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A Review on MoS2 Energy Applications: Recent Developments and Challenges

College of Engineering, United Arab University, P.O. Box 15551, Al Ain 15551, United Arab Emirates
Author to whom correspondence should be addressed.
Energies 2021, 14(15), 4586;
Submission received: 22 June 2021 / Revised: 19 July 2021 / Accepted: 26 July 2021 / Published: 29 July 2021
(This article belongs to the Special Issue Novel 2D Energy Materials and Devices)


Molybdenum disulfide (MoS2) is a promising transition metal dichalcogenide (TMD) that has exceptional electronic, magnetic, optical, and mechanical properties. It can be semiconducting, superconducting, or an insulator according to its polymorph. Its bandgap structure changes from indirect to direct when moving towards its nanostructures, which opens a door to bandgap engineering for MoS2. Its supercapacitive and catalytic activity was recently noticed and studied, in order to include this material in a wide range of energy applications. In this work, we present MoS2 as a future material for energy storage and generation applications, especially solar cells, which are a cornerstone for a clean and abundant source of energy. Its role in water splitting reactions can be utilized for energy generation (hydrogen evolution) and water treatment at the same time. Although MoS2 seems to be a breakthrough in the energy field, it still faces some challenges regarding its structure stability, production scalability, and manufacturing costs.

1. Introduction

MoS2 is one of the transition metal dichalcogenides (TMDs) that has gained a high reputation in recent years due to its distinct chemical, electronic, mechanical, magnetic, and optical properties [1,2]. Its unique properties enabled its use in different applications such as sensing applications, high-efficiency field effect transistors, and energy and medical (curing) applications. MoS2 exists in different crystalline structures, such as hexagonal (H), tetrahedral (T), or rhombohedral (R). It naturally exists as 2H MoS2, and its most popular structures are the semiconducting 2H and 3R phases and the 1T metallic phase, where 2H is more stable but less conductive than 1T. Metallic MoS2 has a higher conductivity (105 times) than semiconducting 2H MoS2 and high catalytic activity [3].
MoS2 is expected to substitute silicon in the electronics industry in the next nano era [4,5,6,7] and has attracted attention to be used in energy applications [8,9]. MoS2 energy applications can be summarized into two main categories: energy storage devices (batteries and supercapacitors, Etc) and energy generation, where MoS2 acts as a catalyst in energy generation reactions, as shown in Figure 1. Hydrogen is known to be a promising clean source of energy, but, still, different studies have been conducted to obtain it at a low cost and with affordable methods. Two main reactions are needed for hydrogen generation: hydrogen evolution reactions (HERs) and oxygen evolution reactions (OERs). MoS2 is used as a catalyst for both reactions during the water splitting process, which is a clean and cheap substitute when compared to hydrogen extraction from coal or natural gas [10]. It is to be noted that MoS2 is also a catalyst in CO2 reduction reactions, which is a cheap substitute for expensive metal catalysts [11]. Many previous reviews discussed the properties of MoS2, its synthesis, its applications, and the future expectations about it [12,13,14,15,16,17], and some were dedicated to its energy applications [18,19]. In this work, we present a comprehensive study of MoS2 applications including one of the most important applications, solar cells, that was not deeply discussed in previous reviews. Since 1929, MoS2 has been introduced as a dry lubricant in mechanics [20,21,22,23,24] and engines, with more than 1000 papers published on it [25]. The hexagonal packed structure and the weak van der Waal forces between its layers make the movement of layers easier. Recently, nano-MoS2 quantum dots were used as a liquid lubricant [26] for a better engine efficiency, where they showed a friction coefficient of 0.061, which is much lower than that for pure paroline oil (0.169). Inorganic fullerene-like (IF) MoS2 nanoparticles were examined in other works [27,28] and were found to have a very low friction coefficient of 0.04 under ultra-high vacuum (UHV). The effect of the crystal structure of IF-MoS2 on its lubrication properties was also studied [29], and it was found that IF-MoS2 nanoparticles with poor crystallization and a large number of defects reduce the friction between steel surfaces better than crystalline IF-MoS2.
In this review, we first introduce the structure and properties of MoS2, especially those which are promising for energy applications, and then we discuss some synthesizing techniques for energy applications. We divide the energy applications part into two main categories: energy storage and energy generation, and then we discuss the challenges facing MoS2 in the energy industry.

2. Structure and Properties

MoS2 layers are formed by covalent bonds between sulfur and molybdenum S-Mo-S, as a layer of Mo sandwiched between two layers of sulfur. The layers are connected together through weak van der Waal forces [30]. MoS2 exists in many phases, where its characteristics and properties differ according to its phase. The 1T phase is an octahedral structure, while 2H and 3R are trigonal prismatic structures [31]. The 3R phase showed better catalytic activity in hydrogen evolution reactions than the 2H and 1T phases [32]; however, not much work has been conducted on the 3R MoS2 phase. Monolayer 2H-MoS2 is semiconducting, with a direct bandgap of ~1.8 eV [33,34]. 2H MoS2 exists in nature and is stable under ambient temperature. Metallic MoS2 is a metastable structure that does not exist in nature and is synthesized from the 2H phase or formed by controlled transitions, e.g., using an electron beam [35], ion intercalation [36], or laser irradiation [37,38]. It has superconductivity and high catalytic activity [39] that render it promising for energy applications. Although the metallic phase of MoS2 has challenges with stability and synthesis, research is directed towards it because of its high conductivity, which renders it promising for energy storage applications, such as its use in supercapacitors [40,41] and batteries [42,43,44].
The 1T MoS2 phase is metastable and coexists with other phases such as 1T’, 1T’’, and 1T’’’ (Figure 2). The phases are easily transformed to the 2H phase by annealing at nearly 70 °C [45]. The 1T’ phase is a superconductor, while 1T’’’ can be either a superconductor or an insulator depending on the synthesizing technique [45]. Generally, the 1T metastable phases have superconductivity and catalytic activity in hydrogen evolution reactions, which directed energy studies to these metastable phases. However, their electronic and magnetic properties and their device applications have not been studied extensively due to their metastability. A quantum spin Hall effect is expected from the 1T’ polytype [46]. The 1T metallic phase was proposed to decrease the contact resistance in ultrathin MoS2 transistors [36,47]. The 1T phase is laid over the 2H semiconducting phase (which is known for its high resistance (0.7–10 kΩ μm)) to decrease the contact resistance to 200–300 Ω μm at zero gate bias.

3. Synthesis

There are two main approaches to synthesizing transition metal dichalcogenides (TMDs); the top-down approach and the bottom-up approach [15,48]. Top-down techniques are mainly exfoliation techniques, while bottom-up methods grow MoS2 over a substrate. Bottom-up techniques include different types of depositions such as chemical vapor deposition (CVD), physical layer deposition (PVD), and atomic layer deposition (ALD). Solution-based techniques in preparing MoS2 layers are considered as a bottom-up approach, which are known to be scalable and of low cost in contrast to exfoliation techniques that lack scalability [17]. Different types of exfoliation techniques are used to synthesize MoS2 such as mechanical exfoliation, liquid-phase exfoliation, and ion intercalation, which is categorized into lithium and non-lithium ion intercalation methods [49]. A study in [50] showed that the effect of intercalation cations such as Na+, Ca2+, Ni2+, and Co2+ on MoS2 lowers the overpotential for hydrogen evolution reactions (HER). On the other hand, hydrothermal and solvothermal synthesis mechanisms are solution-based bottom-up techniques where the material is synthesized in closed vessels under high temperature and pressure [48]. When the process is carried out in water, it is called a hydrothermal technique, and when it is conducted with non-aqueous solvents, it is called a solvothermal technique. Different works discussed the above techniques in detail [51,52,53,54,55,56]; however, here, we are more concerned with techniques that have a low cost and are scalable to be used in energy applications on a large scale. We will focus on lithium ion intercalation as a top-down method and solution-based techniques as some of the bottom-up techniques. Additionally, we will focus on the synthesis of the 1T MoS2 phase since this is the most used in energy applications due to its high conductivity.

3.1. Lithium Intercalation and Exfoliation

In order to obtain the 1T MoS2 phase, MoS2 is intercalated with alkali metals such as potassium (K) or Li, and the product is hydrated and then oxidized [25,57]. Through hydration reactions, electrons transfer from the alkali metal to MoS2, which maintains the octahedral coordination of Mo atoms. Excess electrons are then removed through oxidation, while the octahedral coordination is kept the same with little distortion. The ligand—the ion attached to Mo through a coordinate bond—is responsible for the metallic conductivity and the metastable structure of 1T MoS2, where three degenerate d orbitals are occupied by two electrons; thus, crystal distortion occurs. The distortion breaks the degenerency and stabilizes the structure. The excess electrons can also stabilize the 1T phase. The different phases and crystalline structures of 2D MoS2 and distorted 1T MoS2 were investigated in detail [25]. It is to be noted that the 1T metallic phase does not have an exact d2 electronic configuration because this configuration yields a 3 a 3 a   superstructure which is not metallic, but restacking MoS2 with incomplete oxidation yields a 3 a a superstructure which is metallic. Restacked MoS2 and 1T metallic MoS2 are considered the same due to the octahedral coordination of Mo atoms. When MoS2 is treated with reducing agents such as n-butyllithium or LiBH4, lithium ions intercalate into MoS2 and separate its layers, forming LiMoS2. LiMoS2 disperses in water, forming 2D MoS2 flakes, which are then filtered or precipitated to form restacked MoS2 flakes [25]. It is then exfoliated using sonication. The restacking causes the transformation of 2D MoS2 into 1T MoS2, which is the dominating phase. Additionally, the geometry of MoS2 changes from prismatic to octahedral. As a result, the material shifts from semiconducting to metallic, with a 3 a a orthorhombic superlattice [58]. The advantage of this method is that we can control the distance between MoS2 layers by changing the amount of intercalating Li; however, the production scalability of this technique is limited. Additionally, some lithium residues may exist with the MoS2 layers, which affects its performance. One solution to the residue problem is to use the electrochemical lithium intercalation and exfoliation technique. The work in [59] produced the MoS2 metallic phase from the semiconducting phase, where MoS2 was assembled as an anode in lithium-ion battery semicells and then charged to a certain voltage to obtain the MoS2 metallic phase. Another work used bulk MoS2 as a cathode and lithium foil as an anode [60]. The Li content and MoS2 metallic phase can be controlled by the applied voltage.

3.2. Hydrothermal and Solvothermal Synthesis

The hydrothermal and solvothermal synthesis techniques are bottom-up synthesis techniques based on chemical reactions at high temperatures. They do not require catalysts or hazardous materials in their reactions as with other techniques, which renders them the preferred techniques. The synthesis is conducted through chemical solutions of precursors and surfactants with the solvent at a temperature above the boiling point of the solvent. The synthesis process is easy and can be produced on a large scale. Many trials to prepare metallic MoS2 through these techniques were performed, and we summarize them in Table 1.

3.3. Other Methods

Some other novel techniques to produce MoS2 for energy applications such as the one in [70] were based on the direct synthesis of MoS2 on p-Si through thermolysis, where a (NH4)2MoS4 precursor is deposited onto a non-oxide substrate. The substrate has to be a super-hydrophilic surface, meaning an extra step is added when MoO3 is deposited over the p-Si substrate to convert it from a poor hydrophilic to a super-hydrophilic surface. The method was controllable, and the produced MoS2/p-Si heterojunction was tested for solar hydrogen production and showed good results, as shown in Figure 3. It is worth mentioning that the synthesis of atomically thin MoS2 photoanodes, AT-MoS2, using CVD and ALD techniques can be used in water splitting and wastewater treatment [71]. This work proposes the idea of studying the combination of water treatment and hydrogen production in future studies for efficient and environmentally friendly approaches.

