In Situ Templating Approach To Fabricate Small-Mesopore-Dominant

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In-Situ Templating Approach to Fabricate Small-Mesopore-Dominant SDoped Porous Carbon Electrodes for Supercapacitors and Li-Ion Batteries Yun Lu, Qing Zhang, Sheng Lei, Xun Cui, Shuyi Deng, and Yingkui Yang ACS Appl. Energy Mater., Just Accepted Manuscript • DOI: 10.1021/acsaem.9b00777 • Publication Date (Web): 24 Jul 2019 Downloaded from pubs.acs.org on July 25, 2019

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ACS Applied Energy Materials

In-Situ Templating Approach to Fabricate SmallMesopore-Dominant

S-Doped

Porous

Carbon

Electrodes for Supercapacitors and Li-Ion Batteries

Yun Lu,‡b Qing Zhang,‡a Sheng Lei,a Xun Cui,a Shuyi Deng,a and Yingkui Yang a,b,*

a

Hubei Engineering Technology Research Centre of Energy Polymer Materials,

School of Chemistry and Materials Science, South-Central University for Nationalities, Wuhan 430074, China E-mail: [email protected]

b

School of Materials Science and Engineering, Hubei University, Wuhan 430062,

China

‡

These two authors equally contribute to this work.

ACS Paragon Plus Environment

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Abstract To enable large capacity and high rate capability of porous carbon electrodes for lithium-ion batteries (LIBs) and supercapacitors, the combination of doping active heteroatoms, tailoring pore architectures, and narrowing pore sizes is a powerful engineered strategy. However, such porous carbons with multiple synergistic effects are almost impossible to be achieved simultaneously by conventional synthesis methods in few steps. Herein, two mechanistically-coupled polymers of poly(2thiophenemethanol) (PThM) and SiO2 in one step process, were synchronically produced by twin-polymerization of a single-source hybrid monomer of tetrathenyloxysilane consisting of tetraethyl orthosilicate (TEOS) and ThM moieties. The resultant interpenetrated SiO2/PThM composites were then subjected to thermal annealing and subsequent etching, yielding a mesopore-dominant S-doped porous carbon (SPC-1) with large-micropores (1.3–2.0 nm), narrow pore distribution (1.3– 4.1 nm, centered at 3.1 nm), rich S heteroatoms (>5%), and high specific surface area (792 m2/g). Remarkably, the symmetric supercapacitor based on SPC-1 delivers a specific capacitance of 420 F/g at 0.5 A/g, and an energy density as high as 14.6 W h/kg at the power density of 125 W/kg. As an anode for LIBs, SPC-1 delivers large reversible capacity (571 mAh/g), high rate capability, and excellent cyclic stability (without capacity decay after 500 cycles). More importantly, SPC-1 shows better electrochemical performance compared to a large mesopore (6–30 nm)-dominant Sdoped porous carbon (SPC-2) derived by simultaneous polymerization of TEOS and ThM. This work reports an unusual in-situ templating approach capable of synergistically combining chemical doping and pore engineering of carbonaceous materials for high-performance supercapacitors and LIBs. Keywords:

twin-polymerization;

nanoporous

carbons;

supercapacitors; batteries


in-situ

template;

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1. Introduction Sustainable and renewable resources such as sun and wind power play a critical role in replying to the fast consumption of finite fossil fuels and the ever-increasing demand for clean energy. As sun dose not shine all day long and wind is impossible to blow on demand, and electrochemical energy storage technologies are thus emerging as alternative strategies to cope with the intermittent nature of renewable energy sources.1 Representative supercapacitors and lithium ion batteries (LIBs) have been recognized as primary power sources to shift great dependence from the fossil energy.2 Such energy systems are also serving as the key to the large-scale deployment of electrical vehicles and smart power grids.3 Numerous previous reports have assigned equal importance to supercapacitors and batteries based on their respective advantages.4 However, substantial improvements in electrochemical performance by developing new electrode materials are still necessary to meet practical requirements of high energy, high power, and long lifespan.5 Carbonaceous active materials are currently recognized as the most promising electrode materials for commercial LIBs and supercapacitors.6 However, graphitic carbon anodes usually possess relatively low theoretical capacity (372 mA h/g for graphite), sluggish lithium diffusion kinetics, and poor rate capability.7 Commercially available activated carbons for supercapacitors also suffer from low capacitance and low energy density (ca. 5 Wh/kg) especially at a high rate.8 In this context, nanostructured porous carbons have proverbially been explored to achieve high energy and power requirements due to their large active surface/interface accessible to Li-ions and electrolyte ions, high electronic conductivity, 3D loose skeletons (vs. graphite) allowing for fast ion transport, and negligible volume variation.9, 10 The past years have witnessed considerable progress in nanoporous carbon



