Heterogeneous Nanostructure Based on 1T-Phase MoS2 for

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Heterogeneous Nanostructure Based on 1T Phase MoS2 for Enhanced Electrocatalytic Hydrogen Evolution Zhipeng Liu, Zhichao Gao, Yuhua Liu, Maosheng Xia, Runwei Wang, and Nan Li ACS Appl. Mater. Interfaces, Just Accepted Manuscript • Publication Date (Web): 11 Jul 2017 Downloaded from http://pubs.acs.org on July 11, 2017

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ACS Applied Materials & Interfaces

Heterogeneous Nanostructure Based on 1T Phase MoS2 for Enhanced Electrocatalytic Hydrogen Evolution Zhipeng Liu, † Zhichao Gao, † Yuhua Liu, † Maosheng Xia, † Runwei Wang, ‡ Nan Li*† † Key Laboratory of automobile materials (Jinlin University), Ministry of Education, College of Materials Science and Engineering, Jinlin University, 2699 Qianjin Street, Changchun, 130012, P. R. China ‡ State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University, Changchun, 130012, P. R. China KEYWORDS: hydrogen evolution reaction, electrocatalysts, 1T phase MoS2, heterogeneous nanostructure, hydrothermal synthesis, water splitting.

ABSTRACT

As an electrocatalyst, conventional 2H phase MoS2 suffers from limited active sites and inherently low electroconductivity. Phase transitions from 2H to 1T have been proposed as an effective strategy to optimize the catalytic activity. However, complicated chemical exfoliation is generally involved. Here, MoS2 heterogeneous phase nanosheets with a 1T phase (1T/2H-MoS2)

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generated in situ were prepared through a facile hydrothermal method. The locally introduced 1T phase MoS2 can not only contribute more active sites but also markedly promote the electronic conductivity. Because of this unique structure, the as-synthesized 1T/2H-MoS2 nanosheets exhibit remarkable performance for the hydrogen evolution reaction with a small overpotential of 220 mV at 10 mA/cm2, a small Tafel slope of 61 mV/dec and robust stability. This work facilities the development of two-dimensional heterogeneous nanostructure with enhanced applications.

1. INTRODUCTION Sustainable hydrogen production through electrochemical water splitting has been proposed as an ideal solution for energy crises and global warming1-3 However, if electrochemical water splitting is to achieve satisfactory efficiency, it requires an appropriate catalyst with low cost as well as high activity in the hydrogen evolution reaction (HER).4-6 During the past few years, molybdenum disulfide (MoS2) has received considerable attention because of its high activity, tunable properties, and abundance.7-9 Commonly, MoS2 occurs in a thermodynamically stable 2H phase with a lamellar hexagonal structure, in which the individual S–Mo–S layers weakly bond with each other through van der Waals forces.10, 11 Nevertheless, as an electrocatalyst, this 2H phase suffers from scarce active sites that are limited to edges, and the basal planes are chemically inert.12-14 Besides, the 2H phase is a semiconductor whose deficient electroconductivity and anisotropic transport have detrimental effects on its catalytic performance.15-17 Unlike its 2H phase counterpart, 1T phase MoS2, which occurs as a octahedral structure, possesses some highly desirable properties such as proliferated active sites on basal planes and metallic electronic conductivity.18-20 Transforming the 2H to the 1T phase, thus, has


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been considered an effective approach to enhancing the HER performance of MoS2 catalysts.16, 18, 19

However, 1T phase MoS2 is metastable in nature and can be obtained only through specific

methods.21, 22 Generally, three strategies are proposed for fabricating 1T phase MoS2: chemical lithium intercalation/extraction exfoliation,23, 24 electron beam irradiation,25 and plasmonic hot injection.26 27 Of these three, chemical lithium intercalation is still the most effective and widely used strategy. But the preparation procedures of chemical lithium intercalation are relatively complicated, the synthesis process can typically last 3 days as the intercalator (n-butyl lithium) tend to form dimeric, trimeric or higher aggregates, which diffuse slowly into the interlayers of MoS2 crystals. Besides, both the intermediary involved (e.g. LixMoS2) and intercalator of nbutyllithium are dangerous materials and highly pyrophoric in air.28-30 Recently, several bottomup routes have been reported as viable approaches to producing 1T phase MoS2.28-34 Nevertheless, it still remains challenging to synthesize 1T phase MoS2 based electrocatalys following a cost-efficient tail to meet the practical applications. In this work, we developed a novel route to synthesis heterogeneous electrocatalysts based on 1T phase MoS2 for efficient hydrogen evolution. Metallic 1T phase MoS2 was generated in-situ via a one-step hydrothermal synthesis with the present of propionic acid. Arose from the high activity and good conductivity of 1T phase, the as synthesized heterogeneous 1T/2H-MoS2 nanosheets exhibited remarkable catalytic activity and favorable kinetics, outperforming pristine 2H-MoS2 nanosheets. Moreover, this synthesis route of 1T phase MoS2 is high-yield, costefficient and easy to operate, which endows this route great promise for practical applications. 2. EXPERIMENTAL SECTION


