Highly Uniform Carbon Sheets with Orientation-Adjustable Ordered

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Highly Uniform Carbon Sheets with Orientation-Adjustable Ordered Mesopores Xin Xi, Dongqing Wu, Lu Han, Yizhen Yu, Yuezeng Su, Wei Tang, and Ruili Liu ACS Nano, Just Accepted Manuscript • DOI: 10.1021/acsnano.8b00576 • Publication Date (Web): 07 May 2018 Downloaded from http://pubs.acs.org on May 8, 2018

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Highly Uniform Carbon Sheets with OrientationAdjustable Ordered Mesopores Xin Xi,† Dongqing Wu,*,‡ Lu Han,‡ Yizhen Yu,§ Yuezeng Su,† Wei Tang,† and Ruili Liu*,† †

National Engineering Lab for TFT-LCD Materials and Technologies, Department of Electronic

Engineering, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, People's Republic of China ‡

School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University, 800

Dongchuan Road, Shanghai 200240, People's Republic of China §

State Key Laboratories of Transducer Technology, Shanghai Institute of Technical Physics,

Chinese Academy of Sciences, 500 Yutian Road, Shanghai 200083, People's Republic of China *Corresponding Author: [email protected], [email protected].

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ABSTRACT: A soft-hard template-assisted method towards the unconventional free-standing ordered mesoporous carbon sheets (OMCSs) with uniform hexagonal morphology is developed by applying MgAl-layered double hydroxide (MgAl-LDH) as the hard template, triblock copolymer F127 as the soft template and phenolic resols as the carbon sources. It is found that the surface of MgAl-LDH can induce the morphology variation of resol-F127 monomicelles, leading to the formation of vertically or horizontally aligned mesopore arrays in the OMCSs, which can in turn determine their electrochemical energy storage behaviors in supercapacitors with different configuration. In all-solid-state supercapacitor with two face-to-face electrodes, OMCS with vertical mesopores manifests the best performances among the samples. By contrast, in micro-supercapacitor with in-plane film-like electrodes, OMCS with horizontal mesopores delivers higher energy/power densities than the other OMCSs, which are also comparable to the state-of-art supercapacitors based on ordered mesoporous carbons. The achievement of uniform carbon sheets with orientation adjustable mesopore arrays can help the understanding of their electrochemical storage mechanism and allow the optimization of the performances according to the device configuration, thus providing a powerful tool for the manipulation of energy storage devices in nanoscale.

KEYWORDS: soft-hard template, ordered mesopores, monomicelles, carbon sheets, supercapacitors


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The enthusiasm for the controllable fabrication of mesoporous carbons originates from their tremendous potentials in adsorption, separation, catalysis, and energy storage.1-5 Specifically, the mono-dispersed mesoporous carbon nanomaterials with uniform morphologies are highly attractive since they can integrate the intriguing features of mesopores and homogeneous nanostructures into a single entity, thus leading to unique properties and applications.6-10 Therefore, the control over the architectures/dimensionalities of mesoporous carbons and the regulation of their porosities are of equal importance.11-13 In this regard, two-dimensional (2D) or pseudo-2D porous carbons have arouse tremendous interests in the last decade since their sheetlike structures render the sufficient exposure of the pores and the anisotropic transportation of mass and charge carriers.14-16 Moreover, these porous carbon sheets can serve as the lowdimensional building blocks for the construction of more complicated architectures such as aerogels17,18 and films.19-21 In the resultant superstructures, the assembled mesopores can provide oriented channels for the fast transportation of mass, which are of paramount importance in the electrochemical energy storage devices such as supercapacitors and lithium ion batteries.22 However, most of the reported fabrication approaches towards porous carbons,23 such as KOH etching of grapheme,24-27 the activation of biomass28-30 or the pyrolysis of porous polymers31-35 cannot provide satisfactory controllability over the porosities of the resulting carbon sheets, which usually only contain disordered pores with wide size distributions. Recently, Zhao’s group obtained ultra-thin ordered mesoporous carbon (OMC) sheets with the thickness of ~ 1 nm by the carbonization of the block co-polymer/phenolic resol micelles deposited on the pore walls of anodic aluminum oxide.20 With this deposition strategy, the similar OMC sheets could also be formed on silica, graphene oxide and molybdenum disulfide.19,36 Nevertheless, the small thickness of these OMC sheets may cause severe damaging and folding when their supports are


