Transition Metal Chalcogenide Materials Research Articles

Going from Pt to PGM-free Catalysts: Effects of Ink Compositions on PEM Water Electrolysis.

The commercialisation of PEM water electrolysis is still hindered by the necessity of using noble metals that are rare, expensive and therefore unsustainable. To replace the benchmark HER catalyst Pt with more abundant materials, promising non-noble catalysts need to be identified and optimal electrode preparation and electrolysis conditions need to be transferred between catalyst materials to reveal their full potential under industrially relevant conditions. This study investigates the optimal ink composition for spray-coating the cathode regarding the effects on electrode structure, performance and catalyst layer composition. The ratio of catalyst to binder and carbon support was varied as well as the specific carbon material and the resulting electrodes were analysed via polarisation curves, electrochemical impedance spectroscopy, X-ray photo-electron spectroscopy and scanning electron microscopy for three different catalysts. These results show that ink compositions with a catalyst : carbon : binder ratio of 3:1:1 using Carbon Vulcan give the highest performance. Interestingly, resulting trends concerning electrochemical behaviour and electrode structure observed with different characterisation techniques can be transferred between Pt catalysts and non-noble transition metal chalcogenide materials. Boosting the performance via ink optimisation is much more pronounced for the non-noble catalysts, narrowing the gap to competing with noble standard Pt materials.

Ab initio Investigation of quasi-one-dimensional ternary chalcogenides Sr2ZnX3 (X = S, Se, Te) for efficient photovoltaic and thermoelectric applications

The quest for sustainable and renewable energy sources has become a vital global mission. Transition metal chalcogenide materials have garnered significant attention due to their unique low-dimensional physical properties. In this work, we explore the impact of ionic radius in modulating the physical properties of ternary chalcogenides by calculating structural, electronic, optical, and thermoelectric properties of Sr2ZnX3 (X = S, Se, Te) materials using first-principles density functional theory (DFT) as implemented in the WIEN2k program. To evaluate the effect of ionic radius, two novel semiconductors Sr2ZnSe3 and Sr2ZnTe3, were constructed using similar isostructural material Sr2ZnS3. Further optimized structure reveals that the corner-sharing ZnX4 tetrahedra extended along the b-axis confirms the quasi-one-dimensional (Q1D) nature of Sr2ZnX3 materials. Band structure analysis revealed a wide direct bandgap nature with the values of Sr2ZnS3 (3.4 eV), Sr2ZnSe3 (2.8 eV) and Sr2ZnTe3 (1.75 eV), respectively. The lower effective mass of electrons and holes suggests higher carrier mobility and charge recombination rates, vital for photovoltaic applications. The optical properties of the materials are studied in the energy range of 0–10 eV (IR–Vis–UV region). We found that Sr2ZnTe3 material exhibits higher values of dielectric function, absorption coefficient (α≈106 cm−1), refractive index, and lower reflectivity, which indicates its suitability for photovoltaic application. Thermoelectric properties are crucial for assessing material utility in thermoelectric applications, and the study revealed substantial values of the Seebeck coefficient, electrical conductivity, figure of merit (ZT) greater than 2, power factor, and lower electronic thermal conductivity. The studied properties signify Sr2ZnX3 materials as potential candidates for light-emitting semiconductors and thermoelectric applications.

Enhanced field emission characteristics of WS2 nano-films by diamond film and Mo film

WS2 is a type of transition metal chalcogenide materials (TMDCs) that exhibits exceptional photoelectric properties. Due to its atomically sharp edges, WS2 has the capability to enhance the electric field around its edges, thus presenting significant potential in field emission applications. In this study, the electron beam vapor deposition (EBVD) system and microwave plasma chemical vapor deposition (MPCVD) system were used to prepare a series of single-layer WS2 films，single-layer diamond films and diamond/WS2 nano-composite films on N-type highly doped Si substrate, and Mo/WS2 nano-composite films were prepared on Al2O3 ceramic substrate. Based on the characterization and analysis of the microstructure and chemical composition of each thin film layer in the above film devices, the field emission (FE) characteristics of each thin film device are compared and studied. The results demonstrate that the maximum FE current density of diamond/WS2 nano-composite film device is 912 μA/cm2, which is 2.7 times of the maximum FE current density of Mo/WS2 nano-composite film device 330 μA/cm2, and 3.4 times of the maximum FE current density of the single-layer diamond thin film device 267 μA/cm2. The single layer WS2 film did not exhibit measurable FE performance. The working principles of thin film field emission devices with various structures are introduced. It is considered that the diamond layer plays the role of electron accelerating layer, which not only effectively improves the FE characteristics of diamond/WS2 nanocomposite film, but also improves the repeatability and long-term stability of diamond/WS2 nanocomposite film FE devices.

