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(a) SEM image of N-doped graphene/Ni foam; (b) SEM image of N-CNT-G/Ni foam; (c) TEM image of detached N-CNT and graphene sheets; (d) N 1s XPS narrow scan of N-CNT-G/Ni foam.
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Large-scale free-standing porous carbon-based catalyst supports are critically needed for hydrogen evolution reaction (HER) in view of their practical application. In this work, MoS2 nanosheets are uniformly deposited onto N-doped carbon nanotube-graphene (N-CNT-G) hybrids, forming a three-dimensional (3D) free-standing architecture. The designed 3...
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... N-doped graphene and CNTs were readily grown on Ni foams in turn by chemical vapor deposition. SEM images, shown in Fig. 1a and b, revealed a similar morphology to our previously reported non-doped graphene and CNT-graphene foams. 26 The presence of graphene and CNTs was revealed by the TEM images shown in Fig. 1c and S2. † As observed, the obtained multi-walled CNTs had diameters ranging from 20 to 60 nm. The content of the N dopant was about 1.06 at% ...
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... N-doped graphene and CNTs were readily grown on Ni foams in turn by chemical vapor deposition. SEM images, shown in Fig. 1a and b, revealed a similar morphology to our previously reported non-doped graphene and CNT-graphene foams. 26 The presence of graphene and CNTs was revealed by the TEM images shown in Fig. 1c and S2. † As observed, the obtained multi-walled CNTs had diameters ranging from 20 to 60 nm. The content of the N dopant was about 1.06 at% according to the XPS analysis. It was mainly composed of pyr- idinic and pyrrolic N entities, which were depicted by the tting peaks centered at 398.1 and 400.5 eV in Fig. 1d. 28,29 In order to ...
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... by the TEM images shown in Fig. 1c and S2. † As observed, the obtained multi-walled CNTs had diameters ranging from 20 to 60 nm. The content of the N dopant was about 1.06 at% according to the XPS analysis. It was mainly composed of pyr- idinic and pyrrolic N entities, which were depicted by the tting peaks centered at 398.1 and 400.5 eV in Fig. 1d. 28,29 In order to obtain a freestanding N-CNT-G foam, the Ni foam templates encapsulated in the graphene framework were removed by HCl. As demonstrated in the SEM image of the N-CNT-G foam provided in Fig. S1, † the hybrid lm still kept a free-standing feature in a regular foam structure, although some broken junctions were created ...
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... It was mainly composed of pyr- idinic and pyrrolic N entities, which were depicted by the tting peaks centered at 398.1 and 400.5 eV in Fig. 1d. 28,29 In order to obtain a freestanding N-CNT-G foam, the Ni foam templates encapsulated in the graphene framework were removed by HCl. As demonstrated in the SEM image of the N-CNT-G foam provided in Fig. S1, † the hybrid lm still kept a free-standing feature in a regular foam structure, although some broken junctions were created when the Ni foam template was removed. Fig. 2a shows the typical SEM image of the MoS 2 /N-CNT-G hybrid. The MoS 2 /N-CNT-G hybrid has the same free-standing structure as the N-CNT-G foam at low magnication ...
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... in Fig. S1, † the hybrid lm still kept a free-standing feature in a regular foam structure, although some broken junctions were created when the Ni foam template was removed. Fig. 2a shows the typical SEM image of the MoS 2 /N-CNT-G hybrid. The MoS 2 /N-CNT-G hybrid has the same free-standing structure as the N-CNT-G foam at low magnication (Fig. S1a †). Aer MoS 2 deposition (Fig. 2b), the surface of the N- CNTs was uniformly coated by a layer of stacked nanosheets. The MoS 2 /N-CNT composites inherited the one-dimensional morphology from the nanotubes while their diameter increased signicantly. The morphology of the MoS 2 /N-CNT-G was studied by TEM ( Fig. 2c and S2 †). The heavy ...
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... increased signicantly. The morphology of the MoS 2 /N-CNT-G was studied by TEM ( Fig. 2c and S2 †). The heavy MoS 2 coating made the N-CNTs indistinguishable under TEM observation. The MoS 2 nanosheets grew vertically out from the N-CNTs, and their thickness was estimated to be about 50-70 nm by comparing the diameter change between the N-CNTs (Fig. 1c) and MoS 2 /N-CNT. It can be observed that each nanosheet was composed of 6-10 MoS 2 layers with a thickness of $8 nm (Fig. 2d). The interplanar distance of the lattice fringes was approximately 0.63 nm, corresponding to the (002) plane of MoS 2 . 30-32 When deposited onto non-doped CNT-G, the MoS 2 also maintained a similar morphology ...
