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Review

Recent Modification Strategies of MoS2 towards Electrocatalytic Hydrogen Evolution

by
Lei Liu
,
Ning Liu
*,
Biaohua Chen
,
Chengna Dai
and
Ning Wang
College of Environmental Science and Engineering, Beijing University of Technology, Beijing 100124, China
*
Author to whom correspondence should be addressed.
Catalysts 2024, 14(2), 126; https://doi.org/10.3390/catal14020126
Submission received: 4 January 2024 / Revised: 29 January 2024 / Accepted: 1 February 2024 / Published: 5 February 2024
(This article belongs to the Special Issue Recent Advances in Environment and Energy Catalysis)
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Abstract

:
Hydrogen production by the electrolysis of water is a green and efficient method, which is of great significance for achieving sustainable development. Molybdenum disulfide (MoS2) is a promising electrocatalyst for hydrogen evolution reaction (HER) due to its high electrochemical activity, low cost, and abundant reserves. In comparison to the noble metal Pt, MoS2 has poorer hydrogen evolution performance in water electrolysis. Therefore, further modifications of MoS2 need to be developed aiming at improving its catalytic performance. The present work summarizes the modification strategies that have been developed in the past three years on hydrogen evolution from water electrolysis by utilizing MoS2 as the electrocatalyst and following the two aspects of internal and external modifications. The former includes the strategies of interlayer spacing, sulfur vacancy, phase transition, and element doping, while the latter includes the heterostructure and conductive substrate. If the current gap in this paper’s focus on modification strategies for electrocatalytic hydrogen evolution in water electrolysis is addressed, MoS2 will perform best in acidic or alkaline media. In addition to that, the present work also discusses the challenges and future development directions of MoS2 catalysts.

Graphical Abstract

1. Introduction

The massive consumption of fossil fuels has caused a series of environmental problems and also led to energy depletion [1,2,3]. The development of green and pollution-free energy has become an important task of contemporary scientific research. Hydrogen energy is a clean, efficient, and renewable energy source with broad application prospects. At present, hydrogen is mainly produced through methane steam reforming and coal gasification, but it requires fossil energy as raw materials, and CO2 is emitted during the production process, which causes environmental pollution [4]. Hydrogen production by the electrolysis of water is an important clean energy production method, which provides an environmentally friendly and sustainable method for hydrogen energy production. The electrolysis of water is composed of two half-reactions: hydrogen evolution reaction at the cathode, and oxygen evolution reaction at the anode [5,6,7,8]. Problems, such as high overpotential and high energy consumption caused by the cathodic polarization of electrolyzed water, limit its industrial application. In order to improve the efficiency of hydrogen production by electrolysis of water, and reduce process costs, it is necessary to develop efficient cathode catalysts to reduce the overpotential of the reaction [9]. At present, the most effective catalyst for electrolytic water hydrogen evolution is the noble metal Pt, but the high cost and low reserves limit its large-scale application [10,11]. Therefore, there is an urgent need to develop high-performance HER catalysts with a low cost and abundant reserves.
MoS2 has become the focus of research due to its low cost, unique structure, and properties [12,13,14]. According to the arrangement of atomic layers, MoS2 can generally be divided into a thermodynamically stable 2H phase and a metastable 1T phase [15,16]. In nature, MoS2 exists in the 2H phase, which has a two-dimensional lamellar structure similar to graphite, and the layers are connected by van der Waals forces [17]. The monolayer consists of three layers of S-Mo-S atoms, in which two layers of S atoms are symmetrically arranged, while the Mo atom is in the center of the triangular prism formed by S atoms, and is coordinated with the surrounding six S atoms [18]. The “H” in 2H-phase MoS2 represents the coordination structure of this hexagonal crystal system, and the “2” represents the structural period, that is, two layers of S-Mo-S molecular layers are repeatedly stacked as a structural unit. The 1T-phase MoS2 also has a two-dimensional structure. The monolayer is composed of three layers of S-Mo-S atoms, and Mo is sandwiched between two layers of S atoms [17]. However, unlike the 2H phase, in the 1T phase, two layers of S atoms are arranged asymmetrically. Its structure can be described as a result of rotating one layer of S atoms by 60° with the center of the top plane as the rotation center based on the triangular prism structure in the 2H phase [19]. Therefore, the Mo atom in 1T-phase MoS2 is in octahedral coordination with the surrounding six S atoms, corresponding to the “T” in 1T, which means “Trigonal” [18]. Along the c-axis direction, 1T-phase MoS2 is repeatedly stacked with a single atomic layer as a unit, corresponding to the “1” in 1T. MoS2 has good HER activity, but due to its low conductivity and inert basal plane, its performance still lags far behind that of Pt catalysts [20]. In order to further improve the performance of MoS2 in the electrolysis of water for hydrogen evolution, researchers have adopted a variety of regulation strategies, such as inducing phase transitions [21,22,23], manufacturing defects [24,25,26], doping elements [27,28,29], and constructing a heterostructure [30,31,32]. These strategies can optimize the key factors that limit the hydrogen evolution performance of electrolytic water, such as the density of the catalytic active site, conductivity, Gibbs free energy of hydrogen adsorption (ΔGH), etc. The ΔGH is an important parameter to evaluate the HER catalyst, and the ΔGH corresponding to an ideal HER catalyst should be close to zero [28,33].
This work summarizes the modification strategies of MoS2 in the past three years and divides the modification strategies into internal modification and external modification according to whether the original structure has changed. Internal modification refers to methods such as increasing the interlayer spacing, introducing sulfur vacancies, inducing phase transition, and doping elements, while external modification refers to methods such as constructing heterostructures and introducing conductive substrates. Examples are provided for each method. If the modification strategies involved in this work can be fully utilized, the HER performance of MoS2 in acidic or alkaline electrolytes will be the best. Finally, this work discusses the challenges and development directions in developing high-performance MoS2 catalysts.

