Microwave-Assisted Reactant-Protecting Strategy toward Efficient MoS2 Electrocatalysts in Hydrogen Evolution Reaction

Enhancing anti-chlorine corrosion of Ni3S2 by Mo-doping for mimic seawater electrolysis

Designing highly active electrocatalysts that can resist chloride ion (Cl-) corrosion during seawater electrolysis is still a challenge. Here, Mo-doping is introduced to synchronously improve the electrocatalytic activity and anti-chlorine corrosion of Ni3S2 toward the efficient overall seawater splitting. With commercial nickel-molybdenum foam (NMF) as the reactive substrates, Mo-doped Ni3S2 columnar arrays (Mo-Ni3S2/NMF) are fabricated via a one-step hydrothermal process, which expose abundant active sites with the ameliorated surface electronic configurations toward the enhanced binding with *OH (* denotes an active site) but the weakened one with *Cl. As expected, they afford the excellent bi-functionality for both oxygen and hydrogen evolution reactions (OER and HER), with the remarkably improved anti-corrosion to Cl- at anode as compared to pristine Ni3S2. In alkaline mimic seawater (1.0 M NaOH + 0.5 M NaCl), Mo-Ni3S2/NMF requires 330 mV (for OER) and 209 mV (for HER) overpotentials at the current density of ±100 mA cm-2, and a low cell voltage of 1.52 V at 10 mA cm-2 for overall seawater splitting. This work highlights a feasible strategy to explore highly active and stable electrocatalysts for sustainable H2 production.

Reactant conversion-intercalation strategy toward interlayer-expanded MoS2 microflowers with superior supercapacitor performance

In order to avoid the complicated control and fussy procedure associated with foreign species and templates in conventional synthesis strategies, a simple reactant conversion-intercalation strategy is developed to synthesize interlayer-expanded MoS₂ (E-MoS₂) by employing ammonium thiocyanate converted from a thiourea reactant as intercalator. In this strategy, the thiourea plays a bifunctionality role as reactant and intercalator precursor to ensure in situ embedding into the interlayers of MoS₂ to expand the interlayer spacing. The optimal E-MoS₂ obtained presents superior supercapacitor performance with a specific capacity of 246.8 F g^-1 at 0.5 A g^-1 in 1 M Na₂SO₄ electrolyte in a three-electrode system, outperforming pristine MoS₂ prepared by a conventional hydrothermal method (42.5 F g^-1 at 0.5 A g^-1). Furthermore, a symmetric supercapacitor based on an E-MoS₂ electrode delivers a high specific capacity of 261.3 F g^-1 and energy density of 13.3 W h kg^-1 at 0.5 A g^-1, and excellent cycling life with 81.7% capacity retention after 3000 cycles at 2 A g^-1. Density functional theory calculations reveal that the NH₄⁺ and SCN^- can be effectively adsorbed on the surface to be inserted into the interlayers during the growth of MoS₂, resulting in an expanded interlayer spacing of 9.4 Å, and the favorable electrochemical performance stems from the large Na⁺ adsorption capacitance and low diffusion barrier of the E-MoS₂. This work offers a novel intercalation strategy that may be generally applicable to other layer-structured materials, shedding some light on the development of high-performance electrode materials via interface engineering for energy applications.

Enhanced Tetracycline Adsorption of MoS2 via Defect Introduction Under Microwave Irradiation

Defect engineering is a promising method for improving the performance of MoS₂ in various fields. In this study, sulfur-defect-enriched MoS₂ (SD-MoS₂) nanosheets were fabricated via a facile microwave-hydrothermal strategy in 10 min for tetracycline (TC) adsorption applications. The introduction of sulfur defects in MoS₂ induced more exposed unsaturated sulfur atoms at the edge, enhancing the interaction between the adsorbent and antibiotic and improving the adsorption activity of the antibiotic. Density functional theory calculations further revealed that sulfur defects in MoS₂ could alter the electronic structure and exhibited low TC adsorption energy of -2.09 eV. This work provides a new method for fabricating MoS₂ nanosheets and other transition metal dichalcogenide-based adsorbents with enhanced antibiotic removal performance and a comprehensive understanding of antibiotic removal mechanisms in SD-MoS₂.

Cathodic Activation of Titania-Fly Ash Cenospheres for Efficient Electrochemical Hydrogen Production: A Proposed Solution to Treat Fly Ash Waste

