Flower-like CoS2/MoS2 nanocomposite with enhanced electrocatalytic activity for hydrogen evolution reaction

Molybdenum sulfide (MoS₂) has received tremendous attracts for its promising performance in the aspects of hydrogen evolution reaction (HER). To improve the HER activity of MoS₂, we designed a flower-shaped CoS₂/MoS₂ nanocomposite with enhanced HER electroactivity compared with MoS₂ nanosheets by a simple one-step hydrothermal method. The facile approach brings about distinct transformation of the morphology from nanosheets to nanoflower structures. The introduction of Co element into MoS₂ results in the larger active surface area, more edge-terminated structures, and higher conductivity of the CoS₂/MoS₂ nanocomposite, which are good for improving the HER electroactivity. In brief, the optimized catalyst exhibits the low overpotential of 154 mV at 10 mA cm^?2, small Tafel slope of 61 mV dec^?1, and excellent stability in acidic solution.     

Graphene confined MoS2 particles for accelerated electrocatalytic hydrogen evolution

MoS₂ is a promising noble-metal-free electrocatalyst for the hydrogen evolution reaction. Extensive trials have been carried out to increase its low electrical conductivity and insufficient active sites. Here, a remarkable electrocatalyst for hydrogen evolution is developed based on the in-situ preparation of MoS₂ confined in graphene nanosheets. Graphene effectively controls the growth of MoS₂ and immensely increases the conductivity and structural stability of the composite materials. Remarkably, because of the plentiful active sites, sufficient electrical contact and transport, MoS₂ particles confined in graphene nanosheets exhibit an onset overpotential as small as 32 mV, an overpotential approaching 132 mV at 10 mA cm⁻², and a low Tafel slope of 45 mV dec⁻¹. This work presents a reasonable architecture for practical applications in efficient electrocatalytic H₂ generation.     

Hierarchical MoS2 nanosheets integrated Ti3C2 MXenes for electrocatalytic hydrogen evolution

In this study, conductive Ti₃C₂ MXenes were used as a promoter to accelerate charger transfer of MoS₂, realizing highly efficient HER electrocatalysis. A facile hydrothermal strategy is demonstrated to be effective for in situ growth of MoS₂ nanosheets vertically standing on planar Ti₃C₂ nanosheets to form hierarchical heterostructures. Beneficial from the opened layer structures and strong interfacial coupling effect, the resulting MoS₂/Ti₃C₂ heterostructures achieve a giant enhancement in HER activity compared with pristine MoS₂ nanosheets. More specifically, the catalytic current density induced by MoS₂/Ti₃C₂ heterostructures at an overpotential of ∼400 mV is nearly 6.2 times as high as that of the pristine MoS₂ nanosheets. This work uncovers that the Ti₃C₂ nanosheets are ideal candidates for construction of highly active electrocatalysts for water splitting.     

Synthesis and electrocatalytic activity of Ni0.85Se/MoS2 for hydrogen evolution reaction

Recently, the replacement of expensive platinum-based catalytic materials with non-precious metal materials to electrolyze water for hydrogen separation has attracted much attention. In this work, Ni_0.85Se, MoS₂ and their composite Ni_0.85Se/MoS₂ with different mole ratios are prepared successfully, as electrocatalysts to catalyze the hydrogen evolution reaction (HER) in water splitting. The result shows that MoS₂/Ni_0.85Se with a molar ratio of Mo/Ni = 30 (denoted as M30) has the best catalytic performance towards HER, with the lowest overpotential of 118 mV at 10 mA cm⁻², smallest Tafel slope of 49 mV·dec⁻¹ among all the synthesized materials. Long-term electrochemical testing shows that M30 has good stability for HER over at least 30 h. These results maybe due to the large electrochemical active surface area and high conductivity. This work shows that transition metal selenides and sulfides can form effective electrocatalyst for HER.     

Facile hydrothermal synthesis of combined MoSe2PS nanostructures on nickel foam with superior electrocatalytic properties for hydrogen evolution reaction

Producing an efficient and inexpensive electrocatalyst for use in the water electrolysis process is the most efficient and logical way to industrialize this method to produce hydrogen as a clean and alternative fuel for fossil fuels. In this study, combined and unique MoSe₂PS nanostructures are synthesized on nickel foam by three steps hydrothermal process. Microstructural observations reveal the unique morphology of the petals covered by the elongated nano-blades. A high electrocatalytic performance is attained with this nanostructure in hydrogen evolution reaction, so that the 90 mV overpotential is achieved at a current density of ?10 mA/cm². The near-platinum activity is due to the unique and combined nanostructure due to the synergistic properties of S and P on MoSe₂ as well as the high electrochemical active sites in the specimen. Additionally, excellent stability of the synthesized electrocatalyst is observed in the alkaline medium for 30 h, which confirms its potential application in relevant industries such as fuel cells and transportation.     