4. Energy Applications

In this section, we will discuss the energy storage and energy generation applications of MoS2. Batteries and supercapacitors are the main energy storage devices, where MoS2 serves as an anode in lithium-ion and sodium-ion batteries. Although the performance of sodium-ion batteries is low if compared to lithium batteries (due to its atomic structure), sodium is more abundant and less toxic [72]. Na has high stability and a low diffusion energy, but it has lower mobility, which decreases its favorability in batteries. Na-ion batteries have a larger weight but a lower cost than Li-ion batteries, which make them suitable for stationary applications. Not many studies have been conducted on Na-ion batteries until now, but they still represent a low-cost battery choice.

4.1. Energy Storage Applications

4.1.1. Lithium-Ion Batteries (LIB)

Lithium-ion batteries (LIB) have a high capacity and are recycable. Most portable devices have LIB; however, their capacity is still too low to be used in some electrical vehicles. Metallic MoS2 can serve as an anode in LIB due to its high conductivity, specific capacity, and large surface area which enable better intercalation of the incoming ions and enhance the battery’s stability and rate performance [73]. The chemical composition of metallic MoS2 (1T MoS2) was investigated using X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and X-ray diffraction (XRD), and it was found to have binding energies of 228.8 and 231.9 eV corresponding to the 3d5/2 and 3d3/2 components, respectively, for Mo–S bonding. The S 2p components have binding energies of 161.5 eV and 162.5 eV, corresponding to S 2P3/2 and 2P1/2, respectively [43,62]. The bonding of both Mo and S is nearly 1 eV less than that of 2H MoS2.
The research work in this area is based on two directions, namely, whether to enhance the stability of metallic MoS2-based LIB or to enhance the conductivity of 2H MoS2 to serve as an anode in LIB, since it has better stability. In a trial to suppress the high intrinsic electric conductivity of metallic MoS2, it was alligned over graphene with a relatively large separation distance of 0.98 nm between them. The first cycle showed a high capacity of ≈1700 mA h g−1 at a current density of 70 mA g−1 and an initial coulombic efficiency of 70%. The battery had a high capacity of 666 mA g−1 at a high current density of 3500 mA g−1, with a reversible capacity of ≈1700 mA g−1 at a low current density of 70 mA g−1 [61]. MoS2 was mounted on carbon fiber cloth to obtain a high reversible specific capacity of 1789 mA h g−1 at 0.1 A g−1 and a retained capacity of 853 mA h g−1 after 140 cycles at 1 A g−1 [63]. A composite of 1T-MoS2 and conductive molybdate (NiMoO4) was used to obtain a coulombic efficiency of 99.5%, and it had stability after 750 cycle [74]. A pure metallic MoS2 structure was developed in [62] to avoid stability problems in material stacking. The battery had a specific capacity of ≈935 mA h g−1 for 200 cycles at 5 A g−1 that can be increased to 1150 mA h g−1. It had a high rate performance at the current density range from 0.2 to 20 A g−1 and a reversible capacity of 589 mA g−1. Table 2 summarizes some MoS2-based LIB showing the used structure and phase of MoS2 and its specifications.

4.1.2. Sodium-Ion Batteries (NIB)

Since NIB are less efficient than LIB, there is not much research work about the role of MoS2 in Na-ion batteries; however, an early theoretical study in [82] showed that monolayer MoS2 can have a higher Na adsorption when compared to bulk MoS2. It is perfect as an anode electrode in Na-ion batteries, with a theoretical capacity of 335 mA h g−1. The monolayer maintains a lower applicable voltage of 1.0 V when compared to the bulk (1.7–2.0 V). The low mobility of Na is overcome by the monolayer structure because when the dimensions decrease, the diffusion barrier decreases from 0.7 to 0.11 eV. A graphene sandwich of MoS2, MoS2-graphene-MoS2, in [43] had a high capacity of 175 mA h g−1 at a high current density of 2 A g−1 and a reverse capacity of ≈313 mA h g−1 at a low current density of 50 mA g−1. It stabilized at a current density of 313 mA h g−1 after 200 cycles. A dual phase of 2H and 1T MoS2 was used to obtain a capacity of 300 mA h g−1 after 200 cycles and 99% coulombic efficiency. The good interlayer spacing permitted a high reversibility of Na ion intercalation [75]. MoS2 and amorphous carbon (C) microtubes (MTs) in [76] were used to improve the capacity to 563.5 mA h g−1 at 0.2 A g−1 and obtain 86.6% coulombic efficiency with cyclic stability of 484.9 mA h g−1 at 2.0 A g−1. Table 2 summarizes some MoS2-based NIB showing the used structure and phase of MoS2 and its specifications.
It is worth mentioning that, recently, multilayer intercalation of alkali metals (AM) (Li, K, Na) between bilayer graphene was possible and showed a higher storage capacity than the bulk structure [83]. A study in [84] compared the intercalation energetics of bilayer graphene and MoS2 for a number of alkali metals (Li, Na, K, Rb, Cs). The weak van der Waal forces between MoS2 layers enabled easy intercalation of Li ions without excess volume, and the Li storage capacity could reach 700 mA h g−1. The study showed that the storage capacity of MoS2 is significantly lower than graphene, but it can be increased through vertical van der Waals forces between graphene-MoS2 heterostructures where it will benefit from the light weight of graphene and the low formation energy of MoS2.

4.1.3. Supercapacitors

Supercapacitors are energy storage devices that have a lower energy density than batteries and a higher power density, meaning they can be used as a complementary device in electric vechiles beside batteries [73]. MoS2 is a good capacitor since it is formed of layers (sheets) that provide a large area for charge storage, where ions are inserted between layers through intercalation. The layers are exfoliated and then restacked to form electrodes with improved electrochemical features [85]. Carbon-based supercapacitors are leading the market due to their fast charge–discharge, versatile synthesis, and stability [86], but MoS2 can achieve extraordinary capacitances from 400 to 700 F cm−3 [85]. The charge storage mechanism of 1T MoS2 was investigated in [87] for an interlayer spacing ranging from 0.615 to 1.615 nm in ionic liquids. It was found that the highest volumetric and gravimetric capacitances were 118 F cm−3 and 42 F g−1, respectively, and occurred at a MoS2 interlayer spacing of 1.115 nm. A micro-supercapacitor proposed in [77], developed through spraying MoS2 nanosheets on a Si/SiO2 chip followed by laser patterning, had excellent cyclic and electrochemical performance compared to graphene-based micro-supercapacitors. It had a high area capacitance of 8 mF cm−2 and a volumetric capacitance of 178 F cm−3. The idea opens the door for portable and flexible micro-electronic devices. Some studies were directed towards the nano-MoS2 structure, where it showed a better performance in energy storage. Metallic 1T phase MoS2 nanosheets were found to efficiently intercalate ions such as H+, Li+, Na+, and K+ with capacitance values ranging from ∼400 to ∼700 F cm−3 in different aqueous electrolytes [85]. Their coulombic efficiencies were more than 95% and were stable until 5000 cycles. The MoS2 flower-shaped nanostructure was paired with 3D graphene to develop a supercapacitor prototype with dimensions of 23.6 × 22.4 × 0.6 mm3 by stacking a MoS2 nanoflower structure over 3D graphene over a graphite electrode [78]. The prototype had a high specific capacitance Csp of 58 F g−1, an energy density of 24.59 W h Kg−1, and a power density of 8.8 W Kg−1, with an operating window of nearly 2.7 V (−1.5 to +1.2 V). The study represents an inexpensive supercapacitor without the need for ionic liquid media. The nanostructures of MoS2 showed excellent supercapacitance when grown on Ni foam through the hydrothermal process [79]. It was able to maintain 92% of its maximum capacitance after 9000 charge–discharge cycles at 5 A g−1. The study confirmed that the high mass loading of MoS2 nanostructures grown over conducting substrates corresponds to superior energy storage electrodes. A recent work studying the capacitance of MoS2 quantum sheets (QSs) in [80] demonstrated that MoS2 quantum sheets have a high capacitance of 162 F g−1, which is very high if compared to typical MoS2 supercapacitors. MoS2 QSs have an energy density of 14.4 W h kg−1 and a long cycle life. In [81], a 3D interlayer-expanded MoS2/rGO nanocomposite (3D-IEMoS2@G) was synthesized and experimented as an anode in lithium-ion and sodium-ion batteries. It was then modified by pairing it with nitrogen-doped hierarchically porous 3D graphene (N-3DG) to obtain sodium and lithium hybrid supercapacitors (HSCs). The Na-HSC showed an excellent performance of 140 W h kg−1 at 630 W kg−1, and 43 W h kg−1 at an ultra-high power density of 103 kW kg−1 (charge finished within 1.5 s). It can retain its capacitance even after 10,000 cycles. Table 2 summarizes some MoS2-based supercapacitors showing the used structure and phase of MoS2 and its specifications.

4.2. Energy Generation Applications

4.2.1. Hydrogen Evolution Reactions (HER)

Hydrogen was recently studied to substitute fuel as a source of energy. It is not a source of energy by itself but rather a carrier of energy. It has to be manufactured as with electricity. It has to be manufactured from coal or natural gas; however, in both cases, carbon is released, and environmental pollution occurs. It is also generated from water, which represents a better environmental solution. It is not toxic, as opposed to fuel, has a high octane number, and does not cause ozone issues [88]. MoS2 is a cheap catalyst in electrochemical HER [89] and water splitting reactions [90]. The large number of electrostatic active edges and high structural defects makes MoS2 a good catalyst. 1T MoS2 is known to be a better catalyst in HER than 2H MoS2 because of its reactive basal planes, which gains its activity from the hydrogen binding affinity at the surface S sites [91]. Studies have been conducted to enhance the catalytic activity and stability of MoS2 so that it can replace noble metals. The catalytic activity of MoS2 mainly depends on the active edges or the cell vacancies. The work in [92], based on the first-principle density functional theory (DFT), studied different possible cell vacancies of MoS2 and found that the best catalytic activity for MoS2 occurs with Mo and MoS2 cell vacancies. The efficiency of HER is enhanced when compared to platinum catalyst reactions. A later study conducted by the same researchers [90] focused on Mo defects on the inert basal plane of MoS2 and showed its better performance in HER and water splitting reactions. The active sites of MoS2 basal planes are restricted to edges and missing primitive cell vacancies. The weak van der Waal interactions between MoS2 layers result in a hydrophobic characteristic which assigns more importance to layer defects [93]. A detailed study of five types of defects in MoS2 layers was conducted [92]. The study investigated the effect of disulfur vacancy (VS2), vacancy complex of Mo and nearby tri-sulfur (VMoS3), Mo vacancy (VMo), nearby S tri-vacancy (VS3), and VMoS2, and it was found that VMo and VMoS2 can activate inert basal planes and have a role in dissociating water in HER. The Gibbs energy for hydrogen adsorption (Δ G H * 0 )   for VMo is −0.198 eV, and for VS3, it is 0.06 eV, which is comparable to platinum, which has a value of −0.09 eV.
The effect of strain on Mo vacancies in single-layer MoS2 was investigated in [94], where a biaxial compressive strain of 4.5%, carried out by modifying the Mo and S interaction around the vacancy, showed optimal catalytic properties, with Gibbs free energy between −0.03 and −0.04 eV at the active sites. A hybrid catalyst made by growing MoS2 over cobalt diselenide (MoS2/CoSe2) approached the commercial platinum catalyst behavior [95]. The reaction in the acidic electrolyte had a Tafel slope of 36 mV dec−1, onset potential of −11 mV, and exchange current density of 7.3 × 10−2 mA cm−1. A trial to increase the active sites of MoS2 was introduced in [96] using cracked monolayers of 1T MoS2. The monolayers were obtained through hydrothermal synthesis. 2H MoS2 was ultrasonicated with lithium which facilitated the intercalation of MoS2 layers, which were then exfoliated to obtain 1T MoS2. The resulting MoS2 had a favorable HER performance characteristic, with a low overpotential of 156 mV, at 10 mA cm−2 in an acidic medium, and a low Tafel slope of 42.7 mV dec−1. Table 3 summarizes some MoS2 applications in HER.

