Bottom-up Electrosynthesis of Highly Active Tungsten Sulfide (WS3-x) Films for Hydrogen Evolution

Defect Enriched Tungsten Oxide Phosphate with Strategic Sulfur Doping for Effective Seawater Oxidation

The intrinsic ability of defects within the electrocatalysts can be judiciously utilized in designing robust electrocatalysts for efficient seawater oxidation. Herein, we have fabricated a novel tungsten oxide phosphate (W12PO38.5) with optimized sulfur doping triggering the insertion of a large number of defect sites. This allows for boosted OER performance in alkaline freshwater as well as seawater, avoiding the unwanted chlorine evolution reaction. The optimized electrocatalyst achieved high current densities of 500 mA cm-2 at an overpotential of just 387 mV in fresh water and 100 mA cm-2 at 380 mV in alkaline seawater for OER. Besides the excellent catalytic performances, the developed electrocatalyst appeared to be a durable catalyst as well. An interesting electrocatalytic activation caused by the generous electronic redistribution led the electrocatalyst to achieve great stability over 100 h at a 100 mA cm-2 current density in alkaline real seawater.

Impact Electrochemistry of MoS2: Electrocatalysis and Hydrogen Generation at Low Overpotentials

MoS₂ materials have been extensively studied as hydrogen evolution reaction (HER) catalysts. In this study nanoparticulate MoS₂ is explored as a HER catalyst through impact voltammetry. The onset potential was found to be -0.10 V (vs RHE) at pH 2, which was confirmed to be due to HER by scale-up of the impact experiment to generate and collect a sufficient volume of the gas to enable its identification as hydrogen via gas chromatography. This is in contrast to electrodeposited MoS₂, which was found to be stable in pH 2 sulfuric acid solution with an onset potential of -0.29 V (vs RHE), in good agreement with literature. XPS was used to categorize the materials and confirm the chemical composition of both nanoparticles and electrodeposits, with XRD used to analyze the crystal structure of the nanoparticles. The early onset of HER was postulated from kinetic analysis to be due to the presence of nanoplatelets of about 1-3 trilayers participating in the impact reactions, and AFM imaging confirmed the presence of these platelets.

Synthesis of crystalline WS3 with a layered structure and desert-rose-like morphology

Tungsten disulphide has attracted great research interest due to its layered structure as well as physical and chemical properties. A less common type of tungsten sulphide, WS₃, has also been studied as an electrochemical catalyst, but its crystal structure remains unclear because it has only been prepared in the amorphous form. In this work, crystalline WS₃ is synthesized with a desert-rose-like morphology through the sulphurization of WO₃·0.33H₂O in a solvothermal reaction. The composition of WS₃ is confirmed by X-ray photoelectron spectroscopy measurements as well as thermogravimetric experiment. The crystalline WS₃ also has a layered structure and is likely to belong to the trigonal crystal system. Its lattice parameters in the hexagonal description are 5.30 Å × 5.30 Å × 29.0 Å <90 ° × 90 ° × 120°>, which are determined by 3D electron diffraction and powder X-ray diffraction. The WS₃ shows potential as catalyst for the electrochemical hydrogen evolution reaction. Our findings extend the family of layered tungsten sulphide materials.

Facile Synthesis of N-Doped WS2 Nanosheets as an Efficient and Stable Electrocatalyst for Hydrogen Evolution Reaction in Acidic Media

Transition metal chalcogenides have been widely studied as a promising electrocatalyst for the hydrogen evolution reaction (HER) in acidic conditions. Among various transition metal chalcogenides, tungsten disulfide (WS2) is a distinguishable candidate due to abundant active sites and good electrical properties. Herein, we report a facile and selective synthetic method to synthesize WS2 with an intriguing two-dimensional nanostructure by using cysteine (C3H7NO2S) as a chemical agent. In addition, nitrogen can be incorporated during chemical synthesis from cysteine, which may be helpful for enhancing the HER. The electrocatalytic activity of N-doped WS2 exhibits a promising HER in acidic conditions, which are not only higher than W18O49 nanowires and hex-WO3 nanowires, but also comparable to the benchmark Pt/C. Moreover, excellent electrocatalytic stability is also demonstrated for acidic HER during long-term tests, thus highlighting its potential use of practical applications as an electrolyzer.