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2.1 Synthesis of Catalysts 1T/2H-MoS2 nanosheets were prepared through a facile one-step hydrothermal reaction. In a typical synthesis procedure, 1 mmol of sodium molybdate dehydrate (Na2MoO4·2H2O) and 3 mmol of thiourea (CS(NH2)2) were dissolved in a mixed solvent containing 16 mL of deionized water and 8 mL of propionic acid. The mixture was magnetically stirred for 10 min and then poured into a 50 mL Teflon-lined autoclave and heated in an electric oven at 180 °C for 4 h. The autoclave was then allowed to cool to room temperature naturally, and the product was collected after centrifugation. Finally, black 1T/2H-MoS2 nanosheets were rinsed with deionized water and ethanol several times and then dried at 60 °C under vacuum. In a control experiment, 2H-MoS2 nanosheets were synthesized from identical precursors through hydrothermal treatment at 220 °C for 24 h by using deionized water as a solvent. 2.2 Characterization X-ray diffraction (XRD) measurements were performed using a DX2700 diffractometer with a Cu Kα radiation source (λ = 0.15406 nm). X-ray photoelectron spectra were obtained from an ESCALAB 250 electron spectrometer with an Al Kα radiation source (hν = 1486.6 eV). Raman spectra were collected using a micro-Raman spectrometer (Renishaw) with a laser wavelength of 532 nm at 0.2 mW. Scanning electron microscopy (SEM) analysis was conducted with a JEOL JSM-6700F microscope at a 10 kV acceleration voltage. Transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM) were conducted using a JEOL JEM-2100F microscope at a 200 kV acceleration voltage. Specific surface area data were obtained from a JW-BK222 automated sorption system by using the Brunauer–Emmet–Teller (BET) method. 2.3 Electrochemical Measurements Electrochemical tests were performed with a threeelectrode system in a N2-saturated 0.5 M H2SO4 aqueous solution on a CHI660 electrochemical workstation. Catalyst inks were prepared by ultrasonically dispersing 5 mg of MoS2 powder in a


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mixture of 1 mL of ethanol and 50 µL of Nafion. Then, 5 µL of the catalyst ink was drip-coated on a glassy carbon electrode and dried at room temperature for 2 h. The catalyst-coated glassy carbon was applied as a working electrode; a graphite rod and a saturated Hg/HgCl2 sample served as the counter electrode and reference electrode, respectively. Linear sweep voltammetry (LSV) measurements were carried out from 0 to −0.5 V versus a reversible hydrogen electrode (RHE) at a scan rate of 5 mV·s-1, and cyclic voltammetry (CV) measurements were recorded from 0.1 to 0.28 V versus an RHE at a series of scan rates ranging from 20 mV·s-1 to 180 mV·s-1 to evaluate the double-layer capacities of the samples. Tafel slopes were derived from the polarization curves by fitting the polarization curves data to the Tafel equation η = a + b·log j (where η is the overpotential, j is the current density, and b is the Tafel slope). Electrochemical durability was determined by performing CV at a scan rate of 100 mV s1

. Time-dependent current density was obtained under a static overpotential of 200 mV. Nyquist

plots were measured with frequencies ranging from 100 kHz to 0.01 Hz at an overpotential of 200 mV. The impedance data were fitted to a simplified Randles circuit. 3. RESULT AND DISCUSSION The 1T/2H-MoS2 heterogeneous nanosheets was synthesized through a facile one-step hydrothermal method by using sodium molybdate dehydrate and thiourea as starting materials. A mixed solution of propionic acid and water was employed as a solvent (Figure 1). Field-emission scanning electron microscopy (FESEM) and transmission electron microscopy TEM provided insight concerning the microstructure of the 1T/2H-MoS2 sample. It is composed of ultrathin nanosheets with a width of 100–200 nm and thickness of approximately 10 nm. Ripples and corrugations were clearly observed along the nanosheets, as a result of the ultrathin layered