4.2.2. Oxygen Evolution Reactions (OER)

MoS2 acts as a catalyst in OER which is a step in water splitting. Few studies have been conducted related to the role of MoS2 in OER. 1T MoS2 with amorphous nickel–cobalt complexes was used as a catalyst in water splitting to generate hydrogen and oxygen [97]. The method represents a low-cost, easy, and stable way to perform water splitting instead of using expensive noble metal catalysts. Another hybrid nanocomposite made of MoS2 microspheres over Ni foam was proposed in [98]. The study made use of the efficient catalytic activity of MoS2 while increasing its conductivity by attaching it to the conductive Ni foam. The overpotential decreased rapidly (nearly by 290 mV) when compared with RuO2 as a catalyst. MoS2 quantum dots (MSQDs) in [99] were used as a catalyst for OER. The quantum dots were synthesized using (NH4)2MoS4 as a precursor to produce MoS2 quantum dots (MSQDs), and then activation of QDs was carried out using potential cycling under electrolyte conditions to produce the as-synthesized materials after cycling (MSQDs-AC). The catalytic current density increased as the number of potential cycles increased, and it reached its maximum after 50 potential cycles. The technique avoids using carbon that leaves carbon QDs behind which negatively interfere with the process. The resulting MSQDs-AC had the lowest Tafel slope (39 mV dec−1) when compared to other state-of-the-art catalysts such as IrO2/C, and they also had fast reaction kinetics. Table 3 summarizes some of the MoS2 applications in OER.

4.2.3. CO2 Reduction

CO2 is one of the main reasons for climatic change, global warming, and ozone layer decrease. It also causes serious health problems that lead to human death [103]. The direction nowadays is towards reducing CO2 into CO or producing fuel from it. This is called e-fuel (electrofuels), which means producing fuel from hydrogen and CO2 through photocatalytic or electrocatalytic activity. There are a lot of studies regarding the photoreduction of CO2 on semiconductors [104], such as solar-driven CO2 conversion, where the semiconductor used in solar cells acts as a biocatalyst that converts CO2 directly into fuel (methane or ethanol) [105]. Although there may be some extended costs and climatic mitigations in synthetic fuel production, it still represents a cheap and efficient energy source [106].
Metal chalcogenides are known for their catalytic activity in HER, OER, and CO2 reduction [107,108] due to their atomic arrangement and structure. They have good electrical transport and large-scale production. MoS2 is one of the metal chalcogenides that can be used in CO2 reduction reactions due to its excellent light absorption; however, studies are still being conducted to increase its conductivity and catalytic activity to be compared with other noble metal-based catalysts. The catalytic activity of MoS2 in CO2 reduction reactions was investigated in [109]. The inclined (sharp) MoS2 edges could adsorb CO2 and reduce it to CO [100]. A p–n junction Bi2S3/MoS2 composite in [101] showed better light absorption and CO2 adsorption than single catalysts. The high light absorption of p-type MoS2 and high catalytic activity of n-type Bi2S3 were utilized. Nanoflower MoS2 powder prepared through CVD showed enhanced photocatalytic activity [102], as illustrated in Figure 4, but, still, the CO production rate was less than 0.01 μmol-gcat−1 hr−1 at ambient temperature (25 °C), which is very small and can be neglected. When treated with H2, the CO production doubled after 30 min of treatment. The work presented an easy synthesis technique of MoS2 for CO and H2O production, but, still, there is a lot of work to carry out to enhance it. Table 3 summarizes a few works regarding CO2 reduction.

4.2.4. Solar Cells

Amorphous silicon and organic semiconductors are mainly used to synthesize nano-solar cells. As the thickness of solar cells decreases, efficiency increases, and losses and costs decrease [110]. Thin MoS2 monolayers were a good choice to be used in photovoltaics due to their optical characteristics and the easiness of synthesizing very thin structures with favorable properties. A very thin structure (1 nm thick) of MoS2 and graphene was proposed in [111] with triple the efficiency of ordinary photovoltaics. However, the light absorbance of the extra-thin structure was only 10%, which is low when compared with that of silicon (40%). Different structures were proposed to enhance light absorbance or trap the incident light [110,111,112,113,114]. A graphene-MoS2 wedge-shaped microcavity achieved a 90% increase in light absorbance [110]. A heterostructure of mercury cadmium telluride (Hg0.33 Cd0.66 Te) and monolayer MoS2 was used to shift the absorbance of the whole structure to the visible region [112]. The MoS2/GaAs heterostructure layered over hexagonal boron nitride could increase the power conversion efficiency (PCE) to 9.03% [114].
MoS2 flakes were used as a buffer with copper zinc tin sulfide (CZTS) solar cells, where they showed a high efficiency of 17.03% and enhanced thermal stability at high temperatures [115]. They can work as an electron transport layer (ETL) [116] or a hole transport layer (HTL) [117]. The flakes were used as an HTL in [118], where they acted as high-stability cells, with a long shelf time of 800 h and a relatively high efficiency of 3.9%. In [119], a MoS2 film was used to decrease the defects and increase the depth of the depletion region of solar cells, and the performance of the cell was enhanced by decreasing the impurity concentration and increasing the built-in potential at the MoS2/p-Si interface. MoS2 has a role in the newest solar cell structures (organometallic-halide perovskite solar cells) [120], where MoS2 nanoflakes work as a buffer to improve stability and obtain a high efficiency of 14.9%. The open-circuit voltage (Voc) and the short-circuit current (Jsc) are higher than standard cells, as shown in Figure 5. Table 4 summarizes the role of MoS2 in solar cells, whether it acts as a hole transport layer (HLT), as an electron transport layer (ETL), or as a buffer or used with other materials to enhance the efficiency of the solar cell.

5. Challenges

The unique properties of MoS2 enabled its use in various energy storage and generation applications; however, it faces some challenges and needs more improvements to be used on a commercial scale. The synthesis techniques are facing challenges to produce MoS2 on a large scale and with a low cost. If we are moving towards using 2H MoS2 in energy applications, we will have to increase its conductivity, and if we are going to include 1T MoS2, we will have to address its stability. Due to the astounding properties of 1T MoS2 in energy applications, research has focused more on scaling up its production using different synthesis techniques and increasing its stability [122]. Although MoS2-based LIB are competitive in their specific capacities, their cycling stability and manufacturing cost have to be improved [73]. MoS2 enhances LIB safety when used as an interlay or protective layer [123], but, still, there are some concerns about its oxidation in air and its conversion when it is in direct contact with Li, which will affect the battery storage and quality. Moreover, we do not have a full picture of MoS2 layers’ immobilization of polysulfides, and their phase transformation during cycling.
The catalytic activity of MoS2 for energy generation applications is good but it is still less than that of noble metals [124], even though it is a cheap choice if compared to noble metal catalysts. The catalytic activity of platinum has outperformed MoS2 until now [125]. The computational and experimental calculations related to MoS2 doping for its use as a catalyst for HER have still not been fully studied [126,127]. The study of pure MoS2 is nearly mature, but the study of its composites for exceptional characteristics in energy applications needs more research [128]. Reduced graphene oxide with a MoS2 hollow sphere (MoS2-HS) (rGO/MoS2-S) was studied to be used in energy conversion and storage, and it showed enhanced gravimetric capacitance of approximately 318 F g−1, a high specific energy of ~44.1 W h kg−1, a high power output of ~159.16 W kg−1, and good cyclability for above 5000 cycles [129]. It also showed a unique performance in HER with a low overpotential of ~0.16 V, a low Tafel slope of ~75 mV dec−1, and a high current density of ~0.072 mA cm−2. This proves that we have to give MoS2 composites more attention in energy applications. The composite materials of MoS2 with carbon or noble metals or metal oxides need more attention to be used commercially. The purity, crystalline structure, and particle size of MoS2 need more engineering as well.

6. Conclusions

In this review, we presented MoS2 as a future material for energy applications. MoS2 is cheap, abundant, and easily senthesized. Moreover, its photocatalytic and electrocatalytic properties and its structure have paved the way to its use in energy storage devices and energy generation reactions. The high conductivity and the weak van der Waal forces between the layers of the MoS2 metallic phase (1T MoS2) have allowed its use in LIB as an anode where it is easy for Li ions to intercalate between its layers. Additionally, its large area together with its superconductivity and easy restacking renders it optimum for supercapacitors [130]. Its high electrocatalytic and photocatalytic activity has allowed its use as a catalyst in hydrogen evolution reactions and in solar cells where it can be used to reduce CO2 and produce energy as well. The latter will be a comprehensive environmental solution to produce clean energy and decrease the CO2 percentage in our environment. Thin MoS2 layers are known to enhance solar cells’ efficiency, working as an electron transport layer (ETL), a hole transport layer (HTL), or a buffer, but their light absorbency is still low, and that is why different studies have worked on modifying solar cells through heterostructures [131] or modifying the cell shape to increase absorbency.
On the other hand, MoS2 is facing some challenges in its large-scale production with the required properties (fewer impurities, and better conductivity and stability). The works conducted thus far have reached some solutions such as using MoS2 composites [132] or heterostructures or using specific structures to enhance the efficiency and decrease the production cost. Still, there is a lot of work to be conducted to completely substitute other materials, but it will be worth it, since the MoS2 will be an economic, easy, and efficient solution compared to other 2D nanomaterials [133,134,135,136,137,138,139,140,141].

Author Contributions

Conceptualization, O.S. and A.E.M.; methodology, O.S. and A.E.M.; writ-ing—original draft preparation, O.S. and A.E.M.; writing—review and editing, A.E.M.; supervision, A.E.M. All authors have read and agreed to the published version of the manuscript.


This research was funded by United Arab Emirates University UPAR project, grant number 31N393.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.