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... In the XRD pattern of the flexible MoS 2 @Ge/CNFs, the peaks at 39.5 • and 58 • are respectively linked to the (103) and (110) planes of MoS 2 [3]. In addition, the peaks of MoS 2 are weak and broad because of their nanosized or amorphous structure [20,21]. Figure 4a shows the initial cyclic voltammetry curves of the flexible MoS2@Ge/CNFs at 0.01-2.5 V with a scan rate of 0.2 mV s −1 . ...
Germanium is a promising anode material for sodium-ion batteries (SIBs) because of its high theoretical specific capacity, high ion diffusivity, and rate capability. However, large volume changes and pulverization deteriorate the cycling performance. In this study, flexible electrospun germanium/carbon nanofibers (Ge/CNFs) were prepared via electrospinning followed by heat treatment. MoS2 nanoparticles were subsequently anchored on the flexible Ge/CNFs via hydrothermal synthesis. Flexible MoS2 anchored on Ge/CNFs (MoS2@Ge/CNFs) was used as a self-standing binder-free anode in an SIB. Because of the high electronic conductivity of CNFs and the many active sites of MoS2 nanoparticles, a high initial capacity of over 880 mAh/g was achieved at a current density of 0.1 A/g. Moreover, the flexible binder-free MoS2@Ge/CNFs exhibited an excellent C-rate performance with a reversible capacity of over 300 mAh/g at a current density of 2 A/g. Therefore, we demonstrated that flexible binder-free MoS2@Ge/CNFs are a promising electrode candidate for a high-performance rechargeable battery.
... Its analogue WS 2 also has a similar prospective [7] and experiences the same issues as that of MoS 2 has, such as low active site density and poor electronic conductivity, which inevitably inhibit their eletrocatalytic performance in HER. The active site density of the catalyst can usually be increased by the formation of nanoscale structures or dispersion of the active components in highly porous supports [8,9], while the electronic conductivity of the catalyst can normally be enhanced via the combination of the catalytic active components with electronic conductive substrates such as carbon nanotubes, graphene and so on [10,11]. On the other hand, cobalt sulfide is a typical kind of transition metal chalcogenide which is earth abundant and frequently exhibits good OER activities [12]. ...
Hydrogen is one of the most promising sustainable energy among numerous new energy resources. Electrocatalytic water splitting for H2 generation is a clean and sustainable approach due to the use of widely existed water as resource. The searching for efficient and low-cost non-precious metal based electrocatalysts for water splitting, including both cathodic hydrogen evolution reaction (HER) and anodic oxygen evolution reaction (OER), still remains a great challenge. In this work we report a simple method that utilizes the one-pot in-situ synthesized [email protected] (POMs = Polyoxometallates, ZIFs = Zeolitic imidazolate frameworks) as precursor for the production of WS2/Co1-xS/N, S co-doped porous carbon nanocomposite as efficient electrocatalysts. These precursors [email protected] can effectively prevent the agglomeration of metal compound particles during heat treatment and lead to homogeneous dispersion of metal active sites within carbon matrix. The resulting bimetallic Co–W sulfide/heteroatom doped porous carbon composites show significant improvement in electrocatalytic activity towards both OER (Tafel slop of 53 mV dec⁻¹ with overpotential of 0.365 V @10 mA cm⁻² current density in 1 M KOH solution) and HER (Tafel slop of 64 mV dec⁻¹ with overpotential of −0.250 V @−10 mA cm⁻² current density in 0.5 M H2SO4 solution). This work opens up a new way to obtain low cost bifunctional electrocatalysts towards both OER and HER in water splitting.
... The N atoms doped into the MoS 2 lattice can tune the electronic structure of MoS 2 to increase the bond strength to adsorb key ORR species on its edges, which greatly improves the inherent activity of MoS 2 for ORR [27]. It has been reported that N-doping enables the MoS 2 with the minimum energy required for ORR and especially, the energy barrier and overpotential of N-doped MoS 2 are lower than those of Pt-based catalysts [44]. Additionally, the N atoms bonded with C atoms in a sp 2 hybrid orbital (pyridinic N and pyrrolic N) also can create the positive charge density on the adjacent C atoms to accelerate the chemisorption of oxygen [45]. ...