Fly ash (FA) is a waste product generated in huge amounts by coal-fired electric and steam-generating plants. As a result, the use of FA alone or in conjunction with other materials is an intriguing study topic worth exploring. Herein, we used FA waste in conjunction with titanium oxide (TiO2) to create (FA-TiO2) nanocomposites. For the first time, a cathodic polarization pre-treatment regime was applied to such nanocomposites to efficiently produce hydrogen from an alkaline solution. The FA-TiO2 hybrid nanocomposites were prepared by a straightforward solvothermal approach in which the FA raw material was mixed with titanium precursor in dimethyl sulfoxide (DMSO) and refluxed during a given time. The obtained FA-TiO2 hybrid nanocomposites were fully characterized using various tools and displayed a cenosphere-like shape. The synthesized materials were tested as electrocatalysts for the hydrogen evolution reaction (HER) in 0.1 M KOH solution in the dark, employing various electrochemical techniques. The as-prepared (unactivated) FA-TiO2 exhibited a considerable HER electrocatalytic activity, with an onset potential (EHER) value of −144 mV vs. RHE, a Tafel slope (−bc) value of 124 mV dec−1 and an exchange current density (jo) of ~0.07 mA cm−2. The FA-TiO2′s HER catalytic performance was significantly enhanced upon cathodic activation (24 h of chronoamperometry measurements performed at a high cathodic potential of −1.0 V vs. RHE). The cathodically activated FA-TiO2 recorded HER electrochemical kinetic parameters of EHER = −28 mV, −bc = 115 mV dec−1, jo = 0.65 mA cm−2, and an overpotential η10 = 125 mV to yield a current density of 10 mA cm−2. Such parameters were comparable to those measured here for the commercial Pt/C under the same experimental conditions (EHER = −10 mV, −bc = 113 mV dec−1, jo = 0.88 mA cm−2, η10 = 110 mV), as well as to the most active electrocatalysts for H2 generation from aqueous alkaline electrolytes.

Electrocatalytic hydrogen generation using tripod containing pyrazolylborate-based copper(ii), nickel(ii), and iron(iii) complexes loaded on a glassy carbon electrode

Three transition metal complexes (MC) namely, [TpMeMeCuCl(H2O)] (CuC), [TpMeMeNiCl] (NiC), and [TpMeMeFeCl2(H2O)] (FeC) {TpMeMe = tris(3,5-dimethylpyrazolyl)borate} were synthesized and structurally characterized. The three complexes CuC, NiC, and FeC-modified glassy carbon (GC) were examined as molecular electrocatalysts for the hydrogen evolution reaction (HER) in alkaline solution (0.1 M KOH). Various GC-MC electrodes were prepared by loading different amounts (ca. 0.2-0.8 mg cm-2) of each metal complex on GC electrodes. These electrodes were used as cathodes in aqueous alkaline solutions (0.1 M KOH) to efficiently generate H2 employing various electrochemical techniques. The three metal complexes' HER catalytic activity was assessed using cathodic polarization studies. The charge-transfer kinetics of the HER at the (GC-MC)/OH- interface at a given overpotential were also studied using the electrochemical impedance spectroscopy (EIS) technique. The electrocatalyst's stability and long-term durability tests were performed employing cyclic voltammetry (repetitive cycling up to 5000 cycles) and 48 h of chronoamperometry measurements. The catalytic evolution of hydrogen on the three studied MC surfaces was further assessed using density functional theory (DFT) simulations. The GC-CuC catalysts revealed the highest HER electrocatalytic activity, which increased with the catalyst loading density. With a low HER onset potential (E HER) of -25 mV vs. RHE and a high exchange current density of 0.7 mA cm-2, the best performing electrocatalyst, GC-CuC (0.8 mg cm-2), showed significant HER catalytic performance. Furthermore, the best performing electrocatalyst required an overpotential value of 120 mV to generate a current density of 10 mA cm-2 and featured a Tafel slope value of -112 mV dec-1. These HER electrochemical kinetic parameters were comparable to those measured here for the commercial Pt/C under the same operating conditions (-10 mV vs. RHE, 0.88 mA cm-2, 108 mV dec-1, and 110 mV to yield a current density of 10 mA cm-2), as well as the most active molecular electrocatalysts for H2 generation from aqueous alkaline electrolytes. Density functional theory (DFT) simulations were used to investigate the nature of metal complex activities in relation to hydrogen adsorption. The molecular electrostatic surface potential (MESP) of the metal complexes was determined to assess the putative binding sites of the H atoms to the metal complex.

Active Basal Plane Catalytic Activity via Interfacial Engineering for a Finely Tunable Conducting Polymer/MoS2 Hydrogen Evolution Reaction Multilayer Structure

The fixation of the catalyst interface is an important consideration for the design of practical applications. However, the electronic structure of MoS₂ is sensitive to its embedding environment, and the catalytic performance of MoS₂ catalysts may be altered significantly by the type of binding agents and interfacial structure. Interfacial engineering is an effective method for designing efficient catalysts, arising from the close contact between different components, which facilitates charge transfer and strong electronic interactions. Here, we have developed a layer-by-layer (LbL) strategy for the preparation of interfacial MoS₂-based catalyst structures with two types of conducting polymers on various substrates. We demonstrate how the assembled partners in the LbL structure can significantly impact the electronic structures in MoS₂. As the number of bilayers grows, using polypyrrole as a binder remarkably increases the catalytic efficacy as compared to using polyaniline. On the one hand, the ratio of S₂^2- (or S^2-), which is related to the remaining active hydrogen evolution reaction (HER) species, is further increased. On the other hand, density functional theory calculations indicate that the interfacial charge transport from the conducting polymers to MoS₂ may boost the HER activity of the interfacial structure of the conducting polymer/MoS₂ by decreasing the adsorption free energy of the intermediate H* at the S sites in the basal plane of MoS₂. The optimized catalytic efficacy of the (conducting polymer/MoS₂)_n assembly peaks is obtained with 16 assembly cycles. In preparing interfacial catalytic structures, the LbL-based strategy exhibits several key advantages, including the flexibility of choosing assembly partners, the ability to fine-tune the structures with precision at the nanometer scale, and planar homogeneity at the centimeter scale. We expect that this LbL-based catalyst immobilization strategy will contribute to the fundamental understanding of the scalability and control of highly efficient electrocatalysts at the interface for practical applications.

