Self-Templated Growth of Vertically Aligned 2H-1T MoS2 for Efficient Electrocatalytic Hydrogen Evolution

Crystalline Phase Regulates Microbial Methylation Potential of Mercury Bound to MoS2 Nanosheets: Implications for Safe Design of Mercury Removal Materials

Transition-metal dichalcogenides (TMDs) have shown great promise as selective and high-capacity sorbents for Hg(II) removal from water. Yet, their design should consider safe disposal of spent materials, particularly the subsequent formation of methylmercury (MeHg), a highly potent and bioaccumulative neurotoxin. Here, we show that microbial methylation of mercury bound to MoS2 nanosheets (a representative TMD material) is significant under anoxic conditions commonly encountered in landfills. Notably, the methylation potential is highly dependent on the phase compositions of MoS2. MeHg production was higher for 1T MoS2, as mercury bound to this phase primarily exists as surface complexes that are available for ligand exchange. In comparison, mercury on 2H MoS2 occurs largely in the form of precipitates, particularly monovalent mercury minerals (e.g., Hg2MoO4 and Hg2SO4) that are minimally bioavailable. Thus, even though 1T MoS2 is more effective in Hg(II) removal from aqueous solution due to its higher adsorption affinity and reductive ability, it poses a higher risk of MeHg formation after landfill disposal. These findings highlight the critical role of nanoscale surfaces in enriching heavy metals and subsequently regulating their bioavailability and risks and shed light on the safe design of heavy metal sorbent materials through surface structural modulation.

3D Fast Sodium Transport Network of MoS2 Endowed by Coupling of Sulfur Vacancies and Sn Doping for Outstanding Sodium Storage

A sulfur vacancy-rich, Sn-doped as well as carbon-coated MoS2 composite (Vs-SMS@C) is rationally synthesized via a simple hydrothermal method combined with ball-milling reduction, which enhances the sodium storage performance. Benefiting from the 3D fast Na+ transport network composed of the defective carbon coating, Mo─S─C bonds, enlarged interlayer spacing, S-vacancies, and lattice distortion in the composite, the Na+ storage kinetics is significantly accelerated. As expected, Vs-SMS@C releases an ultrahigh reversible capacity of 1089 mAh g-1 at 0.1 A g-1, higher than the theoretical capacity. It delivers a satisfactory capacity of 463 mAh g-1 at a high current density of 10 A g-1, which is the state-of-the-art rate capability compared to other MoS2 based sodium ion battery anodes to the knowledge. Moreover, a super long-term cycle stability is achieved by Vs-SMS@C, which keeps 91.6% of the initial capacity after 3000 cycles under the current density of 5 A g-1 in the voltage of 0.3-3.0 V. The sodium storage mechanism of Vs-SMS@C is investigated by employing electrochemical methods and ex situ techniques. The synergistic effect between S-vacancies and doped-Sn is evidenced by DFT calculations. This work opens new ideas for seeking excellent metal sulfide anodes.

Phase Engineering of W-Doped MoS2 by Magneto-Hydrothermal Synthesis for Hydrogen Evolution Reaction

Molybdenum disulfide (MoS2 ) has been proved as an excellent potential hydrogen evolution reaction (HER) catalyst. Compared with thermodynamically stable 2H-MoS2 , 1T-MoS2 exhibits higher conductivity and catalytic activity, whereas it is usually difficult to prepare since of thermodynamically metastable. Herein, a feasible method is reported to fabricate ambient-stable MoS2 with high concentration 1T phase through magnetic free energy synergistic microstrain induced by W doping under low magnetic field. The 1T phase proportion in MoS2 can be as high as 80% and is ambient-stable for more than one year. The catalyst prepared under a magnetic field of 3 T delivers an overpotential of 195 mV at a current density of 10 mA cm-2 and has a long-term stability over 50 h. This work provides a novel strategy for preparation of MoS2 with high 1T concentration and high stability.