electrode materials by developing new synthesis methods and crafting novel pore architectures in combination with rational doping of heteroatoms.11, 12 The state-ofthe-art approaches to nanoporous carbons have mainly been performed by soft-/hard templating strategies.13 The soft-templating synthesis has been dominated by block copolymer precursors, and often shows a limited threshold of pore size, insufficient structural stability, and collapsing of pores during the pore-creating processes.14 The hard-templating method usually involves the preparation of sacrificial templates, incorporation of organic precursors, subsequent pyrolysis and final removal of templates, thus suffering from multiple steps, poor dispersion of inorganic templates within organic precursors, and inferior control over nanostructures.15 As for pore architectures, an anomalous increase in capacitance was rationally corroborated for a carbide-derived carbon with pore sizes below 1 nm.16, 17 However, such small pores lead to poor rate and power capability due to the limited access to ions and high ion-transport resistance.18 Whereas excessively large pores result in low storage capacity due to the large pore volume accompanied by the limited specific surface area (SSA).19 Pioneering studies have accordingly suggested that mesoporedominant carbon materials exhibit large ion-accessible active surfaces and appropriate pore sizes for fast ion diffusion and transport, thus inducing a compromised balance between the capacitance/capacity and rate capability.20 In addition, chemical doing of heteroatoms (such as N, O, B, S and P) in porous carbons has been reported to show overall improvements in electrochemical reactivity, electronic conductivity, surface wettability and interface compatibility between the electrode and electrolyte. 21, 22 These favorable characteristics provide extra active sites for Li-ion storage and pseudocapacitance as well as rapid transport and transfer of charges, thus enabling high energy and power density for LIBs and


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supercapacitors.23 However, such multiple synergistic effects are almost impossible to achieve by conventional methods in few steps. In this work, an in-situ template approach through twin-polymerization of a single-source hybrid monomer of tetrathenyloxysilane (TTOS, Figure S1) was employed to produce S-doped porous carbon (SPC-1) (Figure 1a). Here tetrathenyloxysilane was initiated by the CF3COOH-catalyzed cleavage of its Si–O–C bonds, and immediately underwent two polymerization reactions on the same timescale.24 Two structurally-different polymers, poly(2-thiophenemethanol) (PThM) and SiO2 were produced synchronically. Nominally, PThM and SiO2 phases are each other's by-products as SiO2 can generate only as rapidly as ThM units are cleaved.25 Therefore, two polymerization reactions of PThM and SiO2 are coupled mechanistically,26 and also limited both in terms of space. This process leads to the formation of an interpenetrated SiO2/PThM composite with a very small domain within a defined time frame.27 The mesopore-dominated hierarchical SPC-1 with a narrow pore size distribution (PSD: 1.3–4.1 nm) was finally achieved after subsequent annealing of SiO2/PThM and etching off SiO2. Here, organic PThM moieties serve as the C/S sources, whereas inorganic SiO2 phases functions as the pore-creating agents, respectively. Noted is that the TTOS monomer has a stoichiometric ratio (1:4) of inorganic TEOS to organic ThM moieties. For comparison, simultaneous polymerization of tetraethyl orthosilicate (TEOS) and ThM with an equivalent feed ratio of 1:4 was also performed in one process step (Figure 1b). However, the S-doped porous carbon (SPC-2) derived from simultaneous polymerization of two individual monomers possesses a wide large-mesopore size distribution (6–30 nm) due to the unrestrained microphase separation as reported in our previous work.28 More importantly,

SPC-1

shows

comprehensive

performance


improvements

in


supercapacitors and LIBs, compared to SPC-2 and the previously-reported porous carbons as described below.

