Exfoliated colloidal MoS2 nanosheet with predominantly 1T phase for electrocatalytic hydrogen production (original) (raw)
Related papers
Conducting MoS2 Nanosheets as Catalysts for Hydrogen Evolution Reaction
Nano Letters, 2013
We report chemically exfoliated MoS 2 nanosheets with a very high concentration of metallic 1T phase using a solvent free intercalation method. After removing the excess of negative charges from the surface of the nanosheets, highly conducting 1T phase MoS 2 nanosheets exhibit excellent catalytic activity toward the evolution of hydrogen with a notably low Tafel slope of 40 mV/dec. By partially oxidizing MoS 2 , we found that the activity of 2H MoS 2 is significantly reduced after oxidation, consistent with edge oxidation. On the other hand, 1T MoS 2 remains unaffected after oxidation, suggesting that edges of the nanosheets are not the main active sites. The importance of electrical conductivity of the two phases on the hydrogen evolution reaction activity has been further confirmed by using carbon nanotubes to increase the conductivity of 2H MoS 2 .
Hydrothermal synthesis of 2D MoS2 nanosheets for electrocatalytic hydrogen evolution reaction
Nanostructured molybdenum disulfide (MoS2) is a very promising catalyst for producing molecular hydrogen by electrochemical methods. Herein, we have designed and synthesized highly electocatalytically active 2D MoS2 nanosheets (NS) from molybdenum trioxide (MoO3) by a facile hydrothermal method and have compared their electrocatalytic activities for hydrogen evolution reaction (HER). The electrochemical characterization was performed using linear sweep voltammetry (LSV) in acidic medium. The MoS2 NS show a HER onset potential at about 80 mV vs. reversible hydrogen electrode (RHE) which is much lower than MoO3 (300 mV). The MoS2 NS and MoO3 show a current density of 25 mA cm2 and 0.3 mA cm2, respectively at an overpotential of 280 mV vs. RHE. The MoS2 NS showed an 83 times higher current density when compared to MoO3. The Tafel slopes of the MoS2 NS and MoO3 were about 90 mV per dec and 110 mV per dec respectively. This suggests that MoS2 NS are a better electrocatalyst when compared to MoO3 and follow the Volmer–Heyrovsky mechanism for HER.
ACS Applied Materials & Interfaces, 2019
The production of MoS2 nanosheets by electrochemical exfoliation routes holds great promise as a means to access this two-dimensional material in large quantities for different practical applications. Yet, the use of electrolytes based on synthetic organic salts and solvents, as well as issues related to the unwanted oxidation and/or phase transformation of the exfoliated nanosheets, constitute significant obstacles that hinder the industrial adoption of the electrochemical approach. Here, we introduce a safe and sustainable method for the cathodic delamination of MoS2 that makes use of aqueous solutions of very simple and widely available salts, mainly KCl, as the electrolyte. Combined with an appropriate biomolecule-based solvent transfer protocol, such an electrolytic exfoliation route is shown to afford colloidally dispersed, oxide-free and phase-preserved MoS2 nanosheets of a high structural quality in considerable yields. The mechanisms behind the efficient aqueous delamination of the bulk MoS2 cathode are also discussed and rationalized on the basis of the penetration of hydrated cations from the electrolyte between its layers and the immediate reduction of the accompanying water molecules. An asymmetric supercapacitor assembled with a cathodic MoS2 nanosheetsingle walled carbon nanotube hybrid as the positive electrode and activated carbon as the negative electrode delivered energy densities (e.g., 26 W h kg-1 at 750 W kg-1 in 6 M KOH) that were competitive with those of other MoS2-based asymmetric devices. When used as a catalyst for the reduction of nitroarenes, the present cathodically exfoliated nanosheets exhibited one of the highest activities reported so far with MoS2 nanostructures, the origin of which is accounted for as well. Overall, by facilitating access to this two-dimensional material through a particularly simple, efficient and cost-effective technique, these results should expedite the practical implementation of MoS2 nanosheets in energy, catalysis and beyond.