"Lewis Base-Hungry" Amorphous-Crystalline Nickel Borate-Nickel Sulfide Heterostructures by In Situ Structural Engineering as Effective Bifunctional Electrocatalysts toward Overall Water Splitting

The development of high-performance, low-cost, and long-lasting electrocatalysts for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is urgently needed for effective electrochemical water splitting. In the present study, an engineering process was employed to prepare "Lewis base-hungry" amorphous-crystalline nickel borate-nickel sulfide (Ni₃(BO₃)₂-Ni₃S₂) heterostructures, which exhibited unprecedentedly high electrocatalytic activity toward both OER and HER in alkaline media. The optimal Ni₃(BO₃)₂-Ni₃S₂/nickel foam (Ni₃(BO₃)₂-Ni₃S₂/NF) electrode displayed an ultralow overpotential of only -92 and +217 mV to reach the current density of 10 mA cm^-2 for HER and OER, respectively. When the Ni₃(BO₃)₂-Ni₃S₂/NF electrode was used as both the anode and cathode for overall water splitting, a low cell voltage of 1.49 V was needed to achieve the current density of 10 mA cm^-2, which was superior to the performance of most noble metal-free electrocatalysts. Results from density functional theory calculations showed that the Lewis base-hungry sites in the heterostructures effectively enhanced the chemisorption of hydrogen and oxygen intermediates, a critical step in HER and OER electrocatalysis. Results from this study highlight the significance of rational design and engineering of heterostructured materials for the development of high-efficiency electrocatalysts.

Hatted 1T/2H-Phase MoS2 on Ni3 S2 Nanorods for Efficient Overall Water Splitting in Alkaline Media

A new hatted 1T/2H-phase MoS₂ on Ni₃ S₂ nanorods, as a bifunctional electrocatalyst for overall water splitting in alkaline media, is prepared through a simple one-pot hydrothermal synthesis. The hat-rod structure is composed mainly of Ni₃ S₂ , with 1T/2H-MoS₂ adhered to the top of the growth. Aqueous ammonia plays an important role in forming the 1T-phase MoS₂ by twisting the 2H-phase transition and expanding the interlayer spacing through the intercalation of NH₃ /NH₄ ⁺ . Owing to the special "hat-like" structure, the electrons conduct easily from Ni foam along Ni₃ S₂ to MoS₂ , and the catalyst particles maintain sufficient contact with the electrolyte, with gaseous molecules produced by water splitting easily removed from the surface of the catalyst. Thus, the electrocatalytic performance is enhanced, with an overpotential of 73 mV, a Tafel slope of 79 mV dec^-1 , and excellent stability, and the OER demonstrates an overpotential of 190 mV and Tafel slope of 166 mV dec^-1 .

Support interactions dictated active edge sites over MoS2-carbon composites for hydrogen evolution

The rational design and synthesis of MoS₂-based electrocatalysts with desirable active sites for the hydrogen evolution reaction have been actively pursued. Herein, we demonstrate a microwave-assisted steam heating method for the rapid and efficient synthesis of lamellar MoS₂-based materials with favorable exposed active edge sites. Based on this new strategy, we have further separately introduced reduced graphene oxide (rGO) and carbon nanotubes (CNTs), two typical carbon allotropes widely used to boost the electrocatalytic activity of MoS₂, to comparatively assess the support interactions and their effects on the electrocatalytic activity of MoS₂. It was found that as compared to rGO, the CNTs afford favorable support interactions, which not only benefit to suppress the oriented in-plane growth of MoS₂ to maximize the exposed edge sites but also ensure the maintainence of their intrinsic activity, thereby synergistically facilitating the exertion of the potential of MoS₂ for HER. Our work conceptually highlights the importance of the support interactions for taming the active edge sites of MoS₂ and is expected to inspire the rational design of layered metal dichalcogenide-based electrocatalysts with favorable active edges for HER.

Hybrid Ni3S2–MoS2 nanowire arrays as a pH-universal catalyst for accelerating the hydrogen evolution reaction

Hybrid Ni₃S₂–MoS₂ NWAs/NF obtained via a facile two-step hydrothermal route shows high catalytic performance toward hydrogen evolution in a pH-universal environment.

Recent advances in synthesis and biosensors of two-dimensional MoS2

Two-dimensional (2D) transition metal dichalcogenides (TMDCs) have attracted tremendous research interests due to their exciting optical properties, large surface area, intercalatable morphologies and excellent electrochemically catalytic activity. Acting as the most typical member in TMDCs family, layer-dependent molybdenum disulfide (MoS₂) with particular direct bandgap of 1.8 eV in monolayer has been widely applied in various biosensors with high sensitivity and selectivity. In this review, the preparation methods of MoS₂, together with MoS₂-based biosensors for detecting cells and biomolecules (such as glucose, DNA and antigens) would be summarized. In addition, the current challenges and future perspectives are outlined for the applications of biosensors based on 2D MoS₂.