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removed.20 Therefore, the fabrication of self-supportable OMC sheets with both controllable porosity and ordered morphology is still a highly challenging task. Herein, we report a soft-hard template-assisted approach towards unconventional free-standing OMC sheets (OMCSs) with MgAl-layered double hydroxide (MgAl-LDH) serving as the hard template, triblock copolymer F127 as the soft template and phenolic resols as the carbon sources. It is found that the interactions between MgAl-LDH and the resol-F127 monomicelles have a strong impact on the orientation of the mesopores in the OMCSs, thus rendering the controllable fabrication of OMCSs with vertically or horizontally aligned mesopore arrays, which can in turn influence their electrochemical energy storage behaviors in supercapacitors with different configurations. In the all-solid-state supercapacitor (ASSS) with two face-to-face electrodes, OMCS having vertical mesopore arrays shows outstanding energy density (28.9 Wh kg-1) and power density (288 kW kg-1), comparable to the state-of-the-art supercapacitors based on OMCs. On the other hand, OMCS containing horizontal mesopore arrays in micro-supercapacitors (MSCs) with in-plane film-like electrodes delivers a high power density of 242 W cm-3, outperforming most of the OMCs. More importantly, the fabrication of carbon sheets with orientation adjustable mesopore arrays can help the understanding of the electrochemical storage mechanism and allow the optimization of the device performances according to their configuration, thus providing a powerful tool for the manipulation of energy storage devices in nanoscale.


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RESULTS AND DISCUSSION

Figure 1. Schematic illustration of the fabrication process for the OMCSs. a) The coassembly of triblock copolymer F127 and low-molecular-weight phenolic resols leads to the formation of the resol-F127 monomicelles. b) The deposition of monomicelles on the surface of MgAl-LDH with the help of interface-induced interactions. c) The cross-linking and solidify of resol via the hydrothermal treatment. d) The formation of OMCS/LDH by the carbonization of the monomicelle/LDH composites. e) OMCS can be obtained after etching away the hard template. As shown in Figure 1, the pre-prepared resol-F127 monomicelles in weak alkaline aqueous solution can gradually deposit on the surface of MgAl-LDH with the assistance of hydrogenbonding37,38 and electrostatic interactions.39,40 The hydrothermal treatment after the deposition of monomicelles render the cross-linking and solidify of resol. The subsequent thermal treatment leads to the carbonization of resol, which can be confirmed by the X-ray photoelectron


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spectroscopy (XPS) measurements (Figure S1). The products from thermal treatment are subsequently etched with hydrochloride acid and sodium hydroxide to eliminate the residue of MgAl-LDH,41,42 thus generating the hexagonal OMC sheets. And the effective removal of hard template can be verified by the results from XPS (Figure S2 and Table S1) and the inductively coupled plasma-optical emission spectroscopy (ICP-OES, Table S2). By adjusting the amount of MgAl-LDH and resol-F127 monomicelle, four samples were obtained and denoted as OMCS-0 (no addition of MgAl-LDH), OMCS-1 (mass ratio of MgAl-LDH and resol-F127 monomicelle ~ 1 : 3), OMCS-2 (~ 1 : 1.5) and OMCS-3 (~ 1 : 1), respectively.

Figure 2. Morphology of the OMCSs. The cross-sectional SEM images of a) OMCS-1, and b) OMCS-2. The SEM images of c) OMCS-1, and d) OMCS-2. The inset of c) marks the hexagonal patterns of mesopores (scale bar: 25 nm). The morphology of OMCSs were first characterized by field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). As shown in Figure S3,