Solution-Based Synthesis of Few-Layer WS2 Large Area Continuous Films for Electronic Applications

Unlike MoS2 ultra-thin films, where solution-based single source precursor synthesis for electronic applications has been widely studied, growing uniform and large area few-layer WS2 films using this approach has been more challenging. Here, we report a method for growth of few-layer WS2 that results in continuous and uniform films over centimetre scale. The method is based on the thermolysis of spin coated ammonium tetrathiotungstate ((NH4)2WS4) films by two-step high temperature annealing without additional sulphurization. This facile and scalable growth method solves previously encountered film uniformity issues. Atomic force microscopy (AFM) and transmission electron microscopy (TEM) were used to confirm the few-layer nature of WS2 films. Raman and X-Ray photoelectron spectroscopy (XPS) revealed that the synthesized few-layer WS2 films are highly crystalline and stoichiometric. Finally, WS2 films as-deposited on SiO2/Si substrates were used to fabricate a backgated Field Effect Transistor (FET) device for the first time using this precursor to demonstrate the electronic functionality of the material and further validate the method.

Near infrared-light responsive WS2 microengines with high-performance electro- and photo-catalytic activities

Tungsten disulfide (WS2)-based micromotors with enhanced electrochemical and photo-catalytic activities are synthesized using a greatly simplified electrochemical deposition protocol at room temperature involving exclusively tungstic acid and sulfate as metal and sulfur sources without further building chemistry. The WS2-based micromotors exhibit dual electrochemical and photo-catalytic behavior in the inner and outer layers, respectively, due to the combination of the unique properties of the sp2 hybridized WS2 outer layer with highly reactive WS2-induced inner catalytic layers, accounting for this material's exclusive enhanced performances. A rough inner Pt-Ni layer allows tailoring the micromotor propulsion, with a speed increase of up to 1.6 times after external control of the micromotor with a magnetic field due to enhanced fuel accessibility. Such a coupling of the attractive capabilities of WS2 with enhanced micromotor movement holds considerable promise to address the growing energy crisis and environmental pollution concerns.

Molecular Routes to Two-Dimensional Metal Dichalcogenides MX2 (M = Mo, W; X = S, Se)

New synthetic access to two-dimensional transition metal dichalcogenides (TMDCs) is highly desired to exploit their extraordinary semiconducting and optoelectronic properties for practical applications. We introduce here an entirely novel class of molecular precursors, [M^IV(XEtN(Me)EtX)₂] (M^IV = Mo^IV, W^IV, X = S, Se), enabling chemical vapor deposition of TMDC thin films. Molybdenum and tungsten complexes of dianionic tridentate pincer-type ligands (HXEt)₂NR (R = methyl, tert-butyl, phenyl) produced air-stable monomeric dichalcogenide complexes, [W(SEtN(Me)EtS)₂] and [Mo(SEtN(Me)EtS)₂], displaying W and Mo centers in an octahedral environment of 4 S and 2 N donor atoms. Owing to their remarkable volatility and clean thermal decomposition, both Mo and W complexes, when used in the chemical vapor deposition (CVD) process, produced crystalline MoS₂ and WS₂ thin films. X-ray diffraction analysis and atomic-scale imaging confirmed the phase purity and 2D structural characteristics of MoS₂ and WS₂ films. The new set of ligands presented in this work open ups convenient access to a scalable and precursor-based synthesis of 2D transition metal dichalcogenides.

Two-Dimensional Materials on the Rocks: Positive and Negative Role of Dopants and Impurities in Electrochemistry

Two-dimensional (2D) materials, such as graphene and transition-metal chalcogenides, were shown in many works as very potent catalysts for industrially important electrochemical reactions, such as oxygen reduction, hydrogen and oxygen evolution, and carbon dioxide reduction. We critically discuss here the development in the field, showing that not only dopants but also impurities can have dramatic effects on catalysis. Note here that the difference between dopant and impurity is merely semantic-dopant is an impurity deliberately added to the material. We contest the general belief that all doping has a positive effect on electrocatalysis. We show that in many cases, dopants actually inhibit the electrochemistry of 2D materials. This review provides a balanced view of the field of 2D materials electrocatalysis.