  1. Mak, K.F.; Lee, C.; Hone, J.; Shan, J.; Heinz, T.F. Atomically Thin MoS2: A New Direct-Gap Semiconductor. Phys. Rev. Lett. 2010, 105, 136805. [Google Scholar] [CrossRef] [Green Version]
  2. Lee, K.; Kim, H.-Y.; Lotya, M.; Coleman, J.N.; Kim, G.-T.; Duesberg, G.S. Electrical Characteristics of Molybdenum Disulfide Flakes Produced by Liquid Exfoliation. Adv. Mater. 2011, 23, 4178–4182. [Google Scholar] [CrossRef]
  3. Chang, K.; Hai, X.; Pang, H.; Zhang, H.; Shi, L.; Liu, G.; Liu, H.; Zhao, G.; Li, M.; Ye, J. Targeted Synthesis of 2H- and 1T-Phase MoS2 Monolayers for Catalytic Hydrogen Evolution. Adv. Mater. 2016, 28, 10033–10041. [Google Scholar] [CrossRef]
  4. Hersam, M.C. Emerging Device Applications for Two-Dimensional Nanomaterial Heterostructures. In Proceedings of the 2015 73rd Annual Device Research Conference (DRC), Columbus, OH, USA, 21–24 June 2015; IEEE: Columbus, OH, USA, 2015; p. 209. [Google Scholar]
  5. Zhao, G.-Y.; Deng, H.; Tyree, N.; Guy, M.; Lisfi, A.; Peng, Q.; Yan, J.-A.; Wang, C.; Lan, Y. Recent Progress on Irradiation-Induced Defect Engineering of Two-Dimensional 2H-MoS2 Few Layers. Appl. Sci. 2019, 9, 678. [Google Scholar] [CrossRef] [Green Version]
  6. del Alamo, J.A. Nanometer-Scale III–V CMOS. In Proceedings of the 2016 Compound Semiconductor Week (CSW) Includes 28th International Conference on Indium Phosphide & Related Materials (IPRM) & 43rd International Symposium on Compound Semiconductors (ISCS), Toyama, Japan, 26–30 June 2016; IEEE: Toyama, Japan, 2016; p. 1. [Google Scholar]
  7. Hijazi, A.; Moutaouakil, A.E. Graphene and MoS2 Structures for THz Applications. In Proceedings of the 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), Paris, France, 1–6 September 2019; IEEE: Paris, France, 2019; pp. 1–2. [Google Scholar]
  8. Choudhary, N.; Patel, M.D.; Park, J.; Sirota, B.; Choi, W. Synthesis of Large Scale MoS2 for Electronics and Energy Applications. J. Mater. Res. 2016, 31, 824–831. [Google Scholar] [CrossRef]
  9. Li, Y.; Chang, K.; Sun, Z.; Shangguan, E.; Tang, H.; Li, B.; Sun, J.; Chang, Z. Selective Preparation of 1T- and 2H-Phase MoS2 Nanosheets with Abundant Monolayer Structure and Their Applications in Energy Storage Devices. ACS Appl. Energy Mater. 2020, 3, 998–1009. [Google Scholar] [CrossRef]
  10. Li, X.; Zhao, L.; Yu, J.; Liu, X.; Zhang, X.; Liu, H.; Zhou, W. Water Splitting: From Electrode to Green Energy System. Nano-Micro Lett. 2020, 12, 131. [Google Scholar] [CrossRef] [PubMed]
  11. Hong, X.; Chan, K.; Tsai, C.; Nørskov, J.K. How Doped MoS2 Breaks Transition-Metal Scaling Relations for CO2 Electrochemical Reduction. ACS Catal. 2016, 6, 4428–4437. [Google Scholar] [CrossRef]
  12. Gupta, D.; Chauhan, V.; Kumar, R. A Comprehensive Review on Synthesis and Applications of Molybdenum Disulfide (MoS2) Material: Past and Recent Developments. Inorg. Chem. Commun. 2020, 121, 108200. [Google Scholar] [CrossRef]
  13. Nalwa, H.S. A Review of Molybdenum Disulfide (MoS2) Based Photodetectors: From Ultra-Broadband, Self-Powered to Flexible Devices. RSC Adv. 2020, 10, 30529–30602. [Google Scholar] [CrossRef]
  14. Yadav, V.; Roy, S.; Singh, P.; Khan, Z.; Jaiswal, A. 2D MoS2 -Based Nanomaterials for Therapeutic, Bioimaging, and Biosensing Applications. Small 2019, 15, 1803706. [Google Scholar] [CrossRef] [Green Version]
  15. Sun, J.; Li, X.; Guo, W.; Zhao, M.; Fan, X.; Dong, Y.; Xu, C.; Deng, J.; Fu, Y. Synthesis Methods of Two-Dimensional MoS2: A Brief Review. Crystals 2017, 7, 198. [Google Scholar] [CrossRef]
  16. Krishnan, U.; Kaur, M.; Singh, K.; Kumar, M.; Kumar, A. A Synoptic Review of MoS2: Synthesis to Applications. Superlattices Microstruct. 2019, 128, 274–297. [Google Scholar] [CrossRef]
  17. Samy, O.; Zeng, S.; Birowosuto, M.D.; El Moutaouakil, A. A Review on MoS2 Properties, Synthesis, Sensing Applications and Challenges. Crystals 2021, 11, 355. [Google Scholar] [CrossRef]
  18. Yang, L.; Liu, P.; Li, J.; Xiang, B. Two-Dimensional Material Molybdenum Disulfides as Electrocatalysts for Hydrogen Evolution. Catalysts 2017, 7, 285. [Google Scholar] [CrossRef] [Green Version]
  19. He, Z.; Que, W. Molybdenum Disulfide Nanomaterials: Structures, Properties, Synthesis and Recent Progress on Hydrogen Evolution Reaction. Appl. Mater. Today 2016, 3, 23–56. [Google Scholar] [CrossRef]
  20. Winer, W.O. Molybdenum Disulfide as a Lubricant: A Review of the Fundamental Knowledge. Wear 1967, 10, 422–452. [Google Scholar] [CrossRef] [Green Version]
  21. Joly-Pottuz, L.; Dassenoy, F.; Belin, M.; Vacher, B.; Martin, J.M.; Fleischer, N. Ultralow-Friction and Wear Properties of IF-WS2 under Boundary Lubrication. Tribol. Lett. 2005, 18, 477–485. [Google Scholar] [CrossRef]
  22. Yadgarov, L.; Petrone, V.; Rosentsveig, R.; Feldman, Y.; Tenne, R.; Senatore, A. Tribological Studies of Rhenium Doped Fullerene-like MoS2 Nanoparticles in Boundary, Mixed and Elasto-Hydrodynamic Lubrication Conditions. Wear 2013, 297, 1103–1110. [Google Scholar] [CrossRef]
  23. Sgroi, M.; Gili, F.; Mangherini, D.; Lahouij, I.; Dassenoy, F.; Garcia, I.; Odriozola, I.; Kraft, G. Friction Reduction Benefits in Valve-Train System Using IF-MoS2 Added Engine Oil. Tribol. Trans. 2015, 58, 207–214. [Google Scholar] [CrossRef]
  24. Sgroi, M.F.; Asti, M.; Gili, F.; Deorsola, F.A.; Bensaid, S.; Fino, D.; Kraft, G.; Garcia, I.; Dassenoy, F. Engine Bench and Road Testing of an Engine Oil Containing MoS2 Particles as Nano-Additive for Friction Reduction. Tribol. Int. 2017, 105, 317–325. [Google Scholar] [CrossRef]
  25. Song, I.; Park, C.; Choi, H.C. Synthesis and Properties of Molybdenum Disulphide: From Bulk to Atomic Layers. RSC Adv. 2015, 5, 7495–7514. [Google Scholar] [CrossRef] [Green Version]
  26. Guo, J.; Peng, R.; Du, H.; Shen, Y.; Li, Y.; Li, J.; Dong, G. The Application of Nano-MoS2 Quantum Dots as Liquid Lubricant Additive for Tribological Behavior Improvement. Nanomaterials 2020, 10, 200. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  27. Lahouij, I.; Dassenoy, F.; de Knoop, L.; Martin, J.-M.; Vacher, B. In Situ TEM Observation of the Behavior of an Individual Fullerene-Like MoS2 Nanoparticle in a Dynamic Contact. Tribol. Lett. 2011, 42, 133–140. [Google Scholar] [CrossRef]
  28. Cizaire, L.; Vacher, B.; Le Mogne, T.; Martin, J.M.; Rapoport, L.; Margolin, A.; Tenne, R. Mechanisms of Ultra-Low Friction by Hollow Inorganic Fullerene-like MoS2 Nanoparticles. Surf. Coat. Technol. 2002, 160, 282–287. [Google Scholar] [CrossRef]
  29. Lahouij, I.; Vacher, B.; Martin, J.-M.; Dassenoy, F. IF-MoS2 Based Lubricants: Influence of Size, Shape and Crystal Structure. Wear 2012, 296, 558–567. [Google Scholar] [CrossRef]
  30. Dai, Z.; Jin, W.; Grady, M.; Sadowski, J.T.; Dadap, J.I.; Osgood, R.M.; Pohl, K. Surface Structure of Bulk 2H-MoS2(0001) and Exfoliated Suspended Monolayer MoS2: A Selected Area Low Energy Electron Diffraction Study. Surf. Sci. 2017, 660, 16–21. [Google Scholar] [CrossRef] [Green Version]
  31. Li, X.; Zhu, H. Two-Dimensional MoS2: Properties, Preparation, and Applications. J. Mater. 2015, 1, 33–44. [Google Scholar] [CrossRef] [Green Version]
  32. Toh, R.J.; Sofer, Z.; Luxa, J.; Sedmidubský, D.; Pumera, M. 3R Phase of MoS2 and WS2 Outperforms the Corresponding 2H Phase for Hydrogen Evolution. Chem. Commun. 2017, 53, 3054–3057. [Google Scholar] [CrossRef] [Green Version]
  33. Terrones, H.; López-Urías, F.; Terrones, M. Novel Hetero-Layered Materials with Tunable Direct Band Gaps by Sandwiching Different Metal Disulfides and Diselenides. Sci. Rep. 2013, 3, 1549. [Google Scholar] [CrossRef]
  34. Kadantsev, E.S.; Hawrylak, P. Electronic Structure of a Single MoS2 Monolayer. Solid State Commun. 2012, 152, 909–913. [Google Scholar] [CrossRef]
  35. Lin, Y.-C.; Dumcenco, D.O.; Huang, Y.-S.; Suenaga, K. Atomic Mechanism of the Semiconducting-to-Metallic Phase Transition in Single-Layered MoS2. Nat. Nanotechnol. 2014, 9, 391–396. [Google Scholar] [CrossRef] [PubMed]
  36. Kappera, R.; Voiry, D.; Yalcin, S.E.; Branch, B.; Gupta, G.; Mohite, A.D.; Chhowalla, M. Phase-Engineered Low-Resistance Contacts for Ultrathin MoS2 Transistors. Nat. Mater. 2014, 13, 1128–1134. [Google Scholar] [CrossRef] [PubMed]
  37. Hu, L.; Shan, X.; Wu, Y.; Zhao, J.; Lu, X. Laser Thinning and Patterning of MoS2 with Layer-by-Layer Precision. Sci. Rep. 2017, 7, 15538. [Google Scholar] [CrossRef]
  38. Cho, S.; Kim, S.; Kim, J.H.; Zhao, J.; Seok, J.; Keum, D.H.; Baik, J.; Choe, D.-H.; Chang, K.J.; Suenaga, K.; et al. Phase Patterning for Ohmic Homojunction Contact in MoTe2. Science 2015, 349, 625–628. [Google Scholar] [CrossRef] [PubMed]
  39. Sun, K.; Liu, Y.; Pan, Y.; Zhu, H.; Zhao, J.; Zeng, L.; Liu, Z.; Liu, C. Targeted Bottom-up Synthesis of 1T-Phase MoS2 Arrays with High Electrocatalytic Hydrogen Evolution Activity by Simultaneous Structure and Morphology Engineering. Nano Res. 2018, 11, 4368–4379. [Google Scholar] [CrossRef]