Figure 1. Synthesis routes of (a) SPC-1 derived from twin polymerization of a single-source hybrid monomer of TTOS, and (b) SPC-2 derived from simultaneous polymerization of two individual monomers of ThM and TEOS.

2. Results and Discussion 2.1. Structural Characteristics of SPC-1 The mass amount of SiO2 loading in the composite is about 45% (Figure S2), consistent with the stoichiometric ratio of TTOS precursor. After full removal of SiO2 phase from the interpenetrated SiO2/PThM composite, the resulted SPC-1 exhibits an irregular micro-sized flake morphology consisting of continuous networks (Figure 2a, c). High-resolution TEM images further reveal a disorder-dominated porous microstructure with corrugated and interconnected wormhole-like nanopores (Figure 2d, e). Some graphitic microdomains inside SPC-1 can be also identified by the twisted ribbon-like planes with a spacing of 0.38 nm. Energy-dispersive X-ray spectrometry (EDS) mappings clearly show that C (86.9%), O (7.2%), and S (5.9%)


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elements are uniformly distributed over the whole SPC-1 surface (Figure 2b), suggesting successful doping of S heteroatoms into the carbon skeleton.

Figure 2. (a) SEM and (c-e) TEM images of SPC-1, and its (b) STEM and EDS mapping patterns

The nitrogen adsorption/desorption isothermal measurement (Figure 3) was further executed to determine SSA and pore size distribution (PSD). The calculated SSA and total pore volume of SPC-1 are 792 m2/g and 1.14 cm3/g, respectively, much higher than those of SPC-2 (507 m2/g, 0.34 cm3/g).28 Furthermore, the isotherm profile (Figure 3a) of SPC-1 suggests the coexistence of micropores and dominant mesopores.29 Of note, at the relative pressure of P/P0>0.9, the abrupt increase in the adsorption amount (Figure 3a) suggests the presence of lager mesopores (20–25 nm) (Figure 3b). The whole isothermal curve is consistent with a distinct type-I triangular hysteresis. As shown in Figure 3b, SPC-1 shows two distinctive regions in the narrow range of 1.3–4.1 nm, giving an average pore size diameter of 3.1 nm, and the



mesopore/total pore volume ratio is about 86.3%. The mechanistically-coupled growth of PThM and SiO2 restricted within a 3D space leads to a narrow smallmesopore PSD after removing the in-situ formed SiO2. However, SPC-2 (Figure S3) has a wide large-mesopore size distribution (6–30 nm) with an average pore diameter of 17.0 nm due to the unrestrained microphase separation of organic PThM from SiO2 during the polymerization of two individual monomers.28 Therefore, SPC-1 with rich small-mesopore and an appropriate proportion of large-micropores enables its high SSA and large pore volume favorable for high-density energy storage. 16

Figure 3. (a) Nitrogen adsorption/desorption isotherm, (b) pore size distribution curve, (c) XRD pattern, and (d) Raman spectrum of SPC-1.

The XRD pattern of SPC-1 shows two diffraction peaks centered at 2θ=23° and 44° (Figure 3c), corresponding to its (002) and (101) lattice planes, respectively. The wide and strong peak at 2θ=23° is an attribute of the concomitant of amorphous state and few


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graphitic microdomains, similar to SPC-2.28 The calculated lattice spacing of (002) is 0.38 nm due to the introduction of large-sized S atoms in the carbon matrix.30 It has been reported that the lattice spacing of (002) of porous carbons without heteroatoms is generally less than 0.36 nm.30, 31 Furthermore, the Raman spectrum (Figure 3d) of SPC-1 exhibits D- and G-band at 1348, and 1597 cm-1, respectively. The integrated intensity ratio of D to G band (ID/IG) for SPC-1 is 1.65, suggesting the presence of abundant defects and/or disorders capable of providing numerous active sites for energy storage.32

Figure 4. XPS spectrum (a), and high-resolution C 1s (b) and S 2p (c) spectra of SPC-1.

