Great wall structure inspired 2D@2D hetero-layered W-doped MoS₂ for an enhanced hydrogen evolution reaction

Abstract

Doping engineering of 2D layered molybdenum disulfide (MoS₂) results in attractive catalytic activity for the hydrogen evolution reaction (HER); however, it is limited by its unclear mechanisms. Herein, inspired by the Great Wall structure, this work reports 2D@2D hetero-layered MoS₂/graphene nanosheets with rational modulation of W doping through the hydrothermal method. Results indicate that an optimal W doping of 12.5% in W_0.125Mo_0.875S₂-G presents the highest catalytic activity, which delivers the lowest overpotential of 306 mV at 100 mA cm⁻² and a Tafel slope of 62.2 mV dec⁻¹. Compared to W_0.125Mo_0.875S₂, W_0.125Mo_0.875S₂-G exhibits enhanced HER performance owing to the introduction of graphene. Theoretical calculation results indicate that the density of states (DOS) intensity near the Fermi level was enhanced with W doping, thus resulting in faster reaction kinetics. Our work provides new insights into the electrocatalytic mechanism of doping engineering of MoS₂ for an efficient HER.

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1. Introduction

Considering the severely increasing energy crisis and environmental issues, exploring a clean and renewable energy source is urgently demanded. Hydrogen, owing to its high energy density of 143 kJ g⁻¹ and sustainable production, has attracted extensive attention as one of the most promising alternatives to fossil fuels.^1,2 The hydrogen evolution reaction (HER) due to electrocatalytic water splitting is a widely accepted method to produce hydrogen, in which efficient electrocatalysts are indispensable.^3–7 Pt and Pt group metals are considered optimal electrocatalysts for the HER. However, these noble metals are restricted by their resource scarcity and high cost. Therefore, the development of novel electrocatalysts with merits of low cost, high efficiency, and abundance for future hydrogen generation holds great significance.^8,9

Recently, two-dimensional (2D) transition metal dichalcogenide (TMD) materials have been extensively exploited as efficient electrocatalysts for the HER.^10–14 Among them, molybdenum disulphide (MoS₂), as a typical 2D TMD material, is appealing in the field of electrocatalytic HERs owing to its low cost, abundance, and good catalytic activity.^15,16 MoS₂ is an edge-terminated catalyst, in which only edge sites are catalytically active. Its poor electrical conductivity and limited active sites hinder its performance as a highly efficient HER catalyst. To address these issues, researchers have focused on combining MoS₂ with other functional materials to enhance its conductivity and active sites.^17–19 One such material is graphene, which has high electrical conductivity, large surface area, and good stability. The incorporation of graphene into MoS₂ has shown significant improvements in its HER activity.^20–22 Liu et al. have demonstrated that the integration of MoS₂ and graphene in a well-assembled 2D hybrid architecture produced rich electrochemically active reaction sites, exhibiting remarkable collective properties in terms of electron transport and H⁺ trapping.²³ In addition, doping MoS₂ with heteroatoms has been reported to modulate the active edge sites and bonding energy of MoS₂ catalysts.^24–27 Researchers have reported that a significant proportion of S atoms in MoS₂ basal planes is catalytically inert. Transition metal atoms such as Fe, Co, Ni, and Cu were reported to be doped into MoS₂ edges to enhance the catalytic activity of S-edge sites.²⁸ However, some recent works demonstrated that the doping of heteroatoms at the edge shows a weak effect on the HER performance improvement of MoS₂.^29,30 The influence of doping on the HER catalytic performance of MoS₂ is still not clear enough. Further investigations are urgently demanded for in-depth exploration of the working mechanisms. Recently, researchers have reported tungsten (W)-doped MoS₂ as an efficient electrocatalyst for the HER.^31,32 W, as a representative transition metal, has physical and chemical properties similar to those of Mo, and the band structure of WS₂ is also identical to that of MoS₂.³³ The atomic radius of W element is larger than that of Mo element.³⁴ Hence, the substitutional W doping will induce lattice distortion, but still maintain the original morphology of MoS₂, which is conducive to promoting the electrocatalytic performance of MoS₂.

In this work, we designed and constructed 2D@2D hetero-layered W-doped MoS₂/graphene nanosheets (denoted as W-MoS₂-G) via a hydrothermal method as an electrocatalyst for the HER. The W-MoS₂-G nanosheets with various doping concentrations were synthesized to investigate the effect of doping engineering on HER performance. Density functional theory (DFT) calculations were conducted to gain insight into the working mechanism of W doping. The incorporation of W atoms into MoS₂ can enhance the DOS intensity near the Fermi level, leading to fast reaction kinetics. Our results can bring inspiration for the design of MoS₂ and other advanced 2D materials for enhancing the HER performance.

