Ni–MoS2 composite coatings as efficient hydrogen evolution reaction catalysts in alkaline solution

It remains an important project for the development of water splitting electrolyze to design and synthesis of more efficient non-noble metal catalyst. In this work, a structured Ni–MoS₂ composite coating has been synthesized under supergravity fields with nickel sulphamate bath containing suspended MoS₂ submicro-flakes. X-ray diffraction patterns indicate that the MoS₂ submicro-flakes have been successfully incorporated into the Ni matrix. Additionally, SEM shows that the prepared Ni–MoS₂ composite coatings display finer grain size than the pure Ni coatings, which can increase the electrochemistry surface area and the active site of hydrogen evolution reaction. Therefore, due to the synergistic effect of molybdenum disulfide and nickel, the Ni–MoS₂ composite coatings are directly used as binder-free electrode, which exhibits outstanding electrocatalytic activity for HER in 1.0 M NaOH solution at room temperature. The Ni–MoS₂ composite coatings demonstrated an outstanding performance toward the electrocatalytic hydrogen production with low overpotential (100 mA cm^?2 at η = 207 mV), a Tafel slope as small as 65 mV dec^?1, and stable cycling performance (1200 cycles). The preeminent HER performance of this catalyst suggests that it may hold great promise for practical applications.     

Efficient hydrogen evolution electrocatalysts from LixMoS2 nanoparticles on three-dimensional substrate

Molybdenum disulfide (MoS₂), as a promising catalyst, has been widely investigated for hydrogen evolution reaction (HER). But the low density and poor reactivity of active sites, poor electrical transport, and inefficient electrical contact to the catalyst, leads to the modest performance. In this work, we demonstrate an effective route to overcome those issues by decorating the conductive Li_xMoS₂ nanoparticles on the three-dimensional carbon fiber paper (CFP) through combining hydrothermal method and lithium intercalation. Thus, the dense Li_xMoS₂ nanoparticles of the surface can provide the large number of exposed active sites, the highly-conductive Li_xMoS₂ nanoparticles and CFP substrate can facilitate the transfer of electron not only between the Li_xMoS₂ nanoparticles and CFP, but also between the whole sample and current collector, and the porous networked structure can enable the diffusion and penetration of electrolyte. Prompted by those advantage, the as-prepared samples exhibit outstanding HER catalytic activity with the small Tafel slope of 62 mv dec^?1 and the low overpotential of ?115.6 mV vs RHE at an electrocatalytic current density of 10 mA cm^?2. Chronoamperometric current test for 10 h confirms the long-term stability of the catalyst.     

Electrochemical growth of MoSx on Cu foam: A highly active and robust three-dimensional cathode for hydrogen evolution

In this paper, we report a highly active and robust three-dimensional (3D) Cu foam@MoS_x electrode for electrocatalytic hydrogen evolution reaction (HER) prepared by a simple and controllable electrochemical deposition method. Highly conductive Cu foam scaffold with exposed 3D frameworks can not only ensure an intimate interface for facilitate a fast electron transfer but also render the deposited amorphous MoS_x with abundant exposed active sites and large contact area for electrolyte diffusion. As a result, the optimized Cu foam@MoS_x electrode exhibits high activity for electrocatalytic H₂ evolution in 0.5 M H₂SO₄, the required overpotentials to reach current densities of 10 and 100 mA cm^?2 are 200 and 250 mV, respectively. Moreover, the Cu foam@MoS_x electrode shows no obvious deactivation after 2000 potential cycling and also retains its outstanding electrocatalytic activity after 10 h bulk electrolysis for H₂ evolution due to the robust adhesion of MoS_x. This work provides a new strategy to the development of highly active HER electrocatalyst by integrating high-surface-area and conductive substrate and the favorable surface structures of active components.     