  40. Yang, S.; Zhang, K.; Wang, C.; Zhang, Y.; Chen, S.; Wu, C.; Vasileff, A.; Qiao, S.-Z.; Song, L. Hierarchical 1T-MoS2 Nanotubular Structures for Enhanced Supercapacitive Performance. J. Mater. Chem. A 2017, 5, 23704–23711. [Google Scholar] [CrossRef]
  41. Geng, X.; Zhang, Y.; Han, Y.; Li, J.; Yang, L.; Benamara, M.; Chen, L.; Zhu, H. Two-Dimensional Water-Coupled Metallic MoS2 with Nanochannels for Ultrafast Supercapacitors. Nano Lett. 2017, 17, 1825–1832. [Google Scholar] [CrossRef]
  42. Li, P.; Yang, Y.; Gong, S.; Lv, F.; Wang, W.; Li, Y.; Luo, M.; Xing, Y.; Wang, Q.; Guo, S. Co-Doped 1T-MoS2 Nanosheets Embedded in N, S-Doped Carbon Nanobowls for High-Rate and Ultra-Stable Sodium-Ion Batteries. Nano Res. 2019, 12, 2218–2223. [Google Scholar] [CrossRef]
  43. Geng, X.; Jiao, Y.; Han, Y.; Mukhopadhyay, A.; Yang, L.; Zhu, H. Freestanding Metallic 1T MoS2 with Dual Ion Diffusion Paths as High Rate Anode for Sodium-Ion Batteries. Adv. Funct. Mater. 2017, 27, 1702998. [Google Scholar] [CrossRef]
  44. Tang, W.; Wang, X.; Xie, D.; Xia, X.; Gu, C.; Tu, J. Hollow Metallic 1T MoS2 Arrays Grown on Carbon Cloth: A Freestanding Electrode for Sodium Ion Batteries. J. Mater. Chem. A 2018, 6, 18318–18324. [Google Scholar] [CrossRef]
  45. Shang, C.; Fang, Y.Q.; Zhang, Q.; Wang, N.Z.; Wang, Y.F.; Liu, Z.; Lei, B.; Meng, F.B.; Ma, L.K.; Wu, T.; et al. Superconductivity in the Metastable 1 T’ and 1 T’’’ Phases of MoS2 Crystals. Phys. Rev. B 2018, 98, 184513. [Google Scholar] [CrossRef] [Green Version]
  46. Qian, X.; Liu, J.; Fu, L.; Li, J. Quantum Spin Hall Effect in Two-Dimensional Transition Metal Dichalcogenides. Science 2014, 346, 1344–1347. [Google Scholar] [CrossRef] [Green Version]
  47. Kappera, R.; Voiry, D.; Yalcin, S.E.; Jen, W.; Acerce, M.; Torrel, S.; Branch, B.; Lei, S.; Chen, W.; Najmaei, S.; et al. Metallic 1T Phase Source/Drain Electrodes for Field Effect Transistors from Chemical Vapor Deposited MoS2. APL Mater. 2014, 2, 092516. [Google Scholar] [CrossRef] [Green Version]
  48. Coogan, Á.; Gun’ko, Y.K. Solution-Based “Bottom-up” Synthesis of Group VI Transition Metal Dichalcogenides and Their Applications. Mater. Adv. 2021, 2, 146–164. [Google Scholar] [CrossRef]
  49. Kaushik, S.; Tiwari, U.K.; Choubey, R.K.; Singh, K.; Sinha, R.K. Study of Sonication Assisted Synthesis of Molybdenum Disulfide (MoS2) Nanosheets. Mater. Today Proc. 2020, 21, 1969–1975. [Google Scholar] [CrossRef]
  50. Attanayake, N.H.; Thenuwara, A.C.; Patra, A.; Aulin, Y.V.; Tran, T.M.; Chakraborty, H.; Borguet, E.; Klein, M.L.; Perdew, J.P.; Strongin, D.R. Effect of Intercalated Metals on the Electrocatalytic Activity of 1T-MoS2 for the Hydrogen Evolution Reaction. ACS Energy Lett. 2018, 3, 7–13. [Google Scholar] [CrossRef]
  51. Muratore, C.; Hu, J.J.; Wang, B.; Haque, M.A.; Bultman, J.E.; Jespersen, M.L.; Shamberger, P.J.; McConney, M.E.; Naguy, R.D.; Voevodin, A.A. Continuous Ultra-Thin MoS2 Films Grown by Low-Temperature Physical Vapor Deposition. Appl. Phys. Lett. 2014, 104, 261604. [Google Scholar] [CrossRef] [Green Version]
  52. Lin, Z.; Liu, Y.; Halim, U.; Ding, M.; Liu, Y.; Wang, Y.; Jia, C.; Chen, P.; Duan, X.; Wang, C.; et al. Solution-Processable 2D Semiconductors for High-Performance Large-Area Electronics. Nature 2018, 562, 254–258. [Google Scholar] [CrossRef]
  53. Choi, S.H.; Stephen, B.; Park, J.-H.; Lee, J.S.; Kim, S.M.; Yang, W.; Kim, K.K. Water-Assisted Synthesis of Molybdenum Disulfide Film with Single Organic Liquid Precursor. Sci. Rep. 2017, 7, 1983. [Google Scholar] [CrossRef] [Green Version]
  54. Tan, X.; Kang, W.; Liu, J.; Zhang, C. Synergistic Exfoliation of MoS2 by Ultrasound Sonication in a Supercritical Fluid Based Complex Solvent. Nanoscale Res. Lett. 2019, 14, 317. [Google Scholar] [CrossRef]
  55. Lee, Y.; Lee, J.; Bark, H.; Oh, I.-K.; Ryu, G.H.; Lee, Z.; Kim, H.; Cho, J.H.; Ahn, J.-H.; Lee, C. Synthesis of Wafer-Scale Uniform Molybdenum Disulfide Films with Control over the Layer Number Using a Gas Phase Sulfur Precursor. Nanoscale 2014, 6, 2821. [Google Scholar] [CrossRef] [Green Version]
  56. Kim, S.J.; Kang, M.-A.; Kim, S.H.; Lee, Y.; Song, W.; Myung, S.; Lee, S.S.; Lim, J.; An, K.-S. Large-Scale Growth and Simultaneous Doping of Molybdenum Disulfide Nanosheets. Sci. Rep. 2016, 6, 24054. [Google Scholar] [CrossRef] [Green Version]
  57. Wypych, F.; Schöllhorn, R. 1T-MoS2, a New Metallic Modification of Molybdenum Disulfide. J. Chem. Soc. Chem. Commun. 1992, 1386–1388. [Google Scholar] [CrossRef]
  58. Heising, J.; Kanatzidis, M.G. Exfoliated and Restacked MoS2 and WS2: Ionic or Neutral Species? Encapsulation and Ordering of Hard Electropositive Cations. J. Am. Chem. Soc. 1999, 121, 11720–11732. [Google Scholar] [CrossRef]
  59. Coleman, J.N.; Lotya, M.; O’Neill, A.; Bergin, S.D.; King, P.J.; Khan, U.; Young, K.; Gaucher, A.; De, S.; Smith, R.J.; et al. Two-Dimensional Nanosheets Produced by Liquid Exfoliation of Layered Materials. Science 2011, 331, 568–571. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  60. Zeng, Z.; Yin, Z.; Huang, X.; Li, H.; He, Q.; Lu, G.; Boey, F.; Zhang, H. Single-Layer Semiconducting Nanosheets: High-Yield Preparation and Device Fabrication. Angew. Chem. Int. Ed. 2011, 50, 11093–11097. [Google Scholar] [CrossRef]
  61. Xiang, T.; Fang, Q.; Xie, H.; Wu, C.; Wang, C.; Zhou, Y.; Liu, D.; Chen, S.; Khalil, A.; Tao, S.; et al. Vertical 1T-MoS2 Nanosheets with Expanded Interlayer Spacing Edged on a Graphene Frame for High Rate Lithium-Ion Batteries. Nanoscale 2017, 9, 6975–6983. [Google Scholar] [CrossRef]
  62. Jiao, Y.; Mukhopadhyay, A.; Ma, Y.; Yang, L.; Hafez, A.M.; Zhu, H. Ion Transport Nanotube Assembled with Vertically Aligned Metallic MoS2 for High Rate Lithium-Ion Batteries. Adv. Energy Mater. 2018, 8, 1702779. [Google Scholar] [CrossRef]
  63. Wu, M.; Zhan, J.; Wu, K.; Li, Z.; Wang, L.; Geng, B.; Wang, L.; Pan, D. Metallic 1T MoS2 Nanosheet Arrays Vertically Grown on Activated Carbon Fiber Cloth for Enhanced Li-Ion Storage Performance. J. Mater. Chem. A 2017, 5, 14061–14069. [Google Scholar] [CrossRef]
  64. Yang, J.; Wang, K.; Zhu, J.; Zhang, C.; Liu, T. Self-Templated Growth of Vertically Aligned 2H-1T MoS2 for Efficient Electrocatalytic Hydrogen Evolution. ACS Appl. Mater. Interfaces 2016, 8, 31702–31708. [Google Scholar] [CrossRef]
  65. Liu, Q.; Shang, Q.; Khalil, A.; Fang, Q.; Chen, S.; He, Q.; Xiang, T.; Liu, D.; Zhang, Q.; Luo, Y.; et al. In Situ Integration of a Metallic 1T-MoS2/CdS Heterostructure as a Means to Promote Visible-Light-Driven Photocatalytic Hydrogen Evolution. ChemCatChem 2016, 8, 2614–2619. [Google Scholar] [CrossRef]
  66. Liu, Q.; Li, X.; He, Q.; Khalil, A.; Liu, D.; Xiang, T.; Wu, X.; Song, L. Gram-Scale Aqueous Synthesis of Stable Few-Layered 1T-MoS2: Applications for Visible-Light-Driven Photocatalytic Hydrogen Evolution. Small 2015, 11, 5556–5564. [Google Scholar] [CrossRef] [PubMed]
  67. Wang, J.; Wang, N.; Guo, Y.; Yang, J.; Wang, J.; Wang, F.; Sun, J.; Xu, H.; Liu, Z.-H.; Jiang, R. Metallic-Phase MoS2 Nanopetals with Enhanced Electrocatalytic Activity for Hydrogen Evolution. ACS Sustain. Chem. Eng. 2018, 6, 13435–13442. [Google Scholar] [CrossRef]
  68. Geng, X.; Sun, W.; Wu, W.; Chen, B.; Al-Hilo, A.; Benamara, M.; Zhu, H.; Watanabe, F.; Cui, J.; Chen, T. Pure and Stable Metallic Phase Molybdenum Disulfide Nanosheets for Hydrogen Evolution Reaction. Nat. Commun. 2016, 7, 10672. [Google Scholar] [CrossRef] [Green Version]
  69. Yao, Y.; Ao, K.; Lv, P.; Wei, Q. MoS2 Coexisting in 1T and 2H Phases Synthesized by Common Hydrothermal Method for Hydrogen Evolution Reaction. Nanomaterials 2019, 9, 844. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  70. Hasani, A.; Le, Q.V.; Tekalgne, M.; Choi, M.-J.; Lee, T.H.; Jang, H.W.; Kim, S.Y. Direct Synthesis of Two-Dimensional MoS2 on p-Type Si and Application to Solar Hydrogen Production. NPG Asia Mater. 2019, 11, 47. [Google Scholar] [CrossRef] [Green Version]
  71. Chi, Z.; Zhao, J.; Zhang, Y.; Yu, H.; Yu, H. The Fabrication of Atomically Thin-MoS2 Based Photoanodes for Photoelectrochemical Energy Conversion and Environment Remediation: A Review. Green Energy Environ. 2021, S246802572100090X. [Google Scholar] [CrossRef]
  72. Jiao, Y.; Hafez, A.M.; Cao, D.; Mukhopadhyay, A.; Ma, Y.; Zhu, H. Metallic MoS2 for High Performance Energy Storage and Energy Conversion. Small 2018, 14, 1800640. [Google Scholar] [CrossRef] [PubMed]
  73. Saha, D.; Kruse, P. Editors’ Choice—Review—Conductive Forms of MoS2 and Their Applications in Energy Storage and Conversion. J. Electrochem. Soc. 2020, 167, 126517. [Google Scholar] [CrossRef]
  74. Li, Z.; Zhan, X.; Zhu, W.; Qi, S.; Braun, P.V. Carbon-Free, High-Capacity and Long Cycle Life 1D–2D NiMoO4 Nanowires/Metallic 1T MoS2 Composite Lithium-Ion Battery Anodes. ACS Appl. Mater. Interfaces 2019, 11, 44593–44600. [Google Scholar] [CrossRef] [PubMed]
