Construction of MoS 2 -rGO Hybrid Catalyst: An Efficient and Highly Stable Electrocatalyst for Enhanced Hydrogen Generation Reactions

doi:10.21203/rs.3.rs-3399744/v1

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Construction of MoS 2 -rGO Hybrid Catalyst: An Efficient and Highly Stable Electrocatalyst for Enhanced Hydrogen Generation Reactions

https://doi.org/10.21203/rs.3.rs-3399744/v1

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It has been hypothesized that molybdenum disulfide, also known as MoS₂, is an attractive option for the synthesis of hydrogen with a high degree of efficiency. It is preferred to construct a hybrid based on MoS₂ in order to increase the catalytic efficiency, and it is vital to have a grasp of the nature of catalysis in order to make advances in this sector. In this paper, we use reduced graphene oxide, generally known as rGO, to create a MoS₂@rGO hybrid catalyst with a number of favorable characteristics for the hydrogen evolution process (HER). The MoS₂@rGO hybrids are next subjected to a battery of analytical tests, including TGA, XRD, TEM, XPS, Raman and BET. 1T MoS₂@rGO hybrids demonstrated short Tafel slopes (46 and 52 mV.dec^-1) and low levels of overall (70 and 71 mV versus RHE) in both alkaline and acidic electrolytes, allowing for a high current density of 10 mA.cm². The findings show that HER exists in flawed heterostructures. Because 1T phase molybdenum disulfide (MoS₂) has more functional sites and a higher intrinsic permeability, it is responsible for the catalyst's outstanding HER efficiency. This paper presents a novel way for fabricating highly active and responsive HER catalysts, as well as a way that is both feasible and practical for fabricating defective-MoS₂@rGO heterostructures.

Hybrid

MoS2

RGO

Hydrogen evolution

Discovering ways to lessen our reliance on petroleum and coal, and so limit ecological challenges and the rate of the release of greenhouse gases, is not only critical, but also one of the most pressing global worries. As a result, green and environmentally friendly energy sources have established as the leading contenders [1]. Hydrogen (H₂), on the other energy, is a plentiful emerald vitality source with a net calorific output and no carbon footprint. It also has the potential to significantly address the needs of both the economy and society at large [2]. As a direct result, there is an immediate need to think of environmentally friendly techniques of manufacturing hydrogen. Electrolysis of naturally freshwater supplies predicts performance and is a forerunner in energy transfer. The HER is a significant innovation for hydrogen production, with exceptionally good reaction effects [3]. Inherently renewable water electrolyte demonstrates tremendous dedication and is a clear frontrunner for energy transfer. Traditional electrochemical HER, on the other hand, employs expensive electrocatalysts such as the noble metal palladium in order to capitalise on the enormous value of these HER approaches (Pt). Numerous possible alternatives to platinum, such as metallic substances and metal-free combination catalysts, have been investigated; nevertheless, because of their low catalytic activity, all of these options need a higher amount of input electrical power [4, 5]. Numerous potential future Pt substitutes have been researched. As a result, there is a pressing need for innovative electrocatalysts that are both low-cost and widely available in order to reduce HER reaction overpotentials [6].