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OMCS-0 is in the form of spheres with the diameters of ~ 90 - 120 nm. With the utilization of MgAl-LDH, OMCS-1, OMCS-2 and OMCS-3 have a regular hexagonal shape with an average lateral size of ~ 3 - 4 μm, which perfectly replicate the sheet-like morphology of the hard template (Figure S4 and S5), implying their better mechanical stability than the ultrathin OMC sheets20. The cross-sectional SEM and TEM images of the three OMCSs disclose that their thickness is ~ 9 nm (Figure 2 and S6), which has no obvious relevance with the mass ratio of resol-F127 monomicelle to MgAl-LDH. The broken edges of some OMCSs (Figure S7) imply that these carbon sheets are produced by pairs, confirming that the resol-F127 monomicelles are deposited on both sides of MgAl-LDH during the self-assembly process (Figure 1). As expected, both SEM and TEM characterizations indicate the existence of ordered mesopores on the surface of the OMCSs (Figure 2 and Figure 3). More importantly, the porosities of the sheet-like OMCSs exhibit obvious dependence on the adding amount of MgAl-LDH. In the case of OMCS-1, the mesopores with the sizes of ~ 10 nm are vertically grown on the carbon sheets in a highly ordered hexagonal pattern (Figure 2c and 3b). In contrast, the incremental concentration of MgAl-LDH during the fabrication of OMCS-2 causes the formation of the fingerprint-like mesopores with the diameters of ~ 10 nm aligned parallel to its surface (Figure 2d and 3d). With the highest adding amount of MgAl-LDH in the three samples, OMCS-3 contains lots of irregular defects, which are randomly distributed between the domains of channel-shaped mesopores (Figure S8).


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Figure 3. Well-defined hexagonal OMCSs with highly ordered mesopores. TEM images of a), b) OMCS-1 and c), d) OMCS-2. X-ray diffraction (XRD), synchrotron small-angle X-ray scattering (SAXS) and Raman spectroscopy were further applied to survey the microstructures of the samples. As compared in Figure S9, the characteristic diffractions from MgAl-LDH are absent in the XRD profiles of the OMCSs, implying the complete removal of the hard template by the etching process, which is in good agreement with the XPS and ICP results. The broad diffractions at around 26° and 44° (Figure S9b) are indexed to the (002) and (100)/(101) planes of graphitic carbon.18 More importantly, The SAXS patterns of OMCS-1 with vertical mesopores show two resolved scattering peaks with the q values of ~ 0.46 and ~ 0.79 nm-1, which can be indexed as the (100) and (110) reflections of a highly ordered hexagonal mesostructure.1 In contrast, only one scattering peak with the q values of ~ 0.47 nm-1 can be found in the SAXS patterns of OMCS-2, attributable to the (100) plane of its mesopore arrays.1 In the Raman spectra of the OMCSs


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(Figure S10a), the two peaks at ~ 1350 and ~ 1590 cm-1 are attributable to the characteristic D band and G band of carbon, respectively, which are similar to the Raman results of previously reported mesoporous carbon sheets.18,20 Although the four OMCSs have distinct different architectures and porosities, the XRD and Raman spectra of them indicate that they have similar graphitic degree, which is reasonable since they are obtained from the same carbonization conditions. The N2 adsorption and desorption measurements of the OMCSs were conducted to provide a better understanding on their porosities. As indicated in Figure S10b, all the samples manifest type-IV isotherms with hysteresis loops, which are distinct characteristics of the mesoporous materials.1 Different from the other three sheet-like OMCSs, OMCS-0 has a H1-type hysteresis loop, typical for spherical samples with ordered mesopores.43 In contrast, OMCS-1, OMCS-2 and OMCS-3 show H3/H4 hysteresis loops, which are often found in 2D mesoporous materials.18,44 The Brunauer-Emmett-Teller (BET) surface areas of OMCS-0, OMCS-1, OMCS-2 and OMCS-3 are 714, 650, 640 and 479 m2 g-1, respectively, which are higher than the previously reported composites of OMC/graphene aerogel,18 mesoporous carbon nanosheets20 and nitrogen-doped mesoporous carbon nanosheets.45 On the other hand, the pore volume for OMCS-3 (0.94 cm3 g-1) is larger than OMCS-0 (0.83 cm3 g-1), OMCS-1 (0.76 cm3 g-1) and OMCS-2 (0.80 cm3 g-1), which should be owing to its defective surfaces.