  75. Wu, J.; Liu, J.; Cui, J.; Yao, S.; Ihsan-Ul-Haq, M.; Mubarak, N.; Quattrocchi, E.; Ciucci, F.; Kim, J.-K. Dual-Phase MoS2 as a High-Performance Sodium-Ion Battery Anode. J. Mater. Chem. A 2020, 8, 2114–2122. [Google Scholar] [CrossRef]
  76. Pan, Q.; Zhang, Q.; Zheng, F.; Liu, Y.; Li, Y.; Ou, X.; Xiong, X.; Yang, C.; Liu, M. Construction of MoS2/C Hierarchical Tubular Heterostructures for High-Performance Sodium Ion Batteries. ACS Nano 2018, 12, 12578–12586. [Google Scholar] [CrossRef]
  77. Cao, L.; Yang, S.; Gao, W.; Liu, Z.; Gong, Y.; Ma, L.; Shi, G.; Lei, S.; Zhang, Y.; Zhang, S.; et al. Direct Laser-Patterned Micro-Supercapacitors from Paintable MoS2 Films. Small 2013, 9, 2905–2910. [Google Scholar] [CrossRef] [PubMed]
  78. Singh, K.; Kumar, S.; Agarwal, K.; Soni, K.; Ramana Gedela, V.; Ghosh, K. Three-Dimensional Graphene with MoS2 Nanohybrid as Potential Energy Storage/Transfer Device. Sci. Rep. 2017, 7, 9458. [Google Scholar] [CrossRef] [Green Version]
  79. Manuraj, M.; Kavya Nair, K.V.; Unni, K.N.N.; Rakhi, R.B. High Performance Supercapacitors Based on MoS2 Nanostructures with near Commercial Mass Loading. J. Alloy. Compd. 2020, 819, 152963. [Google Scholar] [CrossRef]
  80. Nardekar, S.S.; Krishnamoorthy, K.; Pazhamalai, P.; Sahoo, S.; Mariappan, V.K.; Kim, S.-J. Exceptional Interfacial Electrochemistry of Few-Layered 2D MoS2 Quantum Sheets for High Performance Flexible Solid-State Supercapacitors. J. Mater. Chem. A 2020, 8, 13121–13131. [Google Scholar] [CrossRef]
  81. Zhan, C.; Liu, W.; Hu, M.; Liang, Q.; Yu, X.; Shen, Y.; Lv, R.; Kang, F.; Huang, Z.-H. High-Performance Sodium-Ion Hybrid Capacitors Based on an Interlayer-Expanded MoS2/RGO Composite: Surpassing the Performance of Lithium-Ion Capacitors in a Uniform System. NPG Asia Mater. 2018, 10, 775–787. [Google Scholar] [CrossRef]
  82. Su, J.; Pei, Y.; Yang, Z.; Wang, X. Ab Initio Study of Graphene-like Monolayer Molybdenum Disulfide as a Promising Anode Material for Rechargeable Sodium Ion Batteries. RSC Adv. 2014, 4, 43183–43188. [Google Scholar] [CrossRef]
  83. Kühne, M.; Börrnert, F.; Fecher, S.; Ghorbani-Asl, M.; Biskupek, J.; Samuelis, D.; Krasheninnikov, A.V.; Kaiser, U.; Smet, J.H. Reversible Superdense Ordering of Lithium between Two Graphene Sheets. Nature 2018, 564, 234–239. [Google Scholar] [CrossRef]
  84. Chepkasov, I.V.; Ghorbani-Asl, M.; Popov, Z.I.; Smet, J.H.; Krasheninnikov, A.V. Alkali Metals inside Bi-Layer Graphene and MoS2: Insights from First-Principles Calculations. Nano Energy 2020, 75, 104927. [Google Scholar] [CrossRef]
  85. Acerce, M.; Voiry, D.; Chhowalla, M. Metallic 1T Phase MoS2 Nanosheets as Supercapacitor Electrode Materials. Nat. Nanotechnol. 2015, 10, 313–318. [Google Scholar] [CrossRef]
  86. Miao, L.; Song, Z.; Zhu, D.; Li, L.; Gan, L.; Liu, M. Recent Advances in Carbon-Based Supercapacitors. Mater. Adv. 2020, 1, 945–966. [Google Scholar] [CrossRef]
  87. Liang, Z.; Zhao, C.; Zhao, W.; Zhang, Y.; Srimuk, P.; Presser, V.; Feng, G. Molecular Understanding of Charge Storage in MoS2 Supercapacitors with Ionic Liquids. Energy Environ. Mater. 2021, eem2.12147. [Google Scholar] [CrossRef]
  88. Balat, M. Potential Importance of Hydrogen as a Future Solution to Environmental and Transportation Problems. Int. J. Hydrog. Energy 2008, 33, 4013–4029. [Google Scholar] [CrossRef]
  89. Gao, M.-R.; Chan, M.K.Y.; Sun, Y. Edge-Terminated Molybdenum Disulfide with a 9.4-Å Interlayer Spacing for Electrochemical Hydrogen Production. Nat. Commun. 2015, 6, 7493. [Google Scholar] [CrossRef] [Green Version]
  90. Ye, K.; Li, M.; Luo, J.; Wu, B.; Lai, L. The H2O Dissociation and Hydrogen Evolution Performance of Monolayer MoS2 Containing Single Mo Vacancy: A Theoretical Study. IEEE Trans. Nanotechnol. 2020, 19, 163–167. [Google Scholar] [CrossRef]
  91. Tang, Q.; Jiang, D. Mechanism of Hydrogen Evolution Reaction on 1T-MoS2 from First Principles. ACS Catal. 2016, 6, 4953–4961. [Google Scholar] [CrossRef]
  92. Ye, K.; Li, M.; Luo, J.; Wu, B.; Lai, L. Activating Inert Basal Plane of MoS2 for H2O Dissociation and HER via Formation of Vacancy Defects: A DFT Study. In Proceedings of the 2019 IEEE 19th International Conference on Nanotechnology (IEEE-NANO), Macao, China, 22–26 July 2019; IEEE: Macao, China, 2019; pp. 48–53. [Google Scholar]
  93. Li, J.; Joseph, T.; Ghorbani-Asl, M.; Kolekar, S.; Krasheninnikov, A.V.; Batzill, M. Mirror Twin Boundaries in MoSe2 Monolayers as One Dimensional Nanotemplates for Selective Water Adsorption. Nanoscale 2021, 13, 1038–1047. [Google Scholar] [CrossRef] [PubMed]
  94. Ye, K.; Lai, L.; Li, M.; Luo, J.; Wu, B.; Ren, Z. Strain Effect on the Hydrogen Evolution Reaction of V Mo -SLMoS2. IEEE Trans. Nanotechnol. 2020, 19, 192–196. [Google Scholar] [CrossRef]
  95. Gao, M.-R.; Liang, J.-X.; Zheng, Y.-R.; Xu, Y.-F.; Jiang, J.; Gao, Q.; Li, J.; Yu, S.-H. An Efficient Molybdenum Disulfide/Cobalt Diselenide Hybrid Catalyst for Electrochemical Hydrogen Generation. Nat. Commun. 2015, 6, 5982. [Google Scholar] [CrossRef] [PubMed]
  96. Li, Y.; Wang, L.; Zhang, S.; Dong, X.; Song, Y.; Cai, T.; Liu, Y. Cracked Monolayer 1T MoS2 with Abundant Active Sites for Enhanced Electrocatalytic Hydrogen Evolution. Catal. Sci. Technol. 2017, 7, 718–724. [Google Scholar] [CrossRef]
  97. Li, H.; Chen, S.; Jia, X.; Xu, B.; Lin, H.; Yang, H.; Song, L.; Wang, X. Amorphous Nickel-Cobalt Complexes Hybridized with 1T-Phase Molybdenum Disulfide via Hydrazine-Induced Phase Transformation for Water Splitting. Nat. Commun. 2017, 8, 15377. [Google Scholar] [CrossRef] [PubMed]
  98. Yan, K.; Lu, Y. Direct Growth of MoS2 Microspheres on Ni Foam as a Hybrid Nanocomposite Efficient for Oxygen Evolution Reaction. Small 2016, 12, 2975–2981. [Google Scholar] [CrossRef] [PubMed]
  99. Mohanty, B.; Ghorbani-Asl, M.; Kretschmer, S.; Ghosh, A.; Guha, P.; Panda, S.K.; Jena, B.; Krasheninnikov, A.V.; Jena, B.K. MoS2 Quantum Dots as Efficient Catalyst Materials for the Oxygen Evolution Reaction. ACS Catal. 2018, 8, 1683–1689. [Google Scholar] [CrossRef]
  100. Asadi, M.; Kumar, B.; Behranginia, A.; Rosen, B.A.; Baskin, A.; Repnin, N.; Pisasale, D.; Phillips, P.; Zhu, W.; Haasch, R.; et al. Robust Carbon Dioxide Reduction on Molybdenum Disulphide Edges. Nat. Commun. 2014, 5, 4470. [Google Scholar] [CrossRef] [Green Version]
  101. Kim, R.; Kim, J.; Do, J.Y.; Seo, M.W.; Kang, M. Carbon Dioxide Photoreduction on the Bi2S3/MoS2 Catalyst. Catalysts 2019, 9, 998. [Google Scholar] [CrossRef] [Green Version]
  102. Meier, A.J.; Garg, A.; Sutter, B.; Kuhn, J.N.; Bhethanabotla, V.R. MoS2 Nanoflowers as a Gateway for Solar-Driven CO2 Photoreduction. ACS Sustain. Chem. Eng. 2019, 7, 265–275. [Google Scholar] [CrossRef]
  103. Jacobson, T.A.; Kler, J.S.; Hernke, M.T.; Braun, R.K.; Meyer, K.C.; Funk, W.E. Direct Human Health Risks of Increased Atmospheric Carbon Dioxide. Nat. Sustain. 2019, 2, 691–701. [Google Scholar] [CrossRef]
  104. He, J.; Janáky, C. Recent Advances in Solar-Driven Carbon Dioxide Conversion: Expectations versus Reality. ACS Energy Lett. 2020, 5, 1996–2014. [Google Scholar] [CrossRef] [PubMed]
  105. Tanaka, Y.; Hasanuzzaman, M. A Review of Global Current Techniques and Evaluation Methods of Photocatalytic CO2 Reduction. In Proceedings of the 5th IET International Conference on Clean Energy and Technology (CEAT2018), Kuala, Lumpur, 5–6 September 2018; Institution of Engineering and Technology: Kuala Lumpur, Malaysia, 2018; p. 6. [Google Scholar]
  106. Ueckerdt, F.; Bauer, C.; Dirnaichner, A.; Everall, J.; Sacchi, R.; Luderer, G. Potential and Risks of Hydrogen-Based e-Fuels in Climate Change Mitigation. Nat. Clim. Chang. 2021, 11, 384–393. [Google Scholar] [CrossRef]
  107. Shao, X.; Zhang, X.; Liu, Y.; Qiao, J.; Zhou, X.-D.; Xu, N.; Malcombe, J.L.; Yi, J.; Zhang, J. Metal Chalcogenide-Associated Catalysts Enabling CO2 Electroreduction to Produce Low-Carbon Fuels for Energy Storage and Emission Reduction: Catalyst Structure, Morphology, Performance, and Mechanism. J. Mater. Chem. A 2021, 9, 2526–2559. [Google Scholar] [CrossRef]
  108. Yin, J.; Jin, J.; Lin, H.; Yin, Z.; Li, J.; Lu, M.; Guo, L.; Xi, P.; Tang, Y.; Yan, C. Optimized Metal Chalcogenides for Boosting Water Splitting. Adv. Sci. 2020, 7, 1903070. [Google Scholar] [CrossRef] [Green Version]
  109. Xie, Y.; Li, X.; Wang, Y.; Li, B.; Yang, L.; Zhao, N.; Liu, M.; Wang, X.; Yu, Y.; Liu, J.-M. Reaction Mechanisms for Reduction of CO2 to CO on Monolayer MoS2. Appl. Surf. Sci. 2020, 499, 143964. [Google Scholar] [CrossRef]
  110. Wu, Y.-B.; Yang, W.; Wang, T.-B.; Deng, X.-H.; Liu, J.-T. Broadband Perfect Light Trapping in the Thinnest Monolayer Graphene-MoS2 Photovoltaic Cell: The New Application of Spectrum-Splitting Structure. Sci. Rep. 2016, 6, 20955. [Google Scholar] [CrossRef] [Green Version]