First row conversion alloying elements [7–9], TMDs [10–13], phosphorides [14–16], and others are examples of potentially efficient electrocatalysts for HER that are both economical and abundant on Earth. MoS₂, with its unique structure comparable to graphite, is one of the materials considered to be a possible alternative for platinum due to its superior electrochemical properties as well as economic benefits. [17, 18]. The exposed edge sites of MoS₂ have a thermally neutral free power for gas adsorption, according to studies using density functional theory. This is in contrast to the basal plane's catalytic activity, which is present on the same surface. Because there aren't enough active sites, the overall efficiency of large-scale hydrogen synthesis suffers. As a result, the catalytic activity of MoS₂ has been the subject of extensive research and development in recent years [21–23]. This is a direct outcome of this being the case. It has been established, both theoretically and experimentally, that the nanostructure design of MoS₂ using rGO is a method that is not only appealing but also simple to implement and effective in its results. This has been proved to be a technique that is an approach that is not only appealing but also simple to implement and effective in its outcomes. Many investigations have shown that building MoS₂ arrays coupled to a reduced graphene oxide (rGO) substrate can yield high HER activity with appropriate timing. As a result, what are the primary variables that have contributed to increasing electrocatalysis The exceptional catalytic performance towards HER was thought to be attributable to two controllable parameters within the MoS₂@graphene hybrid. HER is an abbreviation for human oestrogen receptors. To begin, the induced graphene substrate promotes the production of monodisperse MoS₂ nanosheets rather than clumping, resulting in a rise in the variety of accessible edge sites. Second, the high electrical conductivity of RGO may contribute to the enhanced HER efficiency; it allows electrons to travel quickly from tractor trailer MoS₂ to an external circuit [24, 25]. This could be one of the causes for her increased efficiency. Furthermore, the heterojunction found in the MoS₂@RGO hybrid may play an important role in the HER process. This heterojunction possesses a distinct set of chemical characteristics. Using molybdenum trioxide, thiourea, and graphene oxide, we developed a robust in-situ hydrothermal approach for producing MoS₂@rGO heterostructures utilising 1T phase MoS₂. This enabled us to build effective the MoS₂@rGO heterostructures (GO). Figure 1 depicts the entire method. At a current density of 10 mAcm^− 2, the MoS₂@rGO hybrid with a higher MoS₂ loading dose (MSG) had a power density of 239 mV. In comparison, raw MoS₂ (MoS2, 400 mV) and naked rGO (> 600 mV) had lower values. The synergistic effects of 1T phase MoS₂ and rGO are expected to lead to outstanding electrocatalytic HER activity in these MoS₂@rGO heterostructures.

2.1. Synthesis of MoS₂@RGO hybrid composites

Both thiourea and ammonium molybdate were able to be dissolved in 100 milliliters of deionized (DI) water thanks to the 2:1 molar weight ratio between the two substances. The dissolved homogeneous solutions were added, along with a quantity of five percent more hydrazine and hydrochloric acid, and the process was carried out at room temperature. In each case, deionized water and ultrasonic aid were utilised to disperse GO for thirty minutes. The two dispersions from the above were then mixed, and thiourea was added while the mixture was mechanically agitated for another half hour. Following that, fifty millilitres of the dispersion was placed in a corrosion resistance sterilizer with a Teflon lining and held at a temperature of 180 degrees for twenty-four hours. During the hydrothermal treatment, GO underwent a change that resulted in the creation of reduced graphene oxide (rGO). The MoS₂@rGO heterostructures were dried at 80 degrees Celsius for 12 hours after being centrifuged and rinsed with deionized water and ethanol three times each. The inclusion of GO was not included in the procedure of producing pure MoS₂, and the other parameters were the same as previously mentioned.

2.2. HER activity test

Using a ZIVE SP1 (Wonatech) electrochemical apparatus, studies in acid (0.5 M H2SO4) and alkaline (1 M KOH) electrolytes were carried out at RT. We used a three-electrode layout for electrochemical investigations, with a carbon rod counter electrode, NF as the positive terminal, and either silver chloride (AgCl) or mercury oxide (HgO) as the source node. To make active electrodes, CB, active materials (1T MoS₂ and 1T MoS₂@rGO), and PVDF were combined in a slurry with a weight ratio of 10:80:10. The combination also contained N-methyl-2-pyrrolidone. The NF was then immersed in the sludge and sterilized for 12 hours at 90 ^oC. In the polarisation testing, initial impedance compensating (iR compensation) was used. Using electrochemical impedance spectroscopy, researchers investigated the impact of changing frequency in both basic and acidic situations (EIS).

3.1. XRD analysis

The diffraction pattern of the as-prepared MoS₂-based sample was determined using X-ray crystallography. Only hexagonal MoS₂ crystalline structures were apparent in the XRD patterns of MoS₂, MoS₂/rGO hybrid, and MoS₂/rGO hybrid in Fig. 3a. The crystal planes of MoS₂ (100), (103), and (110) were found using sharp patterning at 2 = 32.8^o, 39.8^o, and 58.5^o, respectively (JCPDS No.37-1492). There were also no further peaks in the sequence, indicating that the commodity is extremely pure. The presence of (002) peak along with MoS₂ related peaks in the MoS₂@RGO composite sample demonstrate that successful formation of heterostructure composites [26]. Moreover, the intensity of RGO to efficiently inhibit stacking of the MoS₂ layers was demonstrated by a significant drop in the diffraction peaks following its addition [27].