The XPS survey scan spectrum of SPC-1 presents the O 1s, C 1s, S 2s, and S 2p peaks with binding energies at 532.4, 285.1, 218.2, and 163.7 eV, respectively (Figure 4a). The high-resolution C 1s spectrum (Figure 4b) can be fitted by three peaks consisting of sp3 C–C (284.8 eV), C–S (285.6 eV), and C–O/O–C=O (288.3 eV) bonds. The further deconvolution of the S 2p core spectrum (Figure 4c) generates two peaks



located at 164.9 and 163.8 eV, corresponding to the S 2p3/2 and S 2p1/2 of C–S–C bonds due to its spin–orbit couplings. 31, 32 The atomic percentage of S doped in SPC-1 is 5.2%, consistent with the EDS result. The amount of S is also higher than those of S-doped carbon materials reported previously.28,

33

Such S-enriched mesopore-dominant

carbons would enable reversible redox reactions and the improved electrolyte wettability and compatibility, thus promising high capacity storage.

2.2. Electrochemical performance of symmetric supercapacitors Electrochemical performance of symmetric supercapacitors based on SPC-1 and SPCwas examined in a two-electrode system in 6.0 M KOH. The CV profiles (Figure 5a, c) display an approximate rectangle and a slight deviation with increasing the scan rate from 10 to 200 mV/s, implying an excellent rate capability. 38, 40 The GCD profiles (Figure 5b, d) also exhibit a roughly-symmetrical triangle with negligible voltage drops with increasing the current density from 0.5 to10 A/g, due to their low charge transfer resistances.38 Based on the GCD curves, the SPC-1 device delivers specific capacitances of 420, 402, 382, 360, and 352 F/g at 0.5, 1, 2, 5, and 10 A/g, respectively. However, the SPC-2 capacitor delivers much lower specific capacitances of 219, 205, 196, 185, and 180 F/g at the same current densities. The SPC-1 capacitor retains 83.8% of initial capacitance, comparable to SPC-2 (82.2%) after a 20-time increase in the current density. Furthermore, the energy density and power density are superior to what have been reported from commercial activated carbons and chemically-doped carbons (Figure 5e). For instance, the SPC-1 device shows an energy density of 14.6 Wh/kg at the power density of 125 W/kg. The energy density remains as high as 12.3 Wh/kg at the power density of 2,500 W/kg, implying an outstanding power capability. Electrochemical performance of SPC-1 and SPC-2 were further evaluated by


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electrochemical impedance spectroscopy (EIS) (Figure S4) and cycling stability. As compared with SPC-2 and general porous carbons, 43, 44 the SPC-1 device shows lower equivalent series (0.79 Ω) and charge-transfer (9.8 Ω) resistances due to its overall improvements in the ion-accessibility, electrochemical activity, surface wettability, and interface compatibility.44 In addition, the SPC-1 capacitor retains 96.8% of initial capacity comparable to SPC-2 (94.4%) after running at 10.0 A/g for 10,000 cycles (Figure 5f), showing excellent cycling life.

Figure 5. (a) CV and (b) GCD curves of SPC-1, (c) CV and (d) GCD curves of SPC-2, (e) Ragone plots of SPC materials and the previously-reported carbons (Ra,34 Rb,35 Rc,36 Rd,37 and Re38), and (f) cycling performance of SPC-1 and SPC-2 at 10.0 A/g over 10,000 cycles.



