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N,P,S-codoped Hierarchically Porous Carbon Spheres with Wellbalanced Gravimetric/Volumetric Capacitance for Supercapacitors Lijun Yan, Di Li, Tingting Yan, Guorong Chen, Liyi Shi, Zhongxun An, and Dengsong Zhang ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.7b04922 • Publication Date (Web): 18 Feb 2018 Downloaded from http://pubs.acs.org on February 21, 2018

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N,P,S-codoped Hierarchically Porous Carbon Spheres with Well-balanced Gravimetric/Volumetric Capacitance for Supercapacitors Lijun Yan,a Di Li,a Tingting Yan,a Guorong Chen,a Liyi Shi,a Zhongxun Ana,b and Dengsong Zhang＊, a a

School of Environmental and Chemical Engineering, Research Center of Nano Science and

Technology, Shanghai University, No. 99 Shangda Road, Shanghai 200444, P. R. China. b

National Engineering Research Center of Ultracapacitor System for Vehicles, No. 188 Guo Shou Jing

Road, Shanghai 201207, P.R. China. *Corresponding Author. E-mail: [email protected], Fax: +86 21 66137152 Abstract: Due to the wide application of carbon-based materials in supercapacitors, the concern of volumetric capacitance becomes increasingly important. In this work, the N,P,S-codoped hierarchically porous carbon spheres (N,P,S-HCS) has been rationally designed and originally fabricated using the silica colloids as hard templates, polyaniline as carbon and nitrogen souces, phytic acid as phosphorus sources and ammonium persulfate as sulfur sources. Both high volumetric and gravimetric capacitance can be achieved. The as-prepared N,P,S-HCS shows the highest specific capacitance of 274 F g-1 and 219 F cm-3 at a current density of 0.5 A g-1 which reavls a superior performance. Moreover, the cycling ability of the N,P,S-HCS can be maintained over 95 % to the initial capacitance at a high current density of 10 A g-1 for 10 000 charge-discharge cycles. This is mainly contributed to the uniform doping of N, P and S as well as hierarchically porous structure of the N,P,S-HCS. Finally, we assemble it into the all-solid-state symmetric supercapacitors with high energy and power densities of 3.4 W h L-1 with 804 W L-1, respectively. The N,P,S-codoped hierarchically porous carbon spheres with high density show both well volumetric and gravimetric capacitance which make its a promising material for supercapacitors in the practical applications. The present investigations may develop a new direction for the design of carbon materials for the well balance of both high gravimetric and volumetric capacitance. KEYWORDS: heteroatom doping, carbon spheres, capacitance, supercapacitors

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INTRODUCTION Nowadays, due to the rapid of urbanization in the whole world, energy consumptions are severe and endless. So it’s important to improve energy storage and minimize the loss during energy conversion. Rechargeable batteries are the most common way to store energy and thus have been deeply studied. Among various energy storage devices, supercapacitors (SCs) have attracted tremendous attention owing to its ultra-fast charge/discharge rate, long cycle life and stability etc.1,2 SCs also possess great potential in the practical application, which have already been applied in the marketplace, like trolley buses, buses emergency doors, etc.3,4 Although SCs have reached some results, their energy densities are still inferior to redox flow cells (20 to 80 Wh kg-1) and batteries (80 to 200 Wh kg-1), which hinder the further predomination in the energy storage market.5 So the policy for increasing energy density meanwhile maintaining power density and cycling stability is the main issue for SCs. There are diverse materials used as electrode materials for SCs. Unfortunately, all of them have drawbacks and boundaries. Carbon materials, typically behaved as electric double-layer capacitance, can reach considerable gravimetric capacitances by increasing its specific surface area or modifying pore size.6-11 But the carbon materials with high surface area always come up with the low density especially in meso-, macro-porous carbon and thus show relative low volumetric capacitances.12 It seems a contradictory in improving gravimetric and volumetric capacitance simultaneously and the latter hasn’t received enough attentions, which makes the carbon based SCs still in the cradle. To overcome such a dilemma, there are many design strategies as follows: the introduction of pseudocapacitive materials such as conducting polymers, metal oxides or sulfides into carbon frameworks.13-19 But the low conductivity of metal oxides or sulfides and the volume expansion of conducting polymers result in poor cycling stability and rate capability in electrochemistry.20,21 Introducing functional groups or heteroatom (e.g. O, N, P, S and B) into carbon structures, however, can improve the capacitance of carbon materials by either redox activity or conductivity enhancement without incorporating other active materials.22-25 It has been demonstrated that heteroatom doping in carbon framework can provide a pair or lone electron to significantly alter the