3.2. Morphological studies

The hierarchical MoS₂@RGO composites were examined using SEM and are displayed in Fig. 2 (a&b) at various magnifications. The MoS₂ flowers actually indicate a nanosheet construction throughout. Furthermore, the MoS₂ has a multitude of accessible active sites, which is helpful for sonocatalytic activity. Because graphene oxide possesses such a high surface area, MoS₂ nanoparticles may be distributed equally across the RGO. According to these findings, it is highly likely that the MoS₂ nanosheets are hierarchical structures organised and securely attached to the RGO. The TEM photograph of MoS₂ (Fig. 2c) revealed that the material had clumped together into massive clusters and taken on the shape of nanoplates. As illustrated in Fig. 2d, the evolution of pure MoS₂ was more scattered; however, the MoS₂ contained in the MoS₂@rGO hybrid formed in a fashion that was both homogeneous and firmly compacted on the face of the rGO. The lattice gap of MoS₂'s (002) and (101) planes was measured to be 0.63 nm, while the (002) plane measured 0.28 nm (see Fig. 2e). The EDS mapping of the MoS₂@RGO compound is shown in Fig. 2 (f-i). Pure MoS₂ is depicted in the photo as a nanoparticle with the shape of a flower. MoS₂ nanosheets, on the other hand, are evenly distributed among RGO sheets.

3.3.FTIR and Raman spectra analysis

FTIR spectroscopy was utilised to keep monitor of the likelihood that the GO in the hybrids had been transformed to RGO via the hydrothermal pathway (Fig. 3a). The GO sample's spectrum analysis displays a broad and widespread peak at 3000–3750 cm^− 1, suggesting the existence of the O-H stretching vibration [28]. This happens because the GO sample was not completely dried before being analysed. The faint signal observed between 1700 and 1900 cm-1 suggests C = O or COOH. Peaks at 1550–1650 and 1350 cm^− 1 [29] gave solid evidence for the presence of sp2-hybridized C = C and C = O-C. However, the absence of a clear peak at 1700–1900 cm1 in the spectra of MoS₂@RGO hybrids indicates that the C-O and COOH groups have been removed. The utilisation of FTIR spectra revealed that graphene oxide can be successfully converted into reduced graphene oxide via a hydrothermal method. The Raman spectra (Fig. 4b) show two strong peaks at 375 cm^− 1 and 405 cm^− 1, which correspond to the hexagonal MoS2 well as well as the in-plane E_12g and out-of-plane A_1g translational modes [30]. Furthermore, the D peak at 1352 cm^− 1 and the G peak at 1597 cm^− 1 are apparent in all spectrums. The I_D/I_G substantially improve, which measures the intensity of the D peak in relation to the intensity of the G peak, could be used to assess flaws in graphene-based materials. This ratio reflects the D and G peaks. As a result, we know that the I_D/I_G ratio of the test specimens is 1.02 (for RGO) and 1.13 (for MoS₂@RGO), indicating that the instability of MoS₂@RGO is more visible than that of pure RGO. It is widely acknowledged that MoS₂@RGO shown exceptional sonocatalytic activity. This is due to the fact that a larger ID/IG ratio allows for higher levels of electrical conductivity and liquid immersion.

3.4. BET and XPS analysis

The N₂ sorption profiles (Fig. 4(c)) demonstrate the differences in the porous nature of 1T MoS₂ and its RGO hybrid. Often, rGO hybrids display type IV N2 sorption properties, characterised by mesoporous behaviour and rapid adsorption and desorption enrichment [31–33]. It was determined that the surface area of MoS₂@RGO was 106.5 m2/g, whereas that of pure MoS₂ was 55.2 m²/g. Whereas MoS₂ and MoS₂ have pore sizes of around 12 and 7 nm (Fig. 4d). The addition of rGO to the MoS2 nanostructure boosts its surface area, which in turn boosts the likelihood of accessing more active surface area in the combination nanostructure [34]. This, in turn, raises the level of onset and active corners, and it also improves the reflexes at the electrode/electrolyte interaction. XPS (Fig. 5) are conducted to determine the elemental composition and the chemical states of the elements by scanning spectra (Fig. 5a). Likewise, a large C 1 s signal from CC at 285.0 eV and a tiny CO peak at 286.9 eV were seen in the MoS₂@RGO heterostructure (Fig. 5(b)). The significantly reduced graphene oxide to rGO is supported by the somewhat lower signals corresponding to O = C-O and CO. Figure 5(c) shows the overlaid MoS₂@RGO XPS spectrum, which reveals that Mo mostly occurs as Mo 3d_5/2 due to its binding energy of 229.5 eV and as Mo 3d_3/2 due to its binding energy of 232.7 eV. (IV). S 2 s peak at 226.6 eV is typical of MoS₂ [35], hence this further demonstrates the element's existence. Good agreement was found between the sulphide phase and the S2p peaks in Fig. 3(d) at 162.4 (2p_3/2) and 163.5 (2p_1/2) eV with an energy gap of 1.1 eV [36].