2. Internal Modification

2.1. Interlayer Spacing

Abundant active sites can play a crucial role in the HER. The expanded interlayer spacing of MoS2 is beneficial to exposing more active sites and causes the rapid transfer of protons/electrons and the ready release of hydrogen [34]. In addition, the expanded interlayer spacing can optimize the ΔGH at the edge and basal plane of MoS2, promoting the adsorption of surface H and the desorption of hydrogen, which thereby can effectively improve the HER performance of the material [35].
Zhang et al. [36] stirred the solution mixture containing DMF at room temperature and obtained Mo-MOF at 120 °C, which was heated to 200 °C and converted into 200-1T-MoS2. Under the stress of N, N-dimethylformamide oxide, the interlayer spacing of 200-1T-MoS2 was extended to 10.87 Å (Figure 1a). It has an overpotential of 98 mV at 10 mA cm−2 and a Tafel slope of 52 mV dec−1 (Figure 1b,c). Theoretical calculations show that the enlarged crystal plane changes the electronic structure of 1T-MoS2 and reduces the adsorption–desorption potential of protons (Figure 1d) so that 200-1T-MoS2 exhibits efficient HER activity.
Hu et al. [37] used Na2MoO4·2H2O and C2H5NS as raw materials to synthesize 1T/2H-MoS2/NH4+-200 with an interlayer spacing of 0.94 nm under reaction conditions of 200 °C (Figure 2a). They attributed the increase in interlayer spacing to the entry of ammonium ions during the reaction. The increased interlayer spacing is beneficial to the full exposure of the active site and also provides a large channel for ion transport. The 1T/2H-MoS2/NH4+-200 exhibited excellent HER performance with an overpotential of 159.9 mV at 10 mA cm−2 and a Tafel slope of 55.5 mV dec−1 in 0.5 M H2SO4 (Figure 2b,c). In addition, 1T/2H-MoS2/NH4+-200 also had excellent electrochemical stability. After 1000 cyclic voltammetry (CV) cycles, the overpotential of 10 mA cm−2 only dropped by 7.2 mV.
In addition to the methods mentioned in the above examples, other methods of increasing the interlayer spacing of MoS2 have also been reported in the literature [35,38,39]. Jin et al. [35] used H2 as a structural directing agent to synthesize Co-MoS2-1.4 with an interlayer spacing of 10.3 Å, which presents a low overpotential of 56 mV at 10 mA cm−2 and a Tafel slope of 32 mV dec−1. Gao et al. [38] used a microwave-assisted strategy to obtain MoS2 with an interlayer spacing of 9.4 Å, which has excellent HER performance with an overpotential of 149 mV at 10 mA cm−2 and a Tafel slope of 49 mV dec−1. Bui et al. [39] generated graphene in situ and inserted it into the MoS2 layers to obtain MoS2@Gr with an expanded interlayer spacing (9.6 Å) and a significantly improved HER performance compared with MoS2.
Extending the interlayer spacing to improve the HER performance of MoS2 has attracted widespread attention. However, the types of foreign species that support the interlayer expansion of MoS2 and the process of foreign species entering the interlayer gap are not clear. Answering these questions definitively is crucial to developing methods to precisely regulate the interlayer spacing of MoS2. Therefore, future research needs to utilize in situ techniques to track the formation process of interlayer expanded MoS2 in real-time. Real-time measurements can provide new kinetic information and help us understand the origin of MoS2 interlayer expansion.

2.2. Sulfur Vacancy

In the research on hydrogen evolution in electrolytic water from MoS2, sulfur vacancies are one of the important research directions [40,41]. Sulfur vacancies refer to vacancies formed by the absence of some sulfur atoms in the MoS2 crystal lattice. The defect structure is considered to have good catalytic activity in the field of electrocatalysis, especially in water-splitting reactions. Generating sulfur vacancy defects is an effective MoS2 modification strategy, which can activate the inert basal plane by generating a new interstitial state close to the Fermi level, so as to optimize the active site and improve the HER performance of MoS2 [42].
The formation of sulfur vacancies is generally achieved through post-treatment processes. Gu et al. [42] used H2O2 to etch 2H-MoS2 and obtained SV-2H-MoS2 nanosheets containing abundant sulfur vacancies. HAADF-STEM intuitively shows that there are abundant sulfur vacancies on the surface of SV-2H-MoS2 (Figure 3a). The EPR signal intensity of SV-2H-MoS2 is significantly higher than that of 2H-MoS2, indicating that the sulfur vacancy density on the surface of SV-2H-MoS2 is much higher than that of 2H-MoS2 (Figure 3b). Figure 3c,d shows that the overpotential of SV-2H-MoS2 containing abundant sulfur vacancies is 369 mV (@10 mA cm−2), and the Tafel slope is 68.7 mV dec−1, which is significantly lower than that of 2H-MoS2 (686 mV@10 mA cm−2 and 204.1 mV dec−1). It indicates that the generation of sulfur vacancy can significantly improve the HER performance of SV-2H-MoS2.
The salt-assisted chemical vapor deposition (CVD) can be used to directly prepare MoS2 containing abundant sulfur vacancies. Man et al. [43] synthesized a monolayer of MoS2 by the CVD method using Na2MoO4·2H2O and sulfur vapor as Mo and S sources, and SiO2/Si as a substrate. By treating the substrate through the spraying of KCl solutions of different concentrations, the number of sulfur vacancies in the MoS2 basal plane can be adjusted. As shown in Figure 4a, the higher the concentration of KCl solution sprayed on the substrate, the more sulfur vacancies in MoS2, and the MoS2-2.5 obtained after treating the substrate with 2.5 M KCl solution contains the most abundant sulfur vacancies (3.35 × 1014 cm−2). Figure 4b,c shows that the overpotential of MoS2-2.5 is 90 mV at 10 mA cm−2 and the Tafel slope is 54.3 mV dec−1 in 0.5 M H2SO4, which is significantly lower than that of the original MoS2-0 (220 mV@10 mA cm−2 and 211.95 mV dec−1). Compared with MoS2-0, the significantly improved HER performance of MoS2-2.5 can be attributed to the abundant sulfur vacancies on the basal plane. Figure 4d shows that the ΔGH of the V2S and the VS are −0.13 eV and −0.06 eV, respectively, which significantly improves the HER activity of the inert basal plane, indicating that the abundant sulfur vacancies in MoS2 have good catalytic efficiency.
In addition to the above H2O2 etching and CVD methods, other methods are often used to generate sulfur vacancies in the MoS2 [26,44,45]. Ye et al. [44] obtained MoS2 with rich sulfur vacancies by H2 annealing, and these sulfur vacancy defects significantly improved the HER performance of MoS2. Tsai et al. [26] used the electrochemical desulfurization method to remove sulfur atoms on the surface of MoS2. They controlled the extent of desulfurization by regulating the desulfurization potential, thereby improving the HER activity of MoS2. Li et al. [45] used Ar plasma to treat MoS2 samples and obtained SV-MoS2 containing abundant sulfur vacancies, which has good HER performance with an overpotential of 170 mV at 10 mA cm−2 and a Tafel slope of 60 mV dec−1.
Man et al. [43] have demonstrated that single sulfur vacancies and double sulfur vacancies in MoS2 have different effects on HER. The effect of other types of sulfur vacancies on HER is not clear. At present, most of the methods for generating sulfur vacancies are to generate sulfur vacancies at the basal plane and edge of MoS2 at the same time. It is impossible to accurately control the position of sulfur vacancy generation, and there is a lack of research on the effect of sulfur vacancies on the basal plane or edge of MoS2 on HER. Therefore, future research on sulfur vacancies should focus on these issues.