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electron donor–acceptor characteristic and thus the capacitance will be improved.26,27 Hence the heteroatom doped carbon may promote both gravimetric and volumetric capacitances. On the other hand, optimization of the carbon materials with appropriate specific surface area and ordered structures to compact the active materials with increasing density, will improve the volumetric value.28-30 It should be noted that the materials with regular and uniform structure can improve the mass transport and electrochemical stability.31 The ordered porous carbon fabricated by using hard template or soft template, which can in-situ generate pores during the pyrolysis, has attracted great interest.6,7,11,28,30,32 Above all, the heteroatom doped ordered carbon structure seems to solve the unbalanced gravimetric/volumetric capacitance of conventional carbon materials. Herein, we use a facile way to synthesize the N,P,S-codoped hierarchically porous carbon nanospheres (N,P,S-HCS) with both heteroatom doping and superior structure during one-step polymerization reaction to improve both high gravimetric and volumetric capacitance for SCs. Polyaniline (PANI) with nitrogen in rich is more favorable than phenolic resin which has been the conventional materials for carbon.33,34 Additionally, PANI is also unique that it can be doped by most of inorganic and organic acid.35 Phytic acid (PA), a renewable, eco-friendly and an abundant organic acid that is able to be obtained from grains, can be doped with PANI and form uniform multi-element doping after thermolysis.36-38 The overall synthetic procedure of the N,P,S-doped HCS are illustrated in Scheme 1. The six phosphate groups on phytic acid are interacted with several aniline monomers through hydrogen bond or electrostatic attraction to form cross-linked molecules as reported previously.35 Besides, the interactions occurred between aniline and silica through the S+X-I+ pathway in the presence of halide counteranion (Cl-) or the H-bonding between hydroxy in SiO2 and amidogen in aniline.39 Thus the stable dispersion of phytic acid/aniline/silica colloids was formed. After that, the polymerization of as-mentioned solution occurred by adding ammonium persulfate and further reacted overnight. Unlike another oxidant such as ferric trichloride, ammonium persulfate can be used as both oxidant during the polymerization and S source during the carbonization which has been verified before.



Scheme 1. Schematic illustration of the preparation process for the N,P,S-codoped hierarchically porous carbon spheres

EXPERIMENTAL Synthesis of the N,P,S-codoped hierarchically porous carbon spheres The PANI@PA microsphere was synthesized according to a previously reported method with some modifications.39 Typically, 2.55 g silica colloids (LUDOX TM-40, Aldrich) and 1.8 mmol phytic acid (40 wt% in H2O, Aladdin) were dispersed in 140 ml deionized water followed by adding 7 mL hydrochloric acid (1M) under magnetic stirring. After 15 min, 0.56 g aniline monomer was added to further form uniform solution. Then 1.4 g (NH4)2S2O8 (1 molar equivalent to aniline) with 2 mL hydrochloric acid (1M) was injected dropwise. The polymerization was conducted in ice bath (0-5 oC) for 24h. Finally, the mixture was transferred onto heating plate at 90 oC for 6h to fully evaporate the water and further desiccated in the vacuum drying oven at 100 oC overnight. The other samples with different phytic acid content (60 %, 90 % molar ratio to aniline) were fabricated through the method above. The as-prepared PA doped PANI@SiO2 was pyrolyzed at 700-1000 oC under N2 flow in the tube furnace with the temperature ramp rate of 2 oC min-1 and keep it for 2 h. After carbonization, the residual silica was removed by diluted HF solution and further dried in the vacuum drying oven at 60 oC overnight. The as-prepared samples were labeled as N,P,S-HCS-x which x represents the annealing temperature. For comparison, HCS-60 and HCS-90 with 60%, 90% molar ratio to aniline, N doped porous carbon (N-PC) with annealing polyaniline directly, N,P,S-PC with no adding silica template, no-PA-HCS with no adding phytic acid and out-PA-HCS with adding phytic acid after