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

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

Tailoring the physicochemical properties of solution-processed transition metal dichalcogenides via molecular approaches

In this Feature Article we highlight the tremendous progress in solution-processed transition metal dichalcogenides and the molecular approaches employed to finely tune their physicochemical properties.

Earth-Abundant Transition-Metal-Based Electrocatalysts for Water Electrolysis to Produce Renewable Hydrogen

Fundamentals of water electrolysis, and recent research progress and trends in the development of earth-abundant first-row transition-metal (Mn, Fe, Co, Ni, Cu)-based oxygen evolution reaction (OER) and hydrogen evolution (HER) electrocatalysts working in acidic, alkaline, or neutral conditions are reviewed. The HER catalysts include mainly metal chalcogenides, metal phosphides, metal nitrides, and metal carbides. As for the OER catalysts, the basic principles of the OER catalysts in alkaline, acidic, and neutral media are introduced, followed by the review and discussion of the Ni, Co, Fe, Mn, and perovskite-type OER catalysts developed so far. The different design principles of the OER catalysts in photoelectrocatalysis and photocatalysis systems are also presented. Finally, the future research directions of electrocatalysts for water splitting, and coupling of photovoltaic (PV) panel with a water electrolyzer, so called PV-E, are given as perspectives.

Tunable Pt-MoS x Hybrid Catalysts for Hydrogen Evolution

Platinum (Pt)-based materials are inevitably among the best-performing electrocatalysts for hydrogen evolution reaction (HER). MoS₂ was suggested to be a potent HER catalyst to replace Pt in this reaction by theoretical modeling; however, in practice, this dream remains elusive. Here we show a facile one-pot bottom-up synthesis of Pt-MoS _x composites using electrochemical reduction in an electrolytic bath of Pt precursor and ammonium tetrathiomolybdate under ambient conditions. By modifying the millimolar concentration of Pt precursors, composites of different surface elemental composition are fabricated; specifically, Pt_1.8MoS₂, Pt_0.1MoS_2.5, Pt_0.2MoS_0.6, and Pt_0.3MoS_0.8. All electrodeposited Pt-MoS _x hybrids showcase low overpotentials and small Tafel slopes that outperform MoS₂ as an electrocatalyst. Tantamount to electrodeposited Pt, the rate-limiting process in the HER mechanism is determined to be the Heyrovsky desorption across Pt-MoS _x hybrids and starkly swings from the rate-determining Volmer adsorption step in MoS₂. The Pt-MoS _x composites are equipped with catalytic performance that closely mirrors that of electrodeposited Pt, in particular the HER kinetics for Pt_1.8MoS₂ and Pt_0.1MoS_2.5. This work advocates electrosynthesis as a cost-effective method for catalyst design and fabrication of competent composite materials for water splitting applications.

Preferential horizontal growth of tungsten sulfide on carbon and insight into active sulfur sites for the hydrogen evolution reaction

Transition metal dichalcogenides (TMDs) have attracted considerable attention as active electrocatalysts for the hydrogen evolution reaction (HER). Since TMD catalysts are commonly supported on carbon to endow electrical conductivity, understanding the growth behaviour of TMDs on carbon surfaces is crucial, and yet remains to be explored. In this work, we investigated the growth behaviour of tungsten sulfide (WS_x) on carbon surfaces inside the confined nanopores. Experimental and computational studies revealed the preferential bonding between the basal planes of WS_x and carbon surfaces, as well as the subsequent horizontal growth of WS_x. As a result, subnanometer WS_x clusters were formed at a low WS_x loading, and grew into monolayer WS₂ nanoplates with increased WS_x loadings. In contrast, a TMD analogue, MoS₂, favors edge plane bonding with carbon surfaces and subsequent stacking of nanoplate layers, leading to multilayer MoS₂ nanoplates with increased MoS₂ loadings. A time-dependent growth of WS_x further corroborated the formation of WS₂ nanoplates at the expense of ultrasmall WS_x nanoclusters. Interestingly, the sample prepared with a short sulfidation time, which was mainly comprised of WS_x nanoclusters, showed higher HER activity compared to the sample prepared with a prolonged sulfidation time, which mostly contained WS₂ nanoplates. The higher HER activity of WS_x nanoclusters is attributed to the larger density of active bridging S₂^2- sites, compared to the WS₂ nanoplates. These findings may provide important insights into the growth behaviour of layered TMD materials at the nanoscale, as well as potential active species in WS_x for the HER.

