Preparation of ultrathin molybdenum disulfide dispersed on graphene via cobalt doping: A bifunctional catalyst for hydrogen and oxygen evolution reaction

The development of highly active and low-cost catalysts for hydrogen evolution reaction (HER) is significant for the development of clean and renewable energy research. Owing to the low H adsorption free energy, molybdenum disulfide (MoS₂) is regarded as a promising candidate for HER, but it shows low activity for oxygen evolution reaction (OER). Herein, graphene-supported cobalt-doped ultrathin molybdenum disulfide (Co–MoS₂/rGO) was synthesized via a one-pot hydrothermal method. The obtained hybrids modified electrode exhibits a high HER catalytic activity with a low overpotential of 147 mV at the current density of 10 mA cm⁻², a small Tafel slope of 49.5 mV dec⁻¹, as well as good electrochemical stability in acidic electrolyte. Meanwhile, the catalyst shows remarkable OER activity with a low overpotential of 347 mV at 10 mA cm⁻². The superior activity is ascribed not only to the high conductivity originated from the reduced graphene, but also to the synergistic effect between MoS₂ and cobalt.     

MoS2/NiFeS2 heterostructure as a highly efficient electrocatalyst for overall water splitting at high current densities

Searching for efficient, stable and low-cost nonprecious catalysts for oxygen and hydrogen evolution reactions (OER and HER) is highly desired in overall water splitting (OWS). Herein, presented is a nickel foam (NF)-supported MoS₂/NiFeS₂ heterostructure, as an efficient electrocatalyst for OER, HER and OWS. The MoS₂/NiFeS₂/NF catalyst achieves a 500 mA cm⁻² current density at a small overpotential of 303 mV for OER, and 228 mV for HER. Assembled as an electrolyzer for OWS, such a MoS₂/NiFeS₂/NF heterostructure catalyst shows a quite low cell voltage (≈1.79 V) at 500 mA cm⁻², which is among the best values of current non-noble metal electrocatalysts. Even at the extremely large current density of 1000 mA cm⁻², the MoS₂/NiFeS₂/NF catalyst presents low overpotentials of 314 and 253 mV for OER and HER, respectively. Furthermore, MoS₂/NiFeS₂/NF shows a ceaseless durability over 25 h with almost no change in the cell voltage. The superior catalytic activity and stability at large current densities (>500 mA cm⁻²) far exceed the benchmark RuO₂ and Pt/C catalysts. This work sheds a new light on the development of highly active and stable nonprecious electrocatalysts for industrial water electrolysis.     

MoS2-graphene-CuNi2S4 nanocomposite an efficient electrocatalyst for the hydrogen evolution reaction

We present a facile methodology for the synthesis of a novel 2D-MoS₂, graphene and CuNi₂S₄ (MoS₂-g-CuNi₂S₄) nanocomposite that displays highly efficient electrocatalytic activity towards the production of hydrogen. The intrinsic hydrogen evolution reaction (HER) activity of MoS₂ nanosheets was significantly enhanced by increasing the affinity of the active edge sites towards H⁺ adsorption using transition metal (Cu and Ni₂) dopants, whilst also increasing the edge sites exposure by anchoring them to a graphene framework. Detailed XPS analysis reveals a higher percentage of surface exposed S at 17.04%, of which 48.83% is metal bonded S (sulfide). The resultant MoS₂-g-CuNi₂S₄ nanocomposites are immobilized upon screen-printed electrodes (SPEs) and exhibit a HER onset potential and Tafel slope value of – 0.05 V (vs. RHE) and 29.3 mV dec⁻¹, respectively. These values are close to that of the polycrystalline Pt electrode (near zero potential (vs. RHE) and 21.0 mV dec⁻¹, respectively) and enhanced over a bare/unmodified SPE (– 0.43 V (vs. RHE) and 149.1 mV dec⁻¹, respectively). Given the efficient, HER activity displayed by the novel MoS₂-g-CuNi₂S₄/SPE electrochemical platform and the comparatively low associated cost of production for this nanocomposite, it has potential to be a cost-effective alternative to Pt within electrolyser technologies.     