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Figure 4. Electrochemical performances of the ASSSs with the OMCSs as electrode materials. a) CV curves of the samples obtained at 1000 mV s-1. b) CV curves of OMCS-1 at different scan rates from 30 to 3000 mV s-1. c) Galvanostatic charge-discharge curves of OMCS-1 at the current density from 20 to 100 A g-1. d) Specific capacitance retention of the ASSSs with varied current densities. The ordered mesopores and large ion-accessible surface areas of the OMCSs are the appealing features for electrochemical energy storages. To verify these advantages of the OMCSs, symmetric all-solid-state supercapacitors (ASSSs) were fabricated by using them as electrode materials and polyvinyl alcohol (PVA)/H2SO4 gel as electrolyte. The electrochemical performance of the resultant ASSSs was first analyzed with cyclic voltammetry (CV) and galvanostatic charge/discharge tests. As shown in their CV curves at 1000 mV s-1 (Figure 4a), it can be discerned that OMCS-1 reveals a larger capacitive response than OMCS-0, OMCS-2, and OMCS-3. Moreover, the CV curves of all the sheet-like OMCSs display nearly rectangular


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shapes from the range of 30 to 3000 mV s-1 (Figure 4b and Figure S11), indicating the efficient electrical double-layer capacitive behavior. In contrast, obvious distortion can be found in the CV curves of the spherical OMCS-0. According to the galvanostatic charge/discharge cycling curves (Figure 4c and Figure S11), the capacitance of OMCS-1 is about 208 F g-1 at a current density of 0.2 A g-1, much higher than those of OMCS-0 (118 F g-1), OMCS-2 (163 F g-1), and OMCS-3 (121 F g-1), and comparable to the best results from the OMC based supercapacitors (Table S3). OMCS-1 also exhibits a better rate capability than the other samples in this work (Figure 4d). Even at a high current density of 100 A g-1, its capacitance still can be kept at 106 F g-1, superior to OMCS-2 (94 F g-1) and OMCS-3 (60 F g-1), and twice higher than OMCS-0 (48 F g-1).

Figure 5. The structures and performances of the MSCs with sheet-like OMCSs as electrode materials. a) Schematic illustration of the in-plane MSCs. b) Top-view SEM image of the interdigital finger Au electrodes coated with the film of the OMCSs. Inset: cross-section image of the OMCS film. c) CV curves of the MSCs at the scan rate of 5 mV s-


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. d) Specific capacitance retention as a function of scan rates from 5 to 1000 mV s-1. e)

Ragone plots of the MSCs. f) Cycling stability of the MSCs at 1 V s-1 for 20 000 circles. The above electrochemical tests indicate that OMCS-1, OMCS-2, and OMCS-3 are better electrode materials for ASSSs than spherical OMCS-0. It should be noted that the small thicknesses and highly oriented pores of these sheet-like OMCSs are favorable for the transportation of charge carriers within and between these mesoporous sheets when they are fabricated into films. Therefore, these OMCSs are also appealing active materials for in-plane micro-supercapacitors (MSCs, Figure 5). As indicated in Figure 5c, OMCS-1 in MSCs still delivers an impressive specific capacitance of 28 F cm-3 (with an areal capacitance of 8.44 mF cm-2) at 5 mV s-1, which is higher than those of OMCS-2 (18 F cm-3), OMCS-3 (12 F cm-3), spherical OMCS-0 (9.9 F cm-3, Figure S12) and most of the carbon materials (Table S4). Especially, OMCS-1 and OMCS-2 manifest the specific capacitances of 9.7 and 8.2 F cm-3 at a high scan rate of 1000 mV s-1 (Figure 5d), which are about two times higher than that of OMCS3 (4.2 F cm-3). When the scan rates are increased from 5 to 1000 mV s-1, it is interesting that OMCS-2 with horizontal mesopores shows a better initial capacitance retention of 45.9 % than that of OMCS-1 with vertical mesopores (34.5 %). As the results, the MSC with OMCS-1 as electrode material delivers a maximum volumetric energy density of 3.9 mWh cm-3 and power density of 157 W cm-3, while the MSC with OMCS-2 has a higher power density of 242 W cm-3 (Figure 5e), which is also comparable to most of the carbon material based MSCs (Table S4). Additionally, the MSC with OMCS-1 manifests an outstanding cycling stability by maintaining ~ 99% of the initial capacitance after 20 000 cycles at a scan rate of 1000 mV s-1 (Figure 5f).