The aforementioned results clearly demonstrate that SPC-1 possesses much higher specific capacitance, and comparable rate capability and cycling stability with respect to SPC-2. The wide large-mesopore distribution (6–30 nm) for SPC-2 is more favorable for rapid diffusion of electrolyte ions, and however, results in a relatively low SSA and excess unemployed reservoirs.17 This makes SPC-2 have exceptional rate capability but low specific capacitance. In contrast, SPC-1 combines a narrow smallmesopore distribution (1.3–4.1 nm) and a certain proportion of large-micropores, thus enabling large ion-accessible SSA and high pore volume.40 Such a hierarchical SPC-1 not only provides abundant pore spaces for charge accommodation and hence high capacitance, but also ensures effective avenues and short channels for fast diffusion of ions into the interior of active materials and accordingly high-rate performance.41 Meanwhile, chemical doping of S heteroatoms into SPC-1 is capable of improving surface/interface wettability with the electrolyte, facilitating diffusion and penetration of electrolyte ions, and contributing pseudo-capacitance as well.42 This also leads to large specific capacitance and high rate capability. Furthermore, the specific capacitance and high-rate retention of SPC-1 are superior to what were reported from commercial activated carbons and chemically-doped carbons. Therefore, SPC-1 can be regarded as one excellent example of porous carbons to achieving an optimal balance between large capacitance and high rate capability.

2.3. Electrochemical performance of LIB anodes Electrochemical Li storage performance was evaluated by fabricating LIB anodes. As shown in Figure 6a and 6c, SPC-1 and SPC-2 demonstrate similar CV curves at a scan rate of 0.2 mV/s between 0.01 and 3.0 V (vs. Li/Li+). Their irreversible reduction peaks in the range of 0.5 to 1.0 V in the first cathodic scan are due to the electrolyte


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decomposition and the formation of solid-electrolyte interphase (SEI) layer for carbon anodes.45 In comparison with SPC-2, SPC-1 shows a stronger reduction peak due to its larger SSA which increases the contact area between the electrode and electrolyte. The cathodic peak disappears and CV profiles are almost overlapped in the subsequent cycles, indicating the stable SEI layer and high reversibility during the Li-ion insertion/extraction processes. Two pairs of weak redox couples at 0.8/1.3 V and 1.2/2.0 V are attributable to the stepped redox reactions of Li ions on the doped functional groups.31 The reversible redox peaks below 0.8 V correspond to the intercalation/extraction of Li ions into/from the carbon skeleton.22 The CV results suggest that SPC-1 and SPC-2 are electrochemically active, capable of accommodating Li and enhancing reversible capacity.46 Figure 6b and 6d exhibit the GCD profiles of SPC-1 and SPC-2 for the first three cycles at 50 mA/g in the voltage range of 0.01–3.0 V. These voltage profiles consist of two main sloped-regions of low voltage (below 0.8 V) and high voltage (0.8–2.0 V) ranges. The former is assigned to the reversible intercalation/extraction of Li ions from the carbon layers, pores and defects, while the latter is ascribed to the faradic reactions between Li and doped heteroatoms. The GCD observations are consistent with the CV results mentioned above. The initial coulombic eﬃciency of SPC-1 (61.4%) is comparable to that of SPC-2 (63.3%) due to the SEI formation, and both dramatically increase to over 98% in the third cycle. However, SPC-1 delivers an initial charge capacity of 778 mAh/g at 50 mA/g, which is much higher than that of SPC-2 (471 mAh/g) due to the higher SSA of SPC-1 available for energy storage.



Figure 6. Electrochemical performance of SPC anodes in a half-cell configuration countered with Li metal: (a) CV curves and (b) GCD profiles of SPC-1, (c) CV curves and (d) GCD profiles of SPC-2 with the initial three cycles at 0.01–3.0 V.

The rate capabilities of SPC-1 and SPC-2 anodes at various rates of 50–500 mA/g were compared in Figure 7a. The reversible capacity of SPC-1 is 571 mAh/g at 50 mA/g, much higher than SPC-2 (367 mAh/g). After cycling at incremental rates and switching back to 50 mA/g, the specific capacity returns to 575 mAh/g for SPC-1 and 372 mAh/g for SPC-2, implying their high rate capabilities.39 Furthermore, the EIS test before and after cycling are carried out to investigate the charge-transfer resistance (Rct) (Figure 7b). The fresh SPC-1 and SPC-2 anodes demonstrate similar Rct values with one semicircle. However, both electrodes exhibit two semicircles after 500 cycles, corresponding to the stable SEI film (the first semicircle) and Rct (the second semicircle). The Rct after 500 cycles is also lower than that of the fresh electrode for both SPC-1 and SPC-2 due to the electrochemical activation during the repeated Li-ion


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insertion/extraction processes. At an elevated current density of 200 mA/g, SPC-1 and SPC-2 retain the reversible capacity of 373 and 283 mAh/g, respectively, while accompanying by an almost 100% of coulombic eﬃciency over 500 cycles (Figure 7c). These electrochemical performances are superior to the previously-reported carbon anodes (see Table S1).