Cobalt-molybdenum disulfide supported on nitrogen-doped graphene towards an efficient hydrogen evolution reaction

Herein, the cobalt-molybdenum bimetallic sulfide catalysts supported on nitrogen-doped graphene (CoMoS₂/NGO) were facilely synthesized by a one-pot hydrothermal route. These composites exhibit various special nanostructures, rich in abundant edge site exposure and defects, which play an important role in providing active sites for catalyzing hydrogen evolution reaction (HER). When hydrogen peroxide (H₂O₂) was used as an additive in hydrothermal process, the as-fabricated composite exhibited more efficiency towards HER, showing as low onset overpotential (η_on) as −54 mV in 0.5 M H₂SO₄. Typical H₂O₂-assisted composite realized a remarkable cathodic current density of 30 mA cm⁻² at an overpotential η = −137 mV and it possessed a small Tafel slope of 34.13 mV dec⁻¹. Moreover, it exhibited an excellent cycling stability and superior electronic exchange rate. The results prove that CoMoS₂/NGO catalysts have great potential for electrochemical HER.     

Solvothermal synthesis of oxygen-incorporated MoS2-x nanosheets with abundant undercoordinated Mo for efficient hydrogen evolution

Activating the inert basal planes of layered molybdenum disulfide (MoS₂) is critical to deliver its high hydrogen evolution reaction (HER) efficiency. Herein, oxygen-incorparated MoS_x with abundant undercoordinated Mo atoms is fabricated by a facile solvothermal procedure, which realizes synergistically structural and electronic regulations of MoS₂ inert basal planes. Experiment results reveal that oxygen incoparation can effectively modulate the electronic structure and further optimize the intrinsic conductivity, while the defect-rich structure with abundant undercoordinated Mo atoms increases the number of active sites. Moreover, the influence of solvothermal temperature on activity of MoS_2-x is also investigated. The achieved MoS_x electrocatalyst prepared at 220 °C exhibits a superior activity for HER with a low overpotential of 191 mV at 10 mA cm⁻², a small Tafel slope of 67 mV dec⁻¹, and an excellent stability due to the largest surface area and superior conductivity.     

Atomic-scale intercalation of amorphous MoS2 nanoparticles into N-doped carbon as a highly efficient electrocatalyst for hydrogen evolution reaction

The hydrogen evolution reaction (HER) properties of the catalysts are significantly dependent on their microscopic structure. Interfacial engineering at the atomic level is the main approach to design high performance of electrocatalysts. Herein, an interfacial modulation strategy is proposed to fabricate monolayer amorphous MoS₂ nanoparticles with an average of 3.5 nm in diameter stuck in multilayer N-doped carbon (MoS₂/NC), boosting a high HER activity. The amorphous MoS₂ could provide more edge active sites and NC layers endow the fast electron transfer. The XPS, Raman spectra and density functional theory (DFT) calculations reveal that the C–S bond in MoS₂/NC provides the fast electron transfer and decreases H binding energy. Benefiting the unique sandwiched structure, the MoS₂/NC boosts a low overpotential of 152.6 mV at a current density of 10 mA cm⁻², a small Tafel slope of 60.3 mV dec⁻¹, and outstanding long-term stability with 97.3% retention for over 24 h. This strategy provides a new opportunity and development of interfacial engineering for turning intrinsic catalytic activity for water splitting.     

Ultrathin-layered MoS2 hollow nanospheres decorating Ni3S2 nanowires as high effective self-supporting electrode for hydrogen evolution reaction

High-activity and cost-effective transition metal sulfides (TMSs) have attracted tremendous attention as promising catalysts for hydrogen evolution reaction (HER). However, a significant challenge is the simultaneous construction of abundant electrochemical active sites and the fast electronic transmission path to boost a high-efficient HER. Herein, we demonstrate a facile one-step hydrothermal preparation of MoS₂ hollow nanospheres decorating Ni₃S₂ nanowires supported on Ni foam (NF), without any other additional template, surfactant or annealing. In this three-dimensional (3D) heterostructure, the ultrathin-layered MoS₂ hollow nanospheres contribute to the promotion of the total surface area and the electrochemical active sites. Meanwhile, the Ni₃S₂ nanowires are beneficial to the high electrical conductivity. Consequently, the optimized MoS₂/Ni₃S₂/NF-200-24 electrocatalyst presents an extremely superior HER activity to that of individual MoS₂/NF and Ni₃S₂/NF. The HER overpotentials are 85 mV at 10 mA cm⁻² and 189 mV at 100 mA cm⁻², which are also comparable with the state-of-the-art 20% Pt/C/NF electrode at both low and high current.     