MoS2 confined on graphene by triethanolamine for enhancing electrocatalytic hydrogen evolution performance

The reduction of active sites due to reunion and slow electron transfer rates and low electronegativity greatly reduced the catalytic performance of many two-dimensional materials. In this paper, we synthesized composites for partially reducing graphene oxide and molybdenum disulfide (MoS₂@prGO) by one-step hydrothermal method. With the addition of triethanolamine, MoS₂ is highly dispersed on the prGO carrier and converted into the 1T phase MoS₂ (50.4%). Meanwhile, it helps to increase the electron transfer rate of the MoS₂@prGO composites. MoS₂@prGO composites presents a high electron cloud density due to the existence of N atoms and prGO, which promotes the occurrence of hydrogen ion conversion hydrogen reaction and decreases the electrocatalytic hydrogen evolution overpotential. MoS₂@prGO composites exhibits an overpotential of 263 mV at 10 mA/cm² and a small Tafel slope of 60 mV/dec. This work is devoted to offer a new prospect and direction for the improvement of electrochemical HER performance.     

Micrometer‒Scale biomass carbon tube matrix auxiliary MoS2 heterojunction for electrocatalytic hydrogen evolution

Electrocatalytic materials for hydrogen evolution reaction are crucial in water splitting. Developing low‒cost and highly active catalyst remains an enormous challenge. Herein, we reported a simple approach to synthesize a molybdenum disulfide/micrometer‒scale biomass carbon tube matrix (BCTM) which is derived from available and accessible plant wild celery. Molybdenum disulfide (MoS₂) nanosheet could be well dispersed on the BCTM to form porous structure, while the BCTM can enhance the conductivity of MoS₂ nanosheet. The synergistic effects between the MoS₂ nanosheet and BCTM contribute to high hydrogen evolution reaction activity. MoS₂/BCTM shows admirable catalytic ability with a low overpotential of 176 mV at 10 mA cm⁻², a small Tafel slope 51 mV·dec⁻¹, and outstanding stability over 2000 cycles under acidic conditions. This novel strategy provides a low‒cost route to synthesize excellent MoS₂‒based catalyst, which may widely apply in the fields of electrocatalysis and photocatalysis.     

Edge terminated and interlayer expanded pristine MoS2 nanostructures with 1T on 2H phase,for enhanced hydrogen evolution reaction

Pristine molybdenum disulfide (MoS₂) nanostructures with 1T on 2H phase have been prepared by tuning the growth time in hydrothermal synthesis. The optimized sample has an expanded interlayer and it exhibits striking kinetic metrics with an onset potential of - 0.13 V, Tafel slope of 49 mV/decade, and an exchange current density of 3.98 × 10^?3 mA, performing best among the pristine MoS₂ based hydrogen evolution reaction (HER) catalysts reported so far. The edge terminated structure, together with the expanded interlayer, is believed to modify the electronic structure to enhance the conductivity of the compound. The Mott-Schottky analysis of the optimized sample indicated a decrease in band bending and an enhancement in the charge transfer. The promising HER response obtained with sufficiently low growth time and growth temperature for the pristine MoS₂ nanostructures suggests a potential way to design high-performance HER catalysts based on the compound.     

MoS2 grown in situ on CdS nanosheets for boosted photocatalytic hydrogen evolution under visible light

A novel nano-heterojunction photocatalysts of CdS/MoS₂ with appropriate interfacial contact was successfully obtained by the facile two-step hydrothermal synthesis. The MoS₂ ultrathin layer was well combined with CdS nanosheets and formed the interaction, which facilitated the transfer and separation of charges. The CdS/MoS₂ 15 wt% possessed much higher H₂ evolution photocatalytic performance (35.24 mmol h^?1 g^?1), exhibiting an 85.95 times enhancement as compared to that of pure CdS (0.41 mmol h^?1 g^?1). Moreover, the photochemical stability of CdS/MoS₂ heterojunctions was excellent, which showed no significant decrease in activity after four cycles of experiments. The finding provides a novel method to integrate the structure of MoS₂ with CdS, which exhibits great potential in solar energy conversion.     

