2D Single Crystal WSe2 and MoSe2 Nanomeshes with Quantifiable

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2D Single Crystal WSe and MoSe Nanomeshes with Quantifiable High Exposure of Layer Edges from 3D Mesoporous Silica Template Wei-Ming Xu, Kejie Chai, Yi-wen Jiang, Jianbin Mao, Jun Wang, Pengfei Zhang, and Yifeng Shi ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.9b03435 • Publication Date (Web): 19 Apr 2019 Downloaded from http://pubs.acs.org on April 20, 2019

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ACS Applied Materials & Interfaces

2D Single Crystal WSe2 and MoSe2 Nanomeshes with Quantifiable High Exposure of Layer Edges from 3D Mesoporous Silica Template Weiming Xu,*,† Kejie Chai,† Yi-wen Jiang,† Jianbin Mao,† Jun Wang,† Pengfei Zhang† and Yifeng Shi*,‡ †College of Material Chemistry and Chemical Engineering, Hangzhou Normal University, Hangzhou 311121, China ‡Hangzhou Nanosemi Nanomaterials Co., Ltd., Hangzhou, Zhejiang 310010, China

KEYWORDS: transition metal chalcogenides, nanomesh, nanocasting, mesoporous silica KIT-6, hydrogen evolution reaction, active sites

ABSTRACT: The design and fabrication of layered transition metal chalcogenides with high exposure of crystal layer edges is one of the key paths to achieve distinctive performances in their catalysis and electrochemistry applications. Two dimensional WSe2 and MoSe2 nanomeshes with orderly arranged nanoholes were synthesized by using a mesoporous silica material KIT-6 with three dimensional mesoporous structure as a hard template via nanocasting strategy. Each piece of the nanomesh is a single crystal and its c-axis is always perpendicular to the nanomesh plane. The highly porous structure brings these nanomeshes extremely high exposure of layer edges, and the well-defined nanostructure provides an opportunity to quantitatively estimate the specific length

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of the crystal layer edges for the WSe2 and MoSe2 nanomeshes synthesized in this work, which are estimated to be 3.8×1010 and 6.0×1010 m g-1, respectively. The formation of a 2D sheet-like nanomesh structure inside a 3D confined pore space should be attributed to synergistic effect from the crystal self-limitation growth that caused by their layered crystal structures and the spacelimitation effect coming from the unique pore structure of the KIT-6 template. The catalytic activities of the nanomeshes in electrocatalytic hydrogen evolution reaction were also investigated.

INTRODUCTION Layered transition metal dichalcogenides (TMDs) attracted lots of research interest in the last two decades because of their great potentials in sensor, Li/Na/Mg ion batteries, semiconductor devices, and catalysis.1-5 TMDs consist of layered crystal structure with strong in-plane covalent bonding and weak out-of-plane van der Waals force.6 Their edge planes possess much higher surface energy than the basal planes, because all the crystal layer edges are full of dangling bonds.7 Therefore, it was believed for a long time that the layer edges of TMDs crystals provide active sites for the related catalytic reactions, including hydrodesulfurization, hydrogen evolution reaction (HER), oxygen reduction reaction (ORR), methane conversion, etc.7-10 Recently, both theoretical calculation and experimental analysis provided more and more solid evidences for this conjecture.11-13 Consequently, it became a well-tried effective strategy to improve their catalytic activity by fabricating nanostructured TMDs with higher exposure of layer edges to the greatest extent possible.8,14,15 Beside the catalysis application, a higher exposure of layer edge also favors for the kinetics of electrochemical process in case of TMDs are used as electrode materials for Li, Na and Mg ions batteries.16-19 The layer edge exposure ratio becomes a decisive factor in pursuing better performance in these fields.20 However, it was limited by the spontaneously trend of


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reducing surface energy during the crystal growth, and therefore the task of increasing layer edges is still a great challenge. Unlike the acid-base catalysts, the active site number estimation is much hard for redox type catalysts, and therefore the specific surface area is a commonly used index in this case. However, the extremely anisotropic crystal structure of TMDs makes this index lost its validity for TMDs. For example, as the sizes were decreased into submicrometer scale, TMDs materials tend to form fullerene-like nanostructures, such as nanotubes and nano-onions, in which the crystal layers were rolled and pieced together, and thereafter the layer edges were thus mostly eliminated.21 As a consequence, these materials contain almost no layer edge even though they possess a very high specific surface area.22 In addition, TMDs tend to form sheet-like particles with c-axis perpendicular to the sheet plane, in which the layer edges only exist on the side surface, i.e. edge planes, with very tiny occupation ratio of the entire surface.23,24 In an extreme case, if a large TMDs single crystal was perfectly exfoliated into single layers, the surface area will dramatically increase for several orders, while the total length of the layer edges keep unchanged at all. Although lots of efforts have been made in fabricating various nanostructured TMDs with high exposure of layer edges in the past decade, the difficulty in quantitative estimation of layer edges in these materials holds back the fundamental research in this filed.8,15,20,25,26 Recently, Cui’s group reported a synthesis of MoS2, MoSe2 and WSe2 film with vertically aligned crystal layers on various substrates, which provided a very high density of layer edges on top of the films and therefore possess excellent catalytic performance in HER.14,27 However, the utilization of substrate as well as the need of depositing W/Mo thin layer with controlled thickness on the substrate in the first step both make the synthesis can hardly be scaled up or be extended to