Cu–MoS2/rGO hybrid material for enhanced hydrogen evolution reaction performance

Cu doped MoS₂ (Cu–MoS₂)/reduced graphene oxide (rGO) (Cu–MoS₂/rGO) hybrid material is fabricated by a facile one-step solvothermal method. The X-ray diffraction (XRD) results suggest that the doping of Cu does not alter the crystal structure of MoS₂. X-ray photoelectron spectroscopy (XPS) analysis reveal that the doping of Cu atoms influences the electronic structure of MoS₂, which is favorable to increase active sites of edges. Electrochemical impedance spectroscopy (EIS) results indicate that Cu–MoS₂/rGO performed a faster charge-transfer in comparison to MoS₂/rGO hybrid. In addition, the resultant Cu–MoS₂/rGO catalyst with Cu/Mo mole ratio of 9% exhibits a lower overpotential of 199 mV at 10 mA cm⁻², small Tafel slop of 44 mV dec⁻¹ and cycling stability, indicative of enhanced electrocatalytic activity towards HER. The improved performance is attributed to the increased active sites and a synergistic effect between copper and molybdenum, leading to electronic structure change and charge redistribution of MoS₂.     

CoS2/MoS2 decorated with nitrogen doped reduced graphene oxide and multiwalled carbon nanotube 3D hybrid as efficient electrocatalyst for hydrogen evolution reaction

Designing an efficient and stable electrocatalyst made of earth abundant elements to take over expensive noble metal based for Hydrogen Evolution Reaction (HER) have been focused. Cobalt disulfide-molybdenum disulfide nanocomposite supported by nitrogen doped reduced graphene oxide and multiwalled carbon nanotubes (CoS₂/MoS₂@NrGO-MWCNT) is reported as an efficient electrocatalyst for HER. CoS₂/MoS₂@N-rGO-MWCNT and ternary hybrids composed of CoS₂, MoS₂ and N-rGO/MWCNT have been investigated. The catalysts were prepared by facile hydrothermal method, and the optimal doping ratio referred to date cobalt to molybdenum as 2:1 was chosen. It is found that co-existence of CoS₂, MoS₂ brings abundant active sites and incorporation of MWCNT offered stability. Good dispersion of CoS₂ nanoparticles on graphene and MoS₂ sheets is observed. Additionally nitrogen doping on rGO sheets has been carried out to boost up the electronegativity of the catalyst as a support to enhance the catalytic activity of CoS₂/MoS₂ for refine structure and better electrical conductance. Precisely, CoS2/MoS2@N-rGO-MWCNT exhibited smaller tafel slope 73 mV dec^?1 at overpotential 281 mV for current density 10 mA cm^?2 and the substantial stability of 14 h is recorded in 0.5 M H₂SO₄ medium, results suggest that catalyst is viable alternate for HER.     

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.     

One-step synthesis of oxygen incorporated V–MoS2 supported on partially sulfurized nickel foam as a highly active catalyst for hydrogen evolution