In situ growth of MoS2 on carbon nanofibers with enhanced electrochemical catalytic activity for the hydrogen evolution

Developing an effective and facile method to achieve mass production of MoS₂ nanostructures with abundant of edges may be the feasible way to meet the increasing demand for hydrogen evolution electrocatalysts. We developed a facile glucose-assisted hydrothermal method to in-situ grow MoS₂ nanosheets on the commercial carbon nanofibers (CNFs). The controlled growth of MoS₂ on CNFs (MoS₂@CNFs) is leveraged to reveal mass ratio- and structure-dependent catalytic activity in the hydrogen evolution reaction (HER). Due to the unique shell structure, abundant edges of the MoS₂ layer are exposed as active site, as well as the underlying CNFs effectively improves the conductivity, the resulting MoS₂@CNFs hybrid exhibited high electrocatalytic activity in HER. The catalyst demonstrated the lowest overpotential of 52 mV, the highest current density of 101.49 mA cm^?2 at ～200 mV overpotential and the smallest Tafel slope of 49 mV/decade, suggesting the Volmer–Heyrovsky mechanism for the MoS₂-catalyzed HER.     

Flower-like HEA/MoS2/MoP heterostructure based on interface engineering for efficient overall water splitting

The development of cheap, efficient, and active non-noble metal electrocatalysts for total hydrolysis of water (oxygen evolution reaction (OER) and hydrogen evolution reaction (HER)) is of great significance to promote the application of water splitting. Herein, a heterogeneous structured electrode based on FeAlCrMoV high-entropy alloy (HEA) was synthesized as a cost-effective electrocatalyst for hydrogen and oxygen evolution reactions in alkaline media. In combination of the interfacial synergistic effect and the high-entropy coordination environment, flower-like HEA/MoS₂/MoP exhibited the excellent HER and OER electrocatalytic performance. It showed a low overpotential of 230 mV at the current density of 10 mA cm⁻² for OER and 148 mV for HER in alkaline electrolyte, respectively. Furthermore, HEA/MoS₂/MoP as both anode and cathode also exhibited an overpotential of 1.60 V for overall water splitting. This work provides a new strategy for heterogeneous structure construction and overall water splitting based on high-entropy alloys.     

Exfoliated MoS2 with porous graphene nanosheets for enhanced electrochemical hydrogen evolution

Porous graphene (P-rGO) was synthesized from graphene oxide (GO) via a one-pot calcination method with CO₂ as an activation agent at 800 °C. Due to the special porous structure, the surface area of P-rGO can be increased to ～759 m²/g. The P-rGO was then used as a support to incorporate with chemical exfoliated molybdenum disulfide (MoS₂) for the fabrication of MoS₂/P-rGO composite. Compared to bulk MoS₂, the exfoliated MoS₂ is in the 1T phase with a metallic property and smaller charge transfer resistance, thus has a better activity in electrochemical hydrogen evolution reaction (HER). The HER activity of 1T MoS₂ could be further increased after the combination with P-rGO. The overpotential of 1T MoS₂/P-rGO was only ～130 mV vs. RHE, and the corresponding Tafel slope was ～75 mV Dec^?1. The special porous structure and good electric conductivity of P-rGO decrease the charge transfer resistance of the composite without sheltering too many active sites of MoS₂, thus leading to the enhanced HER activity. As an efficient noble metal free HER catalyst, the 1T MoS₂/P-rGO has great potential for large-scale hydrogen production.     

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.     

Defect-rich MoSx/carbon nanofiber arrays on carbon cloth for highly efficient electrocatalytic hydrogen evolution

Engineering MoS₂ catalysts with more active sites and higher conductivity is an effective way to improve its electrochemical activity. Herein, defect-rich amorphous MoS_x/carbon nanofiber (CF) arrays on carbon cloth (CC) support (denoted as MoS_x/CF/CC) was designed and fabricated, which served as an efficient free-standing electrocatalyst for hydrogen evolution reaction (HER) in acid media. This architecture was beneficial to expose more active catalytic sites and improve the electron/ion transport. In addition, abundant defects altered preferred growth direction of MoS_x, resulting in the formation of irregular MoS_x particles at the surface of CF arrays. The as-synthesized MoS_x/CF/CC-2 exhibited excellent stability and superior HER activity, with a small onset overpotential (107 mV) and low Tafel slope (51 mV dec^?1). Such excellent electrochemical performance was attributed to the enriched active sites and shortened charge diffusion distance. This work would pave a new way for rational design and fabrication of defect-rich MoS_x-based composite electrode for renewable energy applications.     