... Owing to these advantages, MWCNTs can be used as one of the most promising supports for nano-sized catalysts. In previous reports, the hybrid of nano-sized MoS 2 /carbon-based material was prepared in the dimethylformamide (DMF) solution, while replacing the not environmental-friendly DMF with water only leads to a simple mixture of nano-sized MoS 2 particles and carbon sources [28][29][30][31][32][33][34][35][36][37] . In this study, a highly effective electrocatalyst for HER which petal-like metallic 1T phase MoS 2 nanosheets (NSs) hydrothermally uniformly grown on the MWCNT surface was successfully synthesized in aqueous solution for the first time. ...
Unique hybrid nanostructure, which consists of multi-wall carbon nanotube (MWCNT) stems and MoS2 nanosheet (NS) leaves, are prepared by a hydrothermal method. The fabricated material can be potentially used as an electrocatalyst for the hydrogen evolution reaction (HER). To our knowledge, as the reaction medium, water is firstly utilized to the synthesis of the 1T phase MoS2 NSs which uniformly grow on the carbon-based materials. As a result, a nanohybrid catalyst with excellent HER electrocatalytic properties, which included an onset potential of as low as 50 mV, a Tafel slope of 43 mV dec⁻¹, and remarkable cycling stability, is produced. The observed outstanding catalytic performance can be attributed to the uniform distribution of the metallic 1T phase of the MoS2 NSs, which are characterized by the presence of multiple active edges as well as the effective electron transport route provided by the conductive MWCNT substrate. This work demonstrates the high potential of the synthesized HER catalyst and proposes a novel, efficient, environmentally friendly, and inexpensive method for its fabrication.
... 6,24,27,32 Coupling molybdenum sulfide with highly conductive supports is an effective strategy to enhance the electron transport toward the active sites of catalyst. Examples include MoS 2 deposited on reduced graphene oxide, 10−13 MoS x deposited on carbon nanotubes, 20,27 MoS x deposited on graphene-protected Ni foam, 28 and so on. Besides, the HER reaction requires constant reactant supply and product removal. ...
... High specific surface area conductive supports such as carbon nanotubes and graphene have been effectively used to support electro-active materials for electrochemical applications. [10][11][12][13]20,27,34,35 After MoS x had been deposited, the MoS x catalysts underwent the reductive activation process. The activation was performed by 10 potential sweeps from 0.2 V to −0.5 V vs SHE. Figure 1b shows the current responses of the MoS x / GCNT/CP-3 electrode during the potential sweeps. ...
In this study, we report on the deposition of amorphous molybdenum sulfide (MoSx, with x ≈ 3) on a high specific surface area conductive support of Graphene-Carbon Nanotube hybrids (GCNT) as the Hydrogen Evolution Reaction (HER) catalysts. We found that the high surface area GCNT electrode could support the deposition of MoSx at much higher loadings compared with simple porous carbon paper or flat graphite paper. The morphological study showed that MoSx was successfully deposited on and was in good contact with the GCNT support. Other physical characterization techniques suggested the amorphous nature of the deposited MoSx. With a typical catalyst loading of 3 mg cm(-2), an overpotential of 141 mV was required to obtain a current density of 10 mA cm(-2). A Tafel slope of 41 mV decade(-1) was demonstrated. Both measures placed the MoSx-deposited GCNT electrode among the best performing molybdenum sulfide-based HER catalysts reported to date. The electrode showed a good stability with only a 25 mV increase in overpotential required for a current density of 10 mA cm(-2), after undergoing 500 potential sweeps with vigorous bubbling present. The current density obtained at -0.5 V vs. SHE (Standard Hydrogen Electrode potential) decreased less than 10% after the stability test. The deposition of MoSx on high specific surface area conductive electrodes demonstrated to be an efficient method to maximize the catalytic performance towards HER.
... This represents less plane defects in the aligned-stacked bN-CNTs as compared to non-aligned bN-CNTs. These ratios show that the as synthesized carbon nanomaterials are not well crystalline/graphitized due to the N-doping inside bN-CNTs and branched structure [62]. Consequently, the graphitization degree exhibited a substantial increase with the formation of aligned-stacked bN-CNTs. ...