Inverse Opal-like Porous MoSex Films for Hydrogen Evolution Catalysis: Overpotential-Pore Size Dependence

Transition metal dichalcogenides (TMDs) are prized as electrocatalysts for hydrogen evolution reaction (HER). Common TMD syntheses entail conditions of high temperatures and reagents that are detrimental to the environment. The electrochemical synthesis of TMDs is advocated as a viable alternative to the conventional synthetic procedures in terms of simplicity, ecological sustainability, and versatility of deposition on various surfaces at room temperature. In this work, we demonstrate the successful fabrication of electrocatalytic inverse opal porous MoSe_x films, where 2 ≤ x ≤ 3, via solid template-assisted electrodeposition from the simultaneous electroreduction of molybdic acid and selenium dioxide as the respective metal and chalcogen precursors in an aqueous electrolyte. The electrosynthesized porous MoSe_x films contain pores with diameters of 0.1, 0.3, 0.6, or 1.0 μm, depending on the size of the polystyrene bead template used. The investigation reveals that porous MoSe_x films with a pore size of 0.1 μm, which prevailed over the other pore sizes, are endowed with the lowest HER overpotential of 0.57 V at -30 mA cm^-2 and a Tafel slope of 118 mV dec^-1, alluding to the adsorption step as rate limiting. Across all pore sizes, the Volmer adsorption step limits the HER mechanism. Nevertheless, the pore size dictates the catalytic activity of the porous MoSe_x films apropos of HER overpotential such that the HER performance of smaller pore sizes of 0.1 and 0.3 μm surpasses those with wider pore sizes of 0.6 and 1.0 μm. The observed trends in their HER behavior may be rationalized by the tunable surface wettability as pore sizes vary. These fundamental findings offer a glimpse into the efficacy of electrodeposited porous TMDs as electrocatalysts and exemplify the feasibility of the electrosynthesis method in altering the morphological structure of the TMDs.

Composition-Graded MoWSx Hybrids with Tailored Catalytic Activity by Bipolar Electrochemistry

Among transition metal dichalcogenide (TMD)-based composites, TMD/graphene-related material and bichalcogen TMD composites have been widely studied for application toward energy production via the hydrogen evolution reaction (HER). However, scarcely any literature explored the possibility of bimetallic TMD hybrids as HER electrocatalysts. The use of harmful chemicals and harsh preparation conditions in conventional syntheses also detracts from the objective of sustainable energy production. Herein, we present the conservational alternative synthesis of MoWS_x via one-step bipolar electrochemical deposition. Through bipolar electrochemistry, the simultaneous fabrication of composition-graded MoWS_x hybrids, i.e., sulfur-deficient Mo_xW_(1-x)S₂ and Mo_xW_(1-x)S₃ (MoWS_x/BPE_cathodic and MoWS_x/BPE_anodic, respectively) under cathodic and anodic overpotentials, was achieved. The best-performing MoWS_x/BPE_cathodic and MoWS_x/BPE_anodic materials exhibited Tafel slopes of 45.7 and 50.5 mV dec^-1, together with corresponding HER overpotentials of 315 and 278 mV at -10 mA cm^-2. The remarkable HER activities of the composite materials were attributed to their small particle sizes, as well as the near-unity value of their surface Mo/W ratios, which resulted in increased exposed HER-active sites and differing active sites for the concurrent adsorption of protons and desorption of hydrogen gas. The excellent electrocatalytic performances achieved via the novel methodology adopted here encourage the empowerment of electrochemical deposition as the foremost fabrication approach toward functional electrocatalysts for sustainable energy generation.

