Growth of 2D Mesoporous Polyaniline with Controlled Pore Structures

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Growth of 2D Mesoporous Polyaniline with Controlled Pore Structures on Ultrathin MoS2 Nanosheets by Block Copolymer Self-Assembly in Solution Hao Tian, Shuyan Zhu, Fugui Xu, Wenting Mao, Hao Wei, Yiyong Mai, and Xinliang Feng ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b13666 • Publication Date (Web): 01 Dec 2017 Downloaded from http://pubs.acs.org on December 3, 2017

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ACS Applied Materials & Interfaces

Growth of 2D Mesoporous Polyaniline with Controlled Pore Structures on Ultrathin MoS2 Nanosheets by Block Copolymer Self-Assembly in Solution Hao Tian a, Shuyan Zhua, Fugui Xua, Wenting Maoa, Hao Weia*, Yiyong Maia*, and Xinliang Fengb a

School of Chemistry and Chemical Engineering, School of Electronic Information and Electrical Engineering, Shanghai Key Laboratory of Electrical Insulation and Thermal Ageing, Shanghai Jiao Tong University, 800 Dongchuan RD, Shanghai 200240, P. R. China b Department of Chemistry and Food Chemistry, Technische Universität Dresden, Mommsenstrasse 4, 01062 Dresden, Germany

Abstract: The development of versatile strategies towards two-dimensional (2D) porous nanocomposites with tunable pore structures is of immense scientific attention in view of their attractive physiochemical properties and a wide range of promising applications. This paper describes a self-assembly approach for the directed growth of mesoporous polyaniline (PANi) with tunable pore structures and sizes on ultrathin free-standing MoS2 nanosheets in solution, which produces 2D mesoporous PANi/MoS2 nanocomposites. The strategy employs spherical and cylindrical micelles, which are formed by controlled solution self-assembly of block copolymers, as the soft templates for the construction of well-defined spherical and cylindrical mesopores in the 2D PANi/MoS2 nanocomposites, respectively. With a potential application as supercapacitor electrode materials, the resultant 2D composites show excellent capacitive performance with a maximum capacitance of 500 F g-1 at a current density of 0.5 A g-1, good rate performance, as well as outstanding stability for charge-discharge cycling. Moreover, the 2D mesoporous nanocomposites offer an opportunity for the study on the influence of different pore structures on their capacitive performance, which helps to understand pore structure-property relationship of 2D porous electrode materials and to achieve their electrochemical performance control. Keywords: 2D materials, block copolymer, self-assembly, mesoporous, pore structure

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Introduction Two-dimensional (2D) materials are of great interest due to their attractive physiochemical properties and a broad range of promising applications, such as in energy storage and conversion, etc.1-7 For example, ultrathin MoS2 nanosheets are one of potential candidates for supercapacitor electrodes owing to their high theoretical pseudocapacitance, which benefits from their large range of oxidation states.8-12 Nevertheless, the actual capacitance of MoS2 is quite small owing to its poor conductivity.13-15 Although recently reported metallic 1T phase of MoS2 monolayers possesses good conductivity,16 they are easy to aggregate and smash when serving as electrode materials, which leads to a significant decrease in their practical conductivity and capacitance.13 This shortage can be overcome by the growth of electrochemically

active

moieties

on

their

surfaces

to

generate

sandwich-like

heterostructures.17,18 Polyaniline (PANi), a type of conducting polymers, has drawn much attention for supercapacitor electrodes owing to their low cost, good conductivity and high storage capacity.19,20 Mesoporous conducting polymers combine the advantages of mesoporous structures with the inherent characteristics of conducting polymers.19,21 Mesoporous architectures may afford an interconnected conductive network and large specific surface areas,22-24 and mesopores generally facilitate ion transport in active electrode materials.24,25 Moreover, pore structure may determine the electrochemical performance of electrode materials.26-29 Thereby, it is expected that rational combination of MoS2 with mesoporous conducting polymers to form 2D sandwich heterostructures with controlled pore structures may produce desirable 2D composites for high-performance supercapacitor electrodes. Nevertheless, due to the difficulties in pattering mesoporous substances on the surfaces of 2D 2 ACS Paragon Plus Environment