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prepare powder form catalyst with large quantity. Large scale fabrication of TMDs materials with quantifiable high exposure of layer edges is still a great challenge.15 In this paper, we report a novel and large scale synthesis of 2D MSe2 (M: W, Mo) nanomeshes with orderly arranged nanoholes by using a 3D mesoporous silica KIT-6 as hard template via nanocasting strategy. Each piece of the nanomeshes fabricated in this work is a single crystal of hexagonal phase MSe2 and its c-axis is always perpendicular to the nanomeshes’ plane. This special structure characteristic as well as the highly porous structure provides an extremely high exposure of crystal layer edges. The specific length of the exposed layer edges for WSe2 and MoSe2 nanomeshes can be directly estimated from TEM images to be 3.8×1010 and 6.0×1010 m g-1, respectively. Thanks to the utilization of 3D mesoporous material as hard template, more than 10 g of product can be produced in one batch synthesis in a small tube furnace (inner diameter: 30 mm). The well-defined structure and the high exposure of active sites make it a promising model material for fundamental research in their applications. RESULTS AND DISCUSSION Mesoporous silica material KIT-6 with a 3D double-gyroid pore structure (Figure 1a) was prepared according to literature report.28 Its XRD pattern (Figure S1) and TEM images (Figure S2) clearly show that the KIT-6 hard template possess a highly ordered mesostructure with cubic Ia3d symmetry.29 The cell parameter of the mesostructure estimated from its XRD pattern is 21.1 nm. Nitrogen sorption analyses (Figure S3) reveal that the specific surface area, pore volume and mean pore size of the KIT-6 template are 635 m2 g-1, 1.12 cm3 g-1 and 8-10 nm, respectively. All these values are very close to those reported in literatures, indicating the template synthesized in this work possess the same mesostructure as described in literatures.28


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Figure 1. Structure models of mesoporous silica template KIT-6 and its possible replicas. Phosphotungstic acid (PTA), the metal precursor, was impregnated into the pore space of the KIT-6 hard template under the help of ethanol solvent as described elsewhere.30 Then the PTA@KIT-6 intermediate was mixed with Se powder and loaded into a quartz boat. The mixture was rapidly heated up to a desired temperature in a tube furnace by directly putting the tube into a hot tube furnace, which has been pre-heated to 300 - 800°C. This special operation brought an ultrafast heating rate, thereby, the PTA@KIT-6 and Se powder mixture reached the reaction temperature in less than 5 min. The initial heating rate was even higher than 200°C min-1 in the first 1-2 minutes. Selenium melted and reacted with a H2 gas flow inside the tube, forming high concentration of H2Se inside the tube chamber. PTA precursor was converted to crystalline WSe2 by reacting with H2Se gas.31 In the final step, silica template was removed by HF aqueous solution as described in experimental section. XRD analysis reveals that the synthesized WSe2 nanomesh material (denoted as NSM-1) prepared from 400 to 700 °C (Figure S5) possess crystal structure of hexagonal phase WSe2 (JCPDS: 71-0600) without any detectable impurity, indicating that the PTA precursor was successfully converted to crystalline WSe2 by H2Se after the high temperature treatment as in those similar synthesis reported in literatures.32 It also shows that a lower temperature of 300°C leads to


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an insufficient conversion of PTA to WSe2, and a higher temperature of 800 °C cause a little over reduction of PTA to metal tungsten by H2 gas flow (Figure S5). SEM and TEM images clearly show that the final product NSM-1 possesses a well-defined two dimensional sheet-like morphology with regularly arranged nanoholes (Figure 2). This is not a rationally designed outcome but an unexpected result. In a conventional nanocasting synthesis, the replica products are expected to copy the intricate 3D structure of the KIT-6 hard template’s pore space and possess a complex 3D structure as that illustrated in Figure 1c.33,34 However, in this case, the obtained NSM-1 possesses a well-defined nanomesh structure with perfect twodimensional sheet-like morphology. The macroscale particle morphology and the mesoscale pore structure are both completely different from the KIT-6 template. Carefully investigation found that the holes in all NSM-1 nanomeshes are always arranged in a centered rectangular lattice configuration with same cell parameter (a: ~25 nm, b: ~43 nm) (Figure 2b and d). The b:a ratio is close to √3. All these geometry features indicate that the WSe2 nanomesh only replicated the 2D {110} planes of the 3D pore space of the KIT-6 template in this special nanocasting synthesis.28,35 This will be further discussed later in more detail. The hole size, wall thickness and layer thickness of all NSM-1 nanomeshes are approximately 14-16, 8-10 and 8-10 nm, respectively, measured from SEM and TEM images. HRTEM analysis reveals that each piece of NSM-1 nanomesh is composed by a single crystal of hexagonal phase WSe2 (Figure 2e, f and Figure S6). More interestingly, the c-axis of the WSe2 crystal is always perpendicular to the nanomesh sheet plane (Figure 2f). The SAED pattern shown in Figure 2h was taken from a single piece of NSM-1 nanomesh, and it shows a clear hexagonal patterned spot array, which confirms that the nanomesh is a single crystal and the c-axis is perpendicular to the


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nanomesh plane. All checked nanomeshes showed the same single crystal nature with same crystal orientation, indicating it was not just a lucky choice.

Figure 2. SEM, TEM, HRTEM images and SAED pattern of WSe2 nanomesh NSM-1 synthesized at 600 °C. As mentioned above, the structure characteristic of the nanomesh product indicates that WSe2 sheet-like crystal exclusively grew along the {110} planes of the 3D mesopore space of the KIT6 template, which means the c-axis of the guest WSe2 crystal always perpendicular to the {110} crystal planes of the host templates’ mesopore space. This destined crystal orientation relationship between the guest crystal and the mesostructured of the host template is another unexpected result.


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Few single crystal 3D mesoporous replica materials have been synthesized by nanocasting method, including Co3O4, Fe2O3, In2O3, Cr2O3, etc.36 However, their crystal orientations do not show any deterministic correlations with the orientations of their mesostructure, which should be ascribed to the huge difference in their periodic cell parameters between the crystal structure of the guest material and the mesostructure of the host template. As in other typical nanocasting synthesis, the wall thickness, the size of the holes and the distance between the holes are determined by the pore size, wall thickness and cell parameter of the KIT-6 template, respectively.34 Therefore, the structures parameters of NSM-1 can be finely tuned by adjusting the structure parameters of the KIT-6 template. As a demonstration, a KIT-6 with a smaller cell parameter and a smaller pore size (4-5 nm) was synthesized by further heating the original KIT-6 template up to 900°C for 2 h (Figure S4). By using this mesoporous silica as the hard template, a NSM-1 nanomesh with smaller hole size (11.5 nm), thinner wall thickness (4-5 nm), and thinner layer thickness (4-5 nm) was successfully prepared (Figure 2g).