3.5. Electrochemical HER analysis

In a 3-electrode configuration at room temperature with electrolytes consisting of 0.5 M H₂SO₄ and 1 M KOH, pure NF, Pt/C, MoS₂, and MoS₂@RGO were studied. The LSV polarization profiles of Pt/C, bare NF, MoS₂, and MoS₂@RGO are shown in Fig. 6(a) and (b), respectively. Figure 6(c) depicts the voltage rise that was recorded throughout all three electrocatalysts in the experiment. Pt/C electrocatalysts have a low redox value (41 and 45 mV against RHE, respectively), while bare NF requires an overpotential of 453 and 464 mV versus RHE to generate a current density of 10 mA.cm² in H₂SO₄ and KOH. Electrocatalysts may be manufactured, and one instance is MoS₂, which needs 118 mV against RHE in acidic medium and 101 mV against RHE in alkaline media to reach 10 at the appropriate potential, accordingly. The contains the following is superior to earlier MoS₂ HER results such as 229 mV@10 mA/cm² [49], 119 mV@15 mA/cm² [37], 232 mV@20 mA/cm² [38], 178 mV@100 mA/cm² [39], and 346 mV@20 mA/cm² [40]. Inactive or substandard active edges for H₂ evolution explain why pure phase MoS₂ performs worse in HER than mixed phase MoS₂. Tafel plots (shown in Fig. 6(d) and e) were also employed to investigate electrocatalyst properties. The following Tafel slopes were derived via a linear fit: In acid media, 32 mV.dec^− 1; in bare NF, 159 mV.dec^− 1; in 1T MoS₂, 128 mV.dec^− 1; and in 1T MoS₂@RGO, 44 mV.dec^− 1. This catalyst clearly outperforms the findings reported with previous published MoS₂ catalysts (Table 1) [41–45]. The excellent electrocatalytic behavior of the 1T MoS₂/rGO combination is further enhanced by its low Tafel slopes. EIS was used in this investigation to decipher the HER dynamics and interfacial effects. Pt/C, bare NF, 1T-MoS₂, and 1T MoS₂@rGO EIS measurements were carried out in acidic and alkaline electrolytes across a frequency range of 0.01 Hz to 100 kHz. Figures 6(f) and (g) illustrate the comparable Nyquist plots in acidic and alkaline environments, respectively. Lower than expected initial resistances confirmed improved NF interaction with electrocatalysts (Rs). Under acidic circumstances, Rs values of 2.63, 2.81, 2.15, and 1.95 were recorded; for Pt/C, bare NF, 1T-MoS₂, and 1T MoS₂@rGO, Rs values of 1.96, 2.22, 2.38, and 1.83 were evaluated, correspondingly. In both acidic and basic solutions, all electrocatalytic displayed tiny semicircles, which can be interpreted as charge-transfer resistance (Rct). The Rct values are 3.56 for acidic, 3.96 for basic, 2.85 for 1T-MoS₂, and 2.30 for 1T-MoS₂@rGO. A low CTR, which implies a high rate of interaction among the electrolyte and the electrode's surface, may be caused by a large number of functional edges, which may additionally contribute to the low CTR. Figure 8(h) and Fig. 8(i), respectively, illustrate the density variations over time for MoS₂/rGO hybrids in acidic and alkaline conditions, etc. The creation of hydrogen by an acidic electrolyte remains unchanged over the whole 24 hours, but the production of hydrogen by an alkaline electrolyte experiences a significant and dramatic reduction after the first 12 hours. Hydrogen ion absorption or H2 bubble accumulation on the electrocatalyst surface may be responsible for inducing inconsistencies in alkaline medium, which ultimately results in a reduction in HER [46]. UPS examined the energy levels of the developed catalysts, MoS₂ and MoS₂@RGO. This was accomplished using the vacuum amount and the Fermi level. Energy levels of 5.96 and 5.47 eV have been calculated for the aforementioned catalysts (Fig. 7a & c). The matching band structure of the electrocatalyst sample is also shown in Fig. 7c. Overall, 24 hours of chronoamperometric studies on 1T MoS₂@rGO electrocatalysts in acid and alkaline solutions revealed the Robust HER characteristic. As a result, the suggested simple and trustworthy approach to synthesise the TMDs MoS₂ layers decorated RGO establishes a fresh route to developing next-generation HER electrocatalysts.