2. Materials and methods

2.1. Materials

All the chemical reagents were bought from Tianjin Guangfu Technology Development Co., Ltd (Tianjin, China). The reagents are as follows: Hydrofluoric acid (HF), nitric acid (HNO₃), hydrochloric acid (HCl), graphite powder, sodium nitrate (NaNO₃), phosphomolybdic acid (H₃[P(Mo₃O₁₀)₄]·xH₂O), L-cysteine (HSCH₂CH(NH₂)CO₂H), phosphotungstic acid (H₃[P(W₃O₁₀)₄]·xH₂O), acetone, and ethyl alcohol.

2.2. Preparation of MoS₂-G

Firstly, graphene oxide was prepared by an improved Hummers’ method.³⁵ A specific quantity of phosphomolybdic acid was introduced into a 22.5 mL aqueous solution of graphene oxide (1 mg mL⁻¹), and the mixture was stirred at room temperature followed by ultrasonic treatment until achieving a homogeneous dispersion. A certain amount of L-cysteine was then added to ensure a Mo : S mole ratio of 1 : 2. The solution was further magnetically stirred until achieving uniformity. Subsequently, the resulting solution was transferred into a reactor, and the reactor was heated in an oven at 180 °C for a duration of 12 hours.

2.3. Preparation of W-MoS₂-G

The MoS₂-G electrode was doped with tungsten, which is a relative of molybdenum, to determine if the hydrogen evolution activity of the molybdenum–tungsten composite material can be further enhanced. Phosphomolybdic acid was added to an aqueous solution of graphite oxide and stirred until uniformly dispersed. L-Cysteine was then introduced and magnetic stirring was continued until uniform dispersion. Phosphotungstic acid was added in a S : (W + Mo) molar ratio of 2 : 1 after thorough mixing. The resulting solution was poured into a reactor and heated at 180 °C for 12 hours.

2.4. Characterization

The crystal structures of the samples were obtained through X-ray diffraction (XRD, Rigaku TTR III). In this experiment, the obtained samples were ground into a powder form and placed on glass slides for scanning with X-rays to obtain the crystal data of the material. Raman spectroscopy was conducted in a Raman microscope (Xplora Plus, Horiba). The morphologies of the samples were examined by using a scanning electron microscope (SEM, JME-7500F, JEOL) and transmission electron microscope (TEM, JEM-2100, JEOL). The chemical states of the samples were characterized by X-ray photoelectron spectroscopy (XPS, Thermo ESCALAB with Al Kα radiation).

2.5. Electrochemical measurements

The electrode system employed in this study for electrochemical testing is a three-electrode configuration. The current collector is carbon cloth, which was cut into the dimensions of 1 cm × 1 cm and assembled within a titanium frame as the working electrode. The auxiliary electrode consists of a graphite rod, while the reference electrode comprises a saturated calomel electrode (SCE). A 0.5 mol L⁻¹ sulfuric acid solution (pH = 0.35) serves as the electrolyte in the three-electrode setup, and all measurements are conducted using an Autolab PGSTAT 302 electrochemical workstation manufactured by Eco Chemie company from Netherlands. Linear sweep voltammetry (LSV) refers to controlling the applied external potential to change at a constant rate (i.e., dφ/dt = const), while simultaneously measuring the current passing through the electrode under the applied potential. The scan rate of LSV is 5 mV s⁻¹ in this experiment. The electrochemical impedance was measured in this experiment under an overpotential of η = 100 mV, with a signal amplitude of 5 mV. Data points were collected from 10⁵ Hz to 0.01 Hz at intervals of 70.

2.6. Theoretical calculation

First-principles DFT calculations were performed with the CASTEP codes, which used a plane wave basis set for the valence electrons and a norm-conserving pseudo-potential for the core electrons. The generalized gradient approximation (GGA) of Perdew–Burke–Ernzerhof was adopted for the exchange and correlation energy. To avoid any artificial interaction between the layers and their images, the thickness of the vacuum was set to be 20 Å. The equilibrium structures were obtained via geometry optimization in the Broyden–Fletcher–Goldfarb–Shanno (BFGS) minimization scheme. A kinetic energy cutoff of 500 eV was used for the wave function expansion and a 3 × 3 × 1 k-point mesh was sampled in the Brillouin zone. And total energy changes were finally reduced to less than 1 × 10⁻⁶ eV per atom, and Hellmann–Feynman forces acting on atoms were converged to less than 0.05 eV Å⁻¹. Additionally, a 4 × 4 × 1 supercell of MoS₂ [001] was used for the adsorption of H₂.