Figure 3. (a, b) SEM and (c) TEM images of NSM-1 synthesized at 600 °C by using ammonium tungstate as a precursor. NSM-1 nanomesh could also be analogously synthesized by using ammonium tungstate as an alternative metal precursor, without making any change in synthetic process and operation


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parameters. SEM and TEM observations both proved that high quality WSe2 nanomesh were also successfully fabricated in this case (Figure 3). The mesoscale structure parameters of the NSM-1 material synthesized from ammonium tungstate precursor do not show any noticeable difference from that synthesized from PTA precursor, indicating it’s a general synthesis method. In addition, thanks to the utilization of 3D mesoporous material as hard template, this synthesis method can be easily scaled up. More than 10 g of product can be produced in one batch synthesis in a small tube furnace (inner diameter: 30 mm), and the final products shows similar structure quality. This is a huge advantage comparing to those previously reported methods which need 2D substrate to construct 2D nanomesh structures. By using phosphomolybdic acid (PMA) as metal precursor, MoSe2 nanomesh (denoted as NSM2) can also be analogously prepared (Figure S5b). The structure parameters of NSM-2 are all very similar to that of NSM-1, because they used the same KIT-6 material as hard template. HRTEM and SAED pattern clearly show that NSM-2 possesses a single crystal nature with its c-axis perpendicular to the nanomesh plane as that of NSM-1 material (Figure 4). This result clearly indicates that it is a general synthesis method for TMDs nanomeshes. It should be noticed that NSM-2 showed lower crystallinity than NSM-1, as revealed by their XRD pattern (Figure S5). TEM observation also found that the particle size of NSM-2 nanomesh was much smaller than that of NSM-1. This may be explained by that molybdenum is much easier to be reduced, which leads to an increasing of crystal nucleation sites and thus reduce the crystal size of the product. All of the above results clearly demonstrated that TMDs will form 2D nanomesh structure inside the 3D mesopore space of KIT-6 by this synthesis method.


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Figure 4. (a) TEM, (b) HRTEM and (c) SAED pattern of MoSe2 nanomesh material NSM-2 synthesized at 600°C. It’s quite unusual that 2D ultrathin WSe2 and MoSe2 single crystal nanomeshes formed inside a host template with a 3D bicontinuous cubic phase pore space. The mesopore space of KIT-6 is always considered to be approximately isotropic in all directions due to its extremely high symmetry (space group Ia3d, space group number 230) (Figure 1a).35 In most published reports, when KIT-6 was used as hard template for nanocasting synthesis, the guest materials usually tend to growth uniformly in all directions inside the pore space of KIT-6 template, and as a result, the final products usually possess spherical particle morphologies.36,37 In this work, the nanomesh products possess a two dimensional sheet-like morphology with the sheet size can even larger than 700 nm, while the thickness is kept at only 8-10 nm. It is undoubtedly that it should be firstly attributed to the anisotropic layered crystal nature of TMDs. It has been widely reported that TMDs tend to form sheet-like morphology to reduce the specific layer edge length, i.e. reduce the edge plane surface percentage, and thus reduce the surface energy.23,24 However, several facts indicate the details of the mesopore space structure also paly very important roles: (1) only one type of pore arrangement was observed for all nanomeshes, which means the guest TMDs crystals do not randomly grow along different directions inside the 3D ordered mesopore space of the host


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template, but only along the {110} planes of the KIT-6 template. (2) The thickness of the sheet is always uniformly around 10 nm, which is similar to the pore diameter of KIT-6 template. These two facts both indicate that the {110} planes of mesoporous silica KIT-6 must possess some unique geometrical characteristics. KIT-6 has a 3D bicontinuous mesopore structure (Figure 1a), which was denoted as doublegyroid structure.38,39 This special structure has attracted lots of research interest due to its extremely high symmetry and the advantage in mass transfer. Its cavity network is separated into two sets of channels by the silica walls (Figure 1b).40 Both sets of channels impenetrate the whole particle while they are non-intersecting between each other (Figure 1c).35 These two sets of channels are mirror symmetric with each other, and they accordingly have exactly the same geometrical characteristics.40 Therefore, we only discuss the 3D structure of one set of the channels in the following parts. Figure 5a displays a 3D structure model for one set channel of the KIT-6 template viewed from the [001] direction. If we look at the structure along the [110] direction as shown in Figure 5b, the periodic 3D channel structure can be described as a stacking structure built by two types of structure units (Figure 5c). One is a 2D continuous space layer (A) unit and the other is an isolated pillar layer (B) unit composed by cylindrical pore array (Figure 5c). The thickness of layer (A) is approximately same with the diameter of the mesopore. If we cut the 3D channels at the center of layer (A) (Figure 5d), the cross-sectional pattern is a perfect nanomesh structure with centered rectangular patterned pores (Figure 5e). The model of the layer (A) without layer (B) (Figure 1d) shows exactly the same structure characteristics with those of our nanomesh products, strongly indicating that MSe2 crystals tend to exclusively grow inside the mesopore pace of layer (A) in our synthesis, leaving the space of layer (B) unoccupied.


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Figure 5. Scheme of the structure model of the pore space of one set of the channels of KIT-6 template. The blue color represents the outer surface of the channel system and the yellow color represents the cross section. The silica wall and the other set of channels of the KIT-6 template are set to invisible in this scheme. By carefully inspecting the mesopore structure of KIT-6 template along different directions (Supplementary movie files), it is found that only the {110} crystal planes can provide such a continuous 2D space with uniform thickness for the growth of TMDs crystals with sheet-like morphology (Figure S7). For example, if we cut the pore space along the directions, the cross sections are either rod-like islands or zigzag strips (Figure S8). That is to say, if the TMDs trying to form a thin sheet-like morphology along the {100} crystal planes of KIT-6, only nanorods or zigzag nanostrips will be produced after the removal of silica template. If we cut the pore space along the directions, triangle stars array is the main pattern of the cross sections (Figure S9). The detailed information about the shapes of the cross sections along different directions can be found in the supporting information. Further detailed information of the double-gyroid structure