Finally, employing an effective hydrothermal method, 1T phase MoS₂@rGO heterostructures was created. Raman, XPS, and XRD analyses were used to determine the molecular structures of MoS₂ and rGO hybrids. FESEM and HRTEM were used to study the sample surfaces in order to understand more about their morphology. Brunauer-Emmett-Teller analysis for 1T MoS₂@RGO hybrid verified surface improvement with a mesoporous structure. The strong HER activity of the as-prepared catalyst is shown by low overpotentials (70 and 71 mV versus RHE), current densities of 10 mA.cm-2, and Tafel slopes of 46 and 52 mV.dec-1 for 1T MoS2@rGO hybrids in acidic and alkaline electrolytes, which accordingly. It has been hypothesized that the enhancement of HER activity is due to the combinatorial effects of greatly higher conductivity and active locations in MoS2@rGO heterostructures. It is possible that this discovery will pave the way for the creation of a feasible approach for the fabrication of highly conducting defective, two-dimensional metal chalcogenides that have higher HER activity.

Conflicts of interest

The authors declare that there is no conflict of interest regarding the research work reported in this manuscript.

Author contributions

Veeranan Arunprasad, P. Siva Karthik, study conceptualization and writing (original draft) the manuscript. Selvam Thulasi, P. Sathish Babu, data curation, formal analysis and writing (review & editing).

Data availability statement
The data that support the findings of this study are available from the corresponding author, upon reasonable request.

Compliance with Ethical Standards

This article does not contain any studies involving animals performed by any of the authors.

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Table 1

MoS₂ based HER properties and the summarized results.

Catalyst	j (mAcm-²) reduction potential was 300 mV (vs RHE)	Tafel slope (mV dec^− 1)	Refs
MoS₂-RGO hybrid	-7	74.5	[41]
Zn@MoS₂	-35	74	[42]
MoS₂-P	-18	80.5	[43]
TiO₂-MoS₂	-30	94	[44]
2H-MoS₂	-8	98	[45]
MoS₂@RGO	-158	46	This work

No competing interests reported.

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Construction of MoS 2 -rGO Hybrid Catalyst: An Efficient and Highly Stable Electrocatalyst for Enhanced Hydrogen Generation Reactions

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Abstract

Figures

1. Introduction

2. Experimental section

2.1. Synthesis of MoS₂@RGO hybrid composites

2.2. HER activity test

3. Results and discussion

3.1. XRD analysis

3.2. Morphological studies

3.3.FTIR and Raman spectra analysis

3.4. BET and XPS analysis

3.5. Electrochemical HER analysis

4. Conclusions

Declarations

References

Tables

Additional Declarations

Status:

Version 1

Construction of MoS 2 -rGO Hybrid Catalyst: An Efficient and Highly Stable Electrocatalyst for Enhanced Hydrogen Generation Reactions

Status:

Version 1

Abstract

Figures

1. Introduction

2. Experimental section

2.1. Synthesis of MoS2@RGO hybrid composites

2.2. HER activity test

3. Results and discussion

3.1. XRD analysis

3.2. Morphological studies

3.3.FTIR and Raman spectra analysis

3.4. BET and XPS analysis

3.5. Electrochemical HER analysis

4. Conclusions

Declarations

References

Tables

Additional Declarations

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2.1. Synthesis of MoS₂@RGO hybrid composites