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structure. For comparison, a pristine 2H phase MoS2 sample (2H-MoS2) was prepared using deionized water as a solvent (Figure 1); electron microscopy images showed a morphology similar to that of 1T/2H-MoS2 (Figure S1a-c in the Supporting Information). The phase structures of 1T/2H-MoS2 and 2H-MoS2 were investigated through XRD. For both samples, the XRD patterns showed the characteristic peaks for 2H phase MoS2 (JCPDS 37-1492). The peaks in 1T/2H-MoS2 showed obvious broadening, which indicated smaller nanodomains.35, 36 The peaks of 1T phase were invisible. This is probably due to the similar peak positions of the 2H and 1T phases, and the widened peaks.37, 38

Figure 1. Schematic of the preparation of 1T/2H-MoS2 and 2H-MoS2. To validate the successful formation of heterogeneous nanostructure, the in-plane structure of 1T/2H-MoS2 was characterized through HRTEM analysis. As shown in Figure 2d, two distinct lattice matrices were identified in the basal plane; 1T phase domains are marked by red circles. A magnified view (Figure 2e) reveals the trigonal lattice (octahedral coordination) of the 1T phase.38, 39 The average size of the 1T phase regions measured through HRTEM was approximately 5 nm, which is in favorable agreement with the broad XRD peaks. The areas marked by blue circles exhibit two 0.28 nm lattice fringes at a 60° angle to each other, which


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corresponds to the (100) and (010) planes of 2H phase MoS2. This feature is consistent with a common honeycomb lattice of trigonal prismatic coordination (Figure 2f).40 In addition to crystalline 1T and 2H domains, defects were observed, especially on the interface between the 1T and 2H phases. These defects were attributed to lattice misfit between different polymorphs. By contrast, the 2H-MoS2 sample exhibited a nearly perfect honeycomb lattice, which ruled out the presence of the 1T phase MoS2 (Figure S1d, e).

Figure 2. (a) Typical FESEM and (b) TEM images of 1T/2H-MoS2 nanosheets; (c) XRD patterns of 1T/2H-MoS2 and 2H-MoS2 nanosheets; (d) typical HRTEM image of the basal plane of 1T/2H-MoS2 nanosheets, and the corresponding zoom-in views of 1T (e) and 2H (f) lattices. The presence of 1T phase in the 1T/2H MoS2 heterogeneous nanostrcture was further attested by performing X-ray photoelectron spectroscopy (XPS) analysis (Figure 3a). The Mo 3d corelevel spectrum of 1T/2H-MoS2 nanosheets was deconvoluted into four peaks. Two weak peaks located at 232.4 eV and 229.2 eV correspond to the characteristic 3d5/2 and 3d3/2 of Mo4+ species


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from the 2H phase, both of which were also detected in the 2H MoS2 sample. A predominant doublet observed at 231.5 eV and 228.3 eV revealed the presence of the 1T phase. In comparison with the peaks of 2H-MoS2, these two peaks shifted by approximately 0.9 eV to a lower bonding energy. In the S 2p region of the 1T/2H-MoS2 spectrum, an additional doublet shifted downward by approximately 0.9 eV relative to the peaks of 2H-MoS2 was observed (Figure S2). Such peak shifts might arise from defects or 1T phase MoS2.41-44 Raman spectroscopy provides additional evidence of coexistence of two phases in the 1T/2H-MoS2 nanosheets (Figure 3b). The characteristic peaks appearing in both samples at 280 cm-1, 375 cm-1, and 404 cm-1 are associated with the E1g, E12g, and A1g bands of the 2H phase, respectively.45, 46 The 1T phase was identified by peaks at 235 cm-1 and 336 cm-1.34, 38 Combining the HRTEM, XPS and Raman analyses, the present of 1T phase MoS2 in 1T/2H-MoS2 nanosheets was confirmed. The concentration of 1T phase was estimated to be approximately 72% according to the XPS result, which is comparable with that of chemically exfoliated MoS2 nanosheets.24, 37, 47

Figure 3. (a) High-resolution Mo 3d core level XP spectra and (b) Raman spectra of 1T/2HMoS2 and 2H-MoS2 nanosheets.