3. Results and discussion

3.1. Physiochemical characterization

The W doped MoS₂ was synthesized via a facile one-step hydrothermal process by using phosphomolybdic acid and L-cysteine as precursors, as schematically illustrated in Fig. 1. The doping concentration can be rationally modulated by adjusting the content of phosphotungstic acid. Graphene was incorporated to enhance the electrical conductivity of MoS₂. Fig. 2a shows the XRD patterns of graphene incorporated MoS₂ with and without W doping (W-MoS₂-G and MoS₂-G). The peaks of MoS₂-G are consistent with those of W-MoS₂-G, indicating that there is no phase transformation after W doping. Both samples exhibit a broad peak at 24.9° due to the existence of graphene.^22,36 The characteristic peak located at 2θ = 43.5° corresponds to the (103) plane of MoS₂ (JCPDS no. 37-1492),^37,38 which shows no other crystal phase. The Raman spectra of W-MoS₂-G and MoS₂-G are presented in Fig. 2b. The Raman band at 146 cm⁻¹ is related to the in-plane shear mode J₁ corresponding to the 1T phase MoS₂, while the characteristic peak of the main in-plane mode E_2g¹ of 2H phase MoS₂ is observed at 380 cm⁻¹, indicating the coexistence of 1T and 2H phase MoS₂ in both the as-synthesized W-MoS₂-G and MoS₂-G samples.^39,40 Besides, the typical Raman active graphene bands (D and G) at 1352 and 1585 cm⁻¹ can also be observed, confirming the incorporation of graphene into MoS₂. With the doping of W, the intensity of Raman spectrum of W-MoS₂-G has enhanced, which indicates that W doping engineering can affect the active graphene bands.

Fig. 1 Schematic of the fabrication of W-MoS₂-G nanosheets.

Fig. 2 (a) XRD patterns and (b) Raman spectra of the W-MoS₂-G and MoS₂-G samples.

To investigate the morphology and structure of W-MoS₂-G, detailed microscopic characterization was performed, as shown in Fig. 3. SEM images in Fig. 3a and b show that W-MoS₂-G presents a highly branched morphology, in which the MoS₂ nanosheets are uniformly generated on the graphene sheets, exposing more edge sites. Previous studies have reported that the edges of MoS₂ nanosheets are the catalytic active sites,^41,42 which are responsible for the high electrocatalytic HER performance. The morphology of MoS₂-G was also characterized, which is similar to that of W-MoS₂-G (Fig. S1, ESI†), reflecting that the W-doping did not change the morphology. To further investigate the subtler structure of W-MoS₂-G, TEM analysis was conducted. As shown in Fig. 3c, MoS₂ nanosheets with a lamellar structure (cross black stripes) are distributed on graphene sheets (flat grey area). The HRTEM in Fig. 3d shows that the MoS₂ nanosheets consist of only a few layers, and the interlayered lattice spacing is 0.83 nm, matching with the (002) crystalline plane of MoS₂.

Fig. 3 (a) and (b) SEM images of W- MoS₂-G in different magnifications. (c) TEM and (d) HRTEM images of W-MoS₂-G.

Fig. 4 presents the SEM-EDX elemental mapping images of W-MoS₂-G. It clearly shows that the C (orange color), Mo (blue color), W (green color), O (red color), and S (purple color) elements are homogeneously distributed in the W-MoS₂-G sample, indicating the successful synthesis of W-MoS₂-G and uniform doping of W atoms.

Fig. 4 (a)–(f) The SEM-EDX elemental mapping images of W-MoS₂-G.