S-Edge-rich MoxSy arrays vertically grown on carbon aerogels as superior bifunctional HER/OER electrocatalysts

Molybdenum disulfide (MoS₂) is a potential earth-abundant electrocatalyst for the hydrogen evolution reaction (HER), but the lack of in-depth understanding of its intrinsic activity still impedes the further optimization and design of MoS₂-based electrocatalysts. Herein, we report a facile in situ hydrothermal synthetic method to prepare vertical Mo_xS_y arrays grown on guar gum-derived carbon aerogels (GCA), termed Mo_xS_y@GCA. The obtained well-assembled Mo_xS_y@GCA architectures consist of uniform, few-layered and S-edge-rich Mo_xS_y nanoflakes with a length of approximately 100 nm, which effectively prevent the inherent stacking among Mo_xS_y layers and connect the charge transfer path between interlayers, thus endowing Mo_xS_y@GCA with a huge number of active sites and high conductivity. Benefitting from all these advantages, the optimal Mo₄S₁₆@GCA exhibited extraordinary HER/OER performances, including a low onset potential for both the HER (24.28 mV) and OER (1.53 V), and a low overpotential at 10 mA cm^-2 for the HER (54.13 mV) and OER (370 mV), which are both extremely close to that of the noble Pt/C. Furthermore, a series of operando Raman spectroscopy measurements on Mo₄S₁₆@GCA were conducted to identify the intrinsic HER/OER-active sites during the HER and OER process. The results show that the S-H bond is generated simultaneously as HER/OER excitation, indicating the rich S-edge may be the intrinsic active site, which will accelerate the HER/OER kinetic process. Density functional theory (DFT) calculations revealed that the observed superb HER/OER activity can be attributed to the synergistic effect of rich S-edge of Mo_xS_y and confinement effect of GCA, which collaboratively promote the proton adsorption and electrocatalytic kinetics. Reasonably, this study will have profound guiding value for the rational tailoring of the microstructure and size of transition metal electrocatalysts via hierarchical porous carbon aerogels.

Making Use of the δ Electrons in K4Mo2(SO4)4 for Visible-Light-Induced Photocatalytic Hydrogen Production

Quadruply bonded dimolybdenum complexes with a σ²π⁴δ² electronic configuration for the ground state have rich metal-centered photochemistry. An earlier study showed that stoichiometric or less amount of molecular hydrogen was produced upon irradiation by ultraviolet light (λ = 254 nm) of K₄Mo₂(SO₄)₄ in sulfuric acid solution, which was attributed to the reductive capability of the ππ* excited state. To make use of the δ electrons for visible-light-induced photocatalytic hydrogen evolution, a multicomponent heterogeneous photocatalytic system containing K₄Mo₂(SO₄)₄ photosensitizer, TiO₂ electron relay, and MoS₂ cocatalyst is designed and tested. With ascorbic acid added as a sacrificial reagent, irradiation by artificial sunlight (AM 1.5) on the reaction in 5 M H₂SO₄ has produced 13 400 μmol g^-1 of molecular hydrogen (based on the Mo₂ complex), which is 30 times higher than the hydrogen yield obtained from the reaction of bare K₄Mo₂(SO₄)₄ with H₂SO₄ under ultraviolet light irradiation. Further improvement of hydrogen evolution is achieved by addition of oxalic acid, along with an electron donor, which gives an additional 50% increase in H₂ yield. Spectroscopic analyses indicate that, in this case, a junction between the Mo₂ complex and TiO₂ is built by the oxalate bridging ligand, which facilitates charge injection and separation from the Mo₂ core. This Mo₂-TiO₂-MoS₂ system has achieved a high hydrogen evolution rate up to 4570 μmol g^-1 h^-1. The efficiency of K₄Mo₂(SO₄)₄ as a metal-centered photosensitizer is also proved by parallel experiments with a dye chromophore, fluorescein, which presents comparable H₂ yields and hydrogen evolution rates. Most importantly, in this study, detailed analyses illustrate that the photocatalytic cycle with hydrogen gas as an outcome of the reaction is established by involvement of the δδ* excited state generated by visible light irradiation. Therefore, this work shows the potential of quadruply bonded Mo₂ complexes as photosensitizers for photocatalytic hydrogen evolution.

