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Chemical Foaming Coupled Self-etching: A Multiscale Processing Strategy for Ultrahigh-Surface-Area Carbon Aerogels Fulai Qi, Zhangxun Xia, Jutao Jin, Xudong Fu, Wei Wei, Suli Wang, and Gongquan Sun ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b16556 • Publication Date (Web): 11 Dec 2017 Downloaded from http://pubs.acs.org on December 12, 2017

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ACS Applied Materials & Interfaces

Chemical Foaming Coupled Self-etching: A Multiscale Processing Strategy for UltrahighSurface-Area Carbon Aerogels Fulai Qi, a,b Zhangxun Xia, a Jutao Jin,c Xudong Fu,a Wei Wei, a Suli Wang, a* Gongquan Sun a* a

Division of Fuel Cell & Battery, Dalian National Laboratory for Clean Energy, Dalian Institute

of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China. b

University of Chinese Academy of Sciences, Beijing 100039, China.

c

School of Environment and Architecture, Dongguan University of Technology, Dongguan

523808, China KEYWORDS: carbon aerogels, chemical foaming, self-etching, ultrahigh surface area, multifuntional applications

ABSTRACT: Due to the unique structure, carbon aerogels have always shown great potential for multifunctional applications. At present, it is highly desirable but remains challenging to tailor the micro-structures in respect of porosity and specific surface area to further expand its significance. A facile chemical foaming coupled self-etching strategy is developed for multiscale processing of carbon aerogels. The strategy is directly realized via the pyrolysis of a multifunctional precursor (pentaerythritol melamine phosphate) without any special drying process and multiple steps. In the micrometer scale, the macroporous scaffold structures with

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interconnected and strutted carbon nanosheets are built up by chemical foaming from decomposition of melamine, whereas the meso/micro-porous nanosheets are formed via selfetching by phosphorus containing species. The delicately hierarchical structures and recordbreaking specific surface area of 2668.4 m2 g-1 render the obtained carbon aerogels great potentials for absorption (324.1–593.6 g g-1 of absorption capacities for varied organic solvents) and energy storage (338 F g-1 of specific capacitance). The construction of such novel carbon nano-architecture will also shed light on the design and synthesis of multifunctional materials.

1. INTRODUCTION With the growing demand for alleviate of energy crisis and environmental pollution, carbonbased nanomaterials used as active component for absorption and energy storage have drawn intensive attentions.1-6 Besides inheriting highly electronic conductance, stability, and mechanical properties from traditional carbon materials, carbon aerogels (CAs) with threedimensional (3D) porous interconnected networks,7-9 possess the tailored micro-structures, which make it much competition in multifunctional applications, including damping materials, thermal and noise insulation, organic reagent absorption, energy conversion and storage etc.7, 10-12 The key to sustain such multifunctional applications strongly depends on the tailored micro-structures of CAs, especially in terms of porosity and high specific surface areas (SSA). Impressive efforts have been made to design and fabricate CAs based on different materials and strategies in recent years. The template-directed methods have been proved to be an effective way to obtain CAs with ordered and controllable porous structures by adopting metal foam, nano-networks, and other nanostructures as hard templates,10, 13-14 which are limited due to their inaccessible templates and multi-step procedures for implementation. Alternatively, the


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template-free routes: i) the carbonization of aerogels, including glucose, bacterial cellulose, and resorcinol-formaldehyde resin;15-18 ii) the assembly of low dimensional carbon nanomaterials,9, 19-21

have also been widely used to fabricate CAs due to their facile and flexible synthesis.

