theoretical calculations reveal that sulfur vacancies at MoS₂ edges are the active sites and the selective production of formate is enabled via a completely new water-mediated hydrogenation mechanism, in which surface OH* and H* species in dynamic equilibrium with water serve as moderate hydrogenating agents for CO₂ with residual O* reduced by hydrogen. This study provides a new route for developing low-cost high-performance catalysts for CO₂ hydrogenation to formate.     

Surface Modulation of Iron-doped MoS2 Nanosheets by Phytic Acid for Enhanced Water Oxidation

Surface modulation and heteroatom doping are important approaches for boosting the electrocatalytic performances of MoS₂ nanosheets. As a molecular electrocatalyst, the natural organic phytic acid (PA) offer attractive intermediate for oxygen evolution reaction (OER). Here, a surface modulation strategy is demonstrated through the decoration of PA onto the basal plane of iron (Fe)-doped MoS₂ nanosheets supported on nickel foam (NF) for boosted OER activity. Experimental results indicate that the PA modification and Fe doping could effectively boost the charge transfer and mass transport during the OER process. Specially, PA2-Fe−MoS₂ grown on NF (PA2-Fe−MoS₂/NF) exhibits excellent OER activity (218 mV@20 mA cm⁻²) and durability, even superior to RuO₂ and many other previously reported OER catalysts. This natural organic molecule modification provides a facile strategy to designing low-cost and efficient electrocatalytic materials.     

Investigation on the Growth Mechanism of Cu2MoS4 Nanotube,Nanoplate and its use as a Catalyst for Hydrogen Evolution in Water

Cu₂MoS₄ is a ternary transition‐metal sulfide that shows great potential in the field of energy conversion and storage, namely catalytic H₂ evolution in water and Li‐, Na‐ or Mg‐ion battery. In this work, we report on a growth mechanism of the single‐crystalline Cu₂MoS₄ nanotube from (NH₄)₂MoS₄ salt and Cu₂O nanoparticle. By probing the nature and morphology of solid products generated in function of reaction conditions we find that the crystalline Cu(NH₄)MoS₄ nanorod is first generated at ambient conditions. The nanorod is then converted into Cu₂MoS₄ nanotube under hydrothermal treatment due to the Kirkendall effect or a selective etching of the Cu₂MoS₄ core. Extending the hydrothermal treatment causes a collapse of nanotube generating Cu₂MoS₄ nanoplate. The catalytic activities of these sulfides are investigated. The Cu₂MoS₄ shows superior catalytic activity to that of Cu(NH₄)MoS₄. Catalytic performance of the former largely depends on its morphology. The nanoplate shows superior catalytic activity to the nanotube, thanks to its higher specific electrochemical surface area.