2.3. Phase Transition

Figure 5 shows the 2H and 1T phases of MoS2, and the different crystalline phases of MoS2 exhibit diverse properties. The 2H-phase MoS2 has semiconductor properties and has a band gap with a length of 1.2~1.9 eV near the Fermi level; the 1T-phase MoS2 has the properties of metal conductor, no band gap near the Fermi level, and thereby has good conductivity [46,47]. The basal plane of the 2H-phase MoS2 is inert, and only the Mo edges are active for the HER [48,49,50,51,52]. Different from 2H-phase MoS2, the active sites of 1T-phase MoS2 are mainly located on the basal plane, and the Mo edge contributes relatively little to the overall HER efficiency. The basal plane of 1T-phase MoS2 has a much larger active surface area than the edge, thus ensuring a higher HER activity [53,54]. Creating a high proportion of 1T-phase MoS2 is of great significance for improving catalytic activity.
Wang et al. [55] developed a simple solvothermal method to synthesize 1T-phase MoS2. They found that the reaction solvent plays a crucial role in regulating the phase state of MoS2: the 2H MoS2 NSH can be obtained by using water as the solvent, while the 1T MoS2 NSP can be obtained by using ethanol as the solvent, where the corresponding content of the 1T phase is 77.68%. (Figure 6a,b). The synthesized 1T MoS2 NSP exhibited excellent electrocatalytic hydrogen evolution performance with an overpotential of 188 mV at 10 mA cm−2 and a Tafel slope of 58.47 mV dec−1 (Figure 6c,d).
The CVD method can also be used to synthesize MoS2 containing a high proportion of 1T phase. Hong et al. [56] used SiO2/Si as the growth matrix, S powder and MoO3 as raw materials, and used the Sb2O3 and NaCl-assisted CVD method to synthesize MoS2 with a 1T phase content of 61.5% (Figure 7a,b). The overpotential of the synthesized 1T-2H MoS2 at 10 mA cm−2 is 212 mV, the Tafel slope is 78 mV dec−1, and the electrochemical performance was significantly higher than that of 2H MoS2 (Figure 7c,d). The S atoms at the 1T–2H phase interface are more conducive to the adsorption of H, which can improve the HER activity on the MoS2 basal plane.
The current synthesis method obtains MoS2 with the coexistence of a 1T phase and a 2H phase; MoS2 containing only a 1T phase is difficult to obtain. The problem that the metastable 1T phase is easily converted to the thermodynamically stable 2H phase has not been completely solved. It is of great value to develop synthetic routes containing only 1T-phase MoS2 and methods to maintain the stability of the 1T phase.

2.4. Element Doping

2.4.1. Metal Doping

Metal doping is an effective method to activate the inert basal of MoS2 and enhance its catalytic activity [57,58]. Doping with metal elements can significantly change the electron density of Mo and S atoms around the doping element, thereby improving the HER activity of MoS2 [27,28]. Commonly used doping elements include Pt, Pd, Ru, Fe, Co, Ni, and Zn [6,27,28,58,59].
Sundara Venkatesh et al. [60] synthesized Ni-MoS2 using Na2MoO4, NH2CSNH2, and Ni(NO3)2·6H2O as precursors (Figure 8a). The SEM image shows that there is no obvious agglomeration of Ni-MoS2 nanosheets (Figure 8b). Figure 8c,d shows that the overpotential of Ni-MoS2 at 10 mA cm−2 is 302.4 mV and the Tafel slope is 66.27 mV dec−1, which is significantly lower than that of MoS2 (406.6 mV@10 mA cm−2 and 95 mV dec−1). The EIS analysis shows that the charge transfer resistance of MoS2 was six times higher than that of Ni-MoS2, which indicated that Ni-doped MoS2 achieved better charge transfer and was beneficial to improving the HER performance of MoS2 (Figure 8e).
Xu et al. [61] synthesized one type of Zn-1T/2H-MoS2 with 1T and 2H phases coexisting by using (NH4)6Mo7O24·4H2O, CH4N2S, and Zn(NO3)2·6H2O as precursors (Figure 9a). The 1T phase content of 1T/2H-MoS2 was 28.2%, while the 1T phase content of Zn-1T/2H-MoS2 increased to 46.0% after the addition of Zn (Figure 9b). The result indicated that Zn doping can lead to an increase in the 1T phase content of MoS2, which is beneficial for improving HER performance. Figure 9c,d shows that the overpotential of Zn-1T/2H-MoS2 is 190 mV (@10 mA cm−2) and the Tafel slope is 58 mV dec−1, and that the HER performance is significantly higher than that of 1T/2H-MoS2 (237 mV@10 mA cm−2 and 71 mV dec−1). After Zn doping, the Cdl of 1T/2H-MoS2 increased from 14.2 mF cm−2 to 33.5 mF cm−2, and the electrochemically active surface area increased from 237 cm2 to 558 cm2, indicating that Zn doping is beneficial to exposing more electrochemically active sites (Figure 9e).
Single-atom catalysts (SACs) have attracted widespread attention due to their maximum atomic efficiency and tunable electronic properties. Wang et al. [62] first synthesized 2H-MoS2 through a hydrothermal method and then used 2H-MoS2 as a substrate to load the noble metal Ru to prepare Ru@2H-MoS2. Figure 10a,b shows that the Ru atoms exist in the form of single atoms in 2H-MoS2. Figure 10c shows that the overpotentials of Ru0.10@2H-MoS2 at 10 mA cm−2 are 168 mV in 0.5 M H2SO4, respectively, which are significantly lower than those of 2H-MoS2 (328 mV@10 mA cm−2). Theoretical calculation proves that the addition of Ru significantly reduces the ΔGH of 2H-MoS2, which makes Ru@2H-MoS2 exhibit excellent HER performance (Figure 10d).
Wang et al. [6] doped transition metals (Fe, Co, and Ni) into 1T-MoS2 through a one-step method to improve the HER performance of 1T-MoS2 in 1 M KOH. The overpotentials of Fe-1T-MoS2, Co-1T-MoS2, and Ni-1T-MoS2 at 10 mA cm−2 are 269 mV, 261 mV, and 199 mV, and the Tafel slopes are 168 mV dec−1, 88.5 dec−1, and 52.7 dec−1, and their HER performance is significantly higher than that of 1T-MoS2 (400 mV@10 mA cm−2 and 237 mV dec−1). Theoretical calculation shows that the doping of Fe, Co, and Ni changes the electronic structure of MoS2, reduces the adsorption of the material to H2O, and increases the possibility of H2O dissociation, which is an important reason for the improvement of the HER performance of the material after metal doping MoS2. Pei et al. [63] synthesized Pt-MoS2 using commercial MoS2 and H2PtCl6 as precursors with an overpotential of 59 mV at 10 mA cm−2 and a Tafel slope of 23.58 mV dec−1 in 0.5 M H2SO4. The synergistic effect between Pt nanoparticles and the edge active sites of MoS2 increases the interlayer conductivity of MoS2, activates the edge active sites, and significantly improves the HER performance of the material. Song et al. [64] doped Pd into 1T-MoS2 nanorods to synthesize Pd-1T-MoS2, which has an overpotential of 170 mV at 10 mA cm−2 and a Tafel slope of 98 mV dec−1 in 0.5 M H2SO4. The addition of Pd introduces more sulfur vacancies in MoS2 and retains the 1T phase content, which is conducive to improving the HER performance of MoS2.