ACS applied materials & interfaces, 2015
Molybdenum disulfide (MoS2) is a promising catalyst for hydrogen evolution reaction (HER) because of its unique nature to supply active sites in the reaction. However, the low density of active sites and their poor electrical conductivity have limited the performance of MoS2 in HER. In this work, we synthesized MoS2 nanosheets on three-dimensional (3D) conductive MoO2 via a two-step chemical vapor deposition (CVD) reaction. The 3D MoO2 structure can create structural disorders in MoS2 nanosheets (referred to as 3D MoS2/MoO2), which are responsible for providing the superior HER activity by exposing tremendous active sites of terminal disulfur of (in MoS2) as well as the backbone conductive oxide layer (of MoO2) to facilitate an interfacial charge transport for the proton reduction. In addition, the MoS2 nanosheets could protect the inner MoO2 core from the acidic electrolyte in the HER. The high activity of the as-synthesized 3D MoS2/MoO2 hybrid material in HER is attributed to the ...
ACS Applied Materials & Interfaces, 2014
Chemically exfoliated MoS 2 (ce-MoS 2) nanosheets that incorporate a large fraction of metallic 1T phase have been recently shown to possess a high electrocatalytic activity in the hydrogen evolution reaction, but the potential of this two-dimensional material as a catalyst has otherwise remained mostly uncharted. Here, we demonstrate that ce-MoS 2 nanosheets are efficient catalysts for a number of model reduction reactions (namely, those of 4-nitrophenol, 4-nitroaniline, methyl orange and [Fe(CN) 6 ] 3-) carried out in aqueous medium using NaBH 4 as a reductant. The performance of the nanosheets in these reactions is found to be comparable to that of many noble metal-based catalysts. The possible reaction pathways involving ce-MoS 2 as a catalyst are also discussed and investigated. Overall, the present results expand the scope of this two-dimensional material as a competitive, inexpensive and earth-abundant catalyst.
ACS Applied Energy Materials, 2020
Heterostructures, particularly the shell−core (2D@1D) nanostructure with atomically thin layers of transition metal dichalcogenides, exhibit an excellent electrocatalytic hydrogen evolution reaction (HER) activity. Herein, we introduce a facile and precisely controlled synthesis of a shell−core heterostructure that comprises TiO 2 nanorods (TNRs) as a core array conformally covered by a continuous monolayer molybdenum disulfide (ML-MoS 2) film as a shell. The TNR array was grown by a hydrothermal process, followed by the conformal coating of the ML-MoS 2 film via metal− organic chemical vapor deposition. Interestingly, the shell−core heterostructure (ML-MoS 2 @TNRs) shows a significant enhancement in the HER activity with an onset overpotential at 140 mV vs reversible hydrogen electrode and a Tafel slope of ∼80 mV/dec. Based on our experimental results together with first-principle calculations, we attribute the enhanced HER performance of ML-MoS 2 @TNRs to the synergetic effect of the following characteristics. (i) A large number of active sites owing to TNRs' high surface to volume ratio. (ii) A considerable reduction in the charge transfer resistance caused by the direct growth of ML-MoS 2 over the TNR array, naturally rendering low electrical loss contacts compared to the conventional transfer process. Moreover, the direction of the built-in electric field in the MoS 2 /TiO 2 heterostructure also facilitates the flow of electrons from the electrode to the electrocatalyst surface, consequently decreasing the charge transfer resistance. (iii) The high intrinsic HER activity of the active sites owing to the low Gibbs free energy of the catalytic surface (ML-MoS 2 @TNRs). Moreover, by virtue of the high crystalline quality of ML-MoS 2 , the ML-MoS 2 @TNRs sample shows excellent stability and working durability. Clearly, these characteristics suggest that our proposed method has great potential for practical applications in the form of large-scale HER devices.