Highly active noble-metal-free catalysts for hydrogen evolution reaction (HER) are essential for the sustainable production of hydrogen. MoS₂ based HER catalysts are potentially competitive to noble metals but facing the challenges of low conductivity, density of active sites and intrinsic activity in basal planes. Herein, oxygen incorporated V–MoS₂ supported on partially sulfurized nickel foam (V–Mo(x)S/NF) are synthesized as binder-free HER catalysts via a one-step in-situ hydrothermal method. By controlling the fed atomic ratios of V/Mo, the optimal V–Mo(0.05)S/NF shows the low HER overpotential of ~31 and ~115 at 10 mA cm⁻² and 100 mA cm⁻², respectively in alkaline electrolyte, which is among the most active noble-metal and noble-metal-free HER catalysts reported. In V–Mo(0.05)S/NF, the introduced V and partially sulfurized nickel foam increases the conductivity. The hedgehog-like morphology ensures the exposure of high-density active sites. More importantly, the incorporated surface oxygen can be readily tuned by the fed atomic ratios of V/Mo, which plays the primary role in promoting the intrinsic HER activity for V–Mo(x)S/NF. This work demonstrates the feasibility of boosting HER through the precise control of incorporated surface oxygen in MoS₂ based catalysts.     

Ethylenediamine-assisted phase engineering of 1T/2H–MoS2/graphene for efficient and stable electrocatalytic hydrogen evolution

1T-MoS₂ exhibits superior eletroconductivity and electrocatalytic activity in hydrogen evolution reaction (HER) over 2H–MoS₂. But its thermodynamic instability severely hinders its practical application. This paper develops a highly active and stable triphasic 1T/2H–MoS₂/graphene heterostructure through a facile one-step hydrothermal route with the assistance of a small organic molecule, ethylenediamine, as the structure-directing reagent. The novel triphasic heterostructure is fabricated by vertically stacking lateral 1T/2H–MoS₂ heterojuctions on graphene. The stability of the 1T phase is associated with the strain effects in the lateral 1T/2H–MoS₂ heterojunctioned nanosheets and the electron coupling effects in the vertical 1T/2H–MoS₂/graphene 2D/2D heterostructure. The content of 1T phase in 1T/2H–MoS₂/graphene can be regulated by adjusting the preparation temperature. The optimized 1T/2H–MoS₂/graphene hybrid contains 40.5% 1T phase and exhibits outstanding HER performance with a low overpotential of 143 mV at current density of 10 mA cm^-2, a small Tafel slope of 64 mV dec^-1 and excellent durability in acid electrolyte. This work highlights a new strategy to utilize structure-directing reagents for fabricating highly efficient MoS₂-based electrocatalysts.     

Multilevel N-doped carbon nanotube/graphene supported cobalt phosphide nanoparticles for electrocatalytic hydrogen evolution reaction

Electrochemical water splitting plays an important role in alternative energy studies, since it is highly efficient and environment-friendly. Accordingly, it is an ideal way of providing alternative to meet the urgent need of finding sustainable and clean energy. This study presents the fabrication of CoP attached on multilevel N-doped CNT/graphene (CoP–CNT/NG) hybrids. The multilevel carbon structure can enhance electrical conductivity efficiently and increase the reaction active area immensely. The obtained electrocatalyst exhibits great electronic conductivity (17.8 s cm⁻¹) and HER activity with low overpotential (155 mV at 10 mA cm⁻²), low Tafel slope (69.1 mV dec⁻¹) in 0.5 M H₂SO₄. In addition, the CoP–CNT/NG displays prominent electrochemical durability after 18 h.     

Advanced catalysts for hydrogen evolution reaction based on MoS2/NiCo2S4 heterostructures in Alkaline Media

There are great challenges to develop and fabricate a high performance, low-cost and stable non-platinum catalyst for hydrogen evolution reaction (HER). In our study, we firstly developed a simple method to successfully fabricate a new MoS₂/NiCo₂S₄ heterostructure by a two-step hydrothermal method, and studied the HER property of MoS₂/NiCo₂S₄, where the as-prepared NiCo-layered double hydroxide (NiCo-LDH) was used as the precursor of NiCo₂S₄. Benefitting from the prominent synergistic effect between NiCo₂S₄ and MoS₂, MoS₂ provided massive catalytic active edge sites, and NiCo₂S₄ enhanced the conductivity of the composite. As a result, the MoS₂/NiCo₂S₄ showed excellent HER catalytic activity, with a current of 10 mA cm⁻² at overpotential of 94 mV for HER and a low Tafel slope of 46 mV dec⁻¹, and good cycling stability in Alkaline Media. As well as, our work offered one promising high active and stable non-platinum catalyst for overall water splitting.     