X-ray photoelectron microscopy (XPS) was further carried out to determine the chemical composition of the samples. Fig. 5 presents the high-resolution XPS spectra of Mo 3d, W 4f, S 2p, and C 1s of W-MoS₂-G, in which all the binding energies are calibrated to C 1s peak position (284.6 eV). As shown in Fig. 5a, there are three characteristic peaks corresponding to Mo 3d_3/2, Mo 3d_5/2, and S 2s. The binding energy peaks at 231.8 and 228.6 eV correspond to Mo 3d_3/2 and Mo 3d_5/2 for the 1T phase, while the peaks at 232.6 and 229.5 eV are attributed to Mo 3d_3/2 and Mo 3d_5/2 for the 2H phase. The peaks shown in Fig. 5b correspond to W 4f_5/2 and W 4f_7/2 for 1T and 2H phases, confirming the existence of W in W-MoS₂-G. The peak located at 37.8 eV corresponds to the presence of oxidation caused by the surface absorption of O₂, H₂O, and CO₂.⁴³ The spectra of S 2p and C 1s (Fig. 5c and d) confirm the existence of MoS₂ and graphene. The binding energies of Mo 3d and S 2p are negatively shifted compared with the undoped MoS₂-G (Fig. S2, ESI†), indicating the increase of electron density in MoS₂ after the incorporation of W element.

Fig. 5 High-resolution XPS spectra of W-MoS₂-G for (a) Mo 3d, (b) W 4f, (c) S 2p, and (d) C 1s.

3.2. Electrocatalytic HER activity and stability

W-MoS₂-G samples with W doping concentrations of 0%, 10%, 12.5%, and 15% were synthesized (denoted as MoS₂-G, W_0.1Mo_0.9S₂-G, W_0.125Mo_0.875S₂-G, and W_0.15Mo_0.85S₂-G, respectively). The electrocatalytic HER performance of the as-obtained samples was investigated through a three-electrode system in 0.5 M H₂SO₄. Fig. 6a shows the LSV plots of the samples. As depicted, the W_0.125Mo_0.875S₂-G exhibits the best HER activity with an overpotential of 306 mV to achieve 100 mA cm⁻², which is much lower than that of MoS₂-G (440 mV), W_0.1Mo_0.9S₂-G (346 mV), and W_0.15Mo_0.85S₂-G (518 mV). The HER performance is firstly improved with the increasing concentration of W doping, but reduced as the concentration continues to increase to 15%. The HER activity of W_0.125Mo_0.875S₂ without incorporation of graphene was also measured for comparison, which is much poorer than that of W_0.125Mo_0.875S₂-G, confirming that the introduction of graphene can highly enhance the electrocatalytic activity of MoS₂.⁴⁴ Besides, the effect of different catalyst loadings on the HER performance has been investigated (Fig. S3, ESI†). A modest catalyst loading of 1.0 mg cm⁻² was adopted. The corresponding Tafel slopes are calculated, as shown in Fig. 6b. The Tafel slope value can be used to predict the reaction mechanism, including Volmer–Heyrovsky mechanism and Volmer–Tafel mechanism. The former one proceeds by the electrochemical adsorption–desorption steps, while the latter one consists of an electrochemical adsorption with chemical desorption process.^26,43 The Tafel slope of W_0.125Mo_0.875S₂-G is the lowest, i.e., 62.2 mV dec⁻¹, indicating the rapid HER kinetics of W_0.125Mo_0.875S₂-G, which follows the Volmer–Heyrovsky mechanism with Heyrovsky's reaction step as the rate-determining step.⁴⁵

Fig. 6 Electrochemical activities of the prepared MoS₂-based materials toward the HER. (a) LSV curves of various catalysts. (b) Tafel plots of the corresponding catalysts. (c) CV curves of W_0.125Mo_0.875S₂-G under a series of scan rates in a certain potential range. (d) ECSA-normalized polarization curves. (e) The galvanostatic curve of W_0.125Mo_0.875S₂-G at a constant current density of 10 mA cm⁻².

To investigate the effect of W doping on the HER performance of MOS₂, the electrochemically active surface areas (ECSA) of the obtained catalysts are examined based on the double-layer capacitance (C_dl).^46,47Fig. 6c displays the CV curves of W_0.125Mo_0.875S₂-G under various scan rates over 0–0.1 V. The C_dl values of all the as-synthesized samples are calculated according to the corresponding CV curves (Fig. 6c and Fig. S4, ESI†), as presented in Fig. 6d. The calculated C_dl value for W_0.125Mo_0.875S₂-G is 95.0 mF cm⁻², which is the highest among the as-prepared catalysts, indicating the largest exposed catalytically active sites for facilitating HER activity at the W doping ratio of 12.5%. With increasing the W doping ratio to 15%, the catalyst shows the smallest C_dl with a low number of active sites. Thus, W doping can enhance the HER activity by increasing the active sites, but there is a modest doping concentration to obtain the optimal electronic structure of MoS₂. Furthermore, except for the electrocatalytic activity, long-term durability is another important parameter to evaluate the catalyst. The stability of W_0.125Mo_0.875S₂-G was examined by galvanostatic testing at a constant current density of 10 mA cm⁻² in 0.5 M H₂SO₄. Obviously, the overpotential of W_0.125Mo_0.875S₂-G remains almost unchanged over 5 h of electrolysis, as presented in Fig. 6e, implying the good stability of W_0.125Mo_0.875S₂-G for long-term HER activity.