Materials Today Chemistry, 2019
Hydrogen is considered as an ideal and sustainable energy carrier because of its high energy density and carbon-free combustion. Electrochemical water splitting is the only solution for uninterrupted, scalable, and sustainable production of hydrogen without carbon emission. However, a large-scale hydrogen production through electrochemical water splitting depends on the availability of earth-abundant electrocatalysts and a suitable electrolyte medium. In this article, we demonstrate that hydrogen evolution reaction (HER) performance of electrocatalytic materials can be controlled by their surface functionalization and selection of a suitable electrolyte solution. Here, we report syntheses of fewlayered MoS 2 nanosheets, NiO nanoparticles (NPs), and multiwalled carbon nanotubes (MWCNTs) using scalable production methods from earth-abundant materials. Magnetic measurements of as-produced electrocatalyst materials demonstrate that MoS 2 nanoflakes are diamagnetic, whereas surfacefunctionalized MoS 2 and its composite with carbon nanotubes have strong ferromagnetism. The HER performance of the few-layered pristine MoS 2 nanoflakes, MoS 2 /NiO NPs, and MoS 2 /NiO NPs/MWCNT nanocomposite electrocatalysts are studied in acidic and alkaline media. For bare MoS 2 , the values of overpotential (h 10) in alkaline and acidic media are 0.45 and 0.54 V, respectively. Similarly, the values of current density at 0.5 V overpotential are 27 and 6.2 mA/cm 2 in alkaline and acidic media, respectively. The surface functionalization acts adversely in the both alkaline and acidic media. MoS 2 nanosheets functionalized with NiO NPs also demonstrated excellent performance for oxygen evolution reaction with anodic current of~60 mA/cm 2 and Tafel slope of 78 mVdec À1 in alkaline medium.
High-performance hydrogen evolution electrocatalysis by layer-controlled MoS2 nanosheets
RSC Advances
Hydrogen is considered as an important clean energy carrier for the energy future and electrocatalytic splitting of water is one of the most efficient technologies for hydrogen production. As one potential alternative to Pt-based catalysts in hydrogen evolution reaction (HER), two-dimensional (2D) molybdenum sulfide (MoS2) nanomaterials have evoked enormous research interest while it remains a great challenge in the structure control for high-performance HER electrocatalysis due to the lack of efficient preparation techniques. Herein, we reported a one-pot chemical method to directly synthesize 2D MoS2 with controllable layers. Multiply-layer MoS2 (ML-MoS2), few-layer MoS2 (FL-MoS2) and single-layer MoS2 coating on carbon nanotubes (SL-MoS2-CNTs) can be efficiently prepared through the modulation of experimental conditions. The enhanced catalytic activity is demonstrated in HER with the layer number of MoS2 nanosheets reducing. Remarkably, the optimized SL-MoS2-CNTs sample showed lo...
Influence of reaction temperature, time and molar ratio on hydrothermal synthesis of MoS2 nanosheets
Digest Journal of Nanomaterials and Biostructures
MoS2 nanosheets (NS) were synthesized using a hydrothermal reaction between sodium molybdate and thiourea. The influence of various parameters like reaction temperature, time and molar ratio on hydrothermal synthesis is studied. It was found that the reaction temperature and molar ratio had a greater impact than reaction time. All these parameters influenced the structural and optical properties of MoS2 that were verified by various characterization techniques like X-ray Diffraction (XRD), UV-Visible (UV) spectroscopy and Photoluminescence (PL) spectroscopy. The thin film of the sample was formed by utilizing drop casting method and current voltage characteristics were measured to calculate the conductivity. The results reveal that optimization of the reaction is must before employing it for certain application and the work will further motivate researchers to utilize it in supercapacitors, Field Effect Transistors (FETs) and various optoelectronic applications.
Study of unique and highly crystalline MoS2/MoO2 nanostructures for electro chemical applications
Materials Research Letters, 2019
We report the synthesis of a spectrum of highly crystalline molybdenum sulphide/oxide-based materials such as MoS 2 (2-H), MoO 2 and unique hybrid MoS 2 /MoO 2 nanostructures through chemical vapour deposition (CVD). The as-fabricated samples were scrutinized with materials characterization techniques. Our results reveal that, by tuning growth parameters, different samples demonstrate unique morphologies, which can be unequivocally tied to their chemical composition. We also explore their potential application as electrochemical catalysts, which we found that in addition to using large specific surface area and conductive substrate to improve interlayer conductivity,chemical heterogeneity and efficient charge transport are also essential for good catalytic activity. IMPACT STATEMENT We successfully fabricated an array of uniquely shaped MoS 2 /MoO 2 nanostructures through a one-step chemical vapour deposition process. The practical application of said nanostructures as electrochemical catalysts has also been demonstrated.