Despite an ultrahigh theoretical SSA of 2630 m2 g-1 of graphene,22-23 the unavoidable agglomeration caused by van der Waals forces24-25 and collapse of the structure caused by capillary force26-28 would significantly diminish the accessible SSA (typically below 500 m2 g-1) and porosity without special drying process. Recently, nonflammable gas were used as space filler to construct a graphene bubble network with a SSA of 1005 m2 g-1, which provides a promising approach for synthesis of 3D carbon network.29 Yet there is still a remarkable gap between such CAs and activated carbon materials (e.g. 2100 m2 g-1 for commercial YP-80 from Kuraray) owning to the absence of effective surface modulation. Accordingly, the construction of macroporous framework and the boost of SSA are two crucial targets for CAs but remain challenging to achieve in a single step. Herein, we successfully realized chemical foaming coupled self-etching strategy via the molecular design of carbonaceous precursor. A lightweight (0.65 mg cm-3) high-surface-area (2668.4 m2 g-1) monolith carbon aerogels (HMCAs) with hierarchical structure were fabricated by the pyrolysis of the multifunctional precursor pentaerythritol melamine phosphate (PMP). The melamine section serves as foaming agent to construct macroporous scaffold, and phosphorus containing species play a role in dehydration and self-etching for micro/meso pores. Benefited for such synergetic procedures, the record-breaking SSA and the delicately hierarchical structures of the CAs deliver great potentials for multifunctional applications in the field of energy and environment. 2. EXPERIMENTALSECTION


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Materials. Pentaerythritol and melamine were purchased from Tianjin Guangfu Chemical Reagent. Phosphoric acid was obtained from Tianjin Kermol Chemical Reagent. Absolute ethanol was received from Fuyu Chemical Reagent. All chemicals were analytical grade and used directly without further purification. Synthesis of PMP. Typically, 29.4 g phosphoric acid and 6.8 g pentaerythritol were added into 250 mL flask and stired for mixing. The esterification was carried out at 120 °C for 1.5 hours under -0.1 Mpa. Meanwhile, 13.6 g melamine was dispersed into 120 mL absolute ethanol and stired for 1.5 hours. Then the dispersed melamine was added into pentaerythritol phosphate with stirring and refluxing at 80 °C for 6 hours. The obtained product was placed for stratification then poured out the transparent solution. The PMP was obtained after the remained product was dried. Synthesis of HMCAs. The obtained PMP was expanded in a tubular furnace at 350 °C for 0.5 hours then elevated temperature to a certain value (850, 950, 1050, 1150 °C) for 4 hours. The heating rate is 5 °C min-1. Finally, the low-density CAs with high-surface-area were obtained and denoted as HMCA-x (850, 950, 1050, 1150), after the furnace was cooled down to room temperature naturally. Characterizations and Instruments. The microstructure was observed by Field emission scanning electron microscopy (FE-SEM, JSM-7800F). Transmission electron microscopy (TEM) and selected area electron diffraction (SAED) were carried out on a JEM-2100F instrument (JEOL). Atomic force microscopy (AFM) analysis was conducted in veeco multimode 3D. The surface area and pore size distributions were determined by the N2 adsorption isotherms at 77.4 K using an Autosorb iQ2 instrument. Before analysis, the samples were out-gassed at 300 °C under


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vacuum for 3 hours. The SSA was calculated using adsorption data by the Multi-Point BrunauerEmmett-Teller (BET) method. Pore size distribution (PSD) curves were computed using the nonlocal hybrid density functional theory (NLDFT) method assuming slit pore geometry for the micropores and cylindrical pore geometry for the mesopores. The crystallographic characterization of the as-synthesized HMCAs was obtained on an X'pert Pro diffractometer with monochromated Cu-Kα radiation (40 kV, 200 mA) at a scan rate of 5° per minute. Raman spectras were recorded using an inVia Raman microscope with 532 nm incident radiation. The Raman shift was calibrated by the G-band position of HOPG (1582 cm-1), and the intensity was normalized by the G-band. Organic Liquids Absorption of HMCAs. The absorption capacity (Q) of HMCAs for various solvents and oils with different density were measured, including petroleum ether, n-hexane, ethanol, kerosene, ethyl acetate, carbon disulfide, dichloroethane, carbon tetrachloride and pump oil. The HMCA were placed inside the organic liquids, and picked out for measurements. The HMCA weights after and before absorption were recorded for calculating Q value. Weight measurements were done quickly to avoid evaporation of absorbed liquids. Electrochemical Performance of HMCAs. The electrochemical characteristics of HMCAs were evaluated with cyclic voltammetry (CV), galvanostatic charge/discharge (GCD) (CHI 760E electrochemical workstation, CHInstruments). The CV and GCD tests were measured in an aqueous 6M KOH electrolyte by a three-electrode system with Pt flake as counter electrode, Ag/AgCl electrode as reference electrode with a potential window from -1 to -0.1 V. The cycle stability test was carried out in two-electrode system which was constructed with a home-made device using two nearly identical (in shape and weight) working electrodes and polyethylene polypropylene blend film as separator. The working electrode was prepared by pressuring the