Improved electrocatalytic hydrogen evolution characteristics in Mn-doped MoS2 nanosheets grown under a non-equilibrium condition

Two-dimensional (2D) monolayer pristine MoS₂ transition metal dichalcogenide (TMDC) is the most investigated material due to its potential applications as a non-precious electrocatalyst for the hydrogen evolution reaction (HER). However, the active edge sites created by sulfur non-stoichiometry and a defect-engineering by selective doping play a vital role in activating inert basal planes and enhancing the HER activity. Herein we report the synthesis of highly disordered Mn-doped 2D-MoS₂ nanospheres by a simple hydrothermal route under a non-equilibrium growth condition. Excess sulfur content in the precursor and electron-rich atmosphere created by Mn-doping results in an increased domain-based defects in the lattice that enhances the number of exposed edge sites, and also exposing more catalytically active high-index planes. Thereby improving its physicochemical properties. The developed electrode shows a low overpotential of 186 mV at a current density of 10 mA/cm² and a low Tafel slope of 79.9mV/dec in acidic electrolytes. In addition, Density Functional Theory based calculation shows that Mn-doping in non-stoichiometric MoS₂ enhances the electronic properties and its role in facilitating hydrogen adsorption and desorption processes with free energy close to that of benchmark Pt is established.     

Synthesis of nitrogen-doped MoSe2 nanosheets with enhanced electrocatalytic activity for hydrogen evolution reaction

Benefiting from improved electrical conductivity, the N-doped MoSe₂ nanosheets show substantially enhanced HER activity with a lower onset overpotential of approximately ?135 mV and a smaller Tafel slope of 62 mV dec^?1, which exhibiting enhanced catalytic performance compared with that of pure MoSe₂. The success of improving the HER performance via the introduction of N dopant offers a new opportunity in the development of high performance MoSe₂-based electrocatalyst.     

Three-dimensional structure of WS2/graphene/Ni as a binder-free electrocatalytic electrode for highly effective and stable hydrogen evolution reaction

Tungsten disulfide (WS₂) has attracted much attention as the promising electrocatalyst for hydrogen evolution reaction (HER). Herein, the three-dimensional (3D) structure electrode composed of WS₂ and graphene/Ni foam has been demonstrated as the binder-free electrode for highly effective and stable HER. The overpotential of 3D WS₂/graphene/Ni is 87 mV at 10 mA cm^?2, and the current density is 119.1 mA cm^?2 at 250 mV overpotential, indicating very high HER activity. Moreover, the current density of 3D WS₂/graphene/Ni at 250 mV only decreases from 119.1 to 110.1 mA cm^?2 even after 3000 cycles, indicating a good stability. The high HER performance of 3D WS₂/graphene/Ni binder-free electrode is superior than mostly previously reported WS₂-based catalysts, which is attributed to the unique graphene-based porous and conductive 3D structure, the high loading of WS₂ catalysts and the robust contact between WS₂ and 3D graphene/Ni backbones. This work is expected to be beneficial to the fundamental understanding of both the electrocatalytic mechanisms and, more significantly, the potential applications in hydrogen economy for WS₂.     

Amorphous MoS2 nanosheets on MoO2 films/Mo foil as free-standing electrode for synergetic electrocatalytic hydrogen evolution reaction

A facile oxidation-sulfidation strategy is proposed to fabricate the vertically aligned amorphous MoS₂ nanosheets on MoO₂ films/Mo foil (MF) as free-standing electrode, which features as the integration of three merits (high conductivity, abundant exposures of active sites, and enhanced mass transfer) into one electrode for hydrogen evolution reaction (HER). Density functional theory (DFT) calculations reveal the strong interaction between MoS₂ and MoO₂, which can enhance the intrinsic conductivity with narrow bandgap, and decreases hydrogen adsorption free energy (ΔG_H1 = ~0.06 eV) to facilitate the HER process. Benefiting from the unique hierarchical structure with amorphous MoS₂ nanosheets on conductive MoO₂ films/MF to facilitate the electron/mass transfer by eliminate contact resistance, controllable number of stacking layers and size of MoS₂ slabs to expose more edge sites, the optimal MoS₂/MoO₂/MF exhibits outstanding activity with overpotential of 154 mV at the current density of 10 mA cm⁻², Tafel slope of 52.1 mV dec⁻¹, and robust stability. Furthermore, the intrinsic HER activity (vs. ECSA) on MoS₂/MoO₂/MF is significantly enhanced, which shows 4.5 and 18.6 times higher than those of MoS₂/MF and MoO₂/MF at overpotential of 200 mV, respectively.     