Towards activation of amorphous MoSx via Cobalt doping for enhanced electrocatalytic hydrogen evolution reaction

Amorphous molybdenum sulfide (a-MoS_x) has been shown as one of the most promising catalysts in acidic electrolytes towards hydrogen evolution reaction (HER). Its intrinsic electrocatalytic activity can be further enhanced via doping and cropping the electronic structure.In this study, one-step electro-deposition was employed to fabricate MoS_xCo_y/TNAs hybrid electrodes using TiO₂ nanotube arrays as support. The microstructure and chemical composition of the samples were characterized via X-ray diffraction (XRD), scanning electron microscope (SEM), tunneling electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), and energy dispersive spectroscopy (EDS). The electrochemical properties of the samples were investigated through linear sweep voltammetry (LSV), cyclic voltammetry (CV), Tafel curves, and electrochemical impedance spectroscopy (EIS). According to experimental results, MoSCo structure was formed after Co²⁺ was incorporated into MoS_x, resulting in increases in both unsaturated Mo and S atoms acting as the active sites that lead to enhancement of intrinsic electrocatalytic activity. The pseudo-capacitance of MoS_xCo_y/TNAs (x = 1.70, y = 0.25) reached 46 mF cm^?2, a 31.4% improvement over 35 mF cm^?2 of MoS_x/TNAs. The onset hydrogen evolution potential, overpotentials at current densities of ?10 mA cm^?2 and –20 mA cm^?2 were recorded at ?92 mV, ?173 mV, and ?209 mV, respectively, reduction of 30 mV, 24 mV, and 28 mV than ?112 mV, ?197 mV, and ?237 mV of MoS_x/TNAs, respectively. This electrode was subjected to 1000-cycle testing and demonstrated stable electrochemical activity, illustrating excellent stability.     

Efficient hydrogen evolution catalyzed by amorphous molybdenum sulfide/N-doped active carbon hybrid on carbon fiber paper

Among numerous noble-metal-free electrocatalysts, molybdenum sulfides are recognized as promising candidates for hydrogen evolution reaction (HER). Owing to abundant under-coordinated sulfur atoms serving as catalytically active centers, intensive spectra studies have revealed that the HER property of amorphous molybdenum sulfide (a-MoS_x) is superior to crystal molybdenum sulfide (c-MoS₂). In this work, nitrogen-doped active carbon (NAC) is obtained through plasma treatment and amorphous MoS_x/NAC hybrid catalyst films are electrodeposited on carbon fiber papers (CFP) which are employed as porous three-dimensional electrodes with low resistivity. The incorporation of NAC increases the electrochemically active surface area, enhances the electron transport, and facilitates the reaction kinetics. Moreover, the functionality durability benefits from synergistic effect between a-MoS_x and NAC. Thus, the obtained hybrid catalyst delivers the excellent HER activity, requiring only 203 mV overpotential to achieve a geometrical current density of 100 mA cm^?2 with a Tafel slope of ～43.9 mV per decade.     

Hierarchical MoS2 nanoflowers on carbon cloth as an efficient cathode electrode for hydrogen evolution under all pH values

In this paper, a facile hydrothermal synthetic strategy was developed for MoS₂ nanoflowers with enlarged interlayer spacing on the carbon cloth (CC) as a high efficiency cathode electrode for hydrogen evolution reaction (HER) under wide pH condition. It was observed that the loading amount of MoS₂ has a major impact on the HER performance, where the optimized MoS₂/CC exhibited a low onset potential of 94 mV and a small Tafel slope of 50 mV dec^?1 in strong acid solution (pH = 0). The improved HER performance can be contributed to the enlarged interlayer spacing, abundant defects and more exposed active sites in the small size MoS₂ nanosheets as revealed by XRD and HRTEM. Meanwhile, it also exhibited relatively good performance for HER under basic and neutral conditions with the overpotentials of 188 (pH = 14) and 230 (pH = 7) mV to achieve current density of 10 mA cm^?2 and the Tafel slopes of 52 and 84 mV dec^?1, respectively.     