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tailored HMCAs on the nickel foam current collector under 10 MPa for 30s. The CS of electrode in three-electrode system was calculated from GCD using the following equation: CS=I∆t/(m∆V) where I, ∆t, m, and ∆V are the applied current density, the discharge time, the mass of the active material mass for a single electrode (g), and the potential window, respectively. 3. RESULTS AND DISCUSSION Inspired by mechanism of action of flame retardant,30 PMP was designed and synthesized as the multifunctional precursor. The typical synthesis of PMP precursor is illustrated in Figure 1a. Firstly, esterification of phosphoric acid and pentaerythritol was adopted to obtain pentaerythritol phosphate. Secondly, the as-prepared pentaerythritol phosphate was neutralized with melamine to produce PMP. The detailed description of synthesis is presented in Experimental Section. The chemical foaming coupled self-etching strategy was based on the unique multifunction features of the obtained PMP. As shown in Figure S1, for the multifunctional PMP precursor, section 1 acts as a carbon source to be converted into carbon frameworks; section 2 supplies gas as space filler for chemical foaming; section 3 is phosphorus containing species to catalyze the dehydration for carbon-formation and etch carbon frameworks for micro/meso pores.31-32 The carbonization and decomposition processes of the PMP precursor were monitored by means of thermogravimetric analysis (TGA) with two main decomposition stages during the whole temperature range shown in Figure S2. In the first stage (350-500 °C), PMP molten and polymerized accompanied by the chemical released non-flammable gases from melamine species.33-34 In the second stage (>850 °C), the self-etching from phosphorus containing species can account for the drastic weight loss.35-36


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The chemical foaming coupled self-etching strategy for the HMCAs is illustrated in Figure 1b. By release of the non-flammable gase in the first stage, the foam-like product with tens of times volume boost than the PMP precursor could be acquired (Figure 1c). The foam-like architecture is packed by interconnected large polyhedral bubbles, where carbonaceous struts constitute the skeletons of the bubbles and carbonaceous membranes are tightly anchored onto them as facets (Figure S3).26 The density of the macroporous scaffold reached up to ca. 7 mg cm-3 (Figure S4). Fourier transform infrared (FTIR) spectra illustrated the obtained HMCA-850 is rich in nitrogen and phosphorus functional groups (Figure. S5). The peaks at 958, 1245, 3159 cm-1 were assigned to the stretching vibrations of phosphate, P-O-C and N-H, respectively.34 And obvious N and P peaks were further observed on the X-ray photoelectron spectroscopy (XPS) survey spectra of HMCA-850 (Figure S6). Due to not yet occurred self-etching, the content of N and P of HMCA850 reach up to 15.48 and 17.71 at.% (Table S1). Based on high resolution XPS spectrum, the peaks centered at 398.4, 399.9 and 401.5 eV in N 1s spectra are corresponding to pyridinic, pyrrolic and graphitic nitrogen, respectively (Figure S6a).35 The P atom is mainly in the form of polyphosphate (133.8 eV) and phosphate ester (134.7 eV) in the macroporous scaffold (Figure S6b).34 Further elevating the temperature to > 850 °C, the surface of carbon frameworks could be modulated via self-etching by the phosphorus containing species to achieve abundant micro/meso pores and large SSA. After etching, no obvious FTIR absorption peaks of functional groups containing N and P were observed for HMCAs (Figure S5). The content of N and P sharply decreased to 1.76 and 1.31 at.% (Table S1) with the elevated temperature to 1050 °C, which were hard to observe on the XPS survey spectra of HMCAs (Figure S7). Accompanied by pyrolysis and self-etching, the resulting ultralight HMCAs feature the average density of ca. 0.65 mg cm-3 (Figure S4) with a few volumes shrink (Figure 1c).