Ag2S/MoS2 Nanocomposites Anchored on Reduced Graphene Oxide: Fast Interfacial Charge Transfer for Hydrogen Evolution Reaction

Hydrogen evolution reaction through electrolysis holds great potential as a clean, renewable, and sustainable energy source. Platinum-based catalysts are the most efficient to catalyze and convert water into molecular hydrogen; however, their large-scale application is prevented by scarcity and cost of Pt. In this work, we propose a new ternary composite of Ag₂S, MoS₂, and reduced graphene oxide (RGO) flakes via a one-pot synthesis. The RGO support assists the growth of two-dimensional MoS₂ nanosheets partially covered by silver sulfides as revealed by high-resolution transmission electron microscopy. Compared with the bare MoS₂ and MoS₂/RGO, the Ag₂S/MoS₂ anchored on the RGO surface (the ternary system Ag₂S/MoS₂/RGO) demonstrated a high catalytic activity toward hydrogen evolution reaction (HER). Its superior electrochemical activity toward HER is evidenced by the positively shifted (-190 mV vs reversible hydrogen electrode (RHE)) overpotential at a current density of -10 mA/cm² and a small Tafel slope (56 mV/dec) compared with a bare and binary system. The Ag₂S/MoS₂/RGO ternary catalyst at an overpotential of -200 mV demonstrated a turnover frequency equal to 0.38 s^-1. Electrochemical impedance spectroscopy was applied to understand the charge-transfer resistance; the ternary sample shows a very small charge-transfer resistance (98 Ω) at -155 mV vs RHE. Such a large improvement can be attributed to the synergistic effect resulting from the enhanced active site density of both sulfides and to the improved electrical conductivity at the interfaces between MoS₂ and Ag₂S. This ternary catalyst opens up further optimization strategies to design a stable and cheap catalyst for hydrogen evolution reaction, which holds great promise for the development of a clean energy landscape.

Molybdenum disulfide nanoflowers mediated anti-inflammation macrophage modulation for spinal cord injury treatment

Spinal cord injury (SCI) can cause locomotor dysfunctions and sensory deficits. Evidence shows that functional nanodrugs can regulate macrophage polarization and promote anti-inflammatory cytokine expression, which is feasible in SCI immunotherapeutic treatments. Molybdenum disulfide (MoS₂) nanomaterials have garnered great attention as potential carriers for therapeutic payload. Herein, we synthesize MoS₂@PEG (MoS₂ = molybdenum disulfide, PEG = poly (ethylene glycol)) nanoflowers as an effective carrier for loading etanercept (ET) to treat SCI. We characterize drug loading and release properties of MoS₂@PEG in vitro and demonstrate that ET-loading MoS₂@PEG obviously inhibits the expression of M1-related pro-inflammatory markers (TNF-α, CD86 and iNOS), while promoting M2-related anti-inflammatory markers (Agr1, CD206 and IL-10) levels. In vivo, the mouse model of SCI shows that long-circulating ET-MoS₂@PEG nanodrugs can effectively extravasate into the injured spinal cord up to 96 h after SCI, and promote macrophages towards M2 type polarization. As a result, the ET-loading MoS₂@PEG administration in mice can protect survival motor neurons, thus, reducing injured areas at central lesion sites, and significantly improving locomotor recovery. This study demonstrates the anti-inflammatory and neuroprotective activities of ET-MoS₂@PEG and promising utility of MoS₂ nanomaterial-mediated drug delivery.

Expanding the interlayers of molybdenum disulfide toward the highly sensitive sensing of hydrogen peroxide

Expandable interlayers in two-dimensional (2D) transition metal dichalcogenides enable the regulation of physicochemical properties toward boosted applications. Herein, interlayer-expanded MoS2 (IE-MoS2) was designed as a sensitive electrochemical biosensor for H2O2via a one-step hydrothermal process employing excessive thiourea. This facile fabrication successfully avoids the complicated manipulations in conventional exfoliation-resembling strategies. The as-obtained IE-MoS2 features an expanded interlayer-spacing of 9.40 Å and metallic electronic configurations. Thereby, it possesses good conductivity and more importantly enhanced binding with the *OH intermediate, accomplishing a fast kinetics of H2O2 reduction (H2O2 + 2e- → 2OH-) and consequently a sensitive response in electrochemical H2O2 sensing. The optimal IE-MoS2 affords a high sensitivity (1706.0 μA mM-1 cm-2) and a low detection limit (0.2 μM), outperforming the non-expanded MoS2 (738.0 μA mM-1 cm-2, 1.0 μM) and most of the previously reported materials free from enzymes. Moreover, it performs well in real samples and in the presence of various interfering substances and can be used to measure the intracellular H2O2 amount of cancer cells; this suggests the possible applications of IE-MoS2 in real-time monitoring, clinical diagnosis and pathophysiology. This study will inspire the rational design of 2D sensing materials via regulation of their interlayer chemistry.

A polymer-direct-intercalation strategy for MoS2/carbon-derived heteroaerogels with ultrahigh pseudocapacitance

The intercalation strategy has become crucial for 2D layered materials to achieve desirable properties, however, the intercalated guests are often limited to metal ions or small molecules. Here, we develop a simple, mild and efficient polymer-direct-intercalation strategy that different polymers (polyethyleneimine and polyethylene glycol) can directly intercalate into the MoS₂ interlayers, forming MoS²-polymer composites and interlayer-expanded MoS₂/carbon heteroaerogels after carbonization. The polymer-direct-intercalation behavior has been investigated by substantial characterizations and molecular dynamic calculations. The resulting composite heteroaerogels possess 3D conductive MoS₂/C frameworks, expanded MoS₂ interlayers (0.98 nm), high MoS₂ contents (up to 74%) and high Mo valence (+6), beneficial to fast and stable charge transport and enhanced pseudocapacitive energy storage. Consequently, the typical MoS₂/N-doped carbon heteroaerogels exhibit outstanding supercapacitor performance, such as ultrahigh capacitance, remarkable rate capability and excellent cycling stability. This study offers a new intercalation strategy which may be generally applicable to 2D materials for promising energy applications.