To further investigate the working mechanism of W doping in the catalytic performance of MoS₂, DFT calculations were carried out to provide a deeper insight into the improved performance of W-doped MoS₂ in the HER process. From the viewpoint of atoms, the insets of Fig. 7a and b show the top view of MoS₂ and W-doped MoS₂ crystal structures with absorbed H atoms based on computational optimization. The structure can well match the XRD results. With the W doping, the DOS intensity near the Fermi level was enhanced from the value of 1.0 × 10⁻⁴ to 1.8 × 10⁻⁴. The result indicates that the W-doped MoS₂ exhibits rapid charge transfer kinetics, which is in good agreement with the Tafel slope.^48,49

Fig. 7 The calculated DOS intensity of (a) MoS₂ and (b) W-doped MoS₂. The insets are top views of MoS₂ and W-doped MoS₂ crystal structures with absorbed H atoms based on computational optimization.

4. Conclusions

In summary, we have reported the rational modulation of W-doped MoS₂ with a unique 2D@2D hetero-layered structure via a hydrothermal method, and investigated the effect of the doping engineering mechanism. The HER performance of MoS₂ is highly related to the doping concentration. The optimal W doping ratio is 12.5%, resulting in the highest HER performance. The overpotential is only 306 mV to reach 100 mA cm⁻² with a Tafel slope of 62.2 mV dec⁻¹. Meanwhile, the as-synthesized W_0.125Mo_0.875S₂-G also presents excellent long-term stability during HER electrolysis. The theoretical calculation results reveal fast reaction kinetics owing to the doping of W. This work brings new inspiration to design efficient TMD-based catalysts and look into the in-depth mechanism for high-performance HER.

Data availability

The data that support the findings of this study are available from the corresponding author upon reasonable request. Data generated and analyzed in this study are included in the article and its ESI.†

Conflicts of interest

The authors declare no conflict of interest.

Acknowledgements

This work is financially supported by Special Funds for Innovation Development of Hangzhou Chengxi Sci-tech Innovation Corridor (KZ20233184), the Talent Start-up Fund offered by NingboTech University (20220301Z0018), 2024 Ningbo “Science and Technology Innovation Yongjiang 2035” Key Technology Breakthrough Program Project (No. 2024Z203), and the development project of Zhejiang Province's “Jianbing” and “Lingyan” (2023C01226).