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As shown in Figure 2a, the ultralight CAs block standing freely on a dandelion relies on its ultralow density. And the HMCAs with different shapes (cube, cylinder, thri-prism and cross) could be obtained by tailoring the foam-like products (Figure S8). The morphological and structural details are demonstrated by SEM (Figure 2b, c) and TEM (Figure 2e-g). The HMCAs are built up by the macroporous scaffolds (Figure 2a) enclosed by the cross-linked carbon nanosheets (Figure 2b) with dimension ranged from a few micrometers to tens of micrometers. Due to the unique structure, the HMCAs could be compressed and released repeatedly with certain mechanical property and durability. Plenty of spaces constructed by this macroporous scaffolds could provide adequate space for solvent absorption. Zooming in on a single nanosheet (Figure 2c), the carbon nonosheet is ultra-thin with uniform wrinkles on the surface. AFM image (Figure 2d) conforms that the thickness of a typical carbon nonosheets is 35-45 nm. Macropores with diameters of 100-300 nm and uniformly dispersed mesopores with diameters of 30-50 nm are both observed within the carbon nanosheets (Figure 1e). The high magnification TEM image (Figure 2f) of the same carbon nanosheets displays abundant mesopores with diameters of 4-10 nm. Interestingly, HRTEM image reveals a dense nanometerscale pore structure with a continuous three-dimensional network surrounded by highly curved, predominantly single or multi-layer graphite carbon (Figure 2g). The SAED pattern with clear diffraction rings confirms their graphite structure. Further crystallographic structures of HMCAs were also examined. The intense G-band at 1598 cm-1 and the broad 2D peak (Raman spectroscopy in Figure 2h) further corroborate the strong graphitization and the presence of multi-layer graphene.39 And each spectrum was fitted to a series of four Lorentzian peaks, centered at 1200, 1350, 1500, and 1598 cm-1 (Figure S9b). These spectra are dominated by characteristic carbon resonances around 1598 cm-1 (G band) and


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1350 cm-1 (D band). Additionally, two broad signals at ca. 1200 and 1510 cm-1 are associated with carbon atoms outside of a perfectly planar graphene network (such as aliphatic or amorphous structures) and integrated five-membered rings or heteroatoms in graphene sheet structures, respectively.40 As shown in The Raman spectra (Figure S9a), with the elevated synthesis temperature, more defects were formed due to the enchanced self-etching, meanwhile crystallinity of HMCA improved, corresponding with the sharp G peak and D peak. And the systematic variation of the intensity ratio of the D and G bands are 0.97, 0.94, and 0.90 for HMCAs carbonized at 950, 1050, and 1150 °C, respectively. The X-ray diffraction patterns of the HMCA-x (950, 1050, 1150) also display two broad peaks at 26° and 43° (Figure 2i and Figure S10), respectively, corresponding to the typical (002) and (100) reflections of graphitic carbons,41 which are consistent with the results of TEM and Raman spectra. Owning to incomplete carbonization, the HMCA-850 presented typically amorphous carbonaceous characteristic. Such graphitic structure mainly results from cyclization and condensation reactions enhanced by the scission of P−O−C bonds of phosphate ester at high temperature.42 To further investigate the porous structure of the HMCAs in detail, nitrogen adsorption/desorption measurements at 77.4 K were carried out. A H4 type hysteresis loop for the HMCA-1050 at relative pressure of ca. 0.4 is typically associated with adsorption of micromesopores.43 At low relative pressure region, the sharply rose adsorbed volume of HMCA-1050 (Figure 3a) correspond to adsorption of micropores. Apart from ultramicropores centered 0.52 nm, there are two concentrated distribution, centered at 1.38 nm and 1.70 nm, respectively. Indeed, the pore size distribution of the HMCA-1050 also shows a well-defined mesopore size distribution (Figure 3b) with an average pore diameter of 4.11 nm. The narrow mesopores distribution centered 3.79 nm and 4.90 nm also coincides with the TEM results. Due to the