Ex Situ Characterization of 1T/2H MoS2 and Their Carbon Composites for Energy Applications, a Review

The growing interest in the development of next-generation net zero energy systems has led to the expansion of molybdenum disulfide (MoS₂) research in this area. This activity has resulted in a wide range of manufacturing/synthesis methods, controllable morphologies, diverse carbonaceous composite structures, a multitude of applicable characterization techniques, and multiple energy applications for MoS₂. To assess the literature trends, 37,347 MoS₂ research articles from Web of Science were text scanned to classify articles according to energy application research and characterization techniques employed. Within the review, characterization techniques are grouped under the following categories: morphology, crystal structure, composition, and chemistry. The most common characterization techniques identified through text scanning are recommended as the base fingerprint for MoS₂ samples. These include: scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Similarly, XPS and Raman spectroscopy are suggested for 2H or 1T MoS₂ phase confirmation. We provide guidance on the collection and presentation of MoS₂ characterization data. This includes how to effectively combine multiple characterization techniques, considering the sample area probed by each technique and their statistical significance, and the benefit of using reference samples. For ease of access for future experimental comparison, key numeric MoS₂ characterization values are tabulated and major literature discrepancies or currently debated characterization disputes are highlighted.

Two-dimensional metal-phase layered molybdenum disulfide for electrocatalytic hydrogen evolution reaction

The two-dimensional (2D) basal plane of metal-phase molybdenum disulphide (1T-MoS₂) provides a large area of active sites to significantly reduce the overpotential of the hydrogen evolution reaction (HER), but the long preparation period limits its industrial application. Here, 1T-MoS₂ catalysts derived from molybdenum blue solution (MBS) were prepared in one step using a rapid high-pressure microwave (MW-MoS₂) strategy. This method eliminated the thermodynamic process with a long time required for Mo-O trioxide bond breakage and reduction (Mo^VI → Mo^IV) of the conventional hydrothermal method. Additionally, the introduction of heteroatomic oxygen atoms effectively reduced the build-up of MW-MoS₂ and improved the monolayer/few-layer state and stability. Impressively, MW-MoS₂ has outstanding electrocatalytic performance, with a low overpotential (62 mV) at 10 mA cm^-2 and a small Tafel slope (42 mV dec^-1). This provides a simple strategy for the rapid preparation of a 2D sulphide HER catalyst with performance close to that of commercial Pt/C.

Boosting Highly Active Exposed Mo Atoms by Fine-Tuning S-Vacancies of MoS2-Based Materials for Efficient Hydrogen Evolution

Guided by the theoretical calculation, achieving an efficient hydrogen evolution reaction (HER) by S-vacancy engineering toward MoS₂-based materials is quite challenging due to the contradictory relationship between the adsorption free energy of hydrogen atoms (ΔG_H) of the exposed Mo atoms (EMAs) and the number of EMAs per unit area (N_EMAs). Herein, we demonstrate a novel one-pot incorporating-assisted compositing strategy to realize fine-tuning the concentration of S-vacancies (C_S-vacancies) of MoS₂-based materials to boost highly active EMAs for efficient HER. In our strategy, S-vacancies are modulated into basal planes of MoS₂ via decreasing the formation energy of S-vacancies by oxygen incorporation; moreover, C_S-vacancies of the basal planes is precisely regulated by simply controlling the molar amount of the Co precursor based on the electron injection effect. At low or excessively high C_S-vacancies, the as-synthesized electrocatalysts lack "highly active EMAs" in quantity or nature. The balance between the intrinsic activity of EMAs and N_EMAs is realized for boosting EMAs with high catalytic performance. The optimal electrocatalysts exhibit excellent activity and stability at fine-tuning C_S-vacancies to 9.61%. Our results will pave a novel strategy for unlocking the potential of an inert basal plane in MoS₂ for high-performance HER.

Transition Metal Dichalcogenides [MX2] in Photocatalytic Water Splitting

The quest for a clean, renewable and sustainable energy future has been highly sought for by the scientific community over the last four decades. Photocatalytic water splitting is a very promising technology to proffer a solution to present day environmental pollution and energy crises by generating hydrogen fuel through a “green route” without environmental pollution. Transition metal dichalcogenides (TMDCs) have outstanding properties which make them show great potential as effective co-catalysts with photocatalytic materials such as TiO2, ZnO and CdS for photocatalytic water splitting. Integration of TMDCs with a photocatalyst such as TiO2 provides novel nanohybrid composite materials with outstanding characteristics. In this review, we present the current state of research in the application of TMDCs in photocatalytic water splitting. Three main aspects which consider their properties, advances in the synthesis routes of layered TMDCs and their composites as well as their photocatalytic performances in the water splitting reaction are discussed. Finally, we raise some challenges and perspectives in their future application as materials for water-splitting photocatalysts.