Mo doped Ni2P nanowire arrays: an efficient electrocatalyst for the hydrogen evolution reaction with enhanced activity at all pH values

We report the successful synthesis of Mo doped Ni₂P nanowires (NWs) on a Ni foam (NF) substrate by a two-step strategy, which could be used as an efficient and stable hydrogen evolution reaction (HER) electrocatalyst over the whole pH range (0-14). Electrochemical investigations demonstrated that Mo doping made the catalytic activity of Ni₂P significantly enhanced. To achieve a current density of 10 mA cm^-2, Mo-Ni₂P NWs/NF required an overpotential of 67 mV in acidic solution, 78 mV in alkaline solution and 84 mV in neutral solution. It also showed superior stability with negligible activity decay after its use in the HER under different pH conditions for 24 h. Such excellent HER activity might originate from the synergistic effect between molybdenum (Mo) and nickel (Ni) atoms. The present work provides a valuable route for the design and synthesis of inexpensive and efficient all-pH HER electrocatalysts.

Electrodeposition of Amorphous Molybdenum Chalcogenides from Ionic Liquids and Their Activity for the Hydrogen Evolution Reaction

This work reports on the general electrodeposition mechanism of tetrachalcogenmetallates from 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide. Both tetrathio- and tetraselenomolybdate underwent anodic electrodeposition and cathodic corrosion reactions as determined by UV-vis spectroelectrochemistry. Electrodeposition was carried out by cycling the potential between the anodic and cathodic regimes. This resulted in a film of densely packed nanoparticles of amorphous MoS_x or MoSe_x as determined by SEM, Raman, and XPS. The films were shown to have high activity for the hydrogen evolution reaction. The onset potential (J = 1 mA/cm²) of the MoS_x film was E = -0.208 V vs RHE, and that of MoSe_x was E = -0.230 V vs RHE. The Tafel slope of MoS_x was 42 mV/decade, and that of MoSe_x was 59 mV/decade.

Few-Layered Trigonal WS2 Nanosheet-Coated Graphite Foam as an Efficient Free-Standing Electrode for a Hydrogen Evolution Reaction

Few-layered tungsten disulfide (WS₂) with a controlled-phase ratio (the highest trigonal-phase ratio being 67%) was exfoliated via lithium insertion. The exfoliated WS₂ nanosheets were then anchored onto three-dimensional (3D) graphite foam (GF) to fabricate free-standing binder-free electrodes. The 3D GF can increase the interfacial contact between the WS₂ nanosheets and the electrolyte and facilitate ion transfer. Without the nonconductive binder, an intimate contact between the WS₂ and GF interface can be created, leading to the improvement of electrical conductivity. In comparison to the pure WS₂ nanosheets, the overpotential for a hydrogen evolution reaction is significantly decreased from 350 mV to 190 mV at 10 mA/cm², and no deactivation occurs after 1000 cycles. The density functional theory computations reveal that the efficient catalytic activity of the trigonal-phase WS₂/GF electrode is attributed to the lower Gibbs free energy for H* adsorption and higher electrical conductivity.

In situ cathodic activation of V-incorporated NixSy nanowires for enhanced hydrogen evolution

In situ cathodic activation (ISCA) of V-incorporated Ni_xS_y nanowires supported on nickel foam (VS/Ni_xS_y/NF) can be realized in an alkaline hydrogen evolution reaction (HER) process, which provides not only clearly enhanced activity but also ultrahigh stability for HER. The ISCA process is continuous linear sweep voltammetry (LSV) on VS/Ni_xS_y/NF as a cathodic electrode with gradually enhanced HER activity. The activated VS/Ni_xS_y/NF (A-VS/Ni_xS_y/NF) demonstrates enhanced HER activity with an overpotential of 125 mV to drive 10 mA cm^-2, which is much lower than that of other samples. It may be predicted that the ISCA-derived amorphous VOOH film covering on A-VS/Ni_xS_y/NF accelerates the HER process, and NiOOH may protect active sites from decaying, leading to excellent activity and structural stability. However, for single metal sulfides, the ISCA process of nickel or vanadium sulfides is not available, implying that the synergistic effect between Ni and V of VS/Ni_xS_y/NF may be the key to drive ISCA in alkaline HER. In addition, its ultra-high stability confirms that the stable active sites and nanostructures of A-VS/Ni_xS_y/NF are derived from ISCA. Therefore, the ISCA of V-incorporated transition metal sulfides in the alkaline HER process may be a facile and promising method to obtain efficient electrocatalysts.