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can be found in literatures.40 In conclusion, only when the sheet-like MSe2 crystal grow along the {110} planes inside the layer (A) space, a continuous 2D nanomesh product can be formed with a uniform thickness of 8-10 nm. Otherwise, the products should be isolated small nanoparticles (< 30 nm) or thin nanoribbons with ~10 nm width, but neither of them has been observed in our experiments. Why the MSe2 guest materials only formed two dimensional sheet-like nanomesh structures with one kind of hole arrangement inside the 3D bicontinuous mesopore space of the KIT-6 template in our synthesis? We believe the behind driving force still comes from the spontaneous trend of reducing surface energy during the growth of TMDs crystals. The layer edges of TMDs crystals possess very high surface energy, and therefore they spontaneously prefer to diminish layer edges as far as possible during the crystal growth.14,30 This is the primary reason for that the MSe2 products tend to grow into sheet-like particle morphology in this synthesis, as in numerous reported syntheses of TMDs.16,23 Among all directions inside the mesopore space of KIT-6 template, the {110} planes leads to a lowest specific length of layer edges. It is quite obvious that the small nanoparticles and the thin nanoribbons, if they could be made by this nanocasting method by growing along {100} or {111} planes of the KIT-6 mesopore space, should have much longer specific layer edge length than the 2D nanomesh products or 3D mesoporous products. As mentioned above, along the [110] direction, the 3D channel of KIT-6 template can be described as a stacking structure built by two types of structure units (Figure 5c), a 2D continuous space layer (A) unit and an isolated pillar layer (B) unit. The formation of 2D nanomesh structure of the final product means the guest materials only selectively occupy the layer (A) unit during crystal growth. It can be explained by the huge volume shrinkage from the PTA precursor to the WSe2 product plus the strong trend in reducing high energy layer edges in crystal growth. For


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example, the conversion of PTA precursor to WSe2 products was accompanied with huge volume shrinkage. Consequently, in each domain, only about 52% of the mesopore space of the KIT-6 template will be occupied by the WSe2 crystal, in spite of that the entire pore space of this domain is filled with PTA precursor before the reaction. In addition, the ultrafast heating rate leading to an ultrafast reaction rate, and therefore it prohibit the long distance migration of metal species, limiting the reaction in an approximately in situ conversion process. The huge volume shrinkage and the in-situ conversion make the TMDs crystals cannot fill up the entire pore space in any domain, which explained the partial occupation result. This is very important because a full occupation will inevitably lead to a 3D replica structure. It has been proved that inside a small cylindrical pore space, the TMDs crystal layer tend to growth along the pore axis because it can reduce the layer edge exposure in this way.30 If the WSe2 single crystal growth into the pillar space in layer (B) unit without change the crystal orientation, the crystal layer of the TMDs will perpendicular to the pore axis of the cylindrical pores in layer (B) unit, this situation will significantly increase the surface energy.30 On the contrary, it’s a better choice for WSe2 crystals to exclusively grow inside the continuous layer (A) unit space to decrease the edge plane percentage, as well as the surface energy. We found that if the heating rate is decrease to 1ºC min-1 to make the long distance migration of metal species possible, the obtained samples no longer possess 2D nanomesh structure, but replicated the entire 3D structure of the double-gyroid pore space as illustrated in Figure 1c and demonstrated in Figure S10-12.This result indicate the ultra-fast heating rate is the key synthetic parameter and the huge volume shrinkage plays an important role in the this general TMDs nanomesh synthesis method. The single crystal TMDs nanomeshes synthesized in this work possess a well-defined nanostructures with regularly arranged holes and the c-axis of the crystal was always perpendicular


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to the nanomesh plane. Therefore, the inner side surface of each holes are exclusively composed by crystal layer edges, known as the edge plane in literatures.41 The top and bottom surface of the nanomeshes are exclusively composed by basal planes. The size of the holes, the distribution density of the holes and the thickness of the sheets are determined by the structure characteristics of the KIT-6 template, which are all can be easily estimated by SEM or TEM observation. Thanks to this well-defined structure, the total length of the layer edges in these nanomeshes can be quite precisely estimated. The specific length of layer edges for NSM-1 and NSM-2 synthesized in this work are estimated to be 3.8×1010 and 6.0×1010 m g-1, respectively. This value equivalent to the specific layer edge length of a thin film of vertically aligned WSe2 and MoSe2 with a thickness of only ~ 4 nm. The ultra-high exposure of layer edges should be attributed to the small diameter (810 nm) of the KIT-6 template, which leads to a very small spacing between those holes. This feature makes it a good candidate as model materials for layer edge related applications. The electrocatalytic HER activities of the WSe2 and MoSe2 nanomeshes in acidic solution were investigated as a demonstration for these special nanostructured TMDs. The as-prepared NSM-1 and NSM-2 samples were dispersed in an ethanol/water mixture and then drop onto a glass carbon electrode (GCE) with 3 mm diameter. The linear sweep voltammetry (LSV) polarization curves were measured in acidic solution (0.5 M H2SO4) with a potential scan rate of 1 mV/S using a typical three-electrode setup, and they are all presented in Figure 6. The onset potential of the polarization curves of the WSe2 nanomesh NSM-1 and MoSe2 nanomesh NSM-2 are estimated to be -237 and -146 mV (Figure 6a inset, derived from the log(j) vs V curves), respectively. Their current densities increases rapidly under more negative over potential and reach 10 mA cm-2 at 315 and -264 mV for NSM-1 and NSM-2. The corresponding Tafel slopes of WSe2 nanomesh and MoSe2 nanomesh are 71 and 69 mV per decade (Figure 6b). These values are closed to the state


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of art samples.14,42-46 Since these two materials possess same mesoscale structure parameters, these results clearly show that MoSe2 is a better candidate for HER reaction as demonstrated in literature reports.42,46 Both of these two materials possess outstanding chemical stabilities. After they were stored in air for half year, the materials showed same activity in HER measurement.