Three dimensional (3D) nanostructured assembly of MoS2-WS2/Graphene as high performance electrocatalysts

A promising electrocatalyst material composed of 2D layered MoS₂-WS₂ heterostructure hierarchically assembled into a 3D highly interconnected macroporous network of graphene was facilely fabricated. This in-situ synthesis method involves hydrothermal reaction followed by moderate thermal annealing which guarantees the uniform distribution of the MoS₂-WS₂ heterojunctions within graphene matrix. The presence of 3D conductive and porous graphene network and the combined merits of MoS₂ and WS₂ endow the resulting 3D MoS₂-WS₂/graphene nanohybrids with unique conductivity pathways and channels for electrons and with outstanding electrocatalytic performance towards enhanced hydrogen evolution reaction (HER). This 3D nanohybrid delivered the small overpotential of 110 mV, and the small Tafel slope of 41 mV per dec, demonstrating high HER activity. Furthermore, the resulting nanohybrids exhibit excellent stability as very trivial drop in the current density was noticed even after 2000 cycles. The superior electrocatalytic performance of 3D MoS₂-WS₂/graphene over other non-precious metal electrocatalysts is accredited to the robust synergism of 2D MoS₂-WS₂ with 3D graphene that offer ample active sites and improved conductivity for HER. The proposed approach can be further extended to modify other layered transition metal dichalcogenides with hierarchical 3D porous structure as a competent electrocatalysts for HER.     

Nitrogen-doped carbon active sites boost the ultra-stable hydrogen evolution reaction on defect-rich MoS2 nanosheets

It remains highly challenging to deploy noble-metal-free technologies for commercial hydrogen evolution reaction (HER) catalytic application. A facile strategy is developed in this work to boost the HER activity on non-noble MoS₂ catalyst by taking advantage of the platinum-like behavior of nitrogen doped carbon (CN) active sites for catalyzing the process from H⁺ to H atom. By doping trace amount of CN with the defect-rich MoS₂ nanosheet catalyst, the HER activity is significantly improved with the onset HER overpotential reduced to 50 mV, close to the value observed for the platinum catalyst, and the operational overpotential at 10 mA/cm² decreases by 65 mV. More importantly, with graphite as the counter electrode, stability of the catalyst is substantially improved. No activity decay is detected after 4000 cycles of cyclic voltammetry (CV) sweeping while the overpotential increment of the prisitine MoS₂/C catalyst after 2000 cycles CV sweeping is high to ca. 15 mV.     

Engineering of molybdenum sulfide nanostructures towards efficient electrocatalytic hydrogen evolution

Water splitting is an appealing way of producing hydrogen fuel, which requires efficient and affordable electrode materials to make the overall process viable. In the last couple years, abundant transition metals (and their compounds and hybrids) attracted ever-growing attention as the alternatives of noble metals. Particularly the layered transition metal dichalcogenide (TMDs) are interesting with their stability and promising electrocatalytic performance for hydrogen evolution reaction (HER). However, the neat TMDs are often poor in terms of the abundance of catalytically active sites and electrical conductivity, which limit their application potential significantly. Herein, as a proof-of-concept, we report on the design of a high-performance electrocatalyst system formed by the decoration of ultrasmall molybdenum sulfide (MoS₂) nanosheets on carbon nanotubes (CNTs). The ultrasmall MoS₂ nanosheets provide distorted lattice, confined size and rich defects, which endows the resulting electrocatalysts (MoS₂/CNT) with abundant active sites. The CNTs, on the other hand, serve as the conductive net for ensuring electrocatalytic performance. As a result, the hybrid electrocatalyst exhibits excellent electrocatalytic performance for HER, achieving a large current density of 100 mA cm⁻² at overpotential of only 281 mV and a small Tafel slope of 43.6 mV dec⁻¹ along with a decent stability. Our results are of high interest for electrocatalyst technologists as well as hydrogen fuel researchers.     