Well-Separated Photoinduced Charge Carriers on Hydrogen Production Using NiS2/TiO2 Nanocomposites.

Photocatalytic hydrogen production is a sustainable and greenhouse-gas-free method that requires an efficient and abundant photocatalyst, which minimizes energy consumption. Currently, interests in transition metal chalcogenide materials have been utilized in different applications due to their quantum confinement effect and low band gaps. In this study, different wt % of NiS2-embedded TiO2 nanocomposites were synthesized by a facile hydrothermal method and utilized for photocatalytic hydrogen production under extended solar irradiation. Among the materials studied, the highest amount (4.185 mmol g-1) of hydrogen production was observed with 15 wt % of the NiS2/TiO2 nanocomposite. The highest photocatalytic activity may be due to the well separation of photoinduced charge carriers on the catalyst, which was confirmed by the electrochemical studies. Thus, we believe that these photocatalysts are promising candidates for future applications.

Liquid Shear Exfoliation of MoS2: Preparation, Characterization, and NO2-Sensing Properties.

2D materials possess great potential to serve as gas-sensing materials due to their large, specific surface areas and strong surface activities. Among this family, transition metal chalcogenide materials exhibit different properties and are promising candidates for a wide range of applications, including sensors, photodetectors, energy conversion, and energy storage. Herein, a high-shear mixing method has been used to produce multilayered MoS2 nanosheet dispersions. MoS2 thin films were manufactured by vacuum-assisted filtration. The structural morphology of MoS2 was studied using ς-potential, UV-visible, scanning electron microscopy (SEM), atomic force microscopy (AFM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Raman spectroscopy (RS). The spectroscopic and microscopic analyses confirm the formation of a high-crystalline MoS2 thin film with good inter-sheet connectivity and relative thickness uniformity. The thickness of the MoS2 layer is measured to be approximately 250 nm, with a nanosheet size of 120 nm ± 40 nm and a number of layers between 6 and 9 layers. Moreover, the electrical characteristics clearly showed that the MoS2 thin film exhibits good conductivity and a linear I-V curve response, indicating good ohmic contact between the MoS2 film and the electrodes. As an example of applicability, we fabricated chemiresistive sensor devices with a MoS2 film as a sensing layer. The performance of the MoS2-chemiresistive sensor for NO2 was assessed by being exposed to different concentrations of NO2 (1 ppm to 10 ppm). This sensor shows a sensibility to low concentrations of 1 ppm, with a response time of 114 s and a recovery time of 420 s. The effect of thin-film thickness and operating temperatures on sensor response was studied. The results show that thinner film exhibits a higher response to NO2; the response decreases as the working temperature increases.

Low thermal expansion for self-compounded Fe1-xCoxS over a wide temperature range

Zero thermal expansion (ZTE) materials have great application prospects benefited by the inhibition of thermal shock and dimensional mismatch. Herein, a novel self-compounded Fe1-xCoxS composite was obtained by a simple low-temperature annealing method. The second non-stoichiometric phase with a few cation vacancies from the thermal annealing is key to optimizing the thermal expansion behavior. The negative thermal expansion (NTE) region of one phase overlaps the positive thermal expansion (PTE) region of another phase to achieve low expansion in the wide temperature zone. As a result, the obtained Fe0.94Co0.06S sample displays near ZTE covering a wide temperature range (αL = 1.9 ppm/K, ΔT = 176 K) by annealing. Furthermore, the synergistic effect from the self-compounded composite can effectively avoid thermal mismatch compared to the traditional composites with matrix and filler. This study provides a new strategy for regulating the thermal expansion of transition metal chalcogenide materials.