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Figure 6. The interface induced co-assembly mechanism of resol-F127 monomicelles on the surface of MgAl-LDH. According to the packing parameter theory (P = v/a0lc, where P is the packing parameter, v is the volume of the hydrophobic chain, a0 is the polar head surface area at the critical micellar concentration, and lc is the chain length), the optimal surface areas of the exposed parts in the resol-F127 monomicelles can be affected by the addition of MgAl-LDH, which can thus lead to the morphology variation of the monomicelles. If P ≤ 1/3, the monomicelles have a tendency to form spherical structures; If 1/3 ≤ P ≤1/2, cylindrical monomicelles are favored.


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Based on the results of structural characterization, an interface induced co-assembly mechanism of resol-F127 monomicelles on the surface of MgAl-LDH can be proposed for the fabrication of OMCSs with controllable porosity (Figure 6). Firstly, the spherical monomicelles are prepared by the co-assembly of phenolic resols and Pluronic triblock copolymer.18,20,43,46 Without the presence of other components, these resol-F127 monomicelles can experience a homogeneously nucleated assembly process to form spherical aggregates, and the following thermal treatment can further generate OMCS-0 as the product. After the addition of MgAlLDH, its hydroxyl-group-rich surface can effectively reduce the repulsion between the resolF127 monomicelles by providing multiple noncovalent forces such as hydrogen bonds37,38 and hydrophilic interactions.47 Therefore, the monomicelles tend to deposit on the surface of MgAlLDH via a heterogeneous nucleation process rather than the self-aggregation into spherical architectures.43 During the deposition step, the packing behaviors of the monomicelles mainly depend on the ratio of MgAl-LDH to the monomicelles, which can be explicated by the packing parameter theory.48-51 With a low concentration of MgAl-LDH, the resol-F127 monomicelles tend to form a hexagonal arrays on both sides of the hard template, which can later be converted to OMCS-1 with vertically aligned mesopores in a p6mm pattern. At this stage, the packing parameter of the resol-F127 monomicelles is supposed to be smaller than 1/3, which render the formation of the spherical morphology. When the amount of MgAl-LDH is increased, less resolF127 monomicelles can be deposited on them, and the interactions between the surface of MgAlLDH and monomicelles can further help to decrease the repulsive forces between the monomicelles.48 Based on the packing parameter theory, the optimal surface areas of the exposed parts (a0) in the resol-F127 monomicelles can be reduced, leading to the increase of the packing parameter over 1/3, which can thus cause the transformation of the monomicelles into cylindrical


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morphology (Figure 6 and S13).49-51 As the result, worm-like mesopore arrays parallel to the surface of MgAl-LDH can be obtained in OMCS-2. The different morphology of the monomicelles on the surface of MgAl-LDH can be confirmed by the SEM images of the asmade composites of resol-F127 monomicelles and MgAl-LDH, in which the ordered mesostructures correspond to the mesopore arrays of OMCS-1 and OMCS-2 can be easily found in their precursors (Figure S14). When the content of MgAl-LDH is further improve, the monomicelles are not enough to enwrap all the surface of MgAl-LDH, which thus causes disordered domains of mesopores in OMCS-3. It is interesting that the variation of the micelles morphology with the ratio of monomicelles and MgAl-LDH is in an opposite trend to our previous work on the composites of OMC and graphene aerogels,18 which should be due to the different hydrophilicity of MgAl-LDH and graphene.48 The tunable aggregation behaviors of resol-F127 monomicelles can be utilized in the fabrication of various OMCs or their composites with controllable porosities by the selection of the assembly conditions and substrates. In general, it is supposed that the electrolyte accessible surface areas are important for the double layer capacitance of porous carbons. However, the highest surface area of OMCS-0 does not result in the best specific capacitance or rate capability among the four OMCSs.4 The excellent electrochemical performance of sheet-like OMCSs in supercapacitors can be attributed to the synergistic effects of their 2D architectures and ordered mesopore arrays, which allow the sufficient exposure of the active sites and minimize the diffusion barriers of electrolyte ions, resulting the high charge storage ability and fast ion transportation.14,16,52 Specifically, the sheetlike architectures of OMCSs allow them to easily form layer-structured packing parallel to the current collectors (Figure S15), which will effectively facilitate the transportation of ions driven by electric field and reduce the resistance within the electrodes.53 Additionally, the defects