Methods to fabricate layered materials are often associated with harsh conditions and complicated manipulations. Here the authors report a polymer-direct-intercalation strategy to synthesize composite heteroaerogels consisting of molybdenum sulfide/carbon nanosheets for high-capacitance supercapacitors.

One-Step Low Temperature Hydrothermal Synthesis of Flexible TiO₂/PVDF@MoS₂ Core-Shell Heterostructured Fibers for Visible-Light-Driven Photocatalysis and Self-Cleaning

Novel flexible and recyclable core-shell heterostructured fibers based on cauliflower-like MoS₂ and TiO₂/PVDF fibers have been designed through one-step hydrothermal treatment based on electrospun tetrabutyl orthotitanate (TBOT)/PVDF fibers. The low hydrothermal temperature avoids the high temperature process and keeps the flexibility of the as-synthesized materials. The formation mechanism of the resultant product is discussed in detail. The composite of MoS₂ not only expands the light harvesting window to include visible light, but also increases the separation efficiency of photo-generated electrons and holes. The as-prepared product has proven to possess excellent and stable photocatalytic activity in the degradation of Rhodamine B and levofloxacin hydrochloride under visible light irradiation. In addition, the TiO₂/PVDF@MoS₂ core-shell heterostructured fibers exhibit self-cleaning property to dye droplets under visible light irradiation. Meanwhile, due to its hydrophobicity, the resultant product can automatically remove dust on its surface under the rolling condition of droplets. Hence, the as-prepared product cannot only degrade the contaminated compounds on the surface of the material, but also reduce the maintenance cost of the material due to its self-cleaning performance. Therefore, the as-prepared product possesses potential applications in degradation of organic pollutants and water treatment, which makes it a prospective material in the field of environmental treatment.

One-dimensional CoS2-MoS2 nano-flakes decorated MoO2 sub-micro-wires for synergistically enhanced hydrogen evolution

CoS2-MoS2 nanoflakes decorated MoO2 (CoMoOS) hybrid submicro-wires with rich active interfaces were synthesized via the sulfuration of CoMoO4. They showed excellent activity while synergistically catalyzing the hydrogen evolultion reaction (HER) in basic media by promoting both the water dissociation and hydrogen absorption steps. Thus, the CoMoOS catalysts only needed 123 mV to achieve 10 mA cm-2 with a small Tafel slope in alkaline solutions, and required 1.68 V to obtain the same current density when assembled into an alkaline electrolyser.

Structural Design and Electronic Modulation of Transition-Metal-Carbide Electrocatalysts toward Efficient Hydrogen Evolution

As the key of hydrogen economy, electrocatalytic hydrogen evolution reactions (HERs) depend on the availability of cost-efficient electrocatalysts. Over the past years, there is a rapid rise in noble-metal-free electrocatalysts. Among them, transition metal carbides (TMCs) are highlighted due to their structural and electronic merits, e.g., high conductivity, metallic band states, tunable surface/bulk architectures, etc. Herein, representative efforts and progress made on TMCs are comprehensively reviewed, focusing on the noble-metal-like electronic configuration and the relevant structural/electronic modulation. Briefly, specific nanostructures and carbon-based hybrids are introduced to increase active-site abundance and to promote mass transportation, and heteroatom doping and heterointerface engineering are encouraged to optimize the chemical configurations of active sites toward intrinsically boosted HER kinetics. Finally, a perspective on the future development of TMC electrocatalysts is offered. The overall aim is to shed some light on the exploration of emerging materials in energy chemistry.

Controlled synthesis of bifunctional particle-like Mo/Mn-NixSy/NF electrocatalyst for highly efficient overall water splitting

Mo/Mn-Ni_xS_y/NF catalyst was successfully synthesized and exhibited excellent catalytic activities and long-term durability.

Synergetic photocatalytic effect between 1 T@2H-MoS2 and plasmon resonance induced by Ag quantum dots

Semiconductor phase transitions and plasma noble metal quantum dots (QDs) for visible-light-driven photocatalysts have attracted significant research interest. In this study, novel microwave hydrothermal and photo-reduction methods are proposed to synthesise a visible-light-driven plasma photocatalytic 1T@2H-MoS₂/Ag composite. Photoelectrochemical results show that the introduction of the 1T phase and Ag significantly enhances the light response range and charge separation. The 1T phase can act as a co-catalyst to provide a high electron concentration. Ag QDs can effectively improve the light absorption and catalytic effect. The synergistic effect between the 1T@2H-MoS₂ microspheres and localised surface plasmon resonance of the Ag QDs can effectively enhance the photocatalytic activity of 1T@2H-MoS₂/Ag. The developed 1T@2H-MoS₂/Ag composite is superior, not only with respect to a visible-light photocatalytic degradation of conventional dyes, but also in the photocatalytic reduction of Cr(VI). Compared with 2H-MoS₂, the catalytic efficiency of 1T@2H-MoS₂/Ag for Cr(VI) and MB is increased by 81% and 41%, respectively. This study demonstrates that the introduction of 1T-MoS₂ and Ag QDs can significantly enhance the catalytic properties of 2H-MoS₂. The microwave and photo-reduction technologies can be employed as green, safe, simple, and rapid methods for the synthesis of noble metal plasma composites.