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uniformly distributed micro/mesopores, the HMCA-1050 present a large pore volume (2.74 cm3 g-1 at p/p0 of 0.99382), and an ultrahigh SSA of 2668.4 m2 g-1 (Table S2). To the best of our knowledge, this is the highest SSA among the reported monolithic CAs (Figure 3c, Table S3), which is 2.5-24.0 times of those for graphene and/or CNTs aerogels,20, 44-46 and even higher than the commercial activated carbon (YP-80 from Kuraray). The ultrahigh SSA and abundant micro/meso-pores arise from self-etching of phosphorus containing species. Due to the absence of self-etching below 850 °C, HMCA-850 only obtain a SSA of 54.7 m2 g-1 (Table S2). As the elevated temperature from 850 ºC to 1150 ºC, the self-etching and crystallization processes occur simultaneously. However, such two processes are contradictory for the texture features. In the range from 850 ºC to 1050 ºC, the self-etching process is dominant for the increasing SBET, micropore area, total pore volume, and micropore volume. Yet the effect of crystallization process overwhelming that of self-etching process with a temperature above 1050 ºC, which results in the reduced SBET, micropore area, total pore volume, and micropore volume. Consequently, the SSA and pore volume of HMCAs presented a volcanic trend accompanied by the developed micro/meso pores and enlarged pore size gradually (Table S2). Based on the observation above, the delicate architecture of the HMCAs delivers great potential for multifunctional applications (Figure 1d, e). In the micrometer scale, the macroporous scaffolds with carbon nanosheets provide enough space for absorption of organic solvents (Figure 1d). In the nano-scale, the micro/meso-porous nanosheets with ultrahigh surface area bring efficient ion storage and mass transport for electrolyte ions (Figure 1e). To confirm the stability of the HMCAs structure for absorption, compression experiments were carried out (the detailed experiments and analysis in supporting information). With the strain of 40, 60 and 80 %, a stress-strain curve with hysteresis behavior was observed due to the


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energy dissipation, which is similar to the reported graphene or CNTs aerogels27 (Figure S11a). After 800 loading-unloading fatigue cycles, the stress-strain curve nearly did not exhibit any change and the macroscopic shape of HMCAs still remain its original macroscopic shape (Figure S11b). The HMCA packed by interconnected highly curved, predominantly single or multi-layer graphite nanosheets is a monolithic structure during chemical foaming, instead of subsequent construction of assemble units. Dispite the ultralow density of the CAs, the unique structure render the CAs a certain mechanical strength, which could be compressed and released repeatedly with remarkable mechanical property and durability. Consequently, the extensive studies on the absorption behaviors were carried out on the HMCAs. As shown in Figure S12, after absorption of organic solvent, the HMCAs could support the weight of the absorbed solvent with almost no change of macroscopic features. An absorption capacitie value of 324.1–593.6 g g-1 s (Q, the ratio of the final weight after full absorption to the initial weight) for varied organic solvents were obtained (Figure 4a and Table S4) with an approximately linear increase dependent on the liquid density. These absorption capacitie values outperform the reported CAs from poplars catkins,47 phenolic polymer-derived CAs,48 and graphene aerogel

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etc. (the

detailed comparation in Table S5). For pump oil, the Q of HMCA-950 is up to 575.6 g g-1, which is 10-100 folds higher than those commercial materials (Figure 4b and Table S6). Compared with the highest performing (UFAs) previously reported, the 80 % improvement was achieved.50 Meanwhile, the HMCAs have a strong operability. After ethanol absorption, the macropous scaffolds for HMCAs were filled with ethanol. Due to effect of gravity and surface tension, the elastic carbon aerogel will be shrunk, which can be observed in many aerogel-based absorbents.51 The HMCAs were not collapsed, which may be attributted the unique skeleton structure. The absorption/release process is highly repeatable by heating to release the absorbed