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materials and in controlling over pore structures, 2D mesoporous conducting polymer/MoS2 heterostructures with different well-defined pore structures have not been achieved as yet, which limits the study on the influence of pore structure on capacitive performance of such nanocomposites. The solution self-assembly of block copolymers provides a versatile strategy for constructing various ordered nanostructures of tunable dimensions, which have proven to be ideal pore-creating soft templates for preparing mesoporous materials with tailorable pore structures.18-23 In this work, we demonstrate a facile self-assembly method for the growth of mesoporous PANi with tunable pore structures on ultrathin free-standing MoS2 nanosheets in solution (Figure 1). This strategy employs amphiphilic block copolymer (BCPs) including synthetic polystyrene-block-poly(ethylene oxide) (PS-b-PEO) and commercial P123 (PEO20-PPO70-PEO20) as the pore-structure-directing agents. The PS-b-PEO diblocks aggregate into spherical micelles of controlled sizes in tetrahydrofuran (THF)/H2O mixed solvents, while P123 forms cylindrical micelles in water. After mixing the micelle solution with those of ultrathin MoS2 nanosheets and aniline, the micelles arrange tightly on the surfaces of the MoS2 sheets through Mo-N coordination and then direct the polymerization of aniline monomers that are absorbed in the PEO domain through H-bonding. The subsequent removal of the copolymer templates yields large-pore mesoporous PANi with well-defined “spherical” or “cylindrical” pores on both surfaces of the MoS2 nanosheets, generating 2D mesoporous PANi/MoS2 sandwich-like nanocomposites (although the pores are not exactly spherical or cylindrical, we apply these two words for convenient expressions). The 2D mesoporous nanocomposites with spherical pores (mPANi/MoS2-1 & 2) possess tunable average pore sizes (12-16 nm) and mean thicknesses (27-35 nm), depending on the PS block 3 ACS Paragon Plus Environment


length

in

the

copolymer

template.

The

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nanocomposites

with

cylindrical

pores

(mPANi/MoS2-3) possess a mean pore diameter of 10 nm and a thickness of 22 nm. The different mPANi/MoS2 composites offer an opportunity for investigating the influence of pore structure on their supercapacitor performance. As a consequence, mPANi/MoS2-1 with an average pore size of 12 nm and large specific surface area of 258 m2 g-1 shows a maximum capacitance of 500 F g-1 at 0.5 A g-1, good rate performance, and excellent stability with ~94% of initial capacitance after 5,000 charge-discharge cycles. This superb performance surpasses those of the other two mPANi/MoS2 counterparts as well as those of many reported pure MoS2, PANi, and MoS2- or graphene-based 2D nanocomposites.16,30-36 Results and Discussion The

ultrathin

MoS2

nanosheets

were

fabricated

by

Li-intercalation

and

ultrasonication-assisted exfoliation method (see Experimental Section).37-39 Transmission electron microscopy (TEM) images reveal 200–500 nm lateral dimensions for the as-exfoliated MoS2 nanosheets; the very low contrast of the sheets indicates their ultrathin feature (Figure 2a). Based on atomic force microscopy (AFM) height profiles (Figure 2b), the nanosheets possess a mean thickness of ~1 nm, close to that (0.6 nm) of a MoS2 monolayer.16 X-ray diffraction (XRD) diagram of the MoS2 nanosheets shows only one peak at small angel position (2 ~ 14o), which is totally different from that of bulk MoS2 (Figure 2c), confirming the ultrathin characteristics of the MoS2 sheets.16,40 Raman spectrum gives an additional peak at 150 cm-1 for the MoS2 nanosheets compared with that of bulk MoS2 (Figure 2d), which manifests partial formation of metallic 1T phase MoS2.16,40 Quantitative analysis by X-Ray photoelectron spectroscopy (XPS) reveals around 60 % for the transition of 2H into


