One-step synthesis and characterization of MoS2/MWNTs electrocatalytic nanocomposite

NGUYEN THI MINH NGUYET -1,2; NGUYEN DUC BINH - 1,3; VINH-DAT VUONG - 1,4; MAI THANH PHONG - 5, THANG VAN LE - 1,2,3 [1- VNU-HCM Key Laboratory for Material Technologies, Ho Chi Minh city University of Technology (HCMUT), 2 - Vietnam National University Ho Chi Minh City, 3 - Faculty of Chemical Engineering, Ho Chi Minh city University of Technology (HCMUT), 4 -Faculty of Materials Technology, Ho Chi Minh city University of Technology (HCMUT), 5 - Ho Chi Minh city University of Technology (HCMUT)]


Nano-structural molybdenum disulfide (MoS) were directly controlled and grafted on multi-walled carbon nanotubes (MWNTs) via one-step wet chemical reaction with microwave support. MoS2 nanoparticles were grown in two type of structures: crystalline- and amorphous-MoS2. The structural, surface morphology of electrocatalytic composites were characterized by X-ray diffraction (XRD), Rama spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). XRD and Raman spectra showed that MoS2 nanoparticles were successfully formed. The SEM and TEM images illustrated unique structures and enshroud distribution in composite samples. The HER Tafel slopes were about 135 mV/decade at -0.223 V (versus NHE) of onset potential and 142 mV/decade at -0.305 V (versus NHE) at onset potential for amorphous- and crystalline-MoS2/MWNTs electrocatalyst, respectively.

Keywords: MoS2/MWNTs, hydrogen evolution reaction (HER), electrocatalyst, microwave assisted reaction, controlled nanostructures.

1. Introduction

Hydrogen gas used as a renewable energy source, which has vigorously pursued to resolve the global issues of severe energy shortage and environmental deterioration. Hydrogen energy have an endless regeneration possibility; therefore, it has a great potential to meet energy needs of human and solve environmental problems and replace the fossil fuel in future. Scalable renewable hydrogen production by water electrolysis is a potential technology to address the global demand for renewable energy. One of the key steps in water electrolysis reaction is HER: 2H+ + 2e- → H2). HER in acidic solution has emerged as the main method of hydrogen production. HER have three mechanisms: (i) Volmer reaction (H3O+ + e → Hads), (ii) Heyrovsky reaction (H3O+ + Hads + e → H2), and (iii) Tafel reaction (2 Hads → H2) [1]. Achieving high energetic efficiency for water electrolysis requires the use of a catalyst to minimize the overpotential necessary to drive the HER [2].

The most effective catalyst for water electrolysis is platinum and platinum-based alloys and composites. Such materials limit the potential of water electrolysis due to their high cost, low durability, and scarce resource. Therefore, many HER catalysts with high performance have been researched such as metal alloy [3], metal oxides [4, 5], transition metal dichalcogenides [6 – 8] and nanostructure carbon [9 – 11]…  Recently, molybdenum disulfide (MoS2), a transition metal dichalcogenide compound, having a significant potential to replace platinum-based electrode. MoS2 has a layer structure, belonging to the group of transition metal dichalcogenides, considered as a potential low-cost HER catalyst because its good catalytic activity, stable, non-toxic and edge-terminated structure [11]. On the other side, the catalytic performance of MoS2 is significantly prevented by low electrical conductivity, poor utilization of active sites, the number of active sites is limited to edges, and low Hads energy on the S edge sites of MoS2 [12]. Because the electronic conductivity of MoS2 is not uniform along with all crystallographic directions, a high electron conducting component is generally combined into the MoS2. Carbon nanotubes (CNTs) have good conductivity, excellent charge/discharge electronic process and a low electrochemical charge transfer resistance [13]. MWNTs are combined with MoS2 to improve disadvantages of MoS2. In this paper, MoS2 grafted onto MWNTs had synthesized by direct microwave assisted method. The obtained amorphous MoS2/MWNTs hybrid catalyst had a unique nanostructure, good conductivity, and expected to be one of the most powerful, efficient, and stable catalysts for HER.

2. Experimental

2.1. Materials

All reagents and solvents were purchased from commercial suppliers. Ammonium molybdate tetrahydrate (AHM) (NH4)6Mo7O24.4H2O and thiourea CH4N2S were purchased from Fisher Scientific. Ethylene glycol (EG) was purchased from Merck. MWNTs (carbon content 95 wt.%) was purchased from BYK.