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liquids (Figure S13), and no change or degrading was observed after 10 cycles, indicating a high structural stability of HMCAs (Figure 4c). Except for the removal of solvent by heating, the organic solvent also can be removed by squeeze (illustrated by the demonstration experiments in Figure S14). Interestingly, owning to the excellent thermal stability of our HMCAs (TGA in Figure S15), the absorbed liquids can be completely removed from the aerogels by burning in air (Figure 4d). The ultrahigh absorption capability and facile regeneration make HMCAs a promising candidate for practical applications in the absorption-removal of organics for environmental protection and pollution control. Owing to the high SSA and hierarchical pore structure, the HMCAs are also promising as binder free electrodes for supercapacitors. The rectangular cyclic voltammetry curves at a series of scan rates from -1 to -0.1 V vs. Ag/AgCl are shown in Figure 5a. And the nearly triangular charge/discharge curves at different current density further confirm ideal capacitive behavior (Figure 5b). The HMCA-1050 provided a discharge capacitance of 338 F g-1 at a current density of 200 mA g-1, which is superior to activated graphene aerogel (186 F g-1),52 multifunctional aerogel (155 F g-1),25 carbonaceous aerogels derived from prolifera-greentide (299 F g-1)43 etc. (the detailed comparation in Table S7). Increasing the current density to 100 A g-1, the HMCA1050 electrodes retained a high gravimetric capacitance of 183 F g-1, indicating a fast kinetics process on the electrode/electrolyte interface (Figure 5c). With regard to the view of practical application, the volumetric capacitance of the electrode materials is a more important parameter for miniaturized supercapacitors. In the evaluation of the capacitive performances of HMCAs samples, the electrodes were fabricated by compaction under the optimized pressure of 10 MPa. The tap density of the compaction electrode was determined by SEM combined with EDX (the details were shown in Figure S16). The tap density increases up to about ca. 1.0 g cm-3 by the


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mechanical compression, which is consistent with the density of carbon aerogels meassured under 10 MPa pressure by the home-made device (as shown in Figure S17). Based on the tap density 1.0 g cm-3, the volumetric capacitance of the carbon aerogels is 338 F cm-3, which outperform the most reported carbon materials, sich as freestanding reduced graphene oxide@polyvinyl alcohol films (206 F cm-3),53 3D graphene and polyaniline nanowire arrays hybrid foams (205.4 F cm-3)54 etc (as shown in Table S8). To further evaluate the practical value as electrode, a electrode with an areal mass loading of 7.64 mg cm-2 (the carbon amount contained in many commercial electrode) was examined (Figure 5d). Due to the excellent capability of HMCA to interact with ions and to transport electrons, the gravimetric capacitance only decreased by 9.5 % from 301 to 286 F g-1 at 200 mA g-1 and the comparable rate performance was obtained. During 10000 constant current charge/discharge cycles at 10 A g-1, the binder free electrodes also displayed outstanding stability (Figure S18). The minor reduced capacitance retention was ascribed to two main reasons: i) removal of unstable surface functional groups, ii) irreversible changes of the electrolyte exposed in air. 4. CONCLUSIONS In conclusions, we developed a facile chemical foaming coupled self-etching strategy by constructing multifunctional precursor (PMP) to obtain hierarchical CAs with a low density (0.65 mg cm-3) and record-breaking SSA of 2668.4 m2 g-1 without any special drying and multiple steps. In this strategy, the melamine section serves as foaming agent to construct macroporous scaffold, and phosphorus containing species play a role of dehydration and selfetching for micro/meso pores. Benefited for such delicate design, remarkable absorption capacities of 324.1–593.6 g g-1 for organic solvent and excellent specific capacitance of 338 F g-1


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as binder free supercapacitor electrodes are delivered. The construction of this novel carbon nano-architecture will shed light on the design and synthesis of multifunctional materials.