2.4.2. Nonmetal Doping

The introduction of non-metallic elements, such as P, F, and N, to enhance the HER performance of MoS2 has been proven to be effective [34,65,66]. Non-metallic dopants with different electronegativities can change the electronic structure of MoS2 and optimize the adsorption/desorption behavior of hydrogen atoms at the active site, thereby improving the HER performance of MoS2 [66].
The F atom has the largest electronegativity in the periodic table of elements and can cause a significant change in the electronic structure of MoS2. Zhang et al. [66] used CHF3 plasma to etch the edges of commercial MoS2 on SiO2/Si wafers and obtained etched MoS2 with significantly increased edge sites (Figure 11a–c). Compared with the original MoS2, the current density of etched MoS2 increased four times at 400 mV. The overpotential of 10 mA cm−2 was reduced from the original 298 mV to 267 mV and the Tafel slope was reduced from the original 92 mV dec−1 to 65 mV dec−1 (Figure 11d,e), which indicated that the modification of F atoms at the edge of MoS2 is an effective strategy to improve the HER performance of MoS2. They also studied the ΔGH at the edge site of MoS2 through theoretical calculations. The ΔGH* of the etched edge is −0.26 eV, which is much smaller than the ∆GH* (−0.55 eV) of the original edge. It indicates that the addition of F weakened the excessive binding of H at the Mo sites, which is beneficial for etched MoS2 to obtain better HER performance.
The P dopant in MoS2 can accelerate the slow HER kinetics [34]. Tian et al. [67] first synthesized MoS2/CC using Na2MoO4·2H2O and CS(NH2)2 as raw materials and the carbon cloth as the carrier. Then, using NaH2PO2·H2O as the P source, P-doped P-MoS2/CC-300 was obtained at 300 °C in a 10% H2/Ar atmosphere (Figure 12a). XPS spectra show that the P atom doping rate of P-MoS2/CC-300 is 2.8 wt.% (Figure 12b). Figure 12c,d shows that the overpotential and the Tafel slope of P-MoS2/CC-300 are 81 mV (@10 mA cm−2) and 98 mV dec−1 in 0.5 M H2SO4, respectively, which are significantly lower than that of MoS2/CC-300 (135 mV@10 mA cm−2 and 142 mV dec−1). These results suggest that the doping of P atoms can regulate the electronic interactions and optimize the electronic structure of MoS2 to enhance the HER activity of MoS2. In addition, P-MoS2/CC-300 also has excellent electrochemical stability. After 3000 CV cycles, the polarization curve of the material did not change significantly. After 15 h of stability testing, the overpotential of 10 mA cm−2 slightly dropped from 87 mV to 93 mV (Figure 12e).
Element doping can improve the HER performance of MoS2. However, the non-noble metal elements Fe, Co, Ni, and Zn, as well as the non-metal elements F and P, can only improve the performance of MoS2 to a limited extent, which is far behind the noble metal Pt. Although the noble metals Pt, Pd, and Ru can greatly improve the HER performance of MoS2, they are expensive, and the actual application cost is high. The use of non-noble metal elements, or non-metal elements and noble metal elements together, can greatly improve the performance of MoS2 while reducing the cost of the catalyst, which will be a promising road.