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1T phase (to be further discussed below). The coexistence of the two phases has been frequently found in ultrathin MoS2 nanosheets fabricated by Li-intercalation.9 Atom transfer radical polymerization (ATRP) method was employed to synthesize PS-b-PEO copolymers;41 the detail procedures are given in the Supporting Information (SI). Nuclear magnetic resonance (NMR) and gel permeation chromatography (GPC) analyses gave degrees of polymerization (DPs) of 60 and 100 for the PS blocks in PS 60-b-PEO114 and PS100-b-PEO114 (the subscripts express DPs), which possess narrow molecular weight polydispersity indices (PDI) of 1.05 and 1.07, respectively (Figures S1-S2). The self-assembly of PS-b-PEO was performed by adding pure water into a THF solution of the copolymer, while the self-assembly of the P123 triblocks was carried out by directly dissolving the copolymer in water to produce aqueous solution, followed by increasing the system temperature to 40 oC (see details in Experimental Section). TEM images verify the formation of narrowly-disperse spherical micelles with mean diameters of 12 ± 1 nm and 15 ± 1 nm from PS60-b-PEO114 and PS100-b-PEO114, respectively (Figure S3). The micelle cores were formed by the aggregation of the hydrophobic PS segments and the coronae around the core were constructed by the hydrophilic PEO coils (Figure 1).21,23 In the micelle core, the average end-to-end distance (h) of an unperturbed PS chain can be expressed by an equation, h=ln1/2, where l is the length of one repeat unit (which is a constant) and n denotes DP of PS. Thus the average core diameter is tunable by altering the mean length of the PS blocks.23 P123 triblocks are known to form cylindrical micelles with a PPO core and a PEO corona under our self-assembly condition and the average core diameter is around 8 nm. Below 40 oC, however, P123 cannot form cylindrical micelles as the hydrophobicity of the PPO blocks reduces as the temperature decreases.42-45 The mixing of solutions of the spherical or 5 ACS Paragon Plus Environment


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cylindrical micelles, MoS2 sheets and aniline induced the synergistic self-assembly of the micelles and aniline monomers on the surfaces of the MoS2 nanosheets (Figure 1). The driving forces for the surface close-packing of the micelles can be attributed to both H-bonding and coordination interaction between Mo and N atoms;17 the H-bonding interaction resulted in the adsorption of aniline molecules in the PEO corona of the micelles as well as the micelle interconnection, while the Mo-N coordination stabilized the anchor of the micelles with aniline in their coronae on the MoS2 surfaces (to be supported below by XPS spectra). The addition of ammonium persulfate (APS) initiated the polymerization of the aniline monomers, which generated PANi network around the BCP templates. During the polymerization, the aniline molecules in the PEO corona, driven by a strong force caused by the polymerization, may migrate from the top to the peripheral empty space of neighboring micelles,20 resulting in the formation of porous networks (Figure 1). Finally, after the removal of the micelle templates by repeated washing with suitable solvents, 2D mesoporous PANi/MoS2 nanocomposites with well-defined spherical or cylindrical pore structures were obtained (Figure 1). The removal of the template was proved by the Fourier-transform infrared (FTIR) spectra of the nanocomposites (Figure S4), in which the characteristic signals of the copolymers disappeared completely. The control experiment without the addition of the MoS2 sheets and BCPs gave rise to nonporous PANi of irregular morphology (Figure S5a), validating the directed growth of porous PANi on the surfaces of the MoS2 nanosheets. Figure 3 shows the structure characterizations of the 2D PANi/MoS2 nanocomposites fabricated by using PS60-b-PEO114 as the template (named as mPANi/MoS2-1); their structural parameters are listed in Table 1. Scanning electron microscopy (SEM) micrographs reveal that mPANi/MoS2-1 possesses closely-arranged spherical pores with a mean diameter of 12 ± 6 ACS Paragon Plus Environment