2-Dimensional layered molybdenum disulfide nanosheets and CTAB-assisted molybdenum disulfide nanoflower for high performance supercapacitor application

In this study, the supercapacitor performance of the hydrothermal synthesized molybdenum disulfide (MoS₂) nanosheets and the cetyltrimethylammonium bromide (CTAB)-assisted MoS₂ nanoflower morphology have been investigated. The as-synthesized MoS₂ nanoflower and nanosheet morphology structures were investigated via field emission scanning electron microscopy (FESEM), and the internal microstructure was examined via high resolution-transmission electron microscopy (HR-TEM) technique. The Fourier transform infrared (FT-IR) spectra were obtained to identify the chemical interaction and the functional groups present in the material. The shifting of the binding energy, oxidation states, and elemental identification were conducted by X-ray photon spectroscopy (XPS). The MoS₂ nanoflower possesses surface defects, which produce numerous active sites. The MoS₂ nanoflower and nanosheet electrodes demonstrate the high specific capacitance (C _sp) values of 516 F g^-1 and 438 F g^-1, respectively, at a current density of 1 A g^-1. However, the MoS₂ nanoflower shows high C _sp due to the large surface area with active edges, making them store more energy in the electrode.

Role of topological surface states and mirror symmetry in topological crystalline insulator SnTe as an efficient electrocatalyst

The surface orientation dependence on the hydrogen evolution reaction (HER) performance of topological crystalline insulator (TCI) SnTe thin films is studied. Their intrinsic activities are determined by linear sweep voltammetry and cyclic voltammetry measurements. It is found that SnTe (001) and (111) surfaces exhibit intrinsic activities significantly larger than the (211) surface. Density functional theory calculations reveal that pure (001) and (111) surfaces are not good electrocatalysts, while those with Sn vacancies or partially oxidized surfaces, with the latter as evidenced by X-ray photoelectron spectroscopy, have high activity. The calculated overall performance of the (001) and (111) surfaces with robust topological surface states (TSSs) is better than that of the lowly symmetric (211) surface with fragile or without TSSs, which is further supported by their measured weak antilocalization strength. The high HER activity of SnTe (001) and (111) is attributed to the enhanced charge transfer between H atoms and TSSs. We also address the effect of possible surface facets and the contrast of the HER activity of the available active sites among the three samples. Our study demonstrates that the TSSs and mirror symmetry of TCIs expedite their HER activity.

Flower-like 1T-MoS2/NiCo2S4 on a carbon cloth substrate as an efficient electrocatalyst for the hydrogen evolution reaction

The 1T-MoS₂/NiCo₂S₄ composite in situ grown on carbon cloth (CC) was successfully prepared by a two-step hydrothermal method as an efficient electrode for the hydrogen evolution reaction. The morphology and composition characterization show that the composite has a flower-like structure with a large number of edges and surfaces exposed, and the content of the 1T phase in MoS₂ is 63%. 1T-MoS₂/NiCo₂S₄/CC exhibits an overpotential of 107 mV at 10 mA cm^-2, and a Tafel slope of 66.4 mV dec^-1 in an alkaline electrolyte. After continuous electrolysis for 24 h at an overpotential of 170 mV, 86% of the original current density was retained in an chronoamperometry measurement. The outstanding catalytic performance of the composite is ascribed to its unique structure, high 1T-MoS₂ content and the synergistic catalysis between 1T-MoS₂ and NiCo₂S₄. This work provides a facile and effective strategy for fabricating the 1T-MoS₂/NiCo₂S₄/CC composite and demonstrates that the composite is expected to be a competitive non-noble HER catalyst.