Defect engineering-driven phase structure design of 2H@1T MoS2 for electrochemical hydrogen evolution reaction

Two-dimensional transition metal chalcogenide materials such as MoS2 have broad application prospects in the field of electrochemical hydrogen evolution reaction (HER) due to their unique electronic structure. Herein, we report a defect engineering strategy for regulating the phase structural components of MoS2. We introduced abundant defects in the MoS2 substrate plane by a facile two-step solvothermal method and induced the surrounding 2H MoS2 lattice to transform into 1T phase. At the same time, hexadecyltrimethylammonium bromide (CTAB), as a common surfactant, was introduced to inhibit the stacking of layered catalysts and increased the proportion of 1T phase by 50%. The existence of high content 1T MoS2 phase possesses excellent catalytic activity with a small Tafel slope of 45.9 mV dec−1 and low overpotential of 182 mV at 10 mA cm−2.

Synthesis and Characterization of the Thin Films NiSe2/Si Heterojunction for Solar Cells

Thin film solar cells are preferable to the researchers and in applications due to the minimum material usage and to the rising of their efficiencies. In particular, thin film solar cells, which are designed based one transition metal chalcogenide materials, paly an essential role in solar energy conversion market. In this paper, transition metals with chalcogenide Nickel selenide termed as (NiSe2/Si) are synthesized. To this end, polycrystalline NiSe2 thin films are deposited through the use of vacuum evaporation technique under vacuum of 2.1x10-5 mbar, which are supplied to different annealing temperatures. The results show that under an annealed temperature of 525 K, the nickel sulfoselenide thin films are polycrystalline with an efficient regularity and best crystalline quality. In addition, the results demonstrate that the intersection argument for the optical properties under investigation provid the direct bandgap, over which the films have inferred on variety (1.55 and 1.75 eV). Overall, the results illustrate that an efficiency of 2.89% can be achieved with 525 K temperature.

SnS2/TiO2 Nanocomposites for Hydrogen Production and Photodegradation under Extended Solar Irradiation

Earth–abundant transition metal chalcogenide materials are of great research interest for energy production and environmental remediation, as they exhibit better photocatalytic activity due to their suitable electronic and optical properties. This study focuses on the photocatalytic activity of flower-like SnS2 nanoparticles (composed of nanosheet subunits) embedded in TiO2 synthesized by a facile hydrothermal method. The materials were characterized using different techniques, and their photocatalytic activity was assessed for hydrogen evolution reaction and the degradation of methylene blue. Among the catalysts studied, 10 wt. % of SnS2 loaded TiO2 nanocomposite shows an optimum hydrogen evolution rate of 195.55 µmolg−1, whereas 15 wt. % loading of SnS2 on TiO2 exhibits better performance against the degradation of methylene blue (MB) with the rate constant of 4.415 × 10−4 s−1 under solar simulated irradiation. The improved performance of these materials can be attributed to the effective photo-induced charge transfer and reduced recombination, which make these nanocomposite materials promising candidates for the development of high-performance next-generation photocatalyst materials. Further, scavenging experiments were carried out to confirm the reactive oxygen species (ROS) involved in the photocatalytic degradation. It can be observed that there was a 78% reduction in the rate of degradation when IPA was used as the scavenger, whereas around 95% reduction was attained while N2 was used as the scavenger. Notably, very low degradation (<5%) was attained when the dye alone was directly under solar irradiation. These results further validate that the •OH radical and the superoxide radicals can be acknowledged for the degradation mechanism of MB, and the enhancement of degradation efficiency may be due to the combined effect of in situ dye sensitization during the catalysis and the impregnation of low bandgap materials on TiO2.