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As expected, the 1T/2H-MoS2 heterogeneous nanosheets showed notable enhancement in catalytic performance. The HER activity of the 1T/2H-MoS2 was measured through LSV. For comparison, the activity of 2H-MoS2 and Pt/C (20 wt%) was also measured. The polarization curves in Figure 4a show that, although it still lagged behind Pt/C, 1T/2H-MoS2 exhibited remarkable catalytic activity. The as-synthesized 1T/2H-MoS2 delivered a small onset potential of approximately 120 mV and an overpotential of 220 mV to reach a current density of 10 mA/cm2, comparable to the chemical exfoliated 1T phase MoS2 and superior to many MoS2 based catalysts (Table S1). By contrast, 2H-MoS2 showed an onset potential near 200 mV, in accordance with previous reports, and substantial H2 evolution (current density = 10 mA/cm2) was not achieved until an overpotential of 320 mV was applied.19 This marked enhancement in catalytic activity proved the notable role of the 1T phase. Corresponding Tafel slopes (Figure 4b) further reflected the positive impact of the incorporated 1T MoS2. Tafel slopes of 61 mV/dec and 155 mV/dec were derived for 1T/2H-MoS2 and 2H-MoS2, respectively. The distinct results suggested that the MoS2 heterogeneous nanostructure containing the 1T phase increases the reaction rate.48, 49


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Figure 4. Electrocatalytic performance of 1T/2H-MoS2 and 2H-MoS2. (a) Polarization curves; (b) corresponding Tafel slopes; (c) linear regressions of differences in current density (J = Ja – Jc) at 0.2 V plotted against the scan rate for estimation of the effective surface area; (d) electrochemical impedance spectroscopy Nyquist plots and corresponding equivalent circuits (inset). To investigate the effect of the 1T phase in the heterogeneous nanostructure, the effective surface areas of the catalysts were estimated on the basis of double-layer capacitance (Cdl) through CV measurements (Figure S3).50 As displayed in Figure 4c, the Cdl value of 1T/2HMoS2 is almost 25.3 times higher than that of 2H-MoS2, corresponding to a much larger active surface area. Because the BET-specific surface areas of the two catalysts are comparable (75 m2/g and 40 m2/g for 1T/2H-MoS2 and 2H-MoS2, respectively) according to nitrogen adsorption measurements, we believe that the marked increase in active surface area is associated with the incorporation of the 1T phase, which provides abundant active sites in the basal plane. The


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exchange current density for 1T/2H-MoS2 and for 2H-MoS2 was calculated as 4.43×10-4 A/cm2 and 2.03×10-4 A/cm2, respectively. The higher exchange current density further proved that the locally introduced 1T phase can promote electron transport throughout the catalysts. Figure 4d shows the Nyquist plots of the 1T/2H-MoS2 and 2H-MoS2 nanosheets. The charge-transfer resistance (Rct) data of the samples were estimated from the semicircle in the low-frequency zone. The 1T/2H-MoS2 heterogeneous nanosheets exhibited substantially lower Rct (approximately 30 Ω) than that of the 2H-MoS2 nanosheets (approximately 2000 Ω), revealing the improved conductivity due to the incorporation of the metallic 1T phase, which can lead to a higher HER rate. The quantity of 1T phase was then regulated by adjusting the hydrothermal temperature. At elevated temperature of 220 °C, the quantity of 1T phase reduced to approximately 17%, yet the morphology was similar to that obtained at 180 ºC (Figure S7). As a result, the catalytic performance of this sample showed a decreasing trend with higher overpotential and Tafel slope, less active sites and lower electroconductivity (Figure S9). This result proved that the HER properties of the heterogeneous nanosheets are closely related to the quantity of 1T phase. The electrochemical stability of the 1T/2H-MoS2 heterogeneous nanostructure was evaluated by conducting the LSV process for 1000 cycles. As depicted in Figure 5a, the curve of 1T/2HMoS2 after 1000 cycles is nearly coincident with the initial one, demonstrating its favorable stability as an HER catalyst. Chronoamperometric measurement confirmed its remarkable longterm electrochemical stability. The catalyst retained 80% of the current density, as evidenced by its I–t curve, after 10 h of testing under a static overpotential of 200 mV (inset of Figure 5). The microstructure of the sample after stability test was further investigated by SEM, which displays the well retained nanosheet morphology (Figure S4a). XPS and Raman spectra also demonstrate