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generated during the removal of hard template1 may also have contribution to the energy storage performance of the OMC sheets.54 More importantly, the combination of ordered mesopore arrays and 2D architectures in the OMCSs provides the opportunity to influence their electrochemical energy storage behaviors with the orientation of the mesopores.18 In ASSSs with two symmetric electrodes, the electrolyte ions move perpendicularly to the OMCS based electrode films (Figure S16). In such a configuration, the mesopores in OMCS-1 can provide vertically oriented channels within and between the sheets for the faster percolation of the electrolyte than the horizontally aligned mesopores in OMCS-2 (Figure S16a and S16b), which will then cause the enhanced rate performances.16,55,56 Differently, when the OMCS sheets are deposited in a thin electrode film of the in-plane MSCs, the fingerprint-like parallel aligned mesopores can serve as the paths with length over hundreds of nanometers for the rapid movement of charge carriers (Figure S16c and S16d).57,58 To verify the above hypothesis, the electrochemical impedance spectra (EIS) of OMCSs based on ASSSs were further recorded (Figure S17). The Nyquist plots of the three sheet-like OMCSs feature nearly vertical curves and the phase angles are close to -90° at very low frequency, indicating the ideal capacitive performances.59,60 A close-up observation (Figure S17b) of their middle frequency regime reveals the shorter Warburg regions for sheet-like OMCSs than that for spherical OMCS-0, suggesting the better diffusion of charge carriers in the electrodes. Therefore, the 2D structures of OMCS-1, OMCS-2 and OMCS-3 are more favorable for the access of electrolyte than the globular structure of OMCS-0, which guarantees a high capacitance even at the high current densities. Furthermore, the low frequency part of the oblique curve from OMCS1 shows a high slope among the OMCSs, thereby revealing a decreased obstruction of ion movement. Therefore, OMCS-1 with perpendicular mesopores delivers an extremely high power


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density of 288 kW kg-1 and large energy density of 28.9 Wh kg-1 with only a 1.0 V potential window (Figure S17d), strongly suggesting the crucial role of planar structure with vertical pores in shortening the ion diffusion path. On the other hand, a further comparison of the frequency response of the MSCs can explain the different performances of the OMCSs. As shown in Figure S18, the Nyquist plots of the MSC with OMCS-2 show the decreased Warburg resistance curve in the of middle-frequency range, revealing a faster transport of the electrolyte ions along the parallel pore structures in the carbon sheets. This observation is consistent with its higher power density and superior capacitance retention. CONCLUSION In this work, we demonstrate a soft-hard template-assisted route to the 2D free-standing carbon sheets with uniform morphology and tunable orientation of the mesopore arrays. As the electrodes in supercapacitors, the OMCSs deliver prominent performances including high capacitance, rate capability and energy/power densities, which are turned out to be governed by their morphologies and porosities. Above all, the surface dependent aggregation behavior of resol-F127 monomicells in this work provides an intriguing platform towards various 2D freestanding porous materials with controllable porosities and a broad range of applications in electrochemical energy storage, biological and medical sciences. EXPERIMENTAL SECTION Reagents and Materials. All the reagents (analytical grade) were purchased from Sinopharm Chemical Reagent Co., Ltd. and used as received without further purification. Ultra-pure water (18 MΩ • cm) was used for the preparation of all the solutions. Preparation of MgAl-LDH. Firstly, MgAl-layered double hydroxide (MgAl-LDH) was prepared