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1 nm (Figure 3a), which accords well with the result obtained by TEM (Figure 3b). AFM profiles not only confirm the 2D mesoporous structure of mPANi/MoS2-1, but also gives a uniform thickness of 27 nm for the nanosheets (Figure 3c), which is close to twice the diameter of PS60-b-PEO114 spherical micelles. Raman spectrum of mPANi/MoS2-1 reveals the presence of MoS2 nanosheets (Figure S6), in which the signal at 150 cm-1 apparently attenuates, suggesting the coverage of PANi on the surface of MoS2. These results demonstrate the sandwich structure of mPANi/MoS2-1, in which mesoporous PANi monolayers grows on both sides of the MoS2 nanosheet. Nitrogen adsorption–desorption analysis gives a typical isotherm of mesoporous structure for mPANi/MoS2-1, from which a specific surface area of 258 m2 g-1 and an average pore diameter of 12 nm are obtained using the Barrett-Joyner-Halenda (BJH) calculation method (Figure 3d). In the XPS spectrum of mPANi/MoS2-1 which is deconvoluted according to similar fashions reported in literature,16, 17, 34, 39

there appears a Mo-N signal (401.1 eV) aside from the signals originating from PANi

and MoS2 (Figure 4a), which is attributed to the Mo-N coordination that stabilizes the patterning of PANi layer on MoS2 sheet.17 In addition, XPS analyses reveal that after the growth of PANi on the MoS2 sheet, the ratios of the 1T to 2H phase of MoS2 are basically identical (1T:2H  1.5:1) regardless of the thickness or the pore structure of the PANi layer (Figure 4b), indicating a highly similar physical nature of MoS2 in the different mPANi/MoS2 samples. The content of Mo element in mPANi/MoS2-1 is determined to be 6.1 wt% by XPS, which is supported by inductively coupled plasma (ICP) spectrometry, while the content of S element is 4.3 wt%. Thus, the molar ratio of Mo to S is calculated to be about 1:2 (Table 1). The mPANi/MoS2-2 nanosheets fabricated by using PS100-b-PEO114 as the template also possess a 2D mesoporous structure (Figure S7), which is highly similar to that of 7 ACS Paragon Plus Environment


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mPANi/MoS2-1. SEM and TEM images reveal an average pore diameter of 16 ± 1 nm for mPANi/MoS2-2 (Figure S7a, b). A uniform thickness of 35 nm was obtained by AFM analysis for the mPANi/MoS2-2 nanosheets (Figure S7c), which is approximately twice the average diameter of PS100-b-PEO114 spherical micelles. Nitrogen adsorption–desorption analysis gives a mean pore size of 15 nm and a specific surface area of 221 m2 g-1 for mPANi/MoS2-2 (Figure S7d). The molar ratio of Mo to S element in mPANi/MoS2-2 is also close to 1:2 according to XPS measurement. Notably, as the pores are created by using the micelle cores with mean diameters (d) depending on the PS block length (d  ln1/2) as the template, the average pore size of mPANi/MoS2 increases accordingly with increasing the DP of the PS block, leading to the corresponding increase of the thickness (related to the pore diameter) and the decrease of the specific surface area. This suggests a good control over the structural parameters of the mPANi/MoS2 nanocomposites through varying the length of the PS segment in the copolymer template. Apart from the above-mentioned pore size and thickness control, the pore architecture of the composites can also be well tailored. However, the intrinsic narrow window in the morphological phase diagram of the self-assembly of PS-b-PEO in solution make it difficult to obtain PS-b-PEO cylindrical micelles.46,47 Therefore, we chose pluronic-type BCPs, i.e. P123, as the pore-building agent, by which the formation of cylindrical micelles is relatively easier to control under appropriate self-assembly conditions.48 Figure 5 presents the structure characterizations of the resultant 2D PANi/MoS2 nanocomposite (mPANi/MoS2-3) and the related structural parameters are listed in Table 1. SEM and TEM micrographs show that mPANi/MoS2-3 possesses closely-packed stripe-like pores with a mean diameter of 10 ±1 nm (Figure 5a,b and Figure S8). A uniform thickness of 22 nm was obtained for the nanosheets 8 ACS Paragon Plus Environment