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the quantity of 1T phase was almost unchanged after the stability test (Figure S4b, c). These results confirm the good structural and composition stability of 1T/2H-MoS2. According to previous reports, 1T phase MoS2 prepared through chemical exfoliation is dynamically unstable and tends to transform to the 2H phase rapidly because of S–S van der Waals interactions. Therefore, we aerated a 1T/2H-MoS2 sample for 30 days and then evaluated its structural durability through LSV measurement (Figure S4d). Even though its stability was inferior to that of a freshly prepared sample, considerable activity was retained. This high stability can be attributed to its unique structure. The as-synthesized nanosheets are of multilayered structure, which are more favorable in thermodynamics than the monolayer of chemically exfoliated 1T phase MoS2. Besides, the 1T phase domains are embraced by amorphous regions and defects, as illustrated in the HRTEM image (Figure 2d). Therefore, the misfit between different polymorphs (1T and 2H) is largely avoided and the lattice stress in the structure is partially released, which stabilizes the 1T phase.


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Figure 5. Stability of 1T/2H-MoS2 nanosheets. LSV curves of 1T/2H-MoS2 before and after 1000 CV cycles and time-dependent current density curve for 1T/2H-MoS2 at an overpotential of 200 mV (inset). On the basis of the aforementioned results, the 1T/2H-MoS2 heterogeneous nanosheets outperformed its 2H-MoS2 counterpart with enhanced activity, favorable kinetics, proliferated active sites and promoted conductivity. These desirable properties are attributed mostly to the remarkable feature of 1T phase MoS2 with proliferated active sites on basal planes and promoted electronic conductivity. Moreover, the small size of 1T and 2H nanodomains and the resulting abundant edges provides additional active sites. Furthermore, the introduction of 1T phase is associated with increase of defects and it offers more unsaturated sites for catalysis. In addition to high catalytic activity, the 1T/2H-MoS2 exhibited higher stability relative to chemically exfoliated 1T phase MoS2 owing to its multilayered structure and the existence of amorphous regions and defects. Notably, the synthesis route is quite scalable, high-yield and cost-efficient. The raw materials involved are inexpensive and the hydrothermal treatment is easy to operate. These aspects render the as-synthesized 1T/2H-MoS2 heterogeneous nanosheets competitive earth abundant electrocatalysts. For the mechanism underlying the formation of the 1T phase, we propose a possible reductionfirst hypothesis in which the Mo(VI) species is reduced to Mo(IV), and then followed by sulfurization. We found that when Na2MoO4·2H2O and CS(NH2)2 were dissolved in the mixed solvent (H2O:CH3COOH = 2:1) at room temperature, the solution turned from colorless to blue after several hours. A similar blue solution was obtained after 1.5 h of hydrothermal treatment in the same solution (Figure S5). The change in color suggests the reduction of Mo (VI), which is


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expected to be associated with the reducibility of CS(NH2)2 in acidic conditions, as shown in the following equation: SC(NH2)2+8H++MoO42-→Mo4++S↓+2H2O+2NH4++CO2↑ The valence of Mo species in the solution was further investigated through CV measurement (Figure 6a). The CV curve of the pristine solvent (black trail) was featureless, whereas an anodic peak emerged at approximately 0.73 V when Na2MoO4·2H2O and CS(NH2)2 were dissolved in the solvent at room temperature (red trail), demonstrating that some Mo species with a lower oxidation state, such as Mo(V) or Mo(IV), was present in the solution. When this solution was further hydrothermally treated for 1.5 h, a downward shift in the anodic peak was observed. This striking shift indicated a lower valence of the Mo species, which was most likely Mo(IV). As illustrated in Figure 6b, Mo(IV) occurs in an octahedral coordination in [MoO6]. Therefore, it is a key species closely relating to the formation of 1T MoS2. During the subsequent sulfurization procedure, O2- ligands in the [MoO6] were locally replaced by S2-, and the octahedral coordination structure was retained, leading to the formation of 1T-phase MoS2. For a reference experiment, Na2MoO4·2H2O and CS(NH2)2 were dissolved in pure water and hydrothermally treated for 1.5 h. Neither a change in color of the solution nor an anodic peak in the CV curve was observed, ruling out the presence of Mo(IV). Consequently, only 2H phase MoS2 was detected, further proving the essential role of Mo(IV) in the formation of 1T MoS2. These distinct phenomena induced by propionic acid also manifested it as a critical element in the hydrothermal system to get 1T phase MoS2. Propionic acid can provide an appropriate acidic condition and result in suitable reducibility of thiourea for the formation of Mo(IV). The ratio of propionic acid was then modulated to investigate its influence on 1T phase MoS2. In term of