A Review on MoS2 Energy Applications: Recent Developments and Challenges

Molybdenum disulfide (MoS2) is a promising transition metal dichalcogenide (TMD) that has exceptional electronic, magnetic, optical, and mechanical properties. It can be semiconducting, superconducting, or an insulator according to its polymorph. Its bandgap structure changes from indirect to direct when moving towards its nanostructures, which opens a door to bandgap engineering for MoS2. Its supercapacitive and catalytic activity was recently noticed and studied, in order to include this material in a wide range of energy applications. In this work, we present MoS2 as a future material for energy storage and generation applications, especially solar cells, which are a cornerstone for a clean and abundant source of energy. Its role in water splitting reactions can be utilized for energy generation (hydrogen evolution) and water treatment at the same time. Although MoS2 seems to be a breakthrough in the energy field, it still faces some challenges regarding its structure stability, production scalability, and manufacturing costs.

Construction of 2D/2D MoS2/g-C3N4 Heterostructures for Photoreduction of Cr (VI)

2D/2D MoS₂/g-C₃N₄ (MCN) surface heterostructures were created by second thermal polymerization of bulk g-C₃N₄ and the reaction of thiourea and MoO₃ at 670 °C. MoS₂ networks grew vertically along the (002) facet on superior thin g-C₃N₄ nanosheets. The layered heterostructures drastically improved the Cr(VI) removal ability. In the dark case, 27% of Cr(VI) was removed within 45 min. The result indicates that the adsorption of Cr(VI) was a chemical adsorption process involving the sharing and transfer of electrons. The equilibrium data indicate that the adsorbent was covered with a monolayer adsorbate, which conformed to the Langmuir isotherm model (R² = 0.9618). In addition, MCN nanocomposites could convert Cr(VI) into non-toxic Cr(III) by photoreduction under visible light irradiation. With an optimized composition, 100% of Cr(VI) was removed within 30 min, which was ∼10 times quicker compared with Cr(VI) removal under dark conditions. Because g-C₃N₄ nanosheets (sample CN₆₇₀) with higher photocurrent density revealed the lowest photoreduction Cr(VI) ability, adsorption plays an important role in Cr(VI) removal. For MoS₂/g-C₃N₄ nanocomposites used in Cr(VI) removal, adsorption and photoreduction were incorporated together to get excellent performance.

Controlling 1T/2H heterophase junctions in the MoS2 microsphere for the highly efficient photocatalytic hydrogen evolution

The 1T/2H heterophase junction MoS2 microspheres were fabricated for a highly efficient photocatalytic hydrogen evolution.

One-pot synthesis of hierarchical Co1-xS/NC@MoS2/C hollow nanofibers based on one-dimensional metal coordination polymers for enhanced lithium and sodium-ion storage

Multicomponent metal sulfides have been recognized as promising anode materials for lithium/sodium-ion storage given their enticing theoretical capacities. However, the simplification of synthetic processes and the construction of heterogeneous interfaces of multimetal sulfides remain great challenges. Herein, a hierarchical 1T-MoS₂/carbon nanosheet decorated Co_1-xS/N-doped carbon (Co_1-xS/NC@MoS₂/C) hollow nanofiber was designed and constructed via a one-pot hydrothermal method using a cobalt-based coordination polymer nanofiber. This nanofiber can transform in-situ into conductive N-doped carbon hollow fibers embedded with active Co_1-xS nanoparticles, enabling the epitaxial growth of MoS₂ nanosheets. Consequently, the Co_1-xS/NC@MoS₂/C composites achieve exceptional lithium/sodium-ion storage performance. Compared to MoS₂/C microspheres and Co_1-xS/NC hollow nanofibers alone, the Co_1-xS/NC@MoS₂/C hollow nanofibers deliver higher discharge capacities (1085.9 mAh g^-1 for lithium-ion batteries (LIBs) and 748.5 mAh g^-1 for sodium-ion batteries (SIBs) at 100 mA g^-1), better capacity retention (910 mAh g^-1 for LIBs and 636.5 mAh g^-1 for SIBs after 150 cycles at 100 mA g^-1), and increased cycling stability (407.2 mAh g^-1 after 1000 cycles for SIBs at 1000 mA g^-1). Furthermore, the kinetic analysis shows that the lithium/sodium-ion storage processes of the Co_1-xS/NC@MoS₂/C electrode are mainly controlled by pseudocapacitance behavior. The excellent electrochemical properties can thus be ascribed to the synergy of the MoS₂/C nanosheets with the enlarged interlayer spacing, good conductivity of the carbon layers, and the Co_1-xS nanoparticles embedded in the hollow nanofibers with extensive reaction sites.