MoS2 nanosheets with peroxidase mimicking activity as viable dual-mode optical probes for determination and imaging of intracellular hydrogen peroxide

The authors describe a dual-mode (colorimetric-fluorometric) nanoprobe for H₂O₂ that was fabricated by covering molybdenum disulfide nanosheets (MoS₂ NS) with ortho-phenylenediamine (OPD). The probe (OPD-MoS₂ NS) was applied to the optical determination of H₂O₂, to the quantitation of cell numbers, and to the detection of intracellular concentrations of H₂O₂. Oxidation by H₂O₂ leads to a colored and fluorescent product (oxidized OPD) with absorption/excitation/fluorescence peaks at 450/450/557 nm. The nanoprobe can detect H₂O₂ in down to 500 nM concentrations, and HeLa cells at levels of 100 cells mL^-1. The detection limit for intracellular H₂O₂ is in the 5.5 to 12.6 μM concentration range when the method is applied to cells at levels of 10²-10⁶ cells mL^-1. Due to its good biocompatibility and easy cell uptake, the nanoprobe also permits sensitive fluorometric imaging of intracellular H₂O₂. It can also comparatively discriminate the change of intracellular oxidation state in living cancerous and normal cells. Graphical abstract Editor, we provided image with high resolution. Please find it in a folder name "MIAC-D-18-00081" in the FTP site. A dual-mode (colorimetric-fluorometric) detection nanoplatform based on OPD-modified MoS₂ nanosheets is used to quantitatively detect H₂O₂, cell numbers and intracellular H₂O₂. The MoS₂ nanoprobes also permit sensitive fluorescence imaging of intracellular H₂O₂, and can discriminate intracellular oxide states in living cancerous and normal cells.

Structure-enhanced removal of Cr(vi) in aqueous solutions using MoS2 ultrathin nanosheets

Molybdenum disulfide (MoS₂) ultrathin nanosheets with enlarged interlayer spacing and defects enables the structure-enhanced removal of Cr(vi), in which the synergistic effects of adsorption and reduction not only captured Cr(vi) from aqueous solutions, but also alleviated the toxicity of chromium to some degree.

Controlled preparation of high quality WS2 nanostructures by a microwave-assisted solvothermal method

WS₂ nanomaterials including nanosheets, nanocones and nanoworms were successfully synthesized by a facile and efficient microwave-assisted solvothermal method.

Hydrothermal synthesis of ternary MoS2xSe2(1−x) nanosheets for electrocatalytic hydrogen evolution

MoS_2xSe_2(1−x) nanosheets exhibit promising electrocatalytic hydrogen evolution activity in acidic media.

Ultradispersed and Single-Layered MoS2 Nanoflakes Strongly Coupled with Graphene: An Optimized Structure with High Kinetics for the Hydrogen Evolution Reaction

As one of the most promising Pt alternatives for cost-effective hydrogen production, molybdenum disulfide (MoS₂), although has been studied extensively to improve its electrocatalytic activity, suffers from scarce active sites, low conductivity, and lack of interaction with substrates. To this end, we anchor ultradispersed and single-layered MoS₂ nanoflakes on graphene sheets via a hybrid intermediate (MoO_x-cysteine-graphene oxide), which not only confines the subsequent growth of MoS₂ on the graphene surface but also ensures the intimate interaction between Mo species and graphene at the initial stage. Mo-O-C bond and a possible residual MoO_3-x layer are proposed to comprise the interface bridging the two inherent incompatible phases, MoS₂ and graphene. This strongly coupled structure together with the highly exposed MoS₂ morphology accelerates the electron injection from graphene to the active sites of MoS₂, and thus the hydrogen evolution reaction (HER) can achieve an overpotential of ∼275 mV at ∼-740 mA cm^-2, and a Pt-like Tafel slope of ∼35 mV dec^-1. Our results shed light on the indispensable role of interfacial interaction within semiconducting material-nanocarbon composites and provide a new insight into the actual activity of MoS₂ toward the HER.

Electrospinning Hetero-Nanofibers of Fe3 C-Mo2 C/Nitrogen-Doped-Carbon as Efficient Electrocatalysts for Hydrogen Evolution

Heterostructured electrocatalysts with multiple active components are expected to synchronously address the two elementary steps in the hydrogen evolution reaction (HER), which require varied hydrogen-binding strength on the catalyst surface. Herein, electrospinning followed by a pyrolysis is introduced to design Fe₃ C-Mo₂ C/nitrogen-doped carbon (Fe₃ C-Mo₂ C/NC) hetero-nanofibers (HNFs) with tunable composition, leading to abundant Fe₃ C-Mo₂ C hetero-interfaces for synergy in electrocatalysis. Owing to the strong hydrogen binding on Mo₂ C and the relatively weak one on Fe₃ C, the hetero-interfaces of Fe₃ C-Mo₂ C remarkably promote HER kinetics and intrinsic activity. Additionally, the loose and porous N-doped carbon matrix, as a result of Fe-catalyzed carbonization, ensures the fast transport of electrolytes and electrons, thus minimizing diffusion limitation. As expected, the optimized Fe₃ C-Mo₂ C/NC HNFs afforded a low overpotential of 116 mV at a current density of -10 mA cm^-2 and striking kinetics metrics (onset overpotential: 42 mV, Tafel slope: 43 mV dec^-1 ) in 0.5 m H₂ SO₄ , outperforming most recently reported noble-metal-free electrocatalysts.