References

1. J. Zhang, T. Wang, P. Liu, Z. Liao, S. Liu, X. Zhuang, M. Chen, E. Zschech and X. Feng, Efficient hydrogen production on MoNi₄ electrocatalysts with fast water dissociation kinetics, Nat. Commun., 2017, 8(1), 15437.
2. S. Dunn, Hydrogen futures: toward a sustainable energy system, Int. J. Hydrogen Energy, 2002, 27(3), 235–264.
3. M. Zeng and Y. Li, Recent advances in heterogeneous electrocatalysts for the hydrogen evolution reaction, J. Mater. Chem. A, 2015, 3(29), 14942–14962.
4. N. Dubouis and A. Grimaud, The hydrogen evolution reaction: from material to interfacial descriptors, Chem. Sci., 2019, 10(40), 9165–9181.
5. W. Liu, X. Niu, J. Tang, Q. Liu, J. Luo, X. Liu and Y. Zhou, Energy-efficient anodic reactions for sustainable hydrogen production via water electrolysis, Chem. Synth., 2023, 3(4), 44.
6. M. Ďurovič, J. Hnát and K. Bouzek, Electrocatalysts for the hydrogen evolution reaction in alkaline and neutral media. A comparative review, J. Power Sources, 2021, 493, 229708.
7. J. Ding, H. Yang, H. Zhang, Z. Wang, Q. Liu, L. Feng, G. Hu, J. Luo and X. Liu, Dealloyed NiTiZrAg as an efficient electrocatalyst for hydrogen evolution in alkaline seawater, Int. J. Hydrogen Energy, 2024, 53, 318–324.
8. W. Liu, W. Liu, T. Hou, J. Ding, Z. Wang, R. Yin, X. San, L. Feng, J. Luo and X. Liu, Coupling Co-Ni phosphides for energy-saving alkaline seawater splitting, Nano Res., 2024, 17(6), 4797–4806.
9. W. Li, K. Liu, S. Feng, Y. Xiao, L. Zhang, J. Mao, Q. Liu, X. Liu, J. Luo and L. Han, Well-defined Ni₃N nanoparticles armored in hollow carbon nanotube shell for high-efficiency bifunctional hydrogen electrocatalysis, J. Colloid Interface Sci., 2024, 655, 726–735.
10. D. Kong, J. J. Cha, H. Wang, H. R. Lee and Y. Cui, First-row transition metal dichalcogenide catalysts for hydrogen evolution reaction, Energy Environ. Sci., 2013, 6(12), 3553–3558.
11. L. Lin, P. Sherrell, Y. Liu, W. Lei, S. Zhang, H. Zhang, G. G. Wallace and J. Chen, Engineered 2D Transition Metal Dichalcogenides—A Vision of Viable Hydrogen Evolution Reaction Catalysis, Adv. Energy Mater., 2020, 10(16), 1903870.
12. C. Zhu, D. Gao, J. Ding, D. Chao and J. Wang, TMD-based highly efficient electrocatalysts developed by combined computational and experimental approaches, Chem. Soc. Rev., 2018, 47(12), 4332–4356.
13. X. Zhang, X. Wang, Q. Yan, R. Gao, J. Zhao, Z. Song, K. Zhu, D. Cao, J. Yao, L. Zheng and G. Wang, Defects engineering and interface regulation on nickel-rich sulphides promoting water/urea/ethanol electrooxidation, Chem. Eng. J., 2024, 486, 150397.
14. Y. Fan, J. Zhang, J. Han, M. Zhang, W. Bao, H. Su, N. Wang, P. Zhang and Z. Luo, In situ self-reconstructed hierarchical bimetallic oxyhydroxide nanosheets of metallic sulfides for high-efficiency electrochemical water splitting, Mater. Horiz., 2024, 11(7), 1797–1807.
15. D. Voiry, M. Salehi, R. Silva, T. Fujita, M. Chen, T. Asefa, V. B. Shenoy, G. Eda and M. Chhowalla, Conducting MoS₂ Nanosheets as Catalysts for Hydrogen Evolution Reaction, Nano Lett., 2013, 13(12), 6222–6227.
16. Z. He and W. Que, Molybdenum disulfide nanomaterials: Structures, properties, synthesis and recent progress on hydrogen evolution reaction, Appl. Mater. Today, 2016, 3, 23–56.
17. Y. Zheng, J. Rong, Y. Zhu, T. Zhang, D. Yang and F. Qiu, Construction of highly dispersed active sites in MoS₂/CuS/C electrocatalyst based on organic–inorganic hybrid nanoflower for efficient hydrogen generation, Appl. Surf. Sci., 2022, 574, 151725.
18. L. Xu, Y. Zhang, L. Feng, X. Li and Q. An, A Scalable Interfacial Engineering Strategy for a Finely Tunable, Homogeneous MoS₂/rGO-Based HER Catalytic Structure, Adv. Mater. Interfaces, 2020, 7(9), 1902022.