Hybrid phase 1T/2H-MoS2 with controllable 1T concentration and its promoted hydrogen evolution reaction

MoS2 has been investigated as a low-cost alternative to Pt in the electrochemical hydrogen evolution reaction. One of the promising methods to further activate MoS2 is phase engineering. MoS2 generally exhibits two kinds of crystalline phases: hexagonal 2H phase and octahedral 1T phase. 1T-MoS2 exhibits much better chemical/physical properties than natural semiconductor 2H-MoS2. However, 1T-MoS2 is metastable and its synthesis is still a challenge. Hybrid 1T/2H-MoS2 has been synthesized under relatively mild conditions, but controlling the 1T/2H ratio is still an issue which has not been discussed in detail. In this study, the synthesis methods of hybrid phase 1T/2H-MoS2 with controllable 1T concentration are investigated. The electrochemical hydrogen evolution reaction is then evaluated for 1T/2H-MoS2 with different 1T concentrations by performing both experiments and theoretical calculations.

Investigating the Redox Properties of Two-Dimensional MoS2 Using Photoluminescence Spectroelectrochemistry and Scanning Electrochemical Cell Microscopy

Control over photophysical and chemical properties of two-dimensional (2D) transition metal dichalcogenides (TMDs) is the key to advance their applications in next-generation optoelectronics. Although chemical doping and surface modification with plasmonic metals have been reported to tune the photophysical and catalytic properties of 2D TMDs, there have been few reports of tuning optical properties using dynamic electrochemical control of electrode potential. Herein, we report (1) the photoluminescence (PL) enhancement and red-shift in the PL spectrum of 2D MoS₂, synthesized by chemical vapor deposition and subsequent transfer onto an indium tin oxide electrode, upon electrochemical anodization and (2) spatial heterogeneities in its photoelectrochemical (PEC) activities. Spectroelectrochemistry shows that positive electrochemical bias causes an initial ten-fold increase in the PL intensity followed by a quick decrease in the enhancement. The PL enhancement and spectrum red-shift are associated with the decrease in nonradiative decay rates of excitons formed upon electrochemical anodization of 2D MoS₂. Additionally, scanning electrochemical cell microscopy (SECCM) study shows that the 2D MoS₂ crystal is spatially sensitive to PEC oxidation at positive potentials. SECCM also shows a photocurrent increase caused by spatially heterogeneous edge-type defect sites of the crystal.

Structural-Phase Catalytic Redox Reactions in Energy and Environmental Applications

The structure-property engineering of phase-based materials for redox-reactive energy conversion and environmental decontamination nanosystems, which are crucial for achieving feasible and sustainable energy and environment treatment technology, is discussed. An exhaustive overview of redox reaction processes, including electrocatalysis, photocatalysis, and photoelectrocatalysis, is given. Through examples of applications of these redox reactions, how structural phase engineering (SPE) strategies can influence the catalytic activity, selectivity, and stability is constructively reviewed and discussed. As observed, to date, much progress has been made in SPE to improve catalytic redox reactions. However, a number of highly intriguing, unresolved issues remain to be discussed, including solar photon-to-exciton conversion efficiency, exciton dissociation into active reductive/oxidative electrons/holes, dual- and multiphase junctions, selective adsorption/desorption, performance stability, sustainability, etc. To conclude, key challenges and prospects with SPE-assisted redox reaction systems are highlighted, where further development for the advanced engineering of phase-based materials will accelerate the sustainable (active, reliable, and scalable) production of valuable chemicals and energy, as well as facilitate environmental treatment.