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by AFM measurements (Figure 5c), which is approximately twice the mean diameter of the P123 cylindrical micelles.42-44 Raman spectrum shows the peaks attributed to MoS2 nanosheets and the attenuation of the signal at 150 cm-1, indicating the coverage of PANi on the MoS2 surfaces (Figure S6). The existence of MoS2 nanosheets in the nanocomposite is confirmed by XPS (Figure 4). In the XPS spectrum, the appearance of the Mo 3p signal that is absent in the spectra of mPANi/MoS2-1 & 2 can be ascribed to the more exposure of MoS2 as a result of the long stripe-like pores. Based on nitrogen adsorption–desorption analysis, mPANi/MoS2-3 possesses an average pore diameter of 9 nm coupled with a specific surface area of 205 m2 g-1 (Figure 5d), which is smaller than those of mPANi/MoS2-1 & 2 due to the larger stripe-like pore structure. XPS analysis gives 5.8 wt% and 4.0 wt% for the Mo and S contents respectively, which are close to those in mPANi/MoS2-1 & 2. Thereby, the molar ratio of Mo to S is also around 1:2. For fundamental study, we studied the effect of pore structure on the capacitive performance of mPANi/MoS2 as electrode materials of supercapacitors, by employing a three-electrode cell with H2SO4 (1 M) as the electrolyte. The cyclic voltammetry (CV) charts of the mPANi/MoS2 samples exhibit a typical pseudocapacitive characteristic with redox peaks (Figure S9).49 Triangular charge-discharge curves are obtained by the galvanostatic measurements (0–0.8 V) at varied current densities (Figure 6a and Figure S10). The specific capacitance (Cs) of mPANi/MoS2 is calculated from the charge-discharge curves in terms of a previously reported method.23 Figure 6b shows that mPANi/MoS2-1 has the highest Cs of about 500 F g-1 at a current density of 0.5 A g-1. Note that Cs of all the mPANi/MoS2 samples are much larger than those of pure PANi (160 F g-1 at 1 A g-1) and thin MoS2 nanosheets (95 F g-1 at 0.5 A g-1), which are close to the reported values for PANi33, 49, 51-53 and MoS2 9 ACS Paragon Plus Environment


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nanosheets16, respectively. Moreover, the Cs of mPANi/MoS2-1 is also superior to those of many reported 2D nanocomposites, such as PANi/reduced graphene oxide (rGO), MoS2/rGO, nonporous PANi/MoS2 and microporous carbon/MoS2, etc. (see comparison in Table S1).30, 32-34, 36, 54, 55

Generally, Cs decreases as discharge current density increases. In our case, the Cs of mPANi/MoS2-1 maintains as high as 179 F g-1 at a high current density of 10 A g-1 (Figure 6b), demonstrating good rate performance. Such performance is better than those of the other two counterparts, most probably due to the higher surface area and lower charge transfer resistance (to be discussed below), which allow for more effective ion/electrode contact and faster charge transfer. The cycling stability of the mPANi/MoS2 samples was also tested and the results are shown in Figure 6c. The capacitance of mPANi/MoS2-1 retains ~94% of the initial value after 5,000 charge-discharge cycles at 10 A g-1, indicating a superb cycling stability of mPANi/MoS2-1, which probably benefits from the more interfacial contact between PANi and MoS2. Electrochemical impedance spectroscopy (EIS) was employed to further understand the reason of the improved capacity of mPANi/MoS2-1. The Nyquist curves show an arc and a spike at the high and low frequency regions, respectively, which are obtained by equivalent circuit simulation (Figure S11). According to the derived arc radius,56 the charge transfer resistance (Rct) follows the order: MoS2 nanosheet (1.3 Ω) < mPANi/MoS2-1 (2.1 Ω) < mPANi/MoS2-2 (2.7 Ω) < mPANi/MoS2-3 (3.5 Ω) < PANi (7.9 Ω). It should be mentioned here that for PANi synthesized in the range of room temperature to 40 oC, the effect of temperature on their electrical conductivity is negligible.57-59 The Rct values of the mPANi/MoS2 composites are between those of the MoS2 nanosheets and pure PANi, whereas 10 ACS Paragon Plus Environment