19. Q. Zhou, Z. Wang, H. Yuan, J. Wang and H. Hu, Rapid hydrogen adsorption-desorption at sulfur sites via an interstitial carbon strategy for efficient HER on MoS₂, Appl. Catal., B, 2023, 332, 122750.
20. Y. Li, H. Wang, L. Xie, Y. Liang, G. Hong and H. Dai, MoS₂ Nanoparticles Grown on Graphene: An Advanced Catalyst for the Hydrogen Evolution Reaction, J. Am. Chem. Soc., 2011, 133(19), 7296–7299.
21. X. Meng, L. Yu, C. Ma, B. Nan, R. Si, Y. Tu, J. Deng, D. Deng and X. Bao, Three-dimensionally hierarchical MoS₂/graphene architecture for high-performance hydrogen evolution reaction, Nano Energy, 2019, 61, 611–616.
22. J. Joyner, E. F. Oliveira, H. Yamaguchi, K. Kato, S. Vinod, D. S. Galvao, D. Salpekar, S. Roy, U. Martinez, C. S. Tiwary, S. Ozden and P. M. Ajayan, Graphene Supported MoS₂ Structures with High Defect Density for an Efficient HER Electrocatalysts, ACS Appl. Mater. Interfaces, 2020, 12(11), 12629–12638.
23. L. Ma, Y. Hu, G. Zhu, R. Chen, T. Chen, H. Lu, Y. Wang, J. Liang, H. Liu, C. Yan, Z. Tie, Z. Jin and J. Liu, In Situ Thermal Synthesis of Inlaid Ultrathin MoS₂/Graphene Nanosheets as Electrocatalysts for the Hydrogen Evolution Reaction, Chem. Mater., 2016, 28(16), 5733–5742.
24. Q. Xiong, Y. Wang, P.-F. Liu, L.-R. Zheng, G. Wang, H.-G. Yang, P.-K. Wong, H. Zhang and H. Zhao, Cobalt Covalent Doping in MoS₂ to Induce Bifunctionality of Overall Water Splitting, Adv. Mater., 2018, 30(29), 1801450.
25. G. Wang, G. Zhang, X. Ke, X. Chen, X. Chen, Y. Wang, G. Huang, J. Dong, S. Chu and M. Sui, Direct Synthesis of Stable 1T-MoS₂ Doped with Ni Single Atoms for Water Splitting in Alkaline Media, Small, 2022, 18(16), 2107238.
26. S. Bolar, S. Shit, J. S. Kumar, N. C. Murmu, R. S. Ganesh, H. Inokawa and T. Kuila, Optimization of active surface area of flower like MoS₂ using V-doping towards enhanced hydrogen evolution reaction in acidic and basic medium, Appl. Catal., B, 2019, 254, 432–442.
27. Y. Xue, X. Bai, Y. Xu, Q. Yan, M. Zhu, K. Zhu, K. Ye, J. Yan, D. Cao and G. Wang, Vertically oriented Ni-doped MoS₂ nanosheets supported on hollow carbon microtubes for enhanced hydrogen evolution reaction and water splitting, Composites, Part B, 2021, 224, 109229.
28. Y. Shi, Y. Zhou, D.-R. Yang, W.-X. Xu, C. Wang, F.-B. Wang, J.-J. Xu, X.-H. Xia and H.-Y. Chen, Energy Level Engineering of MoS₂ by Transition-Metal Doping for Accelerating Hydrogen Evolution Reaction, J. Am. Chem. Soc., 2017, 139(43), 15479–15485.
29. H. Wang, C. Tsai, D. Kong, K. Chan, F. Abild-Pedersen, J. K. Nørskov and Y. Cui, Transition-metal doped edge sites in vertically aligned MoS₂ catalysts for enhanced hydrogen evolution, Nano Res., 2015, 8(2), 566–575.
30. J. Deng, H. Li, S. Wang, D. Ding, M. Chen, C. Liu, Z. Tian, K. S. Novoselov, C. Ma, D. Deng and X. Bao, Multiscale structural and electronic control of molybdenum disulfide foam for highly efficient hydrogen production, Nat. Commun., 2017, 8(1), 14430.
31. H. Wang, L. Ouyang, G. Zou, C. Sun, J. Hu, X. Xiao and L. Gao, Optimizing MoS₂ Edges by Alloying Isovalent W for Robust Hydrogen Evolution Activity, ACS Catal., 2018, 8(10), 9529–9536.
32. D. Zhang, F. Wang, W. Zhao, M. Cui, X. Fan, R. Liang, Q. Ou and S. Zhang, Boosting Hydrogen Evolution Reaction Activity of Amorphous Molybdenum Sulfide Under High Currents Via Preferential Electron Filling Induced by Tungsten Doping, Adv. Sci., 2022, 9(27), 2202445.
33. J. Rong, Y. Ye, J. Cao, X. Liu, H. Fan, S. Yang, M. Wei, L. Yang, J. Yang and Y. Chen, Restructuring electronic structure via W doped 1T MoS₂ for enhancing hydrogen evolution reaction, Appl. Surf. Sci., 2022, 579, 152216.