by the urea-assisted

co-precipitation

approach.41

In

a

typical

procedure,


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Mg(NO3)2•6H2O (5.13 g) and Al(NO3)3•9H2O (3.75 g) were firstly mixed in the aqueous solution of urea (3 M, 200 mL). Transferred to a three-necked glass flask (500 mL) equipped with a reflux condenser, the mixture was stirred at 100 °C for 12 h and then kept at 94 °C for another 12 h without stirring. Subsequently, the resulting suspension of MgAl-LDH was repeatedly washed with water till the pH value approached 7. Finally, the precipitated MgAlLDHs was re-dispersed in ultra-pure water to form a homogenous suspension (~ 12 mg mL-1). Preparation of resol-F127 monomicelles. Typically, phenol (3.0 g) and the solution of formaldehyde (37 wt%, 10.5 mL) were added slowly to the aqueous solution of NaOH (0.1 M, 75 mL) in a three-necked glass flask (250 mL) equipped with a reflux condenser. The mixture was stirred at 70 °C for 0.5 h to obtain a reddish solution of low-molecular-weight phenolic resols. Afterwards, the aqueous solution of triblock copolymer Pluronic F127 (1.47 wt%, 65 mL) was added to the resol solution (18.0 g) and the resulting mixture was stirred at 67 - 70 °C for about 12 h until the color of the mixture turned into crimson, which indicated the formation of the resol-F127 monomicelles (~ 30 mg mL-1).43 Fabrication of OMCSs. The suspensions of MgAl-LDH (~ 12 mg mL-1, 6.0, 12.0, and 18.0 mL) were firstly mixed with the solution of resol-F127 monomicelles (~ 30 mg mL-1, 7.0 mL). The mixture was then diluted to 30 mL with water and transferred into a Teflon lined stainless steel autoclave (50 mL), which was kept still for 6 h for the sufficient contact between MgAlLDH and resol-F127 monomicelles. Consequently, the mixture was hydrothermally treated at 130 °C for 20 h. After cooling to room temperature, the resulting composites of MgAl-LDH and resol-F127 monomicelles were collected via filtration, washed with water and freeze-dried for 24 h. The composites were then thermally treated at 700 °C in nitrogen flow to allow the formation of OMC sheets on the surface of MgAl-LDH. The resulting black solids were treated with the


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aqueous solution of NaOH (15.0 M) at 150 °C for 12 h and HCl (5.0 M) at 80 °C for another 12 h to remove the residue of MgAl-LDH. After filtration, washing with water, and vacuum drying, the OMCSs were finally obtained as black powders. According to the different volumes of the MgAl-LDHs suspensions used in the fabrication process, the OMCSs were named as OMCS-0 (no addition of MgAl-LDHs), OMCS-1 (6.0 mL, mass ratio of MgAl-LDHs and resol-F127 monomicelles ~ 1 : 3), OMCS-2 (12.0 mL, ~ 1 : 1.5) and OMCS-3 (18.0 mL, ~ 1 : 1), respectively. Structural characterizations. Field emission scanning electron microscopy (FE-SEM) images were obtained on a JSM-7800F (JEOL, Japan) at an electric voltage of 3 KV. Transmission electron microscopy (TEM) measurements were conducted on a JEM-2010F (JEOL, Japan) with an accelerating voltage of 200 kV. Samples were dispersed in ethanol and transferred onto a Cu grid for TEM measurements. X-ray diffraction (XRD) patterns were recorded on a Bruker D8 Advance powder Diffractometer (Bruker, Germany) using Cu Kα radiation (40 kV, 40 mA) at the scan rate of 5° min-1 from 10° to 80° (2θ). The SAXS measurements were performed on the BL16B1 beamline of Shanghai Synchrotron Radiation Facility (SSRF). The energy of the X-rays was set to 12 keV and the image acquisition time was 30 s. The powder-like samples were held in evacuated 1 mm capillaries. The residue amount of Mg and Al in OMCS-1 and OMCS-2 were analyzed by inductively coupled plasma-optical emission spectroscopy (ICP-OES) (iCAP7600, Thermo Scientific, USA). Before analysis, approximately 50 mg of the dried and homogenized samples was weighed into quartz vessels, and dispelled for several hours by adding HNO3 (65 - 68 %). Raman spectra were recorded on a Senterra R200-L (Bruker Optics, Germany) with the excitation from the 532 nm line of an Arion laser (5 mW). Nitrogen sorption isotherms were measured on ASAP 2460 (Micromeritics


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Instrument Corp, USA). Before measurements, the samples were degassed in a vacuum at 200 °C for about 12 h. Electrochemical measurement. All the electrochemical measurements were carried out with a CHI 660E electrochemical workstation (Shanghai Chenhua Limited Co.) under ambient condition. The potential ranges for cyclic voltammetry (CV) and galvanostatic charge/discharge (GCD) tests were from 0 to 1 V. To prepare the working electrode, the sample dispersed in ethanol was painted onto a platinum plate without binders and conductive fillers and dried on a heating apparatus. The amount of the sample was calculated by the mass difference of the platinum plate before and after the loading process. Electrochemical impedance spectra (EIS) were recorded in the frequency range of 10 mHz to 0.1 MHz with a 5 mV amplitude referring to the open circuit potential.