Quasi zero-dimensional MoS2 quantum dots decorated 2D Ti3C2Tx MXene as advanced electrocatalysts for hydrogen evolution reaction

Developing advanced noble-metal-free electrocatalysts for the hydrogen evolution reaction (HER) is still a great challenge. Herein, a novel HER catalyst with quasi zero-dimensional (0D) MoS₂ quantum dots (QDs) supported on two-dimensional (2D) Ti₃C₂T_x MXene nanosheets is facilely synthesized. The MoS₂ QDs/Ti₃C₂T_x nanohybrid retains the unique layer structure, and the MoS₂ QDs are in situ formed and distributed uniformly. The obtained MoS₂ QDs/Ti₃C₂T_x catalyst exhibits superior electrocatalytic activity due to its excellent conductivity, abundant of active sites exposed and a high percentage of 1T metallic phase (～76%) of MoS₂ QDs. Remarkably, an early HER overpotential of 220 mV at 10 mA cm^?2 and a small Tafel slope of 72 mV dec^?1 of MoS₂ QDs/Ti₃C₂T_x are achieved in 0.5 M H₂SO₄ solution. In addition, the exchange current density of MoS₂ QDs/Ti₃C₂T_x is ～5 times larger compared with pure MoS₂, thus demonstrating an accelerated charge transfer during the electrocatalytic process.     

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.     

Facile synthesis of MoS2/N-doped macro-mesoporous carbon hybrid as efficient electrocatalyst for hydrogen evolution reaction

A novel three-dimensional (3D) hybrid consisting of molybdenum disulfide nanosheets (MoS₂) uniformly bound at N-doped macro-mesoporous carbon (N-MMC) surface was fabricated by the solvothermal method. The resulting MoS₂/N-MMC hybrid possesses few-layer MoS₂ nanosheets structure with abundant edges of MoS₂ exposed as active sites for hydrogen evolution reaction (HER), in sharp contrast to large aggregated MoS₂ nanoflowers without N-MMC. The high electric conductivity of N-MMC and an abundance of exposed edges on the MoS₂ nanosheets make the hybrid excellent electrocatalytic performance with a low onset potential of 98 mV, a small Tafel slope of 52 mV/decade, and a current density of 10 mA cm^?2 at the overpotential of 150 mV. Moreover, the MoS₂/N-MMC hybrid exhibits outstanding electrochemical stability and structural integrity owing to the strong bonding between MoS₂ nanosheets and N-MMC.     

Phosphorus-doped nickel sulfides/nickel foam as electrode materials for electrocatalytic water splitting

Hydrogen production from electrocatalytic water splitting is viewed as one of the most promising methods to generate the clean energy. In this work, we successfully prepared an electrode material by growing phosphorus-doped Ni₃S₂ (PNi₃S₂) on nickel foam substrate (NF) under hydrothermal conditions. The phosphorus-doping has an obvious effect on the morphology of Ni₃S₂ on the surface of the nickel foam, which probably results in more active sites, higher electrical conductivity and faster mass transfer. The resulting electrode material displays excellent electrocatalytic activities and stability towards both OER (oxygen evolution reaction) and HER (hydrogen evolution reaction). A relatively low overpotential of 306 mV is required to reach the current density of 100 mA cm^?2 for OER and 137 mV at 10 mA cm^?2 for HER in 1 M KOH solution. When PNi₃S₂/NF was used in an electrolyzer for full water splitting, it can generate a current density of 10 mA cm^?2 at 1.47 V with excellent stability for more than 20 h.     

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.     

Pt/Fe-NF electrode with high double-layer capacitance for efficient hydrogen evolution reaction in alkaline media

The electrode with high catalytic activity, low hydrogen overpotential and low cost is desired for hydrogen evolution reaction (HER) via electrocatalytic water splitting. In this study, Pt/Fe-Ni foam (Pt/Fe-NF) electrode was synthesized via cathodic electrodeposition followed by impregnation deposition. Physical and electrochemical properties of Pt/Fe-NF, NF and Pt/NF electrodes were characterized by various techniques. The Pt/Fe-NF electrode exhibited better electrochemical activity for HER under alkaline condition than those of Pt/NF and NF electrodes, owing to the introduction of zero valences Pt and Fe onto the NF, and synergetic effect resulted from the formation of Fe-Ni alloy. Furthermore, Pt/Fe-NF electrode showed extremely high double-layer capacitance (69.1 mFcm^?2), suggesting high active sites for the Pt/Fe-NF. Tafel slope of Pt/Fe-NF was 59.9 mV dec^?1, indicating that the Volmer-Heyrovsky HER mechanism was the rate-limiting step. The Pt/Fe-NF electrode with great electrocatalytic activity is a promising electro-catalyst for industrial hydrogen production from alkaline electrolyte.