Figure 7. Electrochemical performance of SPC-1 and SPC-2 anodes in a half-cell configuration countered with Li metal: (a) rate capability at 50–500 mA/g, (b) Nyquist plots before and after 500 cycles, and (c) long-term stability and coulombic efficiency at 200 mA/g over 500 cycles.

The superior lithium storage performance of SPC-1 originates from its favorable multiple synergistic effects as follows. First, small-mesopore dominated hierarchical SPC-1 possesses a large SSA and appropriate pore sizes accessible to Li ions.47 Second, the combination of a narrow PSD and an enlarged interlayer spacing can significantly reduce the ion scattering and improve the electrode kinetics, thus enhancing the specific capacity and rate capability.39, 48 Finally, the S-doped carbons feature several



merits including: (i) enriched structural defects and active sites for high reactivity,49 (ii) enlarged interlayer spacing and reduced diffusion barrier energy for fast Li-ions insertion/extraction,50 and (iii) enhanced electronic conductivity.31 The S-doping is simultaneously capable of providing additional pseudocapacitance,51-53 reducing the interface resistance,54 and enhancing the lithium storage capacity,49, 56, 57 thus ensuring excellent electrochemical performance for such porous carbon anodes.

3. Conclusions This work reports facile fabrication of S-doped porous carbons by the CF3COOH initiated twin-polymerization of single-source hybrid monomers. The resultant interpenetrated SiO2/PThM composites were further converted into the small mesopore dominated SPC-1 containing a few large micropores as a result of thermal annealing and subsequent etching. For comparison, simultaneous polymerization of two individual monomers, TEOS and ThM was also performed to obtain SPC-2 with a wide large-mesopore size distribution by the same post-treatment procedures. Due to synergistical effects of dominant small-mesopores, narrow PSD, high SSA, and rich S doping, SPC-1 delivers much larger specific capacitances (420 F/g at 0.5 A/g), higher energy density (14.6 W h/kg at the power density of 125 W/kg), and comparable rate and cycling capabilities relative to SPC-2. Furthermore, the SPC-1 anode for LIBs delivers a large reversible capacity of 571 mAh/g, a high rate capability, and an excellent cyclic stability for 500 cycles with a negligible capacity decay. This work proposes an appealing template approach to simultaneous doping and pore engineering of porous carbon materials for LIBs and supercapacitors with integrated large capacities and high rate capabilities.


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4. Experimental Section 4.1. Materials Tetraethyl orthosilicate (TEOS), trifluoroacetic acid, toluene, hydrofluoric acid (HF), dichloromethane, and dimethyl formamide (DMF) are commercially available from Sinopharm Group Chemical Reagent Co. Ltd., China. 2-Thiophenemethanol (ThM, 98%) was purchased from J&K Chemical Co., Ltd. All organic solvents were purified by distillation before use.

4.2. Synthesis of Tetrathenyloxysilane (TTOS) ThM (7.0 mL, 50 mmol), TEOS (2.6 mL, 12.5 mmol) and 0.3 wt.% KOH were mixed at 80°C for 3 h under an argon atmosphere. The generated by-product of ethanol and the residual starting materials were removed by distillation under vacuum. The viscous yellow-brown liquid of twin monomer, TTOS, was obtained finally.