Ni2P/rGO/NF Nanosheets As a Bifunctional High-Performance Electrocatalyst for Water Splitting

The hydrogen generated via the water splitting method is restricted by the high level of theoretical potential exhibited by the anode. The work focuses on synthesizing a bifunctional catalyst with a high efficiency, that is, a nickel phosphide doped with the reduced graphene oxide nanosheets supported on the Ni foam (Ni₂P/rGO/NF), via the hydrothermal approach together with the calcination approach specific to the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). The Raman, X-Ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), Transmission Electron Microscope (TEM), Scanning Electron Microscopy (SEM), High-Resolution Transmission Electron Microscopy (HRTEM), as well as elemental mapping, are adopted to study the composition and morphology possessed by Ni₂P/rGO/NF. The electrochemical testing is performed by constructing a parallel two-electrode electrolyzer (Ni₂P/rGO/NF||Ni₂P/rGO/NF). Ni₂P/rGO/NF||Ni₂P/rGO/NF needs a voltage of only 1.676 V for driving 10 mA/cm², which is extremely close to Pt/C/NF||IrO₂/NF (1.502 V). It is possible to maintain the current density for no less than 30 hours. It can be demonstrated that Ni₂P/rGO/NF||Ni₂P/rGO/NF has commercial feasibility, relying on the strong activity and high stability.

Different phases of few-layer MoS2 and their silver/gold nanocomposites for efficient hydrogen evolution reaction

Three different 1T phase contents of MoS₂ were synthesized; the electrocatalytic performances of their silver/gold nanocomposites toward the HER were investigated.

Unveiling the Origin of the High Catalytic Activity of Ultrathin 1T/2H MoSe2 Nanosheets for the Hydrogen Evolution Reaction: A Combined Experimental and Theoretical Study

2 D transition metal dichalcogenide materials with layered nanostructures and specific phases usually exhibit excellent catalytic activities for the hydrogen evolution reaction (HER). A facile solvothermal process was used to prepare ultrathin noble-metal-free 2 D biphasic MoSe₂ nanosheets composed of a metastable metallic 1T phase and a semiconducting 2H phase. High metallic 1T phase content and few-layer-thick MoSe₂ nanosheets were obtained by tuning the amount of NaBH₄ used in the reaction. The optimal integration of a metallic 1T phase and an environmentally stable 2H phase in MoSe₂ electrocatalysts provides abundant active sites and good conductivity beneficial for the HER. The combination of experimental results and DFT calculations implies that the electrocatalytic activity for the HER on the MoSe₂ surface goes through a collaborative Heyrovsky and Volmer reaction process. The theoretical studies suggest that the presence of 1T-MoSe₂ could reduce the band energy relative to 2H-MoSe₂ and, consequently, accelerate the sluggish HER kinetics of 2H-MoSe₂ . This work provides valuable and novel insights into the understanding of the structure-activity relationships in 2 D transition metal dichalcogenide electrocatalysts.

Vertically aligned MoS2 nanosheets on graphene for highly stable electrocatalytic hydrogen evolution reactions

Conducting an efficient hydrogen evolution reaction (HER) using two-dimensional molybdenum disulphide as electrocatalysts remains a challenging task due to the insufficient active edge sites. In this regard, herein, molybdenum disulphide nanosheets with rich active sulphur sites were vertically grown on the graphene surface via a chemical vapour deposition process. The direct integration of vertically aligned MoS2 nanosheets on graphene forms a van der Waals (vdW) heterojunction, which facilitates a barrier-free charge transport towards the electrolyte as a result of unique and well-matched energy band alignment at the interface. The prospective combination of Ohmic graphene/MoS2 heterostructure and the high electrocatalytic edge activity of sulphur delivers an incredibly and small turn-on potential of 0.14 V vs. RHE in the acid electrolyte solution. Most importantly, the use of a vertical vdW device architecture exhibits nearly 8× improvement in HER than that of its layered counterpart. Moreover, the HER reaction is highly stable over 50 hours of continuous operation even after 150 days. The combined analysis of our study makes it certain that the graphene/MoS2 heterostructure will be an efficient alternative electrode for low-cost and large-scale electrochemical applications.

Graphene/graphene nanoribbon aerogels decorated with S-doped MoSe2 nanosheets as an efficient electrocatalyst for hydrogen evolution

Graphene/graphene nanoribbon (GGNR) aerogels facilitate fast electron and ion transfer while S-doping improves the activity of catalytic sites for efficient hydrogen evolution.