Conversion reaction mechanism of cobalt telluride-carbon composite microspheres synthesized by spray pyrolysis process for K-ion storage

Owing to its similarity to lithium and sodium, potassium has been increasingly used to fabricate potassium ion batteries (KIBs). Following vigorous attempts to identify highly efficient electrode materials, transition metal chalcogenide materials have been identified as promising candidates. In this study, the performance of metal telluride (cobalt telluride) as new anode material for KIBs is investigated. Cobalt telluride-C (CoTe2-C) composite microspheres are synthesized using spray pyrolysis. Thereafter, a facile one-step post-treatment process results in the formation of pure-phase CoTe2-C composite microspheres with uniform composition, owing to the direct embedding of Te within the composite microspheres. Conversely, tellurization via application of H2Te gas results in inhomogeneous CoTe2-C composite microspheres, arising from crystal growth of CoTe2, owing to Ostwald ripening. The conversion reaction mechanism of CoTe2-C microspheres for K-ion storage has been examined using in-situ and ex-situ measurements and the reversible reaction mechanism from the second cycle of the reaction of CoTe2 with K ions, described by the reaction: 2Co + K5Te3 + K2Te ↔ 2CoTe + 2Te + 7 K+ + 7e−. Additionally, at a current density of 0.5 A g−1, the discharge capacity of the CoTe2-C composite was 189.5 mA h g−1 for the 100th cycle.

Emergence of Topologically Nontrivial Spin-Polarized States in a Segmented Linear Chain.

The synthesis of new materials with novel or useful properties is one of the most important drivers in the fields of condensed matter physics and materials science. Discoveries of this kind are especially significant when they point to promising future basic research and applications. van der Waals bonded materials comprised of lower-dimensional building blocks have been shown to exhibit emergent properties when isolated in an atomically thin form [1-8]. Here, we report the discovery of a transition metal chalcogenide in a heretofore unknown segmented linear chain form, where basic building blocks each consisting of two hafnium atoms and nine tellurium atoms (Hf_{2}Te_{9}) are van der Waals bonded end to end. First-principle calculations based on density functional theory reveal striking crystal-symmetry-related features in the electronic structure of the segmented chain, including giant spin splitting and nontrivial topological phases of selected energy band states. Atomic-resolution scanning transmission electron microscopy reveals single segmented Hf_{2}Te_{9} chains isolated within the hollow cores of carbon nanotubes, with a structure consistent with theoretical predictions. van der Waals bonded segmented linear chain transition metal chalcogenide materials could open up new opportunities in low-dimensional, gate-tunable, magnetic, and topological crystalline systems.

Colloidal Ternary Ni1-xCoxSe Alloy Nanocrystals with tunable compositions: Synthesis, Characterization and Electrocatalytic properties for the Oxygen Evolution Reaction

Oxygen evolution reaction(OER) is one of the two half-reactions in water splitting. Sustainable OER is an essential prerequisite in hydrogen production from water. In the past few years, many research efforts have been directed towards the development of electrocatalysts for OER, which are based on noble metals and transition metal oxides. But these materials suffer from poor conductivity. Recently, it has been found that, transition metal chalcogenide materials, especially Ni- and Co- based compounds, can catalyze OER efficiently. However, the research on these systems is at the very beginning, and few syntheses of Ni1-xCoxSe nanocrystals (NCs) have been reported in the literature till now. Herein, we report a simple colloidal synthesis approach to grow ternary Ni1-xCoxSe NCs with tunable composition and study their OER properties. The phase of the nanocrystals is hexagonal irrespective of their composition. The composition of Ni and Co in the NCs can be easily controlled by tuning the experimental parameters. By performing OER on samples with different Ni/Co ratio, we optimized the composition for obtaining high performance OER. The best performing samples exhibit a catalytic OER current of 10 mA/cm2 at a small overpotential of 1.5 V vs. RHE with extended long-term stability. The detailed results will be presented in the meeting. Figure. (a) TEM image of Ni0.37Co0.74Se and (b) Polarization curves of OER for NCs with different Ni/Co ratios Figure 1

Urchin-Shaped Bi2S3/Cu2S/Cu3BiS3 Composites with Enhanced Photothermal and CT Imaging Performance

Urchin-shaped Bi2S3/Cu2S/Cu3BiS3 nanocomposites were successfully prepared in this study through one-pot synthesis, which involved microwave-assisted simultaneous pyrolysis of two precursors. The as-prepared Bi2S3/Cu2S/Cu3BiS3 hybrids exhibit stronger absorption in the near-infrared regime than the individual components, i.e., Bi2S3, Cu2S, and Cu3BiS3. The photothermal conversion efficiency (η) of Bi2S3/Cu2S/Cu3BiS3 composites can even reach 43.8%, which is significantly higher than that seen with most of the transition metal chalcogenide materials. The excellent photothermal performance of Bi2S3/Cu2S/Cu3BiS3 hybrids is likely arising from its unique urchin-like structure, in which needle-like Bi2S3/Cu2S nanocomposites grow from the core of Cu3BiS3. The copresence of Bi2S3 and Cu2S also leads this newly synthesized composite to produce high contrast for X-ray computer tomography imaging, an important property required for a great potential application in theranostic cancer treatment.