Tunably fabricated nanotremella-like Bi2S3/MoS2: An excellent and highly stable electrocatalyst for alkaline hydrogen evolution reaction

Reasonable design of efficient and stable catalysts with low cost and abundant natural reserves is vital for electrocatalytic water splitting. Herein, novel nanotremella-like Bi₂S₃/MoS₂ composites with different mass ratios between Bi₂S₃ and MoS₂ have been successfully prepared through a hydrothermal approach and further applied to hydrogen evolution reaction (HER) in 1.0 M KOH electrolyte for the first time. When the mass ratio of Bi₂S₃ and MoS₂ is 5:5, as-prepared nanotremella-like Bi₂S₃/MoS₂ (marked as BMS-5) manifests favorable HER catalytic activity with overpotential of 124 mV at current density of 10 mA cm⁻² and relatively low Tafel slope of 123 mV dec⁻¹. Moreover, it exhibits an extraordinary durability for uninterrupted hydrogen generation. The enhanced HER performances are ascribed to the synergistic effects between Bi₂S₃ and MoS₂, giving rise to large electrocatalytic active area and fast HER kinetics. The results pave a new path to design and construct excellent Bi₂S₃/MoS₂ nanomaterials for electrocatalytic hydrogen generation.     

Zinc oxide functionalized molybdenum disulfide heterostructures as efficient electrocatalysts for hydrogen evolution reaction

Technology urges to replace the state-of-the-art catalysts such as platinum with low cost, earth abundant and durable electrocatalysts for efficient hydrogen evolution (HER) reaction which is going to become the major sustainable production of energy in future. Herein, we present the heterostructure based MoS₂.ZnO (MZO) heterostructures for successful electrochemical water splitting process. For HER, the prepared MoS₂.ZnO nanocomposites show the over potential as low as 239 mV at cathodic current density 10 mAcm⁻² with an exchange current density of 3.2 μAcm⁻². A Tafel slope of about 62 mV per decade suggested to have the Volmer-Heyrovsky mechanism for the HER process with MoS₂.ZnO nanocomposite as the catalyst. The small Tafel slope indicates a promising electrocatalyst for HER in practical application. The strong interface formation at the MoS₂.ZnO heterostructure facilitates higher catalytic activity and excellent cycling stability. The heterostructure formation based on semiconductor two dimensional (2D) transition metal dichalcogenides (TMDC) open up new avenues for effective manipulation of HER catalysts.     

Phase controlled synthesis and the phase dependent photo-and electrocatalysis of CdS@CoMo2S4/MoS2 catalyst for HER

Herein we report a heterostructure with ultrathin nanosheets of Co-doped molybdenum sulfide on CdS nanorod array (donated as CdS@CoMo₂S₄/MoS₂) by hydrothermal synthesis. Firstly, elemental Co doping MoS₂ (CoMo₂S₄) delivers the double benefits of increased active sites and enhanced conductivity. Secondly, the structural characteristics maximally exposes the MoS₂ edges and enlarges interfacial contact area between the composite catalyst and electrolyte, as well as the efficient interfacial charge transfer. The ratio of CoMo₂S₄/MoS₂ in CdS@CoMo₂S₄/MoS₂ plays a crucial role for the enhanced photo-assistant electrocatalytic hydrogen evolution reaction (HER). We can tune the ratio of CoMo₂S₄/MoS₂ by controlling the preparation time or the ratio of precursor of Co/Mo. The catalyst with predominant MoS₂ phase shows superior photocatalytic HER performance with a high H₂ production rate of 46.60 μmol mg⁻¹ h⁻¹. Meanwhile, the catalyst with predominant CoMo₂S₄ phase exhibits not only relatively low overpotential of 172 mV at 10 mA cm⁻², which outperforms most values that have been reported on catalyst supported on ITO substrate, but also possesses H₂ production rate of 23.47 μmol mg⁻¹ h⁻¹. The superior photo-assistant electrocatalytic HER activity results from the synergistically structural and electronic modulations, as well as the proper energy band alignment between MoS₂ and CdS. This investigation could provide an approach to integrate the electro- and photocatalytic activities for HER, especially the photo responding behaviour at a bias potential which is meaningful to produce H₂ for actual application.     