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polymerization were also fabricated at 800 oC during the similar procedure. Characterizations The microstructure and morphology were obtained on high-resolution transmission electron microscope (Tecnai G2 F20 S-Twin) and field-emission scanning electron microscopy (Nova NanoSEM 450, FEI) operating at 200kV and 20-30kV, respectively. X-ray photoelectron spectroscopy (PHI 5000C ESCA, Perkin Elmer) was used to analyze the element compositions of heteroatom doped HCS through an Mg Kα X-ray source with the pass energy mode at 1253.6eV. X-ray diffraction (D/MAX2200V PC) was performed with Cu Kα at 40kV and 30mA at the scan rate of 2°/min. Fourier transform infrared spectra (AVATAR 370 FT-IR). The Raman spectra (INVIA) was recorded using 633nm laser. The specific surface area was tested by the Brunauer–Emmett–Teller (BET) method with Nitrogen adsorption/sorption isotherms (Autosorb-IQ2). All the samples were outgassed at 240oC for 10 hours and then measured at the relative pressure range from 0.02 to 0.5. The micro pore surface/volume pore and pore size distribution was derived from the t-plot method and QSDFT equilibrium model, respectively. Electrochemical characterization The electrochemical characterization for all the HCS samples were tested in electrochemical workstation (CHI 660D) and using 3-electrode system in a 6M KOH aqueous solution as electrolyte. Nickel foam was selected as current collector. Pt plates and Hg/HgO electrodes were used as counter and reference electrode, respectively. For the working electrode, 4 mg active materials were combined with conducing carbon (Super P) and polytetrafluoroethylene (PTFE) in the mass ratio of 8:1:1. Then dropping ethanol with the mixture into slurry. Finally, the slurry was coated on the Ni foam with 1x1 cm2 area. The as fabricated electrode was put into oven at 120 oC overnight and pressed at 10.0 MPa pressure before tested. For the ASSCs devices of N,P,S-HCS, it were assembled from the two pieces of the above electrode with gel electrolyte. The electrolyte was fabricated by heating 2 g polyvinyl alcohol (PVA) in 15 mL deionized (DI) water at 85oC under the continuous stirring (250 r.p.m) for 1h. After cooling to the room temperature, 1.36 g KOH with 5 mL



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DI water was poured into the former gel and further stirring for 1h. Typically, two pieces of electrodes and the NKK membrane (MPF30AC-100, 2×2 cm2) were immersed in the gel electrolyte for 15 min and air-dried for 5 min. With repeating one more time, the device was assembled by pressing two electrodes on both sides of wetting NKK membrane. Finally, the device was dried at room temperature to remove the excess water. All the tests were carried out using electrochemical workstation. The frequency range from 100kHz to 10mHz was performed in Electrochemical impedance spectroscopy (EIS) with open circuit potential. In the 3-electrode system, the cyclic voltammetry (CV) and galvanostatic charge–discharge (GCD) were tested in the potential window from -1.0 to 0.0 V. Cycling stability was measured by repeating the GCD test for 10000 cycles at 10 A g-1. In the 2-electrode system, CV and GCD were tested in the potential window from 0 to 1.2 V. The related performance was calculated as the following formulations: ×∆

= ×∆

(1)

Where Cg (F g-1) is the specific gravimetric capacitance, I (A) is the current, ∆ (s) is the discharge time, m (g) is the mass of active materials and ∆ (V) is the potential window.

= ×

(2)

Where Cv (F cm-3) is the specific volumetric capacitance, (g cm-3) is the apparent density of the films on Ni foam.

= /ℎ

(3)

Where m (g) is the dried film, A (cm2) is the surface area of film, h (cm) is the average thickness.