Novel Cobalt-Doped Ni0.85Se Chalcogenides (Co xNi0.85- xSe) as High Active and Stable Electrocatalysts for Hydrogen Evolution Reaction in Electrolysis Water Splitting

In this paper, novel cobalt-doped Ni_0.85Se chalcogenides (Co _xNi_{0.85- x}Se, x = 0.05, 0.1, 0.2, 0.3, and 0.4) are successfully synthesized and studied as high active and stable electrocatalysts for hydrogen evolution reaction (HER) in electrolysis water splitting. The morphologies, structures, and composition of these as-prepared catalysts are characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, and transmission electron microscopy. The electrochemical tests, such as linear sweep voltammetry, cyclic voltammetry, electrochemical impedance spectroscopy, and chronoamperometry testing, are performed to evaluate these catalysts' HER catalytic performance including activity and stability. The results indicate that a suitable doping can result in synergetic effect for increasing the catalytic performance. Among different catalysts, Co_0.1Ni_0.75Se shows the highest HER performance. After introducing the reduced graphene oxide (rGO) into this catalyst as the support, the resulted Co_0.1Ni_0.75Se/rGO shows even better performance than unsupported Co_0.1Ni_0.75Se, which are confirmed by the reduction of HER overpotential of Co_0.1Ni_0.75Se/rGO to 103 mV compared to 153 mV of Co_0.1Ni_0.75Se at a current density of 10 mA/cm², and the smaller Tafel slope (43 mV/dec) and kinetic resistance (21.34 Ω) than those of Co_0.1Ni_0.75Se (47 mV/dec, 30.23 Ω). Furthermore, the large electrochemical active surface area and high conductivity of such a Co_0.1Ni_0.75Se/rGO catalyst, induced by rGO introduction, are confirmed to be responsible for the high HER performance.

Uniform small-sized MoS2 from novel solution-based microwave-assisted method with exceptional reversible lithium storage properties

Currently, MoS2 is being investigated as a lithium-ion battery (LIB) anode material because of its high theoretical capacity. However, its significantly low electrochemical activity and cyclic stability limit its utilization. Nevertheless, small-sized MoS2 possibly overcomes these issues. Herein, small-sized MoS2 with uniform particle sizes of about 20-30 nm was prepared via a novel solution-based microwave-assisted precursor pyrolysis method. The resultant MW-MoS2 sample has a high surface area of 96.9 m2 g-1 and large pore volume (0.38 cm3 g-1) with pore size distribution mainly in the meso/macropore scale, which are beneficial for electrolyte storage and low charge carrier conductive resistances. The large pore surface area and volume of the small-sized MoS2 can also ease the volume expansion during the charging and discharging process. As an LIB anode, the MW-MoS2 material exhibits an amazingly large specific capacity of 1355 mA h g-1 at a low current density of 0.5 A g-1. At a high current density of 10 A g-1, a specific capacity of 435 mA h g-1 is obtained, demonstrating its excellent rate capability. Furthermore, a large discharge capacity of 544 mA h g-1 is maintained after 500 cycles at 5 A g-1, indicating its fascinatingly high cyclic stability.

Efficient Hydrogen Production on a 3D Flexible Heterojunction Material

A novel heterojunction material, with electron-rich graphdiyne as the host and molybdenum disulfide as the catalytic center (eGDY/MDS), to produce ultraefficient hydrogen-evolution reaction (HER) at all pH values is described. It is a surprise that the metallic conductor combined from two semiconductor materials, eGDY and MDS, leads to optimal free energy (ΔG_H ) and enhancement in the intrinsic HER catalytic performances. The calculated and experimental results indicate that eGDY/MDS shows greatly enhanced catalytic activities and high stabilities in both acidic and alkaline conditions; these approach the outstanding performances of the state-of-the-art noble-metal-based catalysts. The eGDY/MDS shows better activity than Pt/C in alkaline media and remarkable enhancement in photocurrent density. The high catalytic activity of eGDY/MDS originates from facilitated electronic transfer kinetics, high conductivity, more exposed catalytic active sites, and excellent mass transport.

Metallic 1T-LixMoS2 co-catalyst enhanced photocatalytic hydrogen evolution over ZnIn2S4 floriated microspheres under visible light irradiation

Metallic 1T-Li_xMoS₂ is an effective co-catalyst for photocatalytic hydrogen evolution over ZnIn₂S₄ because of its high electrical conductivity and high densities of active sites.