Figure 6. The LSV polarization curves of (a) Glass carbon electrode (GCE), Pt/C, WSe2 nanomesh and MoSe2 nanomesh measured in N2-purged 0.5 M H2SO4 solution and (b) the corresponding Tafel plots. (c, d) The LSV polarization curves of the MoSe2 nanomesh with different loading amount. The polarization curve of MoSe2 nanomesh NSM-2 with different loading amount was listed in Figure 6c, which exhibit significant difference in their HER polarization curves when the currents were normalized to the projected area of the electrode. The overpotentials at the current density of 10 mA cm-2 decreased from ~ 740 mV (roughly estimated from the extended line of the


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polarization curve) to 435, 322, 282, 264 and 250 mV as the loading amounts were increased from 1.0, to 3.0, 10, 30, 50 and 60 µg (Figure 6c). If we fixed the voltage at -0.300 V vs RHE, the recorded corresponding current density are 0.73, 2.00, 6.20, 16.57, 24.34 and 31.05 mA cm-2, respectively. Although these apparent polarization curves show huge difference as described above, they show quite similar behavior if we plot them in the form of log (current density) vs V as in Figure 6d. These curves clearly show that all of them possess similar onset potentials and similar Tafel slopes. This should be attributed to that all of them were measured from the same material and their active sites possess similar intrinsic catalytic reactivity. The significant improvement of the apparent HER performance in Figure 6c should be exclusively attributed to the increasing of activity sites numbers. Since the specific layer edge length can be estimated from the structure parameters, 6.0×1010 m g-1 for MoSe2 nanomesh, and the active sites for HER reaction only located in the crystal layer edges for a well crystallized non-doping TMDs material, the TOF values can be calculated and described as frequency per nanometer layer edges. For the above mentioned loading amount, from 1.0 to 3.0, 10, 30, 50 and 60 µg, their TOF are estimated to be 2.7, 2.5, 2.3, 2.0, 1.8 and 1.9 per nanometer layer edges at -0.300 V. The slightly decreasing of TOF can be explained by the potential drop from the bottom of the active material layer to the top layer caused by resistance, and the thicker active material layer may slightly affected the mass transfer. Therefore, the highest TOF value, 2.7 S-1 nm-1, represent the instinct catalytic activity of this material. Comparing to the polarization curve presented in the form of current per project area of the electrode as in most literatures, these TOF values represent a more precise data for the evaluation of the intrinsic catalytic activity of this kind of materials.


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It is worth to mention that our samples do not show the best HER performances among all kinds of WSe2- or MoSe2-based materials in literatures, but they are comparable to those state of art powder form pure phase WSe2 and MoSe2 materials.43-46 Therefore, we believe our results demonstrated that a high exposure of active layer edges do benefit for electrocatalytic applications, which is one of the advantages of this highly porous nanomesh structure. Beside the structure control, various strategies have been developed to improve the performance of TMDs in catalysis applications, such as metal or non-metal doping, making multiphase composite structures with carbon/graphene, directly growth of active TMDs on the electrode substrate rather than loading the powder form sample onto the electrode substrate by polymer binders, etc.14,20,42-45,47-50 The first-rate materials are always combined these strategies in one material to achieve the optimized performance. In a lot of literature reports, when a change of apparent HER performance is recorded after a different synthesis condition was taken, it’s hard to analysis whether the improvement comes from the change of active sites number or from the change of intrinsic activity of the active sites. Actually, the 3D mesoporous MoSe2 and WSe2 show similar performance in HER with the 2D nanomeshes, because they also possess high exposure of layer edges due to the ultrathin diameter of the framework (< 10 nm). However, the layer edge exposure ratio can not be quantitatively calculated in this case, and therefore it’s impossible to directly investigate the TOF value as for 2D single crystal nanomeshes. Since the structure characteristic of our nanomeshes are only determined by the template and the specific layer edge length can be directly estimated from the SEM and TEM images, these nanomesh materials can be used as a model material platform for specifically investigating the effectiveness of each optimization strategy without change the structure parameters of the modified materials, which is very important for the fundamental research in this area.


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CONCLUSIONS In conclusion, 2D WSe2 and MoSe2 nanomeshes were synthesized by a novel nanocasting method using mesoporous silica KIT-6 with Ia3d mesostructure as a hard template. The formation of 2D nanostructure inside a 3D mesopore space is attributed to the unique crystal structure of TMDs and the special characteristic of the pore structure of the mesoporous silica KIT-6. The key synthetic parameter to prepare 2D nanomesh is the ultrafast heating rate, which prevent the precursors from long distance migration. The nanomeshes are single crystal with centered rectangular pore arrangement and the c-axis of the crystal is always perpendicular to the nanomesh plane. The highly porous structure brings these nanomeshes extremely high exposure of layer edges, and the well-defined nanostructure provides an opportunity to quantitatively estimate the specific crystal layer edge length. This kind of nanomesh may be used as a model material for quantitative studies in case of the active sites are located in the layer edges. EXPERIMENTAL SECTION Synthesis of hard template KIT-6. 20 g of triblock copolymer P123 was dissolved in a mixture of 33 mL HCl (37%) and 720 mL of distilled water under stirred at 35°C. Then 20 g of n-BuOH was poured into the solution with rigorously stirring for another 60 min. 43 g of tetraethoxysilane (TEOS) was then added in and the mixture was kept under stirring at the same temperature for another 24 h. The above mixture was transferred into a hydrothermal bomb for hydrothermal treatment at 100°C for 24 h under static condition. White solid was collected by filtration and it was then calcined at 550°C for 6 h with a heat rate 1.5°C min-1 in air to remove the surfactant. Synthesis of WSe2 and MoSe2 nanomeshes. 0.8 g of PTA (H3PW12O40·6H2O) was mixed with 0.5 g of KIT-6 and 20 mL of ethanol under stirring in an open vessel at room temperature. After