= P=

E×3600 t

(4) (5)

Where E (Wh cm-3) and P (W cm-3) are the energy density and power density, respectively. V (V) is the working voltage for ASSCs devices and t (s) is the time of discharge.


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RESULTS AND DISCUSSIONS

Figure 1. (a to c) SEM and TEM images of the N,P,S-HCS-800; (d) TEM image of the N,P,S-HCS-800 and corresponding element mapping of C, O, N, P and S. After the carbonization and etching of the as-prepared precursors (Fig. S1a and Fig. S2-4), the N,P,S-codoped hierarchically porous carbon spheres were formed. TEM images of the N,P,S-HCS-800 are shown in the Fig. 1a-c, lots of pores within spheres can be clearly seen without structure collapse. The well dispersed pores are believed to improve the mass transport properties which make the electrolyte ion migration easier in supercapacitors. In addition, with the temperature increased, the structure of N,P,S-HCS keeps well which indicated the stability of the carbon spheres (Fig. S5). But with the increasing of phytic acid, the morphology became more disorder and tended to agglomerate. When the mass ratio of PA reach to 90 %, it shows the irregular structure with pore faded (Fig. S6). The reason could be concluded into two parts: 1) The strong coordinating affinity of PA to aniline may disturb the incorporation between aniline and silica which affect the homogeneous formation of the polymer spheres. 2) Due to the abundant bonding sites on PA, excess PA was absorbed merely on the surface of the spheres. During the heating process, PA spontaneously carbonized into carbon sheets found by He et al.40 As a result, these sheets covered on or between the spheres caused the agglomeration. The sample with 30 % PA doped which shows



most regular sphere-like morphology in the meantime remaining the pore with uniform distribution is similar to the no-PA-HCS and HCS with lower PA content (Fig. S6a-b). Hence, in the following discussion we labeled the 30 % PA addition as optimized amounts for the N,P,S-HCS. The element analysis was also tested in Fig. 2d, the HRTEM image and associated element mapping represent the uniform distribution of C, O, N, P and S for the N,P,S-HCS annealed at 800 oC. The well dispersed heteroatom can be attributed to the homogeneous combination between PA and PANI caused by doping effect which further proves the advantage of PA as a P source.

Figure 2. (a) N2 sorption-desorption isotherms, (b) pore size distribution, (c) specific surface area and (d) pore volume distribution of the N,P,S-HCS with different annealing temperatures and contrast samples. To investigate the optimization of the carbon materials with high density and abundant heteroatom doping which are benefit for achieving both high gravimetric and volumetric capacitance, the effect of annealing temperature and PA adding are analyzed through nitrogen adsorption–desorption isotherms. With the annealing temperature increased, the curve in the region of middle and high pressure (P/Po=0.4-1.0) have the noticeable rise up which verifies the increase of meso- and macropores. This results can be ascribed to the further pyrolysis of the carbon precursor and the silica template. Furthermore, the curves exhibited type-IV isotherm