3. External Modification

3.1. Heterostructure

A large number of studies have proven that MoS2-based electrocatalysts are promising non-noble metal hydrogen evolution catalysts under acidic conditions [68,69,70]. The high kinetic energy barrier of the initial water dissociation process, and the strong adsorption of the formed OH− on the MoS2 surface, lead to slow HER kinetics in alkaline solution [11]. Some researchers have focused on constructing heterostructures to accelerate the slow cracking process of water by MoS2-based catalysts in alkaline solutions [71]. Heterostructures can construct electrochemically active interfaces and enhance interfacial charge transfer dynamics by adjusting the electronic structure of the interface [72]. Due to the synergistic effect at the interface, heterostructures have excellent electrochemical properties compared to those of the single component [73,74]. Based on the advantage of each component, it is critical to rationally design the heterostructure to maximize HER performance.
Electron transfer at the heterostructure interface can optimize ΔGH. Xiang et al. [75] synthesized 1T-MoS2/Ni3S4/CC using a two-step method (Figure 13a). First, Ni(OH)2 nanosheets were grown on carbon cloth to obtain Ni(OH)2/CC. Then, MoS2 nanosheets were grown on Ni(OH)2 nanosheets, wherein the Ni(OH)2 was gradually converted into Ni3S4, and, finally, 1T-MoS2/Ni3S4/CC was obtained. Compared with 1T-MoS2/CC, the Mo 3d5/2 peak of 1T-MoS2/Ni3S4/CC was shifted by −0.2 eV (Figure 13b), indicating that the electron density of Mo atoms increased. Compared with Ni3S4/CC, the 2p3/2 peaks of Ni2+ and Ni3+ of 1T-MoS2/Ni3S4/CC were shifted by +0.6 eV and +0.3 eV (Figure 13c), indicating a decrease in the number of electrons in the Ni atoms. Figure 13d shows that the overpotential of 1T-MoS2/Ni3S4/CC at 10 mA cm−2 is 44 mV, which is significantly lower than that of 1T-MoS2/CC (193 mV@10 mA cm−2), Ni3S4/CC (90 mV@10 mA cm−2), and Ni(OH)2/CC (400 mV@10 mA cm−2). The increase in the electron density of Mo atoms, and the decrease in the electron density of Ni atoms, balance the energy barriers for water dissociation and hydroxyl desorption at Ni sites, which can also optimize ΔGH at Mo edge sites (Figure 13e–g), and the synergistic effect improves the activity of the material’s alkaline HER.
Wu et al. [73] grew a MoS2/Co9S8 heterostructure on carbon cloth through a sulfur–sulfur combination and successfully obtained MoS2@Co9S8/CC. Figure 14a–c shows that compared to MoS2/CC and Co9S8/CC, the peak of Mo4+ has a negative shift (232.4 eV/232.1 eV to 229.2 eV/228.8 eV), and the peak of Co2+ has a positive shift (781.0 eV/797.1 eV to 781.4 eV/797.5 eV), which indicates that electrons are transferred from Co to Mo. The increased electrons around Mo are beneficial to improving the HER activity of the material [76]. Figure 14d shows that the overpotential of MoS2@Co9S8/CC at 10 mA cm−2 is only 73 mV in 1 M KOH solution, which is much lower than that of Co9S8/CC (199 mV), MoS2/CC (157 mV), and CC (373 mV). It indicates that the MoS2/Co9S8 heterostructure greatly improves the HER activity of Co9S8 and MoS2.
Although great progress has been made in developing heterostructures containing MoS2 for the electrolysis of water for hydrogen evolution, the catalytic mechanism is not clear. Synergistic effects are often used in the literature to explain the excellent performance of heterostructures for hydrogen evolution by electrolysis of water. More research is needed in the future to explain the interaction between heterogeneous interfaces to further clarify how the synergistic effects occur.

3.2. Conductive Substrate

Growing MoS2 on a substrate with high electrical conductivity will significantly change the electronic structure and conductivity at the interface of the composite material, which can also optimize the intermediate adsorption energy on the catalyst surface and then obtain high-performance HER materials [77,78]. Commonly used conductive substrates include carbon materials and pure metals [79].
Carbon material is the preferred substrate because of its high conductivity and strong electron-donating ability. Hu et al. [80] first pretreated the conductive substrate carbon fiber paper (CFP) in nitric acid to make it smooth. Then, Ni(OH)2 was grown on CFP to obtain Ni(OH)2/CFP, and the Ni(OH)2 on CFP was further converted into NiS2 by vulcanization reaction at 150 °C. Finally, MoS2 nanosheets were covered on the surface of NiS2 nanosheets at 200 °C to obtain NiS2@MoS2/CFP (Figure 15a). Figure 15b,c shows that the overpotential of NiS2@MoS2/CFP at 10 mA cm−2 is 95 mV and the Tafel slope is 65 mV dec−1 in 0.5 M H2SO4 solution, which is significantly lower than that of NiS2/CFP (198 mV@10 mA cm−2 and 82 mV dec−1). As a conductive substrate, CFP significantly improves the conductivity of the composite material NiS2@MoS2/CFP, which is beneficial to improve the HER performance of NiS2@MoS2/CFP.
The metal substrate has good electrical conductivity. Thereby, the MoS2 is also often grown on metal substrates to enhance its conductivity. Ma et al. [81] annealed Co-Fe PBA at 900 °C to obtain CoFe@NC and then introduced thiourea and sodium molybdate to anchor MoS2 nanosheets on the surface of CoFe@NC to obtain MoS2/CoFe@NC (Figure 16a). Figure 16b,c shows that the overpotential of MoS2/CoFe@NC at 10 mA cm−2 is 172 mV and the Tafel slope is 122.4 mV dec−1 in 1.0 M KOH solution, which is significantly lower than that of CoFe@NC (266 mV@10 mA cm−2 and 111.6 mV dec−1) and MoS2 (330 mV@10 mA cm−2 and 214.0 mV dec−1). The synergistic effect of the CoFe@NC substrate with abundant active sites and high conductivity and MoS2 nanosheets accelerated the electron transfer rate, making MoS2/CoFe@NC have excellent catalytic activity.
Current research focuses on using conductive substrates to improve the HER performance of MoS2 while paying less attention to the stability of the interface between MoS2 and the conductive substrate, and the loading of MoS2. Good interface stability can improve the electron transfer rate and catalytic activity, but an unstable interface may lead to the exfoliation or agglomeration of MoS2 nanoparticles and cause HER performance to decline. It is very important to load the appropriate amount of MoS2 on the conductive substrate. Excessive loading may lead to mass transfer barriers between MoS2 nanoparticles. If the loading amount is too small, the catalytic performance of MoS2 may not be fully exerted. Future research should focus on solving these issues.

4. Conclusions and Outlook

This work summarizes the regulation strategies of MoS2 from two aspects: internal modification and external modification. These regulation strategies include interlayer spacing, sulfur vacancy, phase transition, element doping, heterostructure, and conductive substrate. Figure 17 and Table 1 summarize the data for examples corresponding to the above regulation strategies. Although the HER performance of MoS2 that has been modified using these strategies has been significantly improved, there are still some problems that need to be solved before large-scale industrial application.
First of all, the 1T phase has obvious advantages compared with the 2H phase in the field of electrolysis of water for hydrogen evolution. However, the metastable 1T phase easily transforms into the thermodynamically stable 2H phase, resulting in a decrease in the HER performance of MoS2. Industrial applications require catalysts with excellent long-term stability rather than being limited to dozens of hours in the laboratory. Research on how to maintain the 1T phase stability of MoS2 is of great value for industrial applications. Secondly, single-atom catalysts have broad application prospects in the field of electrolysis of water for hydrogen evolution. At present, the loading of metal single atoms on the MoS2 substrate is low. Increasing the loading of single atoms on the MoS2 substrate can give full play to the catalytic efficiency of the atoms, and further improve the HER performance of the material. However, if the loading of metal atoms is too high, the metal atoms will easily form clusters. Future research should tend to increase the loading of metal single atoms on the MoS2 substrate, so as to maximize the HER performance of the material while ensuring the single-atom state. Thirdly, loading MoS2 on a conductive substrate can effectively improve the HER performance of MoS2. The development of porous conductive substrates to support MoS2 can not only improve the conductivity but also improve the mass transfer efficiency, which will fully enhance the HER performance of the material. Finally, in order to maximize the HER performance of MoS2, two or more modification strategies discussed in this article may be combined.
In general, there is still a lot of room for development in the field of MoS2 towards electrocatalytic hydrogen evolution. With an in-depth understanding of material properties and continuous technological innovation, MoS2 is expected to become an important catalyst in the field of clean energy, promoting the progress and sustainable development of water-splitting technology.