Synergistic effects of 1T-2H MoS2 nanoflowers modified with Ag3PO4 nanoclusters for highly efficient electrochemical activity

The development of highly efficient binary heterostructures with enhanced electrocatalytic activities is vital for reducing the energy consumed by the hydrogen evolution reaction (HER). Herein, we successfully design and synthesize an eco-friendly Ag₃PO₄/1T-2H MoS₂ heterostructure to catalyze the HER process. Micromorphology and microstructure studies show that the Ag₃PO₄ nanoclusters are well dispersed with abundant catalytically active sites on the surface of the 1T-2H MoS₂ nanoflowers. X-ray photoelectron spectroscopy confirms the stable oxidation state and electronic interactions in the 2 wt% Ag₃PO₄/1T-2H MoS₂ nanostructure. Benefitting from the strong electronic interactions and advantages of abundant heterogeneous interfaces and catalytically active sites, the 2 wt% Ag₃PO₄/1T-2H MoS₂ heterostructure delivers excellent and durable electrochemical HER activity in alkaline solution, with a low overpotential of 149 mV for the HER at 10 mA cm⁻², in clear improvement over 1T-2H MoS_2. The enhanced electrocatalytic activity is ascribed to the abundant catalytically active sites, rapid charge transport, and Ag₃PO₄/1T-2H MoS₂ synergism. This study provides a novel strategy for exploring and synthesizing low-cost binary electrocatalysts that enhance the electrochemical HER performance in energy-conversion applications.     

Nano-pom-pom multiphasic MoS2 grown on carbonized wood as electrode for efficient hydrogen evolution in acidic and alkaline media

Molybdenum disulfide (MoS₂), attracts great attention in hydrogen evolution reaction (HER) field, however, low catalytic activity sites and poor conductivity still limit its further application. In this study, an efficient hydrogen evolution electrode with nano-pom-pom multiphasic MoS₂ uniformly grew on porous carbonized wood (NP MoS₂/CW) was developed. Interestingly, the nano-pom-pom are stacked from sheets of MoS₂. Fully exposed active edges of nano-pom-pom MoS₂ and high excellent electrical conductivity of carbonized wood enhance collectively electrocatalytic performance for HER. Specifically, the NP MoS₂/CW electrode requires an overpotential of 109.5 mV and 305 mV to achieve the current density of 10 mA cm⁻² and 400 mA cm⁻², respectively (0.5 M H₂SO₄). NP MoS₂/CW has excellent electrocatalytic performance and stability in acidic and alkaline media due to the perfect combination of NP MoS₂ unique nanostructure and the unique properties of CW. Therefore, the present work provides a promising strategy into the rational development and utilization of MoS₂ for the development of hydrogen evolution.     

P-doped 3D graphene network supporting uniformly vertical MoS2 nanosheets for enhanced hydrogen evolution reaction

In order to optimize the conductivity of molybdenum disulfide (MoS₂) and promote its large-scale application as a catalyst for hydrogen evolution, MoS₂ is usually used to form composites with conductive materials, but these hybrid materials suffer from scare active sites, overlapping and complicate process. In this work, phosphoric acid is used as a builder of stereoscopic structures, which can not only twist graphene sheets into a P-doped three-dimensional (3D) graphene network but also promote surface electron transport between graphene sheets. Without adding additional framework materials such as carbon nanotubes or nickel foam, stereoscopic MoS₂/graphene structures are formed with a large number of twisted graphene sheets to support the vertical growth of MoS₂ and expose the edge sites of MoS₂, showing a low Tafel slope about 35 mV dec⁻¹, a high current density of 900 mA cm⁻² at about 300 mV and a robust stability over 2000 cycles. Thus, this work shows a possibility to synthesize an efficient catalyst on a large-scale for hydrogen evolution reaction, which can promote the realization of hydrogen economy.