VS2: an efficient catalyst for an electrochemical hydrogen evolution reaction in an acidic medium

A single step scalable synthesis for vanadium disulphide (VS₂) was developed and the resulting material shows a better electrocatalytic performance in terms of a low onset potential (15 mV), a lower Tafel slope (36 mV dec⁻¹) and needs only 41 mV to deliver a state-of-the-art current density of 10 mA cm⁻².

TMD-based highly efficient electrocatalysts developed by combined computational and experimental approaches

A thorough review on combined computational and experimental approaches to develop TMD-based highly efficient electrocatalysts by site doping, phase modulation, control of growth morphology and construction of heterostructures.

MoSe2 Nanosheet Array with Layered MoS2 Heterostructures for Superior Hydrogen Evolution and Lithium Storage Performance

Engineering heterostructures of transition metal disulfides through low-cost and high-yield methods instead of using conventional deposition techniques still have great challenges. Herein, we present a conveniently operated and low-energy-consumption solution-processed strategy for the preparation of heterostructures of MoSe₂ nanosheet array on layered MoS₂, among which the two-dimensional MoS₂ surface is uniformly covered with high-density arrays of vertically aligned MoSe₂. The unique compositional and structural features of the MoS₂-MoSe₂ heterostructures not only provide more exposed active sites for sequent electrochemical process, but also facilitate the ion transfer due to the open porous space within the nanosheet array serving as well-defined ionic reservoirs. As a proof of concept, the MoS₂-MoSe₂ heterostructures serve as promising bifunctional electrodes for both energy conversions and storages, which exhibit an active and acid-stable activity for catalyzing the hydrogen evolution reaction, high specific capacity of 728 F g^-1 at 0.1 A g^-1, and excellent durability with a remained capacity as high as 676 mA h g^-1 after 200 cycles.

Electrochemical and SECM Investigation of MoS2/GO and MoS2/rGO Nanocomposite Materials for HER Electrocatalysis

Development of advanced materials for electrocatalytic and photocatalytic water splitting is the key in utilization of renewable energy. In the present work, we have synthesized MoS₂ nanoparticles embedded over the graphene oxide (GO) and reduced graphene oxide (rGO) layer for superior catalytic activity in the hydrogen evolution process (HER). The nanocomposite materials are characterized using different spectroscopic and microscopic measurements. A Tafel slope of ∼40 mV/decade suggested the Volmer-Heyrovsky mechanism for the HER process with MoS₂/GO composite as the catalyst, which indicated that electrochemical desorption of hydrogen is the rate-limiting step. The small Tafel slope indicates a promising electrocatalyst for HER in practical application. MoS₂/GO composite material has shown superior catalytic behavior compared to that of MoS₂/rGO composite material. The HER catalytic activity of the catalysts is explored using scanning electrochemical microscopy (SECM) using the feedback and redox competition mode in SECM. The activation energy for HER activity was calculated, and the values are in the range of 17-6 kJ/mol. The lower value of activation energy suggested faster HER kinetics.

One-step assembly of 2H-1T MoS2:Cu/reduced graphene oxide nanosheets for highly efficient hydrogen evolution

The transition metal dichagenides and their metallic 1T structure are attracting contemporary attentions for applications in high-performance devices because their peculiar optical and electrical properties. The single and few layers 1T structure is generally obtained by mechanical or chemical exfoliation. This work presents facile one-step synthesis of 2H-1T MoS₂:Cu/reduced graphene oxide nanosheets. The experiment results indicated that the MoS₂ and MoS₂:Cu prepared by simple chemical solution reaction possessed 2H-1T structures. The reduced graphene oxide (rGO) incorporation further induced the phase transition from 2H-MoS₂ to 1T-MoS₂ and morphology transition from granular/nanosheet to more nanosheet. The 2H-1T structure and 2H → 1T phase transition, together with the Cu doping and interface effect between the MoS₂ and rGO, remarkably enhanced the conduction and photoconduction of the nanostructures. Thus, Cu doping and rGO incorporation obviously enhanced the catalytic activity and its stability, making the MoS₂:Cu/rGO nanosheet a most active and stable catalyst for hydrogen evolution. This work clearly indicates that the 1T-MoS₂ nanosheets with high catalytic activity for hydrogen evolution can be easily obtained by the facile low temperature chemical method and induction of rGO.