Author Contributions

L.L.: writing (preparation of the original draft) and methodology. N.L.: writing review and editing. C.D.: data curation and conceptualization. N.W.: Formal analysis. B.C.: supervision and validation. All authors have read and agreed to the published version of the manuscript.

Funding

National Key Research and Development Program of China (2023YFB4004703).

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. (a) XRD diffraction patterns of 2H-MoS2, 180-1T-MoS2, and 200-1T-MoS2. (b) Polarization curves and (c) corresponding Tafel slopes of 2H-MoS2, 180-1T-MoS2, and 200-1T-MoS2 in 0.5 M H2SO4. (d) ΔGH of 2H-MoS2 and 1T-MoS2 with interlayer spacings of 6.15 and 10.87 Å, respectively. Reproduced with permission from Ref. [36], Copyright 2023, Wiley.
Figure 1. (a) XRD diffraction patterns of 2H-MoS2, 180-1T-MoS2, and 200-1T-MoS2. (b) Polarization curves and (c) corresponding Tafel slopes of 2H-MoS2, 180-1T-MoS2, and 200-1T-MoS2 in 0.5 M H2SO4. (d) ΔGH of 2H-MoS2 and 1T-MoS2 with interlayer spacings of 6.15 and 10.87 Å, respectively. Reproduced with permission from Ref. [36], Copyright 2023, Wiley.
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Figure 2. (a) Schematic illustration of the synthetic method for catalysts. (b) Polarization curves and (c) corresponding Tafel slopes of catalysts in 0.5 M H2SO4. Reproduced with permission from Ref. [37], Copyright 2023, Elsevier.
Figure 2. (a) Schematic illustration of the synthetic method for catalysts. (b) Polarization curves and (c) corresponding Tafel slopes of catalysts in 0.5 M H2SO4. Reproduced with permission from Ref. [37], Copyright 2023, Elsevier.
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Figure 3. (a) HRTEM image of SV-2H-MoS2. (b) Electron paramagnetic resonance (EPR) patterns of 2H-MoS2 and SV-2H-MoS2. (c) Polarization curves and (d) corresponding Tafel slopes of 2H-MoS2 and SV-2H-MoS2 in 0.5 M H2SO4. Reproduced with permission from Ref. [42], Copyright 2023, Wiley.
Figure 3. (a) HRTEM image of SV-2H-MoS2. (b) Electron paramagnetic resonance (EPR) patterns of 2H-MoS2 and SV-2H-MoS2. (c) Polarization curves and (d) corresponding Tafel slopes of 2H-MoS2 and SV-2H-MoS2 in 0.5 M H2SO4. Reproduced with permission from Ref. [42], Copyright 2023, Wiley.
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Figure 4. (a) Statistics of surface sulfur vacancy density (green line), single sulfur vacancy (VS, purple line), and double sulfur vacancy (V2S, orange line) of MoS2 under different KCl concentrations. (b) Polarization curves and (c) corresponding Tafel slopes of catalysts in 0.5 M H2SO4. (d) Adsorption free energies of H atoms of pristine MoS2, MoS2-V2S, and MoS2-VS. Reproduced with permission from Ref. [43], Copyright 2023, Wiley.
Figure 4. (a) Statistics of surface sulfur vacancy density (green line), single sulfur vacancy (VS, purple line), and double sulfur vacancy (V2S, orange line) of MoS2 under different KCl concentrations. (b) Polarization curves and (c) corresponding Tafel slopes of catalysts in 0.5 M H2SO4. (d) Adsorption free energies of H atoms of pristine MoS2, MoS2-V2S, and MoS2-VS. Reproduced with permission from Ref. [43], Copyright 2023, Wiley.
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Figure 5. Ball and stick models of 2H-phase and 1T-phase MoS2 (yellow represents sulfur atoms, blue represents Mo atoms).
Figure 5. Ball and stick models of 2H-phase and 1T-phase MoS2 (yellow represents sulfur atoms, blue represents Mo atoms).
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Figure 6. (a) Schematic illustrations of the synthesis protocols for the 1T MoS2 NSP and 2H MoS2 NSH. (b) Raman spectra of the 1T MoS2 NSP and 2H MoS2 NSH. (c) Polarization curves and (d) corresponding Tafel slopes of 1T MoS2 NSP, 1T MoS2 NSH, O-2H MoS2 NSH, and 2H MoS2 NSH in 0.5 M H2SO4. Reproduced with permission from Ref. [55], Copyright 2022, American Chemical Society.
Figure 6. (a) Schematic illustrations of the synthesis protocols for the 1T MoS2 NSP and 2H MoS2 NSH. (b) Raman spectra of the 1T MoS2 NSP and 2H MoS2 NSH. (c) Polarization curves and (d) corresponding Tafel slopes of 1T MoS2 NSP, 1T MoS2 NSH, O-2H MoS2 NSH, and 2H MoS2 NSH in 0.5 M H2SO4. Reproduced with permission from Ref. [55], Copyright 2022, American Chemical Society.
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Figure 7. (a) Schematic illustration and atomic structure of 2H MoS2 and 1T-2H MoS2 grown on SiO2/Si. Route 1 represents the growth of 2H MoS2 nanosheets without Sb2O3 participation and Route 2 represents the growth of 1T-2H MoS2 with Sb2O3 participation. (b) Raman spectra of 1T-2H MoS2 and 2H MoS2. (c) Polarization curves and (d) corresponding Tafel slopes of catalysts in 0.5 M H2SO4. Reproduced with permission from Ref. [56], Copyright 2023, Elsevier.
Figure 7. (a) Schematic illustration and atomic structure of 2H MoS2 and 1T-2H MoS2 grown on SiO2/Si. Route 1 represents the growth of 2H MoS2 nanosheets without Sb2O3 participation and Route 2 represents the growth of 1T-2H MoS2 with Sb2O3 participation. (b) Raman spectra of 1T-2H MoS2 and 2H MoS2. (c) Polarization curves and (d) corresponding Tafel slopes of catalysts in 0.5 M H2SO4. Reproduced with permission from Ref. [56], Copyright 2023, Elsevier.