4.3. SPC-1 Derived from Twin Polymerization TTOS (2.6 g) was slowly added to a solution of trifluoroacetic acid (0.2 mL) in toluene (5 mL) under an argon atmosphere. SiO2/poly(2-thiophenemethanol) (SiO2/PThM) composites were then generated at 80°C for 2 h through twin polymerization. The resulted dark brown powder of SiO2/PThM was placed in an alumina crucible for carbonization at 900°C for 2 h under an argon flow, forming S-doped SiO2/C nanohybrids. SPC-1 materials were finally obtained by etching off SiO2 with HF for over 48 h, followed by washing with deionized water and drying at 80°C overnight.

4.4. SPC-2 Derived from Simultaneous Polymerization For comparison, SPC-2 was derived by simultaneous polymerization as described in



our previous publication. 27 A toluene solution of ThM and TEOS was added a solution of trifluoroacetic acid dissolved in toluene under a N2 atmosphere. After the reaction for 3 h at 105°C under vigorous stirring, the resulted dark brown powder of SiO2/PThM was then placed in an alumina crucible for carbonizing at 900°C for 2 h under an argon flow, producing the S-doped SiO2/C nanohybrids. SPC-2 materials were finally obtained by etching off SiO2 with HF for over 48 h, followed by washing with deionized water and drying at 80°C overnight.

4.5. Materials Characterization Transmission electron microscope (TEM) images were obtained from a Tecnai G20 microscope at 200 kV. Field-emission scanning electron microscopy (SEM) analysis and energy dispersed X-ray spectroscopy (EDS) were performed on a Sirion 200 (Netherland) microscope. Thermogravimetric analysis (TGA) was carried out on a Mettler Toledo (Switzerland) at a heating rate of 20°C/min in air. X-ray diffraction (XRD) patterns were collected on a Rigaku D/Max2400 diffractometer equipped with a CuKα radiation source. Raman spectra were analyzed using a Renishaw Raman spectrometer by exciting a 514.5 nm Ar-ion laser. X-ray photoelectron spectra (XPS) were determined by an X-ray photoelectron spectrometer (PHI MultiPak) with an excitation source of Mg Kα. The SSA and PSD were calculated based on the N2 adsorption and desorption isotherms on ASAP 2020 V according to the BrunauerEmmett-Teller (BET) model and nonlocal density functional theory.

4.6. Electrochemical Measurements For the supercapacitor application, the electrochemical performance was conducted on a CHI 760E electrochemical workstation (Chenhua Instrument Co., Shanghai) with


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a symmetric capacitor in a two-electrode system in an aqueous electrolyte of 6 M KOH. The single electrode was prepared by the slurry coated on Cu-foil, and the mass loading of an electrode was ~2 mg/cm2. Symmetric supercapacitors were assembled with a glassy fibrous separator. Before measurements, the working electrodes were soaked in the electrolyte overnight. For LIBs, electrochemical measurements were performed using a coin-type cell (model 2032). The anode electrodes were fabricated by mixing active materials, acetylene black, and polyvinylidene fluoride (8:1:1 in weight) in N-methyl pyrrolidone to form a uniform slurry. The resulted slurry was coated onto a Cu foil, and the solvent was then evaporated at 90°C for 12 h under vacuum. The lithium metal foil was used as the counter electrode and porous membrane (Celgard 2400) was used as the separator to assemble LIB cells. 1 M LiPF6 in a mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) (1:1 in volume) was used as the electrolyte. Cyclic voltammetry (CV) curves were obtained in a voltage range of 0.01–3.0 V at a scan rate of 0.2 mV/s. CV measurements were performed on a CHI 760D electrochemical workstation. Charge/discharge measurements were carried out on an automatic battery testing system of LAND CT2001A model in the range of 0.01 to 3.0 V.

Conflicts of interest The authors declare no competing financial interest.

Acknowledgements This work was supported by the National Natural Science Foundation of China (51673061, 51273057), and the Fundamental Research Funds for the Central Universities (CZP19001).



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Table of Contents Entry

An in-situ templating approach by means of twin polymerization to fabricate small-mesopore-dominant S-doped porous carbons for

high-performance supercapacitors and batteries.


In Situ Templating Approach To Fabricate Small-Mesopore-Dominant

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