Solution‐Based Synthesis and Design of Late Transition Metal Chalcogenide Materials for Oxygen Reduction Reaction (ORR)

Late transition metal chalcogenide (LTMC) nanomaterials have been introduced as a promising Pt-free oxygen reduction reaction (ORR) electrocatalysts because of their low cost, good ORR activity, high methanol tolerance, and facile synthesis. Herein, an overview on the design and synthesis of LTMC nanomaterials by solution-based strategies is presented along with their ORR performances. Current solution-based synthetic approaches towards LTMC nanomaterials include a hydrothermal/solvothermal approach, single-source precursor approach, hot-injection approach, template-directed soft synthesis, and Kirkendall-effect-induced soft synthesis. Although the ORR activity and stability of LTMC nanomaterials are still far from what is needed for practical fuel-cell applications, much enhanced electrocatalytic performance can be expected. Recent advances have emphasized that decorating the surface of the LTMC nanostructures with other functional nanoparticles can lead to much better ORR catalytic activity. It is believed that new synthesis approaches to LTMCs, modification techniques of LTMCs, and LTMCs with desirable morphology, size, composition, and structures are expected to be developed in the future to satisfy the requirements of commercial fuel cells.

Solid-state chemistry on a surface and in a beaker: Unconventional routes to transition metal chalcogenide nanomaterials

This article focuses on two different approaches to create nanoscale transition metal chalcogenide materials. First, we used chemical nanofabrication, a combination of top-down patterning and bottom-up solid-state synthesis, to achieve control over the shape, size, and ordering of the patterned nanomaterials. We demonstrated orientational control over nanocrystals within sub-300 nm patterns of MoS 2 and formed free-standing nanostructures of crystalline NiS 2. In addition, crossed line arrays of mixed metal chalcogenide nanostructures were achieved, and TaS 2 nanopatterns were made by the chemical transformation of tantalum oxide templates. Second, we developed a one-pot procedure using molecular precursors to synthesize two-dimensional NbSe 2, TaS 2 and TaSe 2 nanoplates and one-dimensional NbSe 2 wires depending on the relative amount of surfactants in the reaction mixture. Prospects for these transition metal chalcogenide nanomaterials with controlled shapes and morphologies will be discussed.

Kinetics studies of oxygen reduction in acid medium on novel semiconducting transition metal chalcogenides

The aim of this work was to investigate a Ru-cluster material with a low molybdenum concentration. This latter is considered to act as an adsorption site for molecular oxygen. Transition metal chalcogenide materials based on Mo-Ru-Se for electrocatalytic reduction of molecular oxygen in acid medium were chemically prepared by reacting the transition metal carbonyl compounds and selenium powder in xylene solvent (140 °C). The stoichiometry of the semiconducting electrocatalyst corresponds to (Ru 1 − x Mo x ) y SeO z where 0.02 < x < 0.04; 1 < y < 3 and z ≈ 2 y. Kinetics parameters were obtained using steady state measurements with the rotating ring disk electrode ( rrde) with electrocatalyst deposited on glassy carbon disks or with the powder incorporated in a disk of carbon paste matrix. Oxygen reduction proceeds mostly via a four-electron transfer reaction (96%) to water as determined by the rotating ring disk electrode technique. The heterogeneous rate constants, k 1 (water formation from oxygen), k 2 (hydrogen peroxide formation) and k 3 (water production from generated H 2O 2) were evaluated over the potential range of 0.70 to 0V/ nhe. Temperature dependence (296 K to 338 K) and kinetic parameters were evaluated. It is concluded that minimising the molybdenum content leads to improved electrocatalysis.