  111. Bernardi, M.; Palummo, M.; Grossman, J.C. Extraordinary Sunlight Absorption and One Nanometer Thick Photovoltaics Using Two-Dimensional Monolayer Materials. Nano Lett. 2013, 13, 3664–3670. [Google Scholar] [CrossRef]
  112. Choudhary, S.; Garg, A.K. Enhanced Absorption in MoS2/Hg0.33Cd0.66 Te Heterostructure for Application in Solar Cell Absorbers. IEEE Trans. Nanotechnol. 2019, 18, 989–994. [Google Scholar] [CrossRef]
  113. Abouelkhair, H.M.; Orlovskaya, N.A.; Peale, R.E. Growth of MoS2 Thin Films with Microdome Texture as Omnidirectional Light Trap for Solar Cell Applications. In Proceedings of the 2017 IEEE 44th Photovoltaic Specialist Conference (PVSC), Washington, DC, USA, 25–30 June 2017; IEEE: Washington, DC, USA, 2017; pp. 2324–2329. [Google Scholar]
  114. Lin, S.; Li, X.; Wang, P.; Xu, Z.; Zhang, S.; Zhong, H.; Wu, Z.; Xu, W.; Chen, H. Interface Designed MoS2/GaAs Heterostructure Solar Cell with Sandwich Stacked Hexagonal Boron Nitride. Sci. Rep. 2015, 5, 15103. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  115. Dey, M.; Dey, M.; Alam, S.; Das, N.K.; Matin, M.A.; Amin, N. Study of Molybdenum Sulphide as a Novel Buffer Layer for CZTS Solar Cells. In Proceedings of the 2016 3rd International Conference on Electrical Engineering and Information Communication Technology (ICEEICT), Dhaka, Bangladesh, 22–24 September 2016; IEEE: Dhaka, Bangladesh, 2016; pp. 1–4. [Google Scholar]
  116. Singh, R.; Giri, A.; Pal, M.; Thiyagarajan, K.; Kwak, J.; Lee, J.-J.; Jeong, U.; Cho, K. Perovskite Solar Cells with an MoS2 Electron Transport Layer. J. Mater. Chem. A 2019, 7, 7151–7158. [Google Scholar] [CrossRef]
  117. Iqbal, M.Z.; Nabi, J.; Siddique, S.; Awan, H.T.A.; Haider, S.S.; Sulman, M. Role of Graphene and Transition Metal Dichalcogenides as Hole Transport Layer and Counter Electrode in Solar Cells. Int. J. Energy Res. 2020, 44, 1464–1487. [Google Scholar] [CrossRef]
  118. Capasso, A.; Del Rio Castillo, A.E.; Najafi, L.; Pellegrini, V.; Bonaccorso, F.; Matteocci, F.; Cina, L.; Di Carlo, A. Spray Deposition of Exfoliated MoS2 Flakes as Hole Transport Layer in Perovskite-Based Photovoltaics. In Proceedings of the 2015 IEEE 15th International Conference on Nanotechnology (IEEE-NANO), Rome, Italy, 27–30 July 2015; IEEE: Rome, Italy, 2015; pp. 1138–1141. [Google Scholar]
  119. Xu, H.; Xin, L.; Liu, L.; Pang, D.; Jiao, Y.; Cong, R.; Yu, W. Large Area MoS2/Si Heterojunction-Based Solar Cell through Sol-Gel Method. Mater. Lett. 2019, 238, 13–16. [Google Scholar] [CrossRef]
  120. Liang, M.; Ali, A.; Belaidi, A.; Hossain, M.I.; Ronan, O.; Downing, C.; Tabet, N.; Sanvito, S.; EI-Mellouhi, F.; Nicolosi, V. Improving Stability of Organometallic-Halide Perovskite Solar Cells Using Exfoliation Two-Dimensional Molybdenum Chalcogenides. npj 2D Mater. Appl. 2020, 4, 40. [Google Scholar] [CrossRef]
  121. Abd Malek, N.A.; Alias, N.; Md Saad, S.K.; Abdullah, N.A.; Zhang, X.; Li, X.; Shi, Z.; Rosli, M.M.; Tengku Abd Aziz, T.H.; Umar, A.A.; et al. Ultra-Thin MoS2 Nanosheet for Electron Transport Layer of Perovskite Solar Cells. Opt. Mater. 2020, 104, 109933. [Google Scholar] [CrossRef]
  122. Shi, S.; Sun, Z.; Hu, Y.H. Synthesis, Stabilization and Applications of 2-Dimensional 1T Metallic MoS2. J. Mater. Chem. A 2018, 6, 23932–23977. [Google Scholar] [CrossRef]
  123. Cha, E.; Kim, D.K.; Choi, W. Advances of 2D MoS2 for High-Energy Lithium Metal Batteries. Front. Energy Res. 2021, 9, 645403. [Google Scholar] [CrossRef]
  124. Park, S.; Park, J.; Abroshan, H.; Zhang, L.; Kim, J.K.; Zhang, J.; Guo, J.; Siahrostami, S.; Zheng, X. Enhancing Catalytic Activity of MoS2 Basal Plane S-Vacancy by Co Cluster Addition. ACS Energy Lett. 2018, 3, 2685–2693. [Google Scholar] [CrossRef]
  125. Gao, M.-R.; Xu, Y.-F.; Jiang, J.; Yu, S.-H. Nanostructured Metal Chalcogenides: Synthesis, Modification, and Applications in Energy Conversion and Storage Devices. Chem. Soc. Rev. 2013, 42, 2986. [Google Scholar] [CrossRef]
  126. Lau, T.H.M.; Foord, J.S.; Tsang, S.C.E. 2D Molybdenum Disulphide Nanosheets Incorporated with Single Heteroatoms for the Electrochemical Hydrogen Evolution Reaction. Nanoscale 2020, 12, 10447–10455. [Google Scholar] [CrossRef]
  127. Li, X.L.; Li, T.C.; Huang, S.; Zhang, J.; Pam, M.E.; Yang, H.Y. Controllable Synthesis of Two-Dimensional Molybdenum Disulfide (MoS2) for Energy-Storage Applications. ChemSusChem 2020, 13, 1379–1391. [Google Scholar] [CrossRef]
  128. Wang, T.; Chen, S.; Pang, H.; Xue, H.; Yu, Y. MoS2 -Based Nanocomposites for Electrochemical Energy Storage. Adv. Sci. 2017, 4, 1600289. [Google Scholar] [CrossRef]
  129. Kamila, S.; Mohanty, B.; Samantara, A.K.; Guha, P.; Ghosh, A.; Jena, B.; Satyam, P.V.; Mishra, B.K.; Jena, B.K. Highly Active 2D Layered MoS2 -RGO Hybrids for Energy Conversion and Storage Applications. Sci. Rep. 2017, 7, 8378. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  130. Bu, F.; Zhou, W.; Xu, Y.; Du, Y.; Guan, C.; Huang, W. Recent Developments of Advanced Micro-Supercapacitors: Design, Fabrication and Applications. npj Flex Electron. 2020, 4, 31. [Google Scholar] [CrossRef]
  131. Chaojian, H.; Bo, L.; Qingwei, L.; Lijun, Y.; Yang, W.; Zhan, Y.; Lixin, D. Plasmon-Enhanced Photovoltaic Characteristics of Black Phosphorus-MoS2 Heterojunction. IEEE Open J. Nanotechnol. 2021, 2, 41–51. [Google Scholar] [CrossRef]
  132. Arora, Y.; Shah, A.P.; Battu, S.; Maliakkal, C.B.; Haram, S.; Bhattacharya, A.; Khushalani, D. Nanostructured MoS2/BiVO4 Composites for Energy Storage Applications. Sci. Rep. 2016, 6, 36294. [Google Scholar] [CrossRef] [PubMed]
  133. Moutaouakil, A.E.; Kang, H.-C.; Handa, H.; Fukidome, H.; Suemitsu, T.; Sano, E.; Suemitsu, M.; Otsuji, T. Room Temperature Logic Inverter on Epitaxial Graphene-on-Silicon Device. Jpn. J. Appl. Phys. 2011, 50, 070113. [Google Scholar] [CrossRef] [Green Version]
  134. Moutaouakil, A.E. Two-Dimensional Electronic Materials for Terahertz Applications: Linking the Physical Properties with Engineering Expertise. In Proceedings of the 2018 6th International Renewable and Sustainable Energy Conference (IRSEC), Rabat, Morocco, 5–8 December 2018; IEEE: Rabat, Morocco, 2018; pp. 1–4. [Google Scholar]
  135. Moutaouakil, A.E.; Watanabe, T.; Haibo, C.; Komori, T.; Nishimura, T.; Suemitsu, T.; Otsuji, T. Spectral Narrowing of Terahertz Emission from Super-Grating Dual-Gate Plasmon-Resonant High-Electron Mobility Transistors. J. Phys. Conf. Ser. 2009, 193, 012068. [Google Scholar] [CrossRef]
  136. Moutaouakil, A.E.; Suemitsu, T.; Otsuji, T.; Coquillat, D.; Knap, W. Room Temperature Terahertz Detection in High-Electron-Mobility Transistor Structure Using InAlAs/InGaAs/InP Material Systems. In Proceedings of the 35th International Conference on Infrared, Millimeter, and Terahertz Waves, Rome, Italy, 5–10 September 2010; IEEE: Rome, Italy, 2010; pp. 1–2. [Google Scholar]
  137. Moutaouakil, A.E.; Komori, T.; Horiike, K.; Suemitsu, T.; Otsuji, T. Room Temperature Intense Terahertz Emission from a Dual Grating Gate Plasmon-Resonant Emitter Using InAlAs/InGaAs/InP Material Systems. IEICE Trans. Electron. 2010, E93.C, 1286–1289. [Google Scholar] [CrossRef]
  138. El Moutaouakil, A.; Suemitsu, T.; Otsuji, T.; Videlier, H.; Boubanga-Tombet, S.-A.; Coquillat, D.; Knap, W. Device Loading Effect on Nonresonant Detection of Terahertz Radiation in Dual Grating Gate Plasmon-Resonant Structure Using InGaP/InGaAs/GaAs Material Systems. Phys. Status Solidi C 2011, 8, 346–348. [Google Scholar] [CrossRef]
  139. Tiouitchi, G.; Ali, M.A.; Benyoussef, A.; Hamedoun, M.; Lachgar, A.; Kara, A.; Ennaoui, A.; Mahmoud, A.; Boschini, F.; Oughaddou, H.; et al. Efficient Production of Few-Layer Black Phosphorus by Liquid-Phase Exfoliation. R. Soc. Open Sci. 2020, 7, 201210. [Google Scholar] [CrossRef] [PubMed]
  140. Moutaouakil, A.E.; Fukidome, H.; Otsuji, T. Investigation of Terahertz Properties in Graphene Ribbons. In Proceedings of the 2020 45th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), Buffalo, NY, USA, 8–13 November 2020; IEEE: Buffalo, NY, USA, 2020; pp. 1–2. [Google Scholar]
  141. Moutaouakil, A.E.; Suemitsu, T.; Otsuji, T.; Coquillat, D.; Knap, W. Nonresonant Detection of Terahertz Radiation in High-Electron-Mobility Transistor Structure Using InAlAs/InGaAs/InP Material Systems at Room Temperature. J. Nanosci. Nanotechnol. 2012, 12, 6737–6740. [Google Scholar] [CrossRef]
Figure 1. A schematic diagram for MoS2 energy applications.
Figure 1. A schematic diagram for MoS2 energy applications.
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Figure 2. MoS2 different crystal structures. (a) The top and side views of monolayer MoS2 for H and T phases. (b) Different lattice structures of MoS2 metallic phases 1T’, 1T’’, and 1T’’’. Adapted from [45]. American Physical Society 2018.