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their specific capacitances are apparently higher (Figure 6b), indicating the advantage of the combination of the two materials. Although the thin MoS2 nanosheets have a lower Rct, the aggregation and smash during charge-discharge process significantly reduces their capacitance.16 The coating of PANi can not only inhibit the aggregation and smash of the MoS2 sheets, but also enhance the electrical conductivity of PANi. In addition, the porous structure increases the contact surface area between the nanosheets and the electrolyte. These factors result in much higher specific capacitances of the mPANi/MoS2 composites than those of both the MoS2 nanosheets and pure PANi. On the other hand, the smaller resistance of mPANi@MoS2-1 compared with the other two counterparts, which can be ascribed to the more interfacial contact between the PANi layer and the MoS2 sheet because of the smaller pore size, makes an essential contribution to the enhancement of the electrical conductivity and capacitive performance of the electrode.60 Conclusions In summary, this work applied the strategy of block copolymer self-assembly to solution-based growth of mesoporous PANi with controlled pore structures and sizes on ultrathin

free-standing

MoS2

nanosheets,

yielding

2D

mesoporous

PANi/MoS2

nanocomposites. Spherical and cylindrical micelles formed by the controlled self-assembly of block copolymers including PS-b-PEO and P123 in solution were employed as the templates for the construction of well-defined spherical or cylindrical mesopores in the PANi/MoS2 nanocomposites, which show superior electrochemical performance as supercapacitor electrode materials. The effect of pore structures on the capacitive performance of the nanocomposites was investigated, which revealed that the mPANi/MoS2 nanosheets with the smaller spherical pores (12 nm average diameter) exhibits better electrical conductivity and 11 ACS Paragon Plus Environment


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capacitive performance as a result of their larger specific surface area and more PANi/MoS2 contact interface. The self-assembly strategy holds promise in tunable construction of a wide range of 2D porous materials with various well-defined pore structures, which afford opportunities to better understand pore structure-property relationship of 2D porous materials and to achieve their electrochemical performance control. Experimental Section Preparation of ultrathin MoS2 nanosheets37-39: Typically, 0.2 g of crude MoS2 crystals were immersed in a 2 mL solution of n-butyllithium (2.5 M) for two days in a round-bottom flask filled with nitrogen gas. Then, LixMoS2 was filtered and purified with hexane for over three times. Afterwards, exfoliation was performed by ultrasonicating LixMoS2 in 400 mL water for 1 hour. The mixture was centrifuged for three times to remove excessive lithium in the form of LiOH and unexfoliated residues. Synthesis of mPANi/MoS2-1 & 2: 0.06 g PS-b-PEO was dissolved in 12 mL THF, followed by slow addition of 24 mL H2O to proceed the micellar self-assembly. Afterwards, 30 mL MoS2 solution (0.5 mg/mL) and 70 μL aniline were added into the micelle solution. After 1 hour mild stirring of the mixed solution, 20 mL aqueous solution of APS 10 mg/mL was injected into the mixed solution to initiate the polymerization of aniline. mPANi/MoS2-1 & 2 were obtained by centrifugation and washed with tetrahydrofuran and water for three cycles to remove PS-b-PEO. Pure PANi was prepared under the similar conditions without the addition of MoS2 solution and BCPs, which produced nonporous PANi of irregular morphology, analogous to those synthesized in reported studies.34,49,51 Synthesis of mPANi/MoS2-3: Typically, 0.84 mg P123 was dissolved in a 30 mL MoS2 aqueous solution (0.43 mg/mL). After 1 hour mild stirring, 70 μL aniline was mixed into the 12 ACS Paragon Plus Environment

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solution. The mixture was stirred vigorously at 40 oC for 1 hour, and then 30 mL aqueous solution of APS (12 mg/mL) was injected to trigger the polymerization of aniline. mPANi/MoS2-3 was obtained by centrifugation, followed by washing with ethanol and water for over three cycles to remove P123 and excess ions. Below 40 oC, mPANi/MoS2-3 could not be achieved as P123 could not form cylindrical micelles in water at this temperature range. For the preparation of the mPANi/MoS2 nanocomposites, the above-mentioned concentrations of the ingredients are optimum. If the concentrations of the copolymer and/or aniline monomer were reduced, continuous PANi network could not be formed on the surfaces of MoS2 nanosheets; while additional PANi spheres would appeared if the concentrations of the copolymer and/or aniline monomer were increased (Figure S5b, c). Electrochemical performance evaluation: The electrochemical performance of the mPANi/MoS2 and control samples was evaluated according to reported procedures.23 Working electrodes (2 mg) were made by mixing dried active materials, carbon black, and polytetrafluoroethylene binder in a weight ratio of 7:2:1.