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the ethanol was totally evaporated up, the PTA@KIT-6 composite powder was mixed with 1.3 g of selenium powder. The mixture was then transferred into a quartz boat and putted in the middle of quartz tube at room temperature. A constant hydrogen gas flow (200 mL min-1) was passing by the tube as the reducing agent and protection atmosphere. After 30 min, the quartz tube, with the quartz boat inside it, was directly putted into a tube furnace which had already been pre-heated up to 600°C. The quartz tube was heated up to 600°C in less than 5 min. After keeping the reaction system at this temperature for 4 h, it was took out of the tube furnace and cooled down to room temperature. During the entire heating and cooling processes, a constant hydrogen gas flow (200 mL min-1) was passing by the tube. Two drexel bottles with 2 M NaOH aqueous solution were connected to the outlet pipeline of the tube furnace to absorb the residual H2Se in the H2 gas flow. In order to avoid the threat of H2Se leakage and hydrogen accumulation, the entire equipment was placed inside a fume hood. The silica template was removed by 10% HF aqueous solution for 4 h. Before the silica template removal, a purification process was carried out. The details about the procedure and the result of the purification process are described in supporting information. MoSe2 nanomesh was similarly prepared by using PMA (H3PMo12O40·6H2O) as precursor. Characterization. X-ray diffraction (XRD) pattern was recorded on a Bruker D8 Advance diffractometer with Cu Kα radiation (40 kV, 40 mA). Transmission electron microscopy (TEM) images were collected on a FEI-G2 microscopy. Scanning electron microscopy (SEM) was taken on FEI-quanta-200F. Nitrogen adsorption-desorption isotherms were measured at 77K on a Micromeritics TriStar 3020 porosimeter apparatus. Before taken the measurement, the sample was degassed at 160°C in a vacuum for 12 h. The surface area was calculated by Brumauer-EmmettTeller method using adsorption point in a relative pressure form 0.05 to 0.35, the pore size distribution was calculated on adsorption branch of isotherm using density functional theory (DFT)


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method. The total pore volume, Vp, were estimated from saturation adsorption point at a relative pressure P/P0=0.99. The electrochemical measurements were performed in a PGSTAT 302 N Autolab Potentiostat/Galvanostat (Metrohm) in a standard three-electrode cell system. Graphite rod and Ag/AgCl (in 3 M KCl solution) electrodes were used as the counter and reference electrodes respectively. However, all of the potentials were converted and reported relative to the reversible hydrogen electrode (RHE) in this work. The HER activity was evaluated by measuring polarization curves with linear sweep voltammetry (LSV) at a scan rate of 1 mV s-1 in N2 saturated 0.5 M H2SO4 (pH=0.34) solutions. A commercially available 20 wt% Pt/C (Alfa Aesar) was used as the state of art electrocatalyst for comparison. Typically, in preparation of the working electrode, 1.0 mg of the tested catalyst nanocrystals was dispersed in a mixture of 0.5 g of ethanol and 0.5 ml of water and sonicated for 30 min to make the catalyst ink. An aliquot of the catalyst ink and a ~10 µL of 0.1% Nafion solution in ethanol were drop-coated on a ~3 mm glassy carbon electrode, and dried at room temperature. ASSOCIATED CONTENT Supporting Information. The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami. xxxx. SAXRD, TEM, nitrogen sorption isotherms, and the corresponding pore size distribution curve of the mesoporous silica KIT-6; nitrogen sorption isotherms and the corresponding pore size distribution curves of the KIT-6 template that has been further calcined at 900°C; XRD patterns of WSe2 and MoSe2 nanomeshes prepared at different temperature from 300


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to 800°C; HRTEM image of WSe2 nanomesh NSM-1; typical cross sections of KIT-6’s pore space cut along the , and directions; XRD, SEM, TEM and HRTEM images of 3D mesoporous WSe2 and MoSe2; SEM images of as-made, intermediate and final products. AUTHOR INFORMATION Corresponding Author * E-mail: [email protected] (W.M. Xu) * E-mail: [email protected] (Y.F. Shi) ORCID Weiming Xu: 0000-0003-3257-0078 Yifeng Shi: 0000-0003-1304-5737 Pengfei Zhang: 0000-0001-9859-0237 Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes The authors declare no competing financial interest. ACKNOWLEDGMENTS This work was supported by funding from the Natural Science Foundation of China (21871071, 21673167), the Major Scientific and Technological Innovation Project of Zhejiang (2019C01081) and the Climbing Project of Hangzhou Normal University. We thank Prof. Su for helpful discussions and suggestions.


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REFERENCES (1) Xu, M. S.; Liang, T.; Shi, M. M.; Chen, H. Z. Graphene-Like Two-Dimensional Materials. Chem. Rev. 2013, 113, 3766-3798. (2) Butler, S. Z.; Hollen, S. M.; Cao, L. Y.; Cui, Y.; Gupta, J. A.; Gutierrez, H. R.; Heinz, T. F.; Hong, S. S.; Huang, J. X.; Ismach, A. F.; Johnston-Halperin, E.; Kuno, M.; Plashnitsa, V. V.; Robinson, R. D.; Ruoff, R. S.; Salahuddin, S.; Shan, J.; Shi, L.; Spencer, M. G.; Terrones, M.; Windl, W.; Goldberger, J. E. Progress, Challenges, and Opportunities in Two-Dimensional Materials Beyond Graphene. ACS Nano 2013, 7, 2898-2926. (3) Wang, Q. H.; Kalantar-Zadeh, K.; Kis, A.; Coleman, J. N.; Strano, M. S. Electronics and Optoelectronics of Two-Dimensional Transition Metal Dichalcogenides. Nat. Nanotechnol. 2012, 7, 699-712. (4) Lv, R.; Robinson, J. A.; Schaak, R. E.; Sun, D.; Sun, Y. F.; Mallouk, T. E.; Terrones, M. Transition Metal Dichalcogenides and Beyond: Synthesis, Properties, and Applications of Singleand Few-Layer Nanosheets. Accounts Chem. Res. 2015, 48, 56-64. (5) Gong, C. H.; Zhang, Y. X.; Chen, W.; Chu, J. W.; Lei, T. Y.; Pu, J. R.; Dai, L. P.; Wu, C. Y.; Cheng, Y. H.; Zhai, T. Y.; Li, L.; Xiong, J. Electronic and Optoelectronic Applications Based on 2D Novel Anisotropic Transition Metal Dichalcogenides. Adv. Sci. 2017, 4, 1700231. (6) Eda, G.; Yamaguchi, H.; Voiry, D.; Fujita, T.; Chen, M. W.; Chhowalla, M. Photoluminescence from Chemically Exfoliated MoS2. Nano Lett. 2011, 11, 5111-5116. (7) Chhowalla, M.; Shin, H. S.; Eda, G.; Li, L.-J.; Loh, K. P.; Zhang, H. The Chemistry of TwoDimensional Layered Transition Metal Dichalcogenide Nanosheets. Nat. Chem. 2013, 5, 263-275. (8) Kibsgaard, J.; Chen, Z. B.; Reinecke, B. N.; Jaramillo, T. F. Engineering the Surface Structure of MoS2 to Preferentially Expose Active Edge Sites for Electrocatalysis. Nat. Mater. 2012, 11, 963-969. (9) Furimsky, E. Role of Molybdenum Disulfide and Tungsten Disulfide in Hydrodesulfurization. Catal. Rev.: Sci. Eng. 1980, 22, 371-400. (10) Sun, T.; Wang, J.; Chi, X.; Lin, Y. X.; Chen, Z. X.; Lin, X.; Qiu, C. T.; Xu, Y. S.; Chen, W.; Su, C. L. Engineering the Electronic Structure of MoS2 Nanorods by N and Mn Dopants for Ultra-Efficient Hydrogen Production. ACS Catal. 2018, 8, 7585-7592. (11) Jaramillo, T. F.; Jørgensen, K. P.; Bonde, J.; Nielsen, J. H.; Horch, S.; Chorkendorff, I. Identification of Active Edge Sites for Electrochemical H2 Evolution from MoS2 Nanocatalysts. Science 2007, 317, 100-102. (12) Tuxen, A.; Kibsgaard, J.; Gøbel, H.; Lægsgaard, E.; Topsøe, H.; Lauritsen, J. V.; Besenbacher, F. Size Threshold in the Dibenzothiophene Adsorption on MoS2 Nanoclusters. ACS Nano 2010, 4, 4677-4682. (13) Tsai, C.; Chan, K. R.; Abild-Pedersen, F.; Norskov, J. K. Active Edge Sites in MoSe2 and WSe2 Catalysts for the Hydrogen Evolution Reaction: A Density Functional Study. Phys. Chem. Chem. Phys. 2014, 16, 13156-13164. (14) Kong, D.; Wang, H.; Cha, J. J.; Pasta, M.; Koski, K. J.; Yao, J.; Cui, Y. Synthesis of MoS2 and MoSe2 Films with Vertically Aligned Layers. Nano Lett. 2013, 13, 1341-1347. (15) Lin, Z.; Carvalho, B. R.; Kahn, E.; Lv, R.; Rao, R.; Terrones, H.; Pimenta, M. A.; Terrones, M. Defect Engineering of Two-Dimensional Transition Metal Dichalcogenides. 2D Mater. 2016, 3, 022002.