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FIGURES AND CAPTIONS Figure 1. (a) The synthesis process of PMP precursor. (b) Scheme of expansion/self-etching strategy. (c) Digital photographs expansion/ self-etching strategy. (d, e) The structural models of the HMCAs. Figure 2. (a) Digital photograph of HMCA-950 placed on dandelion. (b,c) SEM images with different magnifications for microscopically architecture of HMCA-950. (d) Image of atomic force microscopy of HMCA-1050. (e-g) TEM images of the HMCA-1050 with different magnifications (inset in (g): SAED). (h) Raman spectum of HMCA-1050. (i) XRD pattern of HMCA-1050 Figure 3. Gas adsorption/desorption analysis of HMCA-1050. (a) High-resolution, low-pressure N2 (77.4 K) adsorption/desorption isotherms. (b) Cumulative pore volume and pore-size distribution (inset) (calculated by using a slit/cylindrical NLDFT model). (c) The summary of SSA of our HMCA, the reported carbon aerogels and porous carbon for supercapacitor and absorption. Figure 4. Absorption properties of HMCAs. (a) Absorption capacities of the HMCA-950 measured for a range of oils and organic solvents in terms of their densities. (b) The diagram of absorption capacities of various absorbents for pump oil. (c) The absorption capacities of repeated absorption/release process of HMCA-950. (d) The removal process of ethanol absorbed into the HMCA-950 by burning. Figure 5. Electrochemical performance of HMCAs in 6M KOH. (a) Cyclic voltammetry curves of HMCA-1050 with different scan rates measured in a three-electrode configuration. (b) Galvanostatic charge/discharge curves of HMCA-1050 under different current densities. (c) The


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specific capacitance of HMCA-1050 calculated at various current densities. (d) The rate performance of HMCA-950 with different mass loading.


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Figure 1. (a) The synthesis process of PMP precursor. (b) Scheme of expansion/self-etching strategy. (c) Digital photographs expansion/ self-etching strategy. (d, e) The structural models of the HMCAs.


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Figure 2. (a) Digital photograph of HMCA-950 placed on dandelion. (b,c) SEM images with different magnifications for microscopically architecture of HMCA-950. (d) Image of atomic force microscopy of HMCA-1050. (e-g) TEM images of the HMCA-1050 with different magnifications (inset in (g): SAED). (h) Raman spectum of HMCA-1050. (i) XRD pattern of HMCA-1050


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Figure 3. Gas adsorption/desorption analysis of HMCA-1050. (a) High-resolution, low-pressure N2 (77.4 K) adsorption/desorption isotherms. (b) Cumulative pore volume and pore-size distribution (inset) (calculated by using a slit/cylindrical NLDFT model). (c) The summary of SSA of our HMCA, the reported carbon aerogels and porous carbon for supercapacitor and absorption.


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Figure 4. Absorption properties of HMCAs. (a) Absorption capacities of the HMCA-950 measured for a range of oils and organic solvents in terms of their densities. (b) The diagram of absorption capacities of various absorbents for pump oil. (c) The absorption capacities of repeated absorption/release process of HMCA-950. (d) The removal process of ethanol absorbed into the HMCA-950 by burning.


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Figure 5. Electrochemical performance of HMCAs in 6M KOH. (a) Cyclic voltammetry curves of HMCA-1050 with different scan rates measured in a three-electrode configuration. (b) Galvanostatic charge/discharge curves of HMCA-1050 under different current densities. (c) The specific capacitance of HMCA-1050 calculated at various current densities. (d) The rate performance of HMCA-950 with different mass loading.


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ASSOCIATED CONTENT Supporting Information. The Supporting Information is available free of charge on the ACS Publications website. Detailed additional experimental informations; digital and SEM images; TGA curves; FTIR spectra; XPS spectra; XRD patterns; Raman spectroscopy; nitrogen adsorption/desorption isotherms; mechanical property; elemental analysis results; absorption and electrochemical performance data. AUTHOR INFORMATION Corresponding Author * [email protected] * [email protected] 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. ACKNOWLEDGMENT This work is financially supported by the National Key Research and Development Program of China (2016YFB0101204), the National Natural Science Foundation of China (21506212). REFERENCES (1)

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Table of Contents Graphic


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