Ag2S/Ag Heterostructure: A Promising Electrocatalyst for the Hydrogen Evolution Reaction

Different metal chalcogenides, being a potential candidate for hydrogen evolution catalysts, have attracted enormous attention in the field of water splitting. In the present study, Ag₂S/Ag is revealed as an efficient catalyst for hydrogen evolution. When a sacrificial template of the CuS nanostructure is used, Ag₂S/Ag heterostructures are synthesized following a simple wet-chemical technique. Two different routes, wet chemical and hydrothermal, are followed to modulate the morphology of the CuS templates from flower ball to wirelike structures, which subsequently results in the formation of Ag₂S nanostructure. Finally, the Ag layer is deposited on Ag₂S with the help of a photoreduction technique. The unique heterostructure of Ag₂S/Ag shows efficient catalytic activity in the H₂ evolution reaction. A Ag₂S/Ag wire can successfully generate a 10 mA/cm² current density at a -0.199 V potential. Ag₂S/Ag contains the micronanostructure where nanoplates of Ag₂S/Ag assemble to give rise to microstructures such as flower balls and wire.

Co9S8@N,P-doped porous carbon electrocatalyst using biomass-derived carbon nanodots as a precursor for overall water splitting in alkaline media

Using biomass-derived carbon nanodots as a precursor, Co₉S₈@N,P-doped porous carbon was fabricated by a molten-salt calcination and post-phosphorization method, and exhibits HER and OER bifunctional catalytic activity.

One-Step Electrodeposition of Co/CoP Film on Ni Foam for Efficient Hydrogen Evolution in Alkaline Solution

The development of high-efficiency catalysts for hydrogen evolution via water splitting has been an effective strategy to solve the energy environmental problems and energy crisis. The abundant-reserving transition metals and their phosphides are becoming attractive Pt alternatives for hydrogen evolution reaction (HER). Herein, a crystalline/amorphous Co/CoP film was facilely prepared on nickel foam (NF) by a one-step electrodeposition technique at room temperature, named Co/CoP-NF. The as-prepared Co/CoP-NF electrocatalyst exhibits excellent electrocatalytic activity for HER, on par with Pt/C, showing a low overpotential of 35 mV at a current density of 10 mA·cm^-2 and small Tafel slope of 71 mV·dec^-1 in 1.0 M NaOH solution. More importantly, the Co/CoP-NF catalyst presents good long-term durability at an overpotential of 60 mV. Moreover, the influence of the electrodeposition parameters on the catalytic performance of the catalyst was discussed. This study offers an effective strategy to develop a non-noble-metal HER catalyst for industrial production of hydrogen.

Valence and oxide impurities in MoS2 and WS2 dramatically change their electrocatalytic activity towards proton reduction

Layered molybdenum disulfide (MoS₂) and tungsten disulfide (WS₂) have received renewed interest in recent years as they are catalytic towards the hydrogen evolution reaction (HER) and they are touted as future replacements of platinum in electrolyzers. There is a significant discrepancy in the found onset potentials of MoS₂ and WS₂ towards the hydrogen evolution reaction. Here we show that the presence of valence sulfide impurities, such as MoS₃ and WS₃, and their oxide counterparts, such as MoO₂, MoO₃ and WO₂, WO₃ can contribute to the catalytic activity towards hydronium reduction to hydrogen of MoS₂ and WS₂. Therefore, it is highly possible that the differences in the reported onset potentials and thus catalytic activities of the MoS₂ and WS₂ are due to the presence of catalytic impurities.