23


Page 24 of 27

(16) Samadi, M.; Sarikhani, N.; Zirak, M.; Zhang, H.; Zhang, H.-L.; Moshfegh, A. Z. Group 6 Transition Metal Dichalcogenide Nanomaterials: Synthesis, Applications and Future Perspectives. Nanoscale Horiz. 2018, 3, 90-204. (17) Liu, H.; Su, D. W.; Zhou, R. F.; Sun, B.; Wang, G. X.; Qiao, S. Z. Highly Ordered Mesoporous MoS2 with Expanded Spacing of the (002) Crystal Plane for Ultrafast Lithium Ion Storage. Adv. Energy Mater. 2012, 2, 970-975. (18) Wang, Y. Y.; Wang, Y. X.; Kang, W. P.; Cao, D. W.; Li, C. X.; Cao, D. X.; Kang, Z. X.; Sun, D. F.; Wang, R. M.; Cao, Y. L. TiO2-Coated Interlayer-Expanded MoSe2/Phosphorus-Doped Carbon Nanospheres for Ultrafast and Ultralong Cycling Sodium Storage. Adv. Sci. 2019, 6, 1801222. (19) Wang, T. Y.; Chen, S. Q.; Pang, H.; Xue, H. G.; Yu, Y. MoS2-Based Nanocomposites for Electrochemical Energy Storage. Adv. Sci. 2017, 4, 1600289. (20) Voiry, D.; Yang J.; Chhowalla, M. Recent Strategies for Improving the Catalytic Activity of 2D TMD Nanosheets Toward the Hydrogen Evolution Reaction. Adv. Mater. 2016, 28, 61976206. (21) Rao, C. N. R.; Govindaraj, A. Synthesis of Inorganic Nanotubes. Adv. Mater. 2009, 21, 4208-4233. (22) Tenne, R. Inorganic Nanotubes and Fullerene-Like Nanoparticles. Nat. Nanotechnol. 2006, 1, 103-111. (23) Zhang, H. Ultrathin Two-Dimensional Nanomaterials. ACS Nano 2015, 9, 9451-9469. (24) Tan, C.; Zhang, H. Two-Dimensional Transition Metal Dichalcogenide Nanosheet-Based Composites. Chem. Soc. Rev. 2015, 44, 2713-2731. (25) Xie, J. F.; Zhang, H.; Li, S.; Wang, R. X.; Sun, X.; Zhou, M.; Zhou, J. F.; Lou, X. W.; Xie, Y. Defect-Rich MoS2 Ultrathin Nanosheets with Additional Active Edge Sites for Enhanced Electrocatalytic Hydrogen Evolution. Adv. Mater. 2013, 25, 5807-5813. (26) 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, 2986-3017. (27) Wang, H.; Kong, D.; Johanes, P.; Cha, J. J.; Zheng, G.; Yan, K.; Liu, N.; Cui, Y. MoSe2 and WSe2 Nanofilms with Vertically Aligned Molecular Layers on Curved and Rough Surfaces. Nano Lett. 2013, 13, 3426-3433. (28) Kim, T.-W.; Kleitz, F.; Paul, B.; Ryoo, R. MCM-48-Like Large Mesoporous Silicas with Tailored Pore Structure: Facile Synthesis Domain in a Ternary Triblock Copolymer-ButanolWater System. J. Am. Chem. Soc. 2005, 127, 7601-7610. (29) Wan, Y.; Zhao, D. On the Controllable Soft-Templating Approach to Mesoporous Silicates. Chem. Rev. 2007, 107, 2821-2860. (30) Shi, Y.; Wan, Y.; Liu, R.; Tu, B.; Zhao, D. Synthesis of Highly Ordered Mesoporous Crystalline WS2 and MoS2 via a High-Temperature Reductive Sulfuration Route. J. Am. Chem. Soc. 2007, 129, 9522-9531. (31) Shi, Y.; Hua, C.; Li, B.; Fang, X.; Yao, C.; Zhang, Y.; Hu, Y.-S.; Wang, Z.; Chen, L.; Zhao, D.; Stucky, G. D. Highly Ordered Mesoporous Crystalline MoSe2 Material with Efficient VisibleLight-Driven Photocatalytic Activity and Enhanced Lithium Storage Performance. Adv. Funct. Mater. 2013, 23, 1832-1838. (32) Chen, F. J.; Wang, J.; Li, B.; Yao, C. H.; Bao, H. F.; Shi, Y. F. Nanocasting Synthesis of Ordered Mesoporous Crystalline WSe2 as Anode Material for Li-Ion Batteries. Mater. Lett. 2014, 136, 191-194.