Hierarchically Porous Electrocatalyst with Vertically Aligned Defect-Rich CoMoS Nanosheets for the Hydrogen Evolution Reaction in an Alkaline Medium

Effective electrocatalysts for the hydrogen evolution reaction (HER) in alkaline electrolytes can be developed via a simple solvothermal process. In this work, first, the prepared CoMoS nanomaterials through solvothermal treatment have a porous, defect-rich, and vertically aligned nanostructure, which is beneficial for the HER in an alkaline medium. Second, electron transfer from cobalt to MoS₂ that reduces the unoccupied d orbitals of molybdenum can also enhance the HER kinetics in an alkaline medium. This has been demonstrated via a comparison of the catalytic performances of CoMoS, CoS, and MoS₂. Third, the solvothermal treatment time evidently impacts the electrocatalytic activity. As a result, after 24 h of solvothermal treatment, the prepared CoMoS nanomaterials exhibit the lowest onset potential (42 mV) and overpotential (98 mV) for delivering a current density of 10 mA cm^-2 in a 1 M KOH solution. Thus, this study provides a simple method to prepare efficient electrocatalysts for the HER in an alkaline medium.

Efficient electrochemical detection of cancer cells on in situ surface-functionalized MoS2nanosheets

In situsurface functionalization by reactant molecules (thiourea) is feasible to engineer MoS₂surfaces with rich amino groups, leading to facile antigen immobilization and thus selective recognition of cancer cells.

Solvent-Assisted Oxygen Incorporation of Vertically Aligned MoS2 Ultrathin Nanosheets Decorated on Reduced Graphene Oxide for Improved Electrocatalytic Hydrogen Evolution

Three-dimensional oxygen-incorporated MoS2 ultrathin nanosheets decorated on reduced graphene oxide (O-MoS2/rGO) had been successfully fabricated through a facile solvent-assisted hydrothermal method. The origin of the incorporated oxygen and its incorporation mechanism into MoS2 were carefully investigated. We found that the solvent N,N-dimethylformamide (DMF) was the key as the reducing agent and the oxygen donor, expanding interlayer spaces and improving intrinsic conductivity of MoS2 sheets (modulating its electronic structure and vertical edge sites). These O dopants, vertically aligned edges and decoration with rGO gave effectively improved double-layer capacitance and catalytic performance for hydrogen evolution reaction (HER) of MoS2. The prepared O-MoS2/rGO catalysts showed an exceptional small Tafel slope of 40 mV/decade, a high current density of 20 mA/cm(2) at the overpotential of 200 mV and remarkable stability even after 2000th continuous HER test in the acid media.

Heteronanowires of MoC-Mo2C as efficient electrocatalysts for hydrogen evolution reaction

MoC–Mo₂C heteronanowires accomplished via controlled carbonization are efficient in the hydrogen evolution reaction due to a synergistic enhancement.

Exploring efficient noble-metal free electrocatalysts for the hydrogen evolution reaction (HER) is one of the most promising pathways for facing the energy crisis. Herein, MoC–Mo₂C heteronanowires composed of well-defined nanoparticles were accomplished via controlled carbonization, showing excellent HER activity, fast kinetic metrics and outstanding stability in both acid and basic electrolytes. In particular, the optimal one consisting of 31.4 wt% MoC displayed a low overpotential (η₁₀ = 126 and 120 mV for reaching a current density of –10 mA cm^–2), a small Tafel slope (43 and 42 mV dec^–1) and a low onset overpotential (38 and 33 mV) in 0.5 M H₂SO₄ and 1.0 M KOH, respectively. Such prominent performance, outperforming most of the current noble-metal free electrocatalysts, was ascribed to the carbide surface with an optimized electron density, and the consequently facilitated HER kinetics. This work elucidates a feasible way toward efficient electrocatalysts via heteronanostructure engineering, shedding some light on the exploration and optimization of catalysts in energy chemistry.

Vertically aligned oxygen-doped molybdenum disulfide nanosheets grown on carbon cloth realizing robust hydrogen evolution reaction

A synergistically optimized oxygen-incorporated MoS₂/carbon cloth hybrid catalyst was successfully fabricated, realizing enhanced hydrogen-evolving activity and superior stability.

Colloidal synthesis of VSe2single-layer nanosheets as novel electrocatalysts for the hydrogen evolution reaction

We present a one-pot colloidal route to synthesize VSe₂, a new type of metallic single-layer nanosheet.