Transition metal dichalcogenides (TMDCs) has gained vast attraction in academia and industry due to their outstanding optical and electrical properties. Among them, molybdenum disulfide (MoS2) is a promising material in the field of thermoelectric due to its high effective mass, Van der Waal’s interaction and anisotropy. In this work, layered structure of molybdenum disulfide is prepared by hydrothermal method and coated on ITO/PET flexible substrate by doctor blade method. The thermoelectric properties of MoS2 are improved with the effect of carbon nanotubes (CNTs) by fabricating the film via layer-by-layer assembly and heterojunction. The presence of (E¹2g and A1g) modes and (D, G and G’) band from Raman spectra confirmed the formation of MoS2 and CNT, respectively. Further the chemical composition is also confirmed from the presence of Mo⁴⁺ and S²⁻oxidation states. The maximum achieved Seebeck coefficient (S), electrical conductivity (σ) and power factor (S²σ) values are − 19.45 µV/K, 430 S/m and 160 nW/mK² at 315 K, respectively, for heterojunction. The achieved maximum power factor for heterojunction is due to the energy carrier filtering effect at the interface of MoS2 and CNT. The current research work paves a new strategy to design a flexible thermoelectric device.
Molybdenum disulfide has received great attention as a promising non-noble catalyst for electro-catalyzed hydrogen evolution reaction. The active sites originated from the limited edge of crystalline molybdenum disulfide is the key to restrict its HER performance. To increase the active sites of molybdenum disulfide through the heteroatom doping with effective synthetic strategy has become the focus of activity improvement. Herein, a facile and efficient strategy was adopted to synthesize oxygen-doped molybdenum sulfide catalyst by utilizing thiourea and sodium molybdate as precursors. It was found that the number of active sites could be regulated by controlling the dosage ratio of thiourea to sodium molybdate. The doped oxygen and abundant S endows molybdenum sulfide a great deal of lattice disorder or defects, thus providing adequate active sites. When the optimized ratio of thiourea to sodium molybdate (40:1), the double layer value of oxygen-doped molybdenum sulfide reached 34.14 mF/cm² (mass loading on glassy carbon electrode was 0.142 mg/cm²) which is considered to be proportional to the electrochemical active area. Raman spectroscopy and X-ray photoelectron spectroscopy confirmed the presence of Mo–O bond and bridging S2²⁻ bonds which endows molybdenum sulfide with a great deal of lattice disorder or defects, thus providing plentiful active sites.
Molybdenum disulfide (MoS2) is regarded as a perfect catalyst for electrochemical hydrogen evolution reaction (HER). However, the active sites are usually concealed due to the unique two dimensional structure of MoS2. Herein, we propose a facile surface engineering modus to improve the HER activity of MoS2. This strategy is demonstrated by in-situ growth of amorphous MoS2 layer on the molybdenum phosphide (MoP) nanoparticles anchored on the carbon nanotubes (MoS2/MoP/CNT). The HER activity is significantly promoted both through the defect engineering of amorphous MoS2 and the synergistic effect between the MoS2 and MoP phases. The MoS2/MoP/CNT sample presents significantly higher HER performance than the pure phase of MoP/CNT and MoS2/CNT samples, requiring overpotentials of 73 and 141 mV to drive a current density of 10 and 100 mA cm⁻².
Development of advanced materials for photoelectrochemical (PEC) water splitting has become an essential issue for efficient, green, and economical hydrogen production. In this context, vertically grown thin sheets of ZnO is developed, which can function as an efficient photoanode in PEC water splitting reaction. Further, the PEC activity of ZnO is enriched by decorating a newly developed co-catalyst, which is amorphous MoSx through efficient charge transportation. MoSx nanostructure is decorated on the surface of ZnO nanosheet via electrodeposition technique. MoSx adorned ZnO shows enhanced activity towards photoanodic PEC water splitting compared to bare ZnO. [email protected]x can generate photocurrent density nearly three times higher compared to bare ZnO at an applied potential of ‘0.5998’ V vs. RHE. Sensitization of MoSx on ZnO surface results in an enhancement in carrier density; [email protected]x shows nearly 7.4-times higher carrier density compared to bare ZnO. Maximum photoconversion efficiency, 0.934% is achieved in the case of [email protected]x. The determined band alignment of ZnO and MoSx indicate the formation of type-II heterostructure which allow facile charge carrier separation. Efficient charge separation is also confirmed with the help of PL spectroscopy. It further restricts the electron-hole recombination in ZnO, leading to enhanced PEC activity. [email protected]x thin sheets are very stable even up to 1000 s under chopped illumination condition.