Figure 2. MoS2 different crystal structures. (a) The top and side views of monolayer MoS2 for H and T phases. (b) Different lattice structures of MoS2 metallic phases 1T’, 1T’’, and 1T’’’. Adapted from [45]. American Physical Society 2018.
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Figure 3. Properties of MoS2/p-Si junction. (a) Photoelectrochemical evaluation of the polarization J-V curves. (b) Tafel slopes. (c) EIS measurements. (d) Stability test over 20 cycles for 11 nm MoS2 thickness. (e) Energy band diagram of 11 nm MoS2 thickness. Reproduced from [70]. NPG Asia Materials 2019.
Figure 3. Properties of MoS2/p-Si junction. (a) Photoelectrochemical evaluation of the polarization J-V curves. (b) Tafel slopes. (c) EIS measurements. (d) Stability test over 20 cycles for 11 nm MoS2 thickness. (e) Energy band diagram of 11 nm MoS2 thickness. Reproduced from [70]. NPG Asia Materials 2019.
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Figure 4. A schmatic diagram of CO2 reduction mechanism using MoS2. (a) A schematic of MoS2 acting as a catalyst for CO production. (b) A schematic showing photogenerated activity on MoS2 surface and the chemical reactions for CO2 reduction, CO formation, and H2O splitting. Adapted from [102]. American Chemical Society 2018.
Figure 4. A schmatic diagram of CO2 reduction mechanism using MoS2. (a) A schematic of MoS2 acting as a catalyst for CO production. (b) A schematic showing photogenerated activity on MoS2 surface and the chemical reactions for CO2 reduction, CO formation, and H2O splitting. Adapted from [102]. American Chemical Society 2018.
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Figure 5. Structure and characteristics of organometallic-hallide pervoskite solar cells: (a) schematic of pervoskite solar cell with 2D MoS2 as a buffer layer; (b) power conversion efficiency of standard solar cell and modified cell with MoS2 layer; (c) Voc versus time for standard and modified cells; (d) Jsc versus time for standard and modified cells. Adapted from [120]. npj 2D Materials and Applications Nature 2020.
Figure 5. Structure and characteristics of organometallic-hallide pervoskite solar cells: (a) schematic of pervoskite solar cell with 2D MoS2 as a buffer layer; (b) power conversion efficiency of standard solar cell and modified cell with MoS2 layer; (c) Voc versus time for standard and modified cells; (d) Jsc versus time for standard and modified cells. Adapted from [120]. npj 2D Materials and Applications Nature 2020.
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Table 1. Solvothermal and hydrothermal synthesis techniques and their applications.
Table 1. Solvothermal and hydrothermal synthesis techniques and their applications.
Synthesis TechniqueSpecificationsApplicationReferences
SolvothermalVertical 1T-MoS2 nanosheets
interlayer spacing = 9.8 Å
Lithium-ion battery
Capacity = 666 mA h g−1 at
current density = 3500 mA g−1
Solvothermal1D metallic MoS2 nanotubeLithium-ion battery
Capacity = 1100 mA h g−1 at current density = 5000 mA g−1 and
capacity = 589 mA h g−1 at a high current density = 20,000 mA g−1
Solvothermal1T-MoS2 nanosheet arraysLithium-ion battery
Reversible specific capacity of
1789 mA h g−1 at 0.1 A g−1 and
a retained capacity of 853 mA h g−1 after 140 cycles at 1 A g−1
Low potential of 203 mV at 10 mA cm−2,
Tafel slope = 60 mV dec−1
SolvothermalSTable 1T-MoS2 slabs
grown on CdS nanorods
Photocatalytic HER
39 times better photocatalytic activity when compared to bare CdS
HydrothermalStabilized 1T-MoS2 layers
Mo–Mo bond length = 2.72 Å
Hydrogen evolution
21 times higher than
pure CdS and 3 times higher than annealed CdS: 2H-MoS2
HydrothermalMetallic MoS2 nanopetals(HER)
Overpotential = 210 mV at current density = 10 mA cm−2 and a Tafel slope of 44 mV dec−1
HydrothermalPure and stable metallic MoS2 nanosheetsHER
Current density of 10 mA cm−2
Overpotential = 175 mV
Tafel slope = 41 mV dec−1
Hydrothermal followed by solvothermal methodBoth 1T and 2H phasesHER
Overpotential = 180 mV
Tafel slope = 88 mV dec−1
Table 2. Energy storage applications of different MoS2 structures.
Table 2. Energy storage applications of different MoS2 structures.
Battery TypeMoS2 PhaseStructureCapacityReferences
Lithium-ion1T (Metallic)Nanotube-like MoS2 over grapheneDischarge capacity = 666 mA h g−1 at
current density = 3500 mA g−1
Lithium-ion1T (Metallic)MoS2 over carbon clothReversible specific capacity = 1789 mA h g−1 at 0.1 Ag−1
Retained capacity = 853 mA h g−1 after 140 cycles at 1 Ag−1
Lithium-ion1T (Metallic)1T MoS2 + (NiMoO4)Charged mass capacity = 940.1 mA h g−1
Discharged mass capacity = 941.6 mA h g−1
Lithium-ion1T (Metallic)Pure MoS2Specific capacity ≈ 935 mA h g−1 for 200 cycles at 5 A g−1
can be increased to 1150 mA h g−1
Sodium-ion1T (Metallic)MoS2-graphene-MoS2Capacity of 175 mA h g−1 at a high current density of 2 A g−1
Reverse capacity of ≈313 mA h g−1 at low current density of 50 mA g−1.
Stabilizes at current density = 313 mA h g−1 after 200 cycles
Sodium-ion2H and 1T MoS2Dual phase of 2H and 1T MoS2Capacity = 300 mA h g−1 after
200 cycles, and
coulombic efficiency = 99%
Sodium-ion2H phase transfers to 1T through chemical reactionsMoS2 and amorphous carbon (C)Capacity = 563.5 mA h g−1 at 0.2 A g−1
Coulombic efficiency = 86.6%
Cyclic stability = 484.9 mA h g−1 at 2 A g−1
Supercapacitor2D MoS2Spraying MoS2 nanosheets on Si/SiO2Area capacitance = 8 mF cm−2, and
volumetric capacitance = 178 F cm−3
SupercapacitorNanoflower-like MoS2 structure3D-graphene/MoS2 nanohybridDimensions 23.6 × 22.4 × 0.6 mm3
Specific capacitance (Csp) = 58 F g−1, energy density of 24.59 W h Kg−1, and power density of 8.8 W Kg−1 with operating window of 2.7 V (−1.5 to +1.2 V)
SupercapacitorBrush-like arrangement MoS2MoS2 nanowires over Ni foamThe high mass loading of MoS2 (30 mg cm−2) retains 92% of maximum capacitance after 9000 charge–discharge cycles at 5 A g−1[79]
SupercapacitorMoS2 QSsExfoliated MoS2 QSs lateral size (5–10 nm)Capacitance = 162 F g−1
Energy density = 14.4 W h kg−1
N-3DG and
Prepared using solvothermal processEnergy density = 140 W h kg−1 at 630 W kg−1, and 43 W h kg−1 at power density of 103 kW kg−1
Lifecycle over 10,000
Table 3. Energy generation applications of different MoS2 structures and composites.
Table 3. Energy generation applications of different MoS2 structures and composites.
Type of ReactionCatalyst UsedSpecificationReferences
HER(MoS2/CoSe2)Tafel slope = 36 mV dec−1
Onset potential = −11 mV
Exchange current density = 7.3 × 10−2 mA cm−2
HER1T MoS2Overpotential = 156 mV, at 10 mA cm−2
Tafel slope = 42.7 mV dec−1
HER/OERAmorphous Ni–Co complexes hybridized with 1T MoS2Overpotentials = 70 mV HER
and 235 mV for OER
at 10 mA cm−2
Tafel slope = 38.1 to 45.7 mV dec−1
OERRhombohedral MoS2 microspheres over conductive NiOverpotential ≈ 310 mV
Tafel slope ≈ 105 mV dec−1
OERMoS2 quantum dots (MSQDs)Overpotential = 280 mV
Tafel slope = 39 mV dec−1
CO2 reductionVertically aligned MoS2 nanoflakes
(2H and 1T phases coexist)
Overpotential = 54 mV
Reduction current density = 130 mA cm−2 at −0.764 V
CO2 reductionp–n junction
Bi2S3/MoS2 composite
Photocatalytic CO2 reduction
20 times higher than single
catalysts under visible light irradiation
CO2 reduction3R MoS2 nanoflower powderSynthesized using CVD
CO production < 0.01 μmol-gcat−1 hr−1 at 25 °C
which is negligible
Table 4. MoS2 applications in solar cells.
Table 4. MoS2 applications in solar cells.
StructureRole of MoS2Enhanced PropertyReferences
Wedge-shaped microcavity
Enhance the
cell performance
Enhance the light absorbance to above 90%[110]
(Hg0.33 Cd0.66 Te) and
monolayer MoS2
Enhance the
cell performance
Shift the cell absorbance to visible light range[112]
Microdome texture on MoS2 thin filmEnhance the
cell performance
Decreases reflections and traps light for incident angles (0–50)[113]
MoS2/GaAs over boron nitrideEnhance the
cell performance
PCE increased to 9.03%[114]
MoS2 spray coating over perovskite cellsHTLPCE = 3.9%[118]
5 monolayer MoS2 nanosheets onto indium tin oxide ITO substrateETLJsc = 16.24 mA cm−2
Voc = 0.56 V
(fill-factor) FF = 0.37
PCE = 3.36%
ZnO-MoS2-CZTSBufferJsc = 29.42 mA cm−2
Voc = 1.01 V
FF = 0.574
Efficiency = 17.03%
Organometallic-halide perovskite solar cellBufferJsc ≈ 22 mA cm−2
Voc ≈ 0.96 V
FF ≈ 0.6
PCE = 14.9%
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Samy, O.; El Moutaouakil, A. A Review on MoS2 Energy Applications: Recent Developments and Challenges. Energies 2021, 14, 4586.

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Samy O, El Moutaouakil A. A Review on MoS2 Energy Applications: Recent Developments and Challenges. Energies. 2021; 14(15):4586.

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Samy, Omnia, and Amine El Moutaouakil. 2021. "A Review on MoS2 Energy Applications: Recent Developments and Challenges" Energies 14, no. 15: 4586.

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