Electrocatalytic hydrogen evolution reaction on sulfur-deficient MoS2 nanostructures

Molybdenum disulfide (MoS₂) is a 2D layered structured material with a Mo:S of 1:2 and is a great attention seeker for hydrogen production through water-splitting. In the present work, we prepared nanostructured MoS_x with different sulfur molar concentrations (x = 2, 1, 0.5) through a one-step hydrothermal method. The decrease in sulfur concentration resulted in a new phase that is MoO₃ with a Mo:S of 1:0.5. The structural, morphological, and optical properties of all the samples were studied through X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Fourier Transform Infrared spectroscopy (FTIR), and Ultraviolet–Visible (UV–Vis) spectroscopy, respectively. Moreover, the electrochemical behavior was studied using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), linear sweep voltammetry (LSV), and Tafel slope. Optimum properties were observed for Mo:S (1:1) with an onset potential of 96 mV, an overpotential of 130 mV for hydrogen evolution reaction (HER) coupled with a specific capacitance of 889 F/g and low charge transfer resistance of 43 Ω. Further, it was noted that the electrocatalytic activity of MoS₁ was better than that of the composite and bare MoO₃. It is proposed that the excellent electrochemical activity arises from sulfur vacancies which provide active sites for HER and a free path for ions to flow through the material.     

A feasible and environmentally friendly method to simultaneously synthesize MoS2 quantum dots and pore-rich monolayer MoS2 for hydrogen evolution reaction

MoS₂ has been one of a widely researched hydrogen evolution reaction (HER) catalyst materials in recent years. However, the basal plane of MoS₂ is considered to be inactive to hinder its further development. Herein, a new mass-scalable and facile intercalation method for the fabrication of multiple products, including pore-rich monolayer MoS₂ (PR MoS₂) and MoS₂ quantum dots (MoS₂ QDs), has been developed via the gas phase etching of bulk MoS₂ in an acetone vapor atmosphere. The obtained monolayer MoS₂ QDs with a narrow lateral size distribution (average size: 2.5 nm) present excitation-independent photoluminescence emission. Furthermore, the PR MoS₂ shows a significantly enhanced HER electrocatalytic activity and good stability in 0.5 M H₂SO₄ solution with a small overpotential of 241 mV at a current density of 10 mA cm⁻². These results demonstrate that the as-prepared PR MoS₂ is very promising for the application in HER.     

Modification of the ultrasonication derived-g-C3N4 nanosheets/quantum dots by MoS2 nanostructures to improve electrocatalytic hydrogen evolution reaction

In this work, graphitic carbon nitride (g-C₃N₄) nanosheets/quantum dots (NS/QD) was prepared using a simple and low-cost procedure. By two steps exfoliation in a bath and tip sonicator, the g-C₃N₄ (NS/QD) was produced from bulk g-C₃N₄. To improve electrocatalytic hydrogen evolution reaction (HER), the g-C₃N₄ (NS/QD) were modified by the MoS₂ nanostructures. Nanocomposite of the g-C₃N₄ (NS/QD) with MoS₂ nanostructures was deposited on a flexible, conductive and three dimensional carbon cloth by a facile and binder-free electrophoretic technique. This electrode exhibited a Tafel slope of 88 mV/dec and an overpotential of 0.28 V vs RHE at −2 mA/cm², lower than that of the g-C₃N₄, and good stability after 1000 cycles and 100 days for HER. The enhanced electrocatalytic performance was attributed to the MoS₂ and g-C₃N₄ nanostructures on three dimensional carbon cloth, leading to high surface area and more number of the exposed active sites for HER. This heterostructure improved charge transport, proton adsorption and hydrogen evolution on the electrode. This work proposes cost-effective, stable and three dimensional g-C₃N₄ based electrode for hydrogen evolution reaction.     