24

Page 25 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(33) Gu, D.; Schuth, F. Synthesis of Non-Siliceous Mesoporous Oxides. Chem. Soc. Rev. 2014, 43, 313-344. (34) Lu, A. H.; Schuth, F. Nanocasting: A Versatile Strategy for Creating Nanostructured Porous Materials. Adv. Mater. 2006, 18, 1793-1805. (35) Yates, T. J. V.; Thomas, J. M.; Fernandez, J.-J.; Terasaki, O.; Ryoo, R.; Midgley, P. A. Three-Dimensional Real-Space Crystallography of MCM-48 Mesoporous Silica Revealed by Scanning Transmission Electron Tomography. Chem. Phys. Lett. 2006, 418, 540-543. (36) Yue, W. B.; Zhou, W. Z. Crystalline Mesoporous Metal Oxide. Prog. Nat. Sci. 2008, 18, 1329-1338. (37) Ren, Y.; Ma, Z.; Bruce, P. G. Ordered Mesoporous Metal Oxides: Synthesis and Applications. Chem. Soc. Rev. 2012, 41, 4909-4927. (38) Hajduk, D. A.; Harper, P. E.; Gruner, S. M.; Honeker, C. C.; Kim, G.; Thomas, E. L.; Fetters, L. J. The Gyroid: A New Equilibrium Morphology in Weakly Segregated Diblock Copolymers. Macromolecules 1994, 27, 4063-4075. (39) Hashimoto, T.; Nishikawa, Y.; Tsutsumi, K. Identification of the "Voided Double-GyroidChannel": A New Morphology in Block Copolymers. Macromolecules 2007, 40, 1066-1072. (40) Scherer, M. R. J. Double-Gyroid-Structured functional materials: synthesis and applications. Springer Science & Business Media, 2013. (41) Tan, S. M.; Ambrosi, A.; Sofer, Z.; Huber, Š.; Sedmidubský, D.; Pumera, M. Pristine Basaland Edge-Plane-Oriented Molybdenite MoS2 Exhibiting Highly Anisotropic Properties. Chem. Eur. J 2015, 21, 7170-7178. (42) Wang, H. T.; Kong, D. S.; Johanes, P.; Cha, J. J.; Zheng, G. Y.; Yan, K.; Liu, N. A.; Cui, Y. MoSe2 and WSe2 Nanofilms with Vertically Aligned Molecular Layers on Curved and Rough Surfaces. Nano Lett. 2013, 13, 3426-3433. (43) Tang, H.; Dou, K. P.; Kaun, C. C.; Kuang, Q.; Yang, S. H. MoSe2 Nanosheets and Their Graphene Hybrids: Synthesis, Characterization and Hydrogen Evolution Reaction Studies. J. Mater. Chem. A 2014, 2, 360-364. (44) Xu, K.; Wang, F. M.; Wang, Z. X.; Zhan, X. Y.; Wang, Q. S.; Cheng, Z. Z.; Safdar, M.; He, J. Component-Controllable WS2(1-x)Se2x Nanotubes for Efficient Hydrogen Evolution Reaction. ACS Nano 2014, 8, 8468-8476. (45) Xu, C.; Peng, S. J.; Tan, C. L.; Ang, H. X.; Tan, H. T.; Zhang, H.; Yan, Q. Y. Ultrathin SDoped MoSe2 Nanosheets for Efficient Hydrogen Evolution. J. Mater. Chem. A 2014, 2, 55975601. (46) Eng, A. Y. S.; Ambrosi, A.; Sofer, Z.; Simek, P.; Pumera, M. Electrochemistry of Transition Metal Dichalcogenides: Strong Dependence on the Metal-to-Chalcogen Composition and Exfoliation Method. ACS Nano 2014, 8, 12185-12198. (47) Gong, Q. F.; Cheng, L.; Liu, C. H.; Zhang, M.; Feng, Q. L.; Ye, H. L.; Zeng, M.; Xie, L. M.; Liu, Z.; Li, Y. G. Ultrathin MoS2(1-x)Se2x Alloy Nanoflakes For Electrocatalytic Hydrogen Evolution Reaction. ACS Catal. 2015, 5, 2213-2219. (48) Kim, J.; Byun, S.; Smith, A. J.; Yu, J.; Huang, J. X. Enhanced Electrocatalytic Properties of Transition-Metal Dichalcogenides Sheets by Spontaneous Gold Nanoparticle Decoration. J. Phys. Chem. Lett. 2013, 4, 1227-1232. (49) Patel, A. B.; Machhi, H. K.; Chauhan, P.; Narayan, S.; Dixit, V.; Soni, S. S.; Jha, P. K.; Solanki, G. K.; Patel, K. D.; Pathak, V. M. Electrophoretically Deposited MoSe2/WSe2 Heterojunction from Ultrasonically Exfoliated Nanocrystals for Enhanced Electrochemical Photoresponse. ACS Appl. Mater. Interfaces 2019, 11, 4093–4102.


25


Page 26 of 27

(50) Li, H.; Peng, Z. J.; Qian, J. W.; Wang, M.; Wang, C. B.; Fu, X. L. C Fibers@WSe2 Nanoplates Core–Shell Composite: Highly Efficient Solar-Driven Photocatalyst. ACS Appl. Mater. Interfaces 2017, 9, 28704–28715.


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SYNOPSIS.


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2D Single Crystal WSe2 and MoSe2 Nanomeshes with Quantifiable

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