CoP Nanoparticles in Situ Grown in Three-Dimensional Hierarchical Nanoporous Carbons as Superior Electrocatalysts for Hydrogen Evolution

The development of efficient and low-cost hydrogen evolution reaction (HER) catalysts is critical for storing energy in hydrogen via water splitting but still presents great challenges. Herein, we report synthesis of three-dimensional (3-D) hierarchical nanoporous carbon (HNC) supported transition metal phosphides (TMPs) for the first time by in situ growth of CoP nanoparticles (NPs) in CaCO3 NP-templated Cinnamomum platyphyllum leaf extract-derived carbon. They were subsequently employed as a HER catalyst, showing an onset potential of 7 mV and an overpotential of 95.8 mV to achieve 10 mA cm(-2), a Tafel plot of 33 mV dec(-1), and an exchange current density of 0.1182 mA cm(-2), of which the onset overpotential and the Tafel plot are the lowest reported for non-noble-metal HER catalysts, and the overpotential to achieve 10 mA cm(-2) and the exchange current density also compare favorably to most reported HER catalysts. In addition, this catalyst exhibits excellent durability with negligible loss in current density after 2000 CV cycles ranging from +0.01 to -0.17 V vs RHE at a scan rate of 100 mV s(-1) or 22 h of chronoamperometric measurement at an overpotential of 96 mV and a high Faraday efficiency of close to 100%. This work not only creates a novel high-performance non-noble-metal HER electrocatalyst and demonstrates the great advantages of the in situ grown 3-D HNC supported TMP NPs for the electrocatalysis of HER but also offers scientific insight into the mechanism for the in situ growth of TMP and their precursor NPs, in which an ultralow reactant concentration and rich functional groups on the 3-D HNC support play critical roles.

Hierarchical Nanocomposite of Hollow N-Doped Carbon Spheres Decorated with Ultrathin WS2 Nanosheets for High-Performance Lithium-Ion Battery Anode

Hierarchical nanocomposite of ultrathin WS2 nanosheets uniformly attached on the surface of hollow nitrogen-doped carbon spheres (WS2@HNCSs) were successfully fabricated via a facile synthesis strategy. When evaluated as an anode material for LIBs, the hierarchical WS2@HNCSs exhibit a high specific capacity of 801.4 mA h g(-1) at 0.1 A g(-1), excellent rate capability (545.6 mA h g(-1) at a high current density of 2 A g(-1)), and great cycling stability with a capacity retention of 95.8% after 150 cycles at 0.5 A g(-1). The Li-ion storage properties of our WS2@HNCSs nanocomposite are much better than those of the previously most reported WS2-based anode materials. The impressive electrochemical performance is attributed to the robust nanostructure and the favorable synergistic effect between the ultrathin (3-5 layers) WS2 nanosheets and the highly conductive hollow N-doped carbon spheres. The hierarchical hybrid can simultaneously facilitate fast electron/ion transfer, effectively accommodate mechanical stress from cycling, restrain agglomeration, and enable full utilization of the active materials. These characteristics make WS2@HNCSs a promising anode material for high-performance LIBs.

Enhanced quantum efficiency from a mosaic of two dimensional MoS2 formed onto aminosilane functionalised substrates

Developing scalable methods of growing two dimensional molybdenum disulphide (2D MoS2) with strong optical properties, on any desired substrates, is a necessary step towards industrial uptake of this material for optical applications. In this study, Si/SiO2 substrates were functionalised using self-assembled monolayers of three different aminosilanes with various numbers of amine groups and molecular lengths as underlayers for enhancing the adherence of the molybdenum precursor. The tetrahedral [MoS4](2-) anion groups from the molybdenum precursor were bonded on these silanised Si/SiO2 substrates afterwards. The substrates were then treated with a combined thermolysis and sulphurisation step. The results showed that silanisation of the substrates using the longest chains and the largest number of amine groups provided a good foundation to grow quasi 2D MoS2 made from adjacent flakes in a mosaic formation. Microscopy and spectroscopy investigations revealed that these quasi 2D MoS2 formed using this long chain aminosilane resulted in flakes with lateral dimensions in micron and submicron ranges composed of adjoining MoS2 pieces of 20 to 60 nm in lateral dimensions, dominantly made of 3 to 5 MoS2 fundamental layers. The obtained quasi 2D MoS2 shows a high internal quantum efficiency of 2.6% associated with the quantum confinement effect and high stoichiometry of the adjoining nanoflakes that form the structure of the sheets. The synthesis technique in this study is reliable and facile and offers a procedure to form large, scalable and patternable quasi 2D MoS2 sheets on various substrates with enhanced optical properties for practical applications.