A novel approach for high-yield solid few-layer MoS2 nanosheets with effective photocatalytic hydrogen evolution

Few-layer molybdenum disulfide (MoS₂) nanosheets are well applied in many field, but the lack of simple methods for the preparation of solid few-layer MoS₂ nanosheets with high yield and quality has greatly restricted their development. In this work, a facile solvothermal treatment coupled with the liquid exfoliation strategy was conducted to produce solid monodispersed few-layer MoS₂ nanosheets from the MoS₂ stack, and the output can reach as high as approximately 0.3 g/g. The few-layer features were confirmed by characterizations of SEM, TEM, Raman spectra, UV–vis absorption spectrum and PL spectrum. The obtained MoS₂ nanosheets exhibit fantastic dispersity and stability in an NMP solution, which can remain uniform even after one year. In general, pure MoS₂ catalysts show no or poor activity for photocatalytic hydrogen evolution as reported in the literature, however, the prepared MoS₂ nanosheets in this work display excellent photocatalytic H₂ evolution performance of 1241.3 μmol g⁻¹ h⁻¹ due to the synergistic structural and electronic modifications, including a bigger specific surface area, additional exposed active edge sites, superior charge separation and transfer efficiency, and higher reduction potential.     

Facile synthesis of NiS2 nanowires and its efficient electrocatalytic performance for hydrogen evolution reaction

Recently, the first-row transition metal dichalcogenides MX₂ (M = Fe, Co, Ni; X = S, Se) have been widely reported as promising catalysts for hydrogen evolution reaction (HER) because of its excellent catalytic activity and earth-abundance. The rational nanostructure designs have been proved as an effective way to improve their catalytic performance. However, the reported one dimension (1D) NiS₂ nanowires for HER suffer from a large Tafel slope. Here, we report a facile synthesis of 1D NiS₂ nanowires and its high efficient catalytic activity in HER. This nanowire structure with large surface area and active sites enables highly efficient electrocatalytic performance in HER with a much smaller Tafel slope (83.5 mV/dec) compared to that of bulk NiS₂ (136 mV/dec) as well as long-term stability. Our work builds up a structure–performance relationship and enriches the synthetic strategy to other efficient catalysts such as first-row transition metal dichalcogenides or transition metal phosphide.     

S-doping induced phase engineering of MoSe2 for hydrogen evolution reaction

MoSe₂ is a promising electrocatalyst for hydrogen evolution reaction (HER). It is confirmed that 1T-MoSe₂ shows better activity for HER compared with 2H-MoSe₂ since of wider interlayer spacing, higher conductivity and better hydrophilicity of 1T-MoSe₂. Realization of 1T-MoSe₂ is still a thorny issue due to its high formation barrier and thermodynamic metastable. Herein, considering the microstrain induced by atomic size mismatch through the substitution of Se by S, the MoSe_2-2xS_2x is prepared via one-pot hydrothermal synthesis, resulting in 70.3% high-purity 1T phase. Additionally, the MoSe_2-2xS_2x shows a low overpotential of 167 mV at 10 mA cm^?2, Tafel slope of 54 mV dec^?1, high double layer capacitance (C_dl) of 13.43 mF cm^?2 and superior cycle stability. The results are ascribed to larger interlayer spacing, high conductivity and good hydrophilicity of 1T phase MoSe_2-2xS_2x. This study provides a simple and feasible route to achieve high-purity TMDs for promoting HER application.     

Defective-MoS2/rGO heterostructures with conductive 1T phase MoS2 for efficient hydrogen evolution reaction

As a two-dimensional material, molybdenum disulfide (MoS₂) exhibits great potential to replace metal platinum-based catalysts for hydrogen evolution reaction (HER). However, poor electrical conductivity and low intrinsic activity of MoS₂ limit its application in electrocatalysis. Herein, we prepare a defective-MoS₂/rGO heterostructures material containing 1T phase MoS₂ and evaluate its HER performance. The experimental results shown that defective-MoS₂/rGO heterostructures exhibits outstanding HER performance with a low overpotential at 154.77 mV affording the current density of 10 mA cm^?2 and small Tafel slope of 56.17 mV dec^?1. The unique HER performance of as-prepared catalyst can be attributed to the presence of 1T phase MoS₂, which has more active sites and higher intrinsic conductivity. While the defects of as-prepared catalyst fully expose the active sites and further improve catalytic activity. Furthermore, the interaction between MoS₂ and rGO heterostructures can accelerate electron transfer kinetics, and effectively ensure that the obtained catalyst displays excellent conductivity and structural stability, so the as-prepared catalyst also exhibits outstanding electrochemical cycling stability. This work provides a feasible and effective method for preparation of defective-MoS₂/rGO heterostructures, which also supplies a new strategy for designing of highly active and conductive catalysts for HER.