2.2. Synthesis MoS2/MWNTs composites

MoS2/MWNTs composites were synthesized directly by microwave assisted reaction. Typical, AHM and thiourea were dissolved in EG under vigorous stirring for 30 min to form a homogeneous solution. MWNTs were added to the solution and sonicated at 60°C for 30 mins. Then, the solution was reacted in microwave oven to produce black solution. Product was collected by centrifugation at 5000 rpm for 5 mins. The washing step was repeated for at least 4 times to ensure that most EG was removed. Finally, the obtained MoS2/MWNTs composite was dried at 90 °C for 24 h. Table 1 shows detailed experimental conditions to control structure of MoS2 grew on MWNTs. 

Table 1. Detail experimental parameters to synthesis MoS2/MWNTs composites


 2.3. Characterizations

2.3.1. Structures and morphologies

The phase structure of the as-prepared samples was investigated by powder X-ray diffraction method using Bruker D8 advance diffractometer with Cu-Kα. The Raman scattering spectra were recorded at room temperature using a HORIBA Xplora Plus micro-Raman spectrometer. The morphological features and elemental content of the composites were examined using a field emission scanning electron microscope (Hitachi S-4800 FESEM System, Japan) operated at an accelerating voltage of 15 kV. High resolution transmission electron microscopy (HR-TEM) was carried out using a JEOL JEM-2100F TEM (JEOL Ltd., Tokyo, Japan) at an acceleration voltage of 200 kV in the bright field image mode.

2.3.2 Electrochemical evaluation

Tafel plot of HER were carried out using a three-electrode cell with in 1 M H2SO4 solution as electrolyte. Saturated calomel electrode (SCE) and platinum plate reference and counter electrodes, respectively. Typically, 10 mg of the MoS2/MWNTs composite and 2.5 mg polyvinylidene fluoride (PVDF) were dispersed in 200 µl EG and 1 µl PVA 1 wt.% mixture, followed by sonication for 30 min to obtain a black homogeneous slurry. Then, a glassy carbon electrode (GCE) with a diameter of 3 mm, which was treated with 10 µl of the catalytic slurry and dried at 90°C. The HER activities of catalysts were evaluated via linear sweep voltammetry (LSV) at a 1 mV s−1 of scan rate and at room temperature. LSV measurements were conducted using PARSTAT 2273 electrochemical workstation.

3. Results and discussion

3.1. Phase structure of MoS2/MWNTs composite

XRD patterns composites prepared with high and low microwave power were shows in Figure 1. Typical and sharp peaks at 2θ of 14°, 33°, 40° and 58° corresponding to (002), (100), (103) and (110) planes of crystalline MoS2, were observed on pattern of high-power prepared sample, while the typical large peaks of amorphous structure distributed in wide window in pattern of low-power prepared sample. The XRD results showed that support of microwave energy helps MoS2 particles grow on surface of MWNTs as well as controls the structure of MoS2 particles. Powerful and instantaneous impact of high microwave power promotes flash growth of crystalline MoS2 particles. As same energy capacity, the low power of the sine wave energy barely enough to stimulate the initial nucleation, followed by cut-off state to stop the particle growth. Therefore, crystalline MoS2 can only grow on MWNTs with support of high-power microwave, while amorphous MoS2 slowly grafted around outer side of MWNTs.

Figure 1: Characterize the structure of MoS2/MWNTs


Raman spectroscopy was also employed to further characterize the structure of MoS2/MWNTs composite. Figure 2 compares the Raman spectra taken from the as obtained crystalline- and amorphous-MoS2/MWNTs. The appearance of two other peaks at around 320 and 520 cm-1 corresponds to Mo-S and S-S bonding, respectively. New peaks at around 450 cm-1 and 630 cm-1 corresponded to oxidation of MoS2 particle by focus of high energy laser beam on the sample in the measurement. The G- and D-band of MWNTs are also located at around 1580 and 1490 cm-1, respectively, consistent with previous reports [24]. It was also found that the typical peak of G- and D-band are mostly overlapped by those of the MoS2 sheets, and their intensity becomes significantly weaker, which suggests a good grafting of MoS2 around the surface of MWNTs.

Figure 2: The Raman spectra taken from the as obtained crystalline- and amorphous-MoS2/MWNTs


3.2. Morphology of MoS2/MWNTs composite

Morphology of as-prepared MoS2/MWNTs composite was observed by SEM and TEM (Figure 3). Surface morphology of crystalline-MoS2/MWNTs (Figure 3a&b) showed that of MoS2 particles was grown to hexagon flake and anchored on outer side of MWNTs, while amorphous-MoS2/MWNTs. The MoS2 nano-flakes was sized in about 20 nm of diameter. Figure 3c&d showed that nanotubes in amorphous composite has lager diameter than in crystalline composite due to enshroud of amorphous MoS­2 as skin of MWNTs. Compared with structural results, SEM and TEM images demonstrated that long time support of low-power microwave can control the slow nucleation of MoS2 slowly as well as uniform graft of MoS2 on MWNTs.