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Figure 8. (a) Schematic illustrations of the synthesis protocols for transition metals decorated MoS2 nanosheets. (b) Scanning electron microscopy (SEM) image of Ni-MoS2 nanosheets with a uniform scale bar of 200 nm. (c) Polarization curves, (d) corresponding Tafel slopes, and (e) Electrochemical impedance spectroscopy (EIS) comparisons of MoS2, Fe-MoS2, Co-MoS2, and Ni-MoS2 in 0.5 M H2SO4. Reproduced with permission from Ref. [60], Copyright 2022, Elsevier.
Figure 8. (a) Schematic illustrations of the synthesis protocols for transition metals decorated MoS2 nanosheets. (b) Scanning electron microscopy (SEM) image of Ni-MoS2 nanosheets with a uniform scale bar of 200 nm. (c) Polarization curves, (d) corresponding Tafel slopes, and (e) Electrochemical impedance spectroscopy (EIS) comparisons of MoS2, Fe-MoS2, Co-MoS2, and Ni-MoS2 in 0.5 M H2SO4. Reproduced with permission from Ref. [60], Copyright 2022, Elsevier.
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Figure 9. (a) Schematic illustrations of the synthesis protocols for Zn-1T/2H-MoS2. (b) X-ray photoelectron spectroscopy (XPS) spectra for Mo 3d of Zn-1T/2H-MoS2 and 1T/2H-MoS2. (c) Polarization curves (lines with symbols represent the data after 100% iR-correction, the solid lines represent the data without iR-correction), (d) corresponding Tafel slopes (100% iR-corrected), and (e) the double layer capacitance (Cdl) of catalysts in 0.5 M H2SO4. Reproduced with permission from Ref. [61], Copyright 2021, Wiley.
Figure 9. (a) Schematic illustrations of the synthesis protocols for Zn-1T/2H-MoS2. (b) X-ray photoelectron spectroscopy (XPS) spectra for Mo 3d of Zn-1T/2H-MoS2 and 1T/2H-MoS2. (c) Polarization curves (lines with symbols represent the data after 100% iR-correction, the solid lines represent the data without iR-correction), (d) corresponding Tafel slopes (100% iR-corrected), and (e) the double layer capacitance (Cdl) of catalysts in 0.5 M H2SO4. Reproduced with permission from Ref. [61], Copyright 2021, Wiley.
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Figure 10. HRTEM images of (a) 1T phase and (b) 2H phase of Ru0.10@2H-MoS2. (c) Polarization curves of catalysts in 0.5 M H2SO4. (d) Free energy diagram for hydrogen evolution of catalysts. Reproduced with permission from Ref. [62], Copyright 2021, Elsevier.
Figure 10. HRTEM images of (a) 1T phase and (b) 2H phase of Ru0.10@2H-MoS2. (c) Polarization curves of catalysts in 0.5 M H2SO4. (d) Free energy diagram for hydrogen evolution of catalysts. Reproduced with permission from Ref. [62], Copyright 2021, Elsevier.
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Figure 11. (a) Schematic illustration of in situ creating on MoS2 by CHF3 plasma. SEM images of (b) pristine MoS2 and (c) etched MoS2. (d) Polarization curves and (e) corresponding Tafel slopes of pristine MoS2 and etched MoS2 in 0.5 M H2SO4. Reproduced with permission from Ref. [66], Copyright 2021, Wiley.
Figure 11. (a) Schematic illustration of in situ creating on MoS2 by CHF3 plasma. SEM images of (b) pristine MoS2 and (c) etched MoS2. (d) Polarization curves and (e) corresponding Tafel slopes of pristine MoS2 and etched MoS2 in 0.5 M H2SO4. Reproduced with permission from Ref. [66], Copyright 2021, Wiley.
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Figure 12. (a) Schematic illustrations of the synthesis protocols for P-MoS2/CC. (b) XPS spectra of P 2p of P-MoS2/CC-300. (c) Polarization curves and (d) corresponding Tafel slopes of MoS2/CC-300, P-MoS2/CC-300, P-MoS2/CC-400, and P-MoS2/CC-500, and (e) durability test of P-MoS2/CC-300 in 0.5 M H2SO4. Reproduced with permission from Ref. [67], Copyright 2022, Elsevier.
Figure 12. (a) Schematic illustrations of the synthesis protocols for P-MoS2/CC. (b) XPS spectra of P 2p of P-MoS2/CC-300. (c) Polarization curves and (d) corresponding Tafel slopes of MoS2/CC-300, P-MoS2/CC-300, P-MoS2/CC-400, and P-MoS2/CC-500, and (e) durability test of P-MoS2/CC-300 in 0.5 M H2SO4. Reproduced with permission from Ref. [67], Copyright 2022, Elsevier.
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Figure 13. (a) Schematic illustrations of the synthesis protocols for 1T-MoS2/Ni3S4/CC. XPS spectra of (b) Mo 3d (The green area represents the 1T phase, the blue area represents the 2H phase, and the red area represents the Mo6+.) and (c) Ni 2p (The green area represents the Ni2+, the blue area represents the Ni3+, and the red and purple areas represent the satellite peaks.) of 1T-MoS2/Ni3S4/CC. (d) Polarization curves in 1 M KOH and (e) free energy diagram of the HER of catalysts. (f) Activation energies for water dissociation and (g) hydroxyl desorption on 1T-MoS2/Ni3S4, with energy along the reaction coordinate relative to each initial state (IS), transition state (TS), and final state (FS). Reproduced with permission from Ref. [75], Copyright 2023, Royal Society of Chemistry.