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product obtained at mixed solvent with a ratio of propionic acid:water = 2:1 (denoted as 1T/2HMoS2-2:1), the quantity of 1T phase is approximately 70% (Figure S9c), which is comparable to that in 1T/2H-MoS2-1:2. While the quantity of 1T phase in 1T/2H-MoS2-1:5 is relatively lower (43%, Figure S9d). This variation tendency suggests propionic acid only affects the formation of 1T phase MoS2 at a relative low proportion, but has no effect under high proportion. Notably, the ratio of propioinc acid in the mixed solvent influences the morphology of products simultaneously (Figure S9a,b), revealing propionic acid also serves as a morphology control agent.

Figure 6 (a) Cyclic votammograms of various solutions in the region of 0.4 to 1.3 V vs RHE. (b, d, e) Schematic illustrations for the evolution process of 1T phase based on Mo (Ⅳ) and (c) the octahedral model of [MoO6]. Along with consumption of the reduction agent, little Mo(IV) was obtained and 2H phase MoS2 emerged, which may account for the phase incorporation in the final products. To prove the hypothesis, we further prolonged the hydrothermal treatment for 8 h. A similar nanosheet


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morphology was observed, and the trigonal lattice of 1T phase MoS2 was identified. However, both the XPS spectra and Raman shifts revealed a decreasing trend for the quantity of the 1T phase (Figure S6b, c). These noteworthy differences induced by extended hydrothermal treatment indicated that 1T phase MoS2 is probably formed at an early stage of the reaction process, whereas 2H MoS2 is formed in reactions with prolonged hydrothermal time. Nevertheless, the catalytic performance was the same for samples prepared with even longer (12 h) hydrothermal treatment (Figure S6d), indicating a similar concentration of 1T phase MoS2. This result proved that 1T phase MoS2 is stable in the hydrothermal process and 2H MoS2 is generated in situ rather than converted from 1T MoS2. All of the observations agree well with the reduction-first-route hypothesis. 4. CONCLUSION In summary, an efficient 1T/2H-MoS2electrocatalyst was successfully synthesized by implanting 1T MoS2 in 2H MoS2nanosheets in situ through a scalable hydrothermal method. Because of the incorporation of the metallic 1T phase, the 1T/2H MoS2 catalyst possesses more active sites as well as improved intrinsic electroconductivity relative to 2H-MoS2. Consequently, a remarkable performance with a small overpotential and favorable kinetics for the HER was achieved. Furthermore, a reduction-first-route growth mechanism for the formation of 1T MoS2wasproposed. This work may provide a new approach to developing two-dimensional layered hetero-nanostructures with enhanced applications. ASSOCIATED CONTENT Supporting Information.


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The following files are available free of charge. SEM and (HR)TEM images of 2H-MoS2. XRD patterns, XPS spectra of 1T/2H-MoS2 and 2HMoS2 and other reference samples. Voltammograms of 1T/2H-MoS2 and 2H-MoS2 at various scan rates. Polarization curves of samples obtained with various reaction time, the freshly prepared 1T/2H-MoS2 and that aged for one month. (PDF) AUTHOR INFORMATION Corresponding Author *Email：[email protected]

ORCID Nan Li: 0000-0002-3614-9558 Funding Sources National Natural Science Foundation of China (No. 21673097). Notes The authors declare no competing financial interest. ACKNOWLEDGMENT This study was supported by the National Natural Science Foundation of China (No. 21673097). REFERENCES (1)

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(2)

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Heterogeneous Nanostructure Based on 1T-Phase MoS2 for

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