ASSOCIATED CONTENT The authors declare no competing financial interests. Supporting Information Available: Additional discussions and figures of the morphology, structure and electrochemical properties of OMCSs. Figures showing (1) The C 1s peaks of the monomicelle/LDH composite; (2) The XPS spectra of OMCS-1; (3) Morphologies and structures of OMCS-0 and MgAl-LDH; (4) SEM images of OMCS-1/LDH, OMCS-2/LDH and OMCS-3/LDH; (5) TEM images of OMCS1 and OMCS-2; (6) The cross-sectional TEM images of OMCS-1 and OMCS-2; (7) TEM images and HRSEM images of OMCS-1 and OMCS-2; (8) TEM images and HRSEM images of OMCS3; (9) XRD and SAXS patterns of the samples; (10) Raman spectra and N2 adsorption-desorption


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isothermals of OMCSs; (11) Electrochemical characterizations of the ASSSs; (12) The performances of the MSCs with spherical OMCSs as electrode materials; (13) HRSEM images and TEM images of the OMCS with both vertical and horizontal mesopores; (14) The SEM images of the as-made composites of resol-F127 monomicelles and MgAl-LDH; (15) Top-view SEM images of the interdigital finger Au electrodes; (16) Schematic depiction of the symmetric ASSSs and in-plane MSCs based on the sheet-like OMCSs; (17) Electrochemical properties of the ASSSs; (18) Electrochemical properties of the MSCs; Tables showing (1) The atom contents of C, O, Mg and Al atoms in the OMCSs; (2) The weight contents of Mg and Al atoms in the OMCSs; (3) The recently reported carbon-based conventional supercapacitors; (4) The recently reported carbon-based MSCs. These materials are available free of charge via the Internet at http://pubs.acs.org.

ACKNOWLEDGMENT This work was financially supported by National Natural Science Foundation of China (61575121, 51772189, 21772120, 21572132 and 21372155), 973 Program of China (2014CB239701), Shanghai Committee of Science and Technology (16JC1400703), MPI-SJTU Partner Group Project for Polymer Chemistry of Graphene Nanoribbons and Aeronautical Science Foundation of China (2015ZF57016). We also thank the Instrumental Analysis Center of Shanghai Jiao Tong University, Advanced Electronics Materials and Devices (AEMD) of Shanghai Jiao Tong University and Shanghai Synchrotron Radiation Facility (SSRF) for the characterization of materials.


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AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]. *E-mail: [email protected]. Author Contributions X.X., R.L. and D.W. conceived and designed the experiments. X.X. carried out the fabrication of nanomaterials and performed material microstructural characterization. X.X., Y.Y. and W. T. contributed to supercapacitors fabrication and electrochemical measurements. X.X., R.L., L.H. Y.S. and D.W. analyzed the relevant data and co-wrote the paper, and all authors discussed the results and commented on the manuscript. The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.

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BRIEFS Free-standing ordered mesoporous carbon sheets (OMCSs) with uniform hexagonal morphology are obtained via a soft-hard template-assisted method, whose electrochemical energy storage behaviors in different supercapacitors manifest obvious dependence on the orientation of their mespore arrays. Keyword: soft-hard template, ordered mesopores, monomicelles, carbon sheets, supercapacitors


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Xin Xi, Dongqing Wu*, Lu Han, Yizhen Yu, Yuezeng Su, Wei Tang, and Ruili Liu*

Highly Uniform Carbon Sheets with Orientation-Adjustable Ordered Mesopores


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Highly Uniform Carbon Sheets with Orientation-Adjustable Ordered

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