Figure 13. (a) Schematic illustrations of the synthesis protocols for 1T-MoS2/Ni3S4/CC. XPS spectra of (b) Mo 3d (The green area represents the 1T phase, the blue area represents the 2H phase, and the red area represents the Mo6+.) and (c) Ni 2p (The green area represents the Ni2+, the blue area represents the Ni3+, and the red and purple areas represent the satellite peaks.) of 1T-MoS2/Ni3S4/CC. (d) Polarization curves in 1 M KOH and (e) free energy diagram of the HER of catalysts. (f) Activation energies for water dissociation and (g) hydroxyl desorption on 1T-MoS2/Ni3S4, with energy along the reaction coordinate relative to each initial state (IS), transition state (TS), and final state (FS). Reproduced with permission from Ref. [75], Copyright 2023, Royal Society of Chemistry.
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Figure 14. XPS spectra of Mo 3d of (a) MoS2/CC and (b) MoS2@Co9S8/CC. (c) XPS spectra of Co 2p of MoS2@Co9S8/CC and Co9S8/CC. (d) Polarization curves of catalysts in 1 M KOH. Reproduced with permission from Ref. [73], Copyright 2021, Elsevier.
Figure 14. XPS spectra of Mo 3d of (a) MoS2/CC and (b) MoS2@Co9S8/CC. (c) XPS spectra of Co 2p of MoS2@Co9S8/CC and Co9S8/CC. (d) Polarization curves of catalysts in 1 M KOH. Reproduced with permission from Ref. [73], Copyright 2021, Elsevier.
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Figure 15. (a) Schematic illustrations of the synthesis protocols for NiS2@MoS2/CFP. (b) Polarization curves and (c) corresponding Tafel slopes of catalysts in 0.5 M H2SO4. Reproduced with permission from Ref. [80], Copyright 2022, American Chemical Society.
Figure 15. (a) Schematic illustrations of the synthesis protocols for NiS2@MoS2/CFP. (b) Polarization curves and (c) corresponding Tafel slopes of catalysts in 0.5 M H2SO4. Reproduced with permission from Ref. [80], Copyright 2022, American Chemical Society.
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Figure 16. (a) Schematic illustrations of the synthesis protocols of MoS2/CoFe@NC. (b) Polarization curves and (c) corresponding Tafel slopes of catalysts in 1.0 M KOH. Reproduced with permission from Ref. [81], Copyright 2023, Elsevier.
Figure 16. (a) Schematic illustrations of the synthesis protocols of MoS2/CoFe@NC. (b) Polarization curves and (c) corresponding Tafel slopes of catalysts in 1.0 M KOH. Reproduced with permission from Ref. [81], Copyright 2023, Elsevier.
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Figure 17. Comparison of performance of MoS2 catalysts obtained using different modification strategies (200-1T-MoS2 [36], 1T/2H-MoS2/NH4+-200 [37], Co-MoS2-1.4 [35], 240-MoS2 [38], SV-2H-MoS2 [42], MoS2-2.5 [43], SV-MoS2 [45], 1T MoS2 NSP [55], 1T-2H MoS2 [56], Ni-MoS2 [60], Zn-1T/2H-MoS2 [61], Ru0.10@2H-MoS2 [62], Fe-1T-MoS2 [6], Co-1T-MoS2 [6], Ni-1T-MoS2 [6], Pt-MoS2 [63], Pd-1T-MoS2 [64], Etched MoS2 [66], P-MoS2/CC-300 [67], 1T-MoS2/Ni3S4/CC [75], MoS2@Co9S8/CC [73], NiS2@MoS2/CFP [80], MoS2/CoFe@NC [81]).
Figure 17. Comparison of performance of MoS2 catalysts obtained using different modification strategies (200-1T-MoS2 [36], 1T/2H-MoS2/NH4+-200 [37], Co-MoS2-1.4 [35], 240-MoS2 [38], SV-2H-MoS2 [42], MoS2-2.5 [43], SV-MoS2 [45], 1T MoS2 NSP [55], 1T-2H MoS2 [56], Ni-MoS2 [60], Zn-1T/2H-MoS2 [61], Ru0.10@2H-MoS2 [62], Fe-1T-MoS2 [6], Co-1T-MoS2 [6], Ni-1T-MoS2 [6], Pt-MoS2 [63], Pd-1T-MoS2 [64], Etched MoS2 [66], P-MoS2/CC-300 [67], 1T-MoS2/Ni3S4/CC [75], MoS2@Co9S8/CC [73], NiS2@MoS2/CFP [80], MoS2/CoFe@NC [81]).
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Table 1. Summary of modification strategies for MoS2 catalysts.
Table 1. Summary of modification strategies for MoS2 catalysts.
StrategyMaterialElectrolyteη10
(mV)		Tafel Slope
(mV dec−1)		Ref.
Interlayer spacing200-1T-MoS20.5 M H2SO49852[36]
1T/2H-MoS2/NH4+-2000.5 M H2SO4159.955.5[37]
Co-MoS2-1.40.5 M H2SO45632[35]
240-MoS20.5 M H2SO414949[38]
Sulfur vacancySV-2H-MoS20.5 M H2SO436968.7[42]
MoS2-2.50.5 M H2SO49054.3[43]
SV-MoS2H2SO4 (pH = 0.2)17060[45]
Phase transition1T MoS2 NSP0.5 M H2SO418858.47[55]
1T-2H MoS20.5 M H2SO421278[56]
Metal dopingNi-MoS20.5 M H2SO4302.466.27[60]
Zn-1T/2H-MoS20.5 M H2SO419058[61]
Ru0.10@2H-MoS20.5 M H2SO416877.5[62]
Fe-1T-MoS21.0 M KOH269168[6]
Co-1T-MoS21.0 M KOH26188.5
Ni-1T-MoS21.0 M KOH19952.7
Pt-MoS20.5 M H2SO45923.58[63]
Pd-1T-MoS20.5 M H2SO417098[64]
Nonmetal dopingEtched MoS20.5 M H2SO426765[66]
P-MoS2/CC-3000.5 M H2SO48198[67]
Heterostructure1T-MoS2/Ni3S4/CC1 M KOH4443[75]
MoS2@Co9S8/CC1 M KOH7378[73]
Conductive substrateNiS2@MoS2/CFP0.5 M H2SO49565[80]
MoS2/CoFe@NC1 M KOH172122.4[81]
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Liu, L.; Liu, N.; Chen, B.; Dai, C.; Wang, N. Recent Modification Strategies of MoS2 towards Electrocatalytic Hydrogen Evolution. Catalysts 2024, 14, 126. https://doi.org/10.3390/catal14020126

AMA Style

Liu L, Liu N, Chen B, Dai C, Wang N. Recent Modification Strategies of MoS2 towards Electrocatalytic Hydrogen Evolution. Catalysts. 2024; 14(2):126. https://doi.org/10.3390/catal14020126

Chicago/Turabian Style

Liu, Lei, Ning Liu, Biaohua Chen, Chengna Dai, and Ning Wang. 2024. "Recent Modification Strategies of MoS2 towards Electrocatalytic Hydrogen Evolution" Catalysts 14, no. 2: 126. https://doi.org/10.3390/catal14020126

APA Style

Liu, L., Liu, N., Chen, B., Dai, C., & Wang, N. (2024). Recent Modification Strategies of MoS2 towards Electrocatalytic Hydrogen Evolution. Catalysts, 14(2), 126. https://doi.org/10.3390/catal14020126

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