Figure 3. SEM and TEM images crystalline-MoS2/MWNTs (a, b)

and amorphous-MoS2/MWNTs (c, d)

sem-and-tem-images-crystalline3.3. Electrocatalytic ability of MoS2/MWNTs composite

Figure 4 and Figure 5 compare the HER activity of the MoS2/MWNTs catalysts with a platinum electrode. The catalytic ability was assessed through two factors: the onset potential value (Vonset) and the Tafel slope. An effective catalyst for HER own less negative Vonset (close to 0 V versus NHE) and small the Tafel slope (close to 40 mV/decade). HER on amorphous-MoS2/MWNTs electrocatalysts had less negative Vonset as well as smaller Tafel slope than on amorphous-MoS2/MWNTs electrocatalysts. Tafel slope of HER depends on the surface coverage of adsorbed hydrogen (Volmer reaction) and a rate-determining recombination (Tafel reaction) or Heyrovsky reaction [14]. This proves that a unique catalytic property for amorphous MoS2 when compared to crystalline forms of MoS2. The number of active sites of nanocrystalline MoS2 is limited to edges and coordinatively unsaturated Mo or S atoms [15]. Amorphous MoS2 and MWNTs has focused on enhancing the edge concentration, the number of active sites to improve the performance of amorphous-MoS2/MWNTs catalyst. On the other hand, the Tafel slopes of these composites were placed in 135-142 mV/decade window, which shows that the catalytic reactions occurring is according to the Heyrovsky-Tafel mechanism.

Figure 4. Linear sweep voltammetry of MoS2/MWNTs composite

and platinum as electrocatalyst for HER


Figure 5. Tafel plot of MoS2/MWNTs composite and platinum

as electrocatalyst for HER


4. Conclusion

MoS2/MWNTs electrocatalytic composites were successfully synthesized by one-step wet chemical reaction with microwave energy support. The characterizations suggested that power of microwave energy can control the structures of MoS2 nanoparticle and graft of them on surface of MWNTs. The amorphous structure of MoS2 skin on MWNTs, which formed by low power microwave, is origin closed to zero of Vonset and high current density. These abilities of amorphous-MoS2/MWNTs allow its applications toward HER.

 NS-CF nanocomposite was successfully prepared by a simple thermal evaporation method. The physical characterization methods suggested that the NS and CF were connected via a thin MoS2 layer which is grown parallel to the CF surface. This special structure may be the origin of the low current density toward HER.


This research is funded by Vietnam National University Ho Chi Minh City (VNU-HCM) under grant number B2017-20-07/HĐ-KHCN. We acknowledge the support of time and facilities from Ho Chi Minh City University of Technology (HCMUT), VNU-HCM for this study.



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1Phòng Thí nghiệm trọng điểm ĐHQG-HCM Công nghệ vật liệu, Trường Đại học Bách khoa TP.HCM

2Đại học Quốc gia Thành phố Hồ Chí Minh

3Khoa Kỹ thuật Hóa học, Trường Đại học Bách khoa TP.HCM

4Khoa Công nghệ Vật liệu, Trường Đại học Bách khoa TP.HCM

5Trường Đại học Bách khoa TP.HCM

Tác giả liên hệ: Lê Văn Thăng -


Molypden disunfua (MoS2) có cấu trúc nano được điều khiển và ghép trực tiếp lên bề mặt của ống nano carbon đa thành bằng phản ứng hóa học có sự hỗ trợ của vi sóng. Hạt nano MoS2 được phát triển thành 2 dạng cấu trúc: tinh thể và vô định hình. Cấu trúc và hình thái bề mặt của sản phẩm được phân tích bằng các phương pháp: nhiễu xạ tia X, phổ Raman, kính hiển vi điện tử quét (SEM) và kính hiển vi điện tử truyền qua (TEM). Phổ nhiễu xạ tia X và Raman cho thấy các hạt nano MoS2 được hình thành trong quá trình phản ứng. Ảnh SEM và TEM thể hiện cấu trúc độc đáo của hai loại vật liệu tổ hợp và sự phân bố đồng đều trong cấu trúc vật liệu. Phản ứng tổng hợp hydro trên xúc tác MoS2-tinh thể hóa/MWNTs và MoS2-vô định hình/MWNTs lần lượt có hệ số Tafel là 142 mV/decade (tại thế bắt đầu phản ứng là -0.305 V, so với điện cực NHE) và 135 mV/decade (tại thế bắt đầu phản ứng là -0.223 V, so với điện cực NHE).

Từ khóa: MoS2/MWNTs, phản ứng tổng hợp hydro, xúc tác điện hóa, phản ứng có hỗ trợ vi sóng, điều khiển cấu trúc nano.

[Tạp chí Công Thương - Các kết quả nghiên cứu khoa học và ứng dụng công nghệ, 

Số 28, tháng 12 năm 2021]