34. J. N. He, Y. Q. Liang, J. Mao, X. M. Zhang, X. J. Yang, Z. D. Cui, S. L. Zhu, Z. Y. Li and B. B. Li, 3D Tungsten-Doped MoS₂ Nanostructure: A Low-Cost, Facile Prepared Catalyst for Hydrogen Evolution Reaction, J. Electrochem. Soc., 2016, 163(5), H299.
35. M. Zhu, Q. Yan, X. Bai, H. Cai, J. Zhao, Y. Yan, K. Zhu, K. Ye, J. Yan, D. Cao and G. Wang, Construction of reduced graphene oxide coupled with CoSe₂-MoSe₂ heterostructure for enhanced electrocatalytic hydrogen production, J. Colloid Interface Sci., 2022, 608, 922–930.
36. Y. Z. N. Htwe, W. S. Chow, Y. Suda, A. A. Thant and M. Mariatti, Effect of electrolytes and sonication times on the formation of graphene using an electrochemical exfoliation process, Appl. Surf. Sci., 2019, 469, 951–961.
37. K. Yao, Z. Xu, Z. Li, X. Liu, X. Shen, L. Cao and J. Huang, Synthesis of Grain-like MoS₂ for High-Performance Sodium-Ion Batteries, ChemSusChem, 2018, 11(13), 2130–2137.
38. Q. Jin, N. Liu, C. Dai, R. Xu, B. Wu, G. Yu, B. Chen and Y. Du, H₂-Directing Strategy on In Situ Synthesis of Co-MoS₂ with Highly Expanded Interlayer for Elegant HER Activity and its Mechanism, Adv. Energy Mater., 2020, 10(20), 2000291.
39. J. Huang, X. Pan, X. Liao, M. Yan, B. Dunn, W. Luo and L. Mai, In situ monitoring of the electrochemically induced phase transition of thermodynamically metastable 1T-MoS₂ at nanoscale, Nanoscale, 2020, 12(16), 9246–9254.
40. M. Acerce, E. K. Akdoğan and M. Chhowalla, Metallic molybdenum disulfide nanosheet-based electrochemical actuators, Nature, 2017, 549(7672), 370–373.
41. M. Wang, L. Fan, D. Tian, X. Wu, Y. Qiu, C. Zhao, B. Guan, Y. Wang, N. Zhang and K. Sun, Rational Design of Hierarchical SnO₂/1T-MoS₂ Nanoarray Electrode for Ultralong-Life Li–S Batteries, ACS Energy Lett., 2018, 3(7), 1627–1633.
42. X. Zhang, F. Zhou, S. Zhang, Y. Liang and R. Wang, Engineering MoS₂ Basal Planes for Hydrogen Evolution via Synergistic Ruthenium Doping and Nanocarbon Hybridization, Adv. Sci., 2019, 6(10), 1900090.
43. S. Bolar, S. Shit, N. C. Murmu, P. Samanta and T. Kuila, Activation Strategy of MoS₂ as HER Electrocatalyst through Doping-Induced Lattice Strain, Band Gap Engineering, and Active Crystal Plane Design, ACS Appl. Mater. Interfaces, 2021, 13(1), 765–780.
44. Y. Li, B. He, X. Liu, X. Hu, J. Huang, S. Ye, Z. Shu, Y. Wang and Z. Li, Graphene confined MoS₂ particles for accelerated electrocatalytic hydrogen evolution, Int. J. Hydrogen Energy, 2019, 44(16), 8070–8078.
45. Y. Wang, W. Qiu, E. Song, F. Gu, Z. Zheng, X. Zhao, Y. Zhao, J. Liu and W. Zhang, Adsorption-energy-based activity descriptors for electrocatalysts in energy storage applications, Natl. Sci. Rev., 2018, 5(3), 327–341.
46. M. A. Lukowski, A. S. Daniel, F. Meng, A. Forticaux, L. Li and S. Jin, Enhanced Hydrogen Evolution Catalysis from Chemically Exfoliated Metallic MoS₂ Nanosheets, J. Am. Chem. Soc., 2013, 135(28), 10274–10277.
47. S. Ma, H. Yuan, L. Cai, X. Wang, H. Long, Y. Chai and Y. H. Tsang, One step synthesis of Fe_4.4Ni₁₇.₆Se₁₆ coupled NiSe foam as self-supported, highly efficient and durable oxygen evolution electrode, Mater. Today Chem., 2018, 9, 133–139.
48. F. Liu, X. Ren, J. Zhao, H. Wu, J. Wang, X. Han, Y. Deng and W. Hu, Inhibiting Sulfur Dissolution and Enhancing Activity of SnS for CO₂ Electroreduction via Electronic State Modulation, ACS Catal., 2022, 12(21), 13533–13541.
49. Q. Yan, Z. Liu, X. Bai, X. Zhang, R. Gao, W. Yuan, Z. Chen, Z. Li and Y. Li, In Situ Formed Edge-Rich Ni₃S₂-NiOOH Heterojunctions for Oxygen Evolution Reaction, J. Electrochem. Soc., 2022, 169(5), 054532.

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Footnote

† Electronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d4nj04168b

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