ASSOCIATED CONTENT Supporting Information Experiment details, supporting figures and calculations, etc. AUTHOR INFORMATION Corresponding Authors *E-mail: [email protected] (Y. M.) [email protected] (H. W.) 13 ACS Paragon Plus Environment


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NOTES The authors declare no competing financial interest. ACKNOWLEDGMENTS The authors are grateful for the Natural Science Foundation of China (51573091, 21774076, 21320102006, 91527304, 81670958 and 61774102), Program for Shanghai Eastern Scholar, Program of the Shanghai Committee of Science and Technology (17JC1403200 and 16JC1400703), and Shanghai Pujiang Program (16PJD027). The Instrumental Analysis Center of Shanghai Jiao Tong University is also appreciated for some measurements.

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Figure 1. Schematic illustration of the synthesis of mesoporous PANi/MoS2 (mPANi/MoS2) nanocomposites with different well-defined pore structures by employing a strategy of block copolymer self-assembly. In the self-assembly of the diblocks (a), the hydrophobic PS or PPO blocks form the cores (red or green color) of the spherical or cylindrical micelles while the hydrophilic PEO chains construct the coronae (blue) around the core (b); the coronae can absorb aniline molecules (c) that will polymerize into PANi network (d). Thus, the pore structure is tunable by varying the morphology of the micelles and the pore size is dependent on the average length of the PS or PPO blocks that form the micelle cores.



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Figure 2. (a) TEM image of the ultrathin MoS2 nanosheets, the inset shows the corresponding electron diffraction pattern of a selected area. (b) AFM height profile of the MoS 2 nanosheet. (c) XRD patterns of bulk MoS2 and the MoS2 nanosheets. (d) Raman spectra of bulk MoS2 and the MoS2 nanosheets.


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Figure 3. Structural characterizations of mPANi/MoS2-1 with spherical pore structure. (a) SEM image. (b) TEM image. (c) AFM height profile. (d) Nitrogen adsorption–desorption isotherm, the inset gives the pore size distribution.



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Figure 4. High-resolution XPS spectra of (a) N 1s and (b) Mo 3d of the different mPANi/MoS2 samples.


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Figure 5. Structural characterizations of mPANi/MoS2-3 with cylindrical pore structure. (a) SEM image. (b) TEM image. (c) AFM height profile. (d) Nitrogen adsorption–desorption isotherms, the inset shows the pore size distribution.



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Figure 6. Electrochemical performance of the mPANi/MoS2 nanocomposites. (a) Galvanostatic charge-discharge curves for mPANi/MoS2-1 at different current densities in 1 M H2SO4 electrolyte. (b) Capacitance retention with increasing current density for the various mPANi/MoS2 samples, pure PANi and thin MoS2 nanosheets, measured under similar conditions. (c) Cycling stability of the mPANi/MoS2 samples evaluated at a high current density of 10 A g-1. (d) Electrochemical impedance spectra of the mPANi/MoS2 samples, pure PANi and thin MoS2 nanosheets; the inset shows the close-up view of the high-frequency region.


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Table 1. Structural parameters of the different mPANi/MoS2 samples PSEM a (nm)

Tb (nm)

PBJH c (nm)

Surface Area d (m2 g-1)

CMo e (wt %)

CS e (wt %)

mPANi/MoS2-1

12 ±1

27

12

258

6.1

4.3

mPANi/MoS2-2

16 ±1

35

15

221

5.6

3.8

mPANi/MoS2-3

10 ±1

22

9

205

5.8

4.0

Samples

a

b

c

Average pore sizes obtained from SEM images. Average thicknesses obtained from AFM images. Average pore sizes calculated from pore size distribution curves using BJH method. d Calculated from nitrogen e

adsorption–desorption isotherms. The contents of Mo the S elements were measured by XPS.



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Graphic for manuscript


Growth of 2D Mesoporous Polyaniline with Controlled Pore Structures

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