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characteristics which indicated the presence of mesopores thus confirming the successful incorporation between PANI and silica colloids (Fig. 2a). The pore size distribution curves have also been measured (Fig. 2b). All of them show hierarchical pores in the narrow pores size distribution and with the temperature rising, the pore size range from 0.5 to 1 nm are increased and further move to the range from 2-4 nm which result the rapid decrease in density. Additionally, the pore size near 32 nm remains unchanged at different temperatures which was caused by the silica template. The pore volume and specific surface area (SSA) of N,P,S-HCS with different temperatures from 700 to 1000 oC are measured to 358, 503, 1189 and 1258 m2 g-1 corresponding to 0.68, 0.78, 1.63 and 1.96 cm3 g-1, respectively (Fig 2c,d). It can be found that when the temperature reach to 900 oC, the SSA of N,P,S-HCS suddenly increased which can be identified as the complete pyrolysis of large molecule of phytic acid with abundant decomposition gases including N and P species thus leading to the severe loss of heteroatom doping.35 On the other hand, although the SSA annealed below 800 oC is quite low, the density is increased corresponding to the lower pore volume. Based on improving volumetric capacitance, we choose the sample annealed at 800 oC as the target temperature owing to higher density and abundant heteroatom doping. Furthermore, to discuss the effect of PA adding, the HCS fabricated with no PA adding and introducing PA after polymerization were also studied (see experimental section). All the samples reveal the similar pore size but different in intensity. The result indicated that the introduction of PA during the synthesis procedure didn’t change the structure of the HCS (Fig 2b). However, the decay in intensity is ascribed to the strong affinity of PA, as it may occupy more bonding sites with aniline rather than silica. The SSA of N,P,S-HCS-800 is inferior to N-HCS-800 which is free of PA during polymerization. It further verified the influence on PA during the polymerization which hindered affinity between silica and aniline. The analogous tendency can be found when we enlarged the mass ratio of PA (Fig. S7a-b). Interestingly, the N,P,S-HCS-800 and out-PA-HCS with PA adding after polymerization show similar SSA but different in pore volume. It indicated that PA exist both outside and inside of the polymer in the N,P,S-HCS while PA was only doped on the surface of the polymer in the out-PA-HCS and the latter result in lower P content (Table S2). Above all, we choose the samples with 30% PA adding during the polymerization step and annealed at 800 oC as optimum condition with moderate



density and well dispersed P doping. The as-mentioned sample was labeled as the N,P,S-HCS if not specified.

Figure 3. (a) The XPS survey spectrum and high-resolution XPS spectra of (b) N1s, (c) P2p and (d) S2p in the N,P,S-HCS-800. To ascertain the chemical and elemental combinations of the N,P,S-HCS, XPS spectrums have been analyzed and element compositions are shown in Fig. 3a and Table S2. The pronounced C1s, O1s, N1s peak with week P2s, P2p, S2p peak indicated the presence of multiple element in the carbon skeleton. Among them, the atomic concentration of S has also been detected which came from the pyrolysis of ammonium persulfate as reported by Meng et al.41,42 The peak for N1s are presented in Fig. 3b. The peak can be further deconvoluted into four types, including pyridinic (398.6 eV), pyrrolic (400.5 eV), quaternary (401.3 eV) and oxidized pyridinic (402.0 eV), respectively. These four types have different positions on carbon skeleton and function in electrochemistry. Among them, pyrrolic N and pyrrole N provide the pseudo-capacitance while quaternary N and oxidized pyridinic N activate the surface to help the electron transportation.39 In the high resolution N1s spectrum, the pyrrolic N dominated due to the mild annealing temperature which followed the variation trend of N doping. For phosphorus doping, the P2p spectra can split into three featured peaks at ~132.2, ~133.4 and 136.4 eV corresponding to C3-PO, C-PO3 and P-S bonds, indicating that P component successfully doped into the N,P,S-HCS through pyrolysis (Fig. 3c). Notably, the P-C peak around 130 eV was almost invisible, suggesting that the P doping was in the form of phosphate functional groups other than incorporating into graphite lattice. Moreover, S2p spectra has also been deconvoluted into two parts, C-S-C (163/164.1 eV) and C-SOx-C (168 eV) species.42 The main peak is


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attributed to the 2p1/2 of S in C-S-C with the weak peak in the form of oxidized S species, labeled as SOxn- (Fig. 3d). The N, P and S doping will result in the improvement of capacitance without increasing SSA which usually cause the low density in carbon materials.

Figure 4. (a) GCD curves of N,P,S-HCS with different annealing temperatures at 0.5 A g-1, (b) the relationship curves between gravimetric (Cg) and volumetric capacitance (CV) of N,P,S-HCS at different annealing temperatures at 0.5A g-1, (c) the CV curve of no-PA-HCS, out-PA-HCS and N,P,S-HCS samples in 6M KOH solution at a scan rate of 10 mV s-1, (d) the relationship of gravimetric/volumetric capacitance for different element doping samples. Another reports’ data are added for comparison. (e) EIS spectra (inset: magnified 0.4-0.9 Ω region) of different contrast samples, (f) cyclic stability and coulombic efficiency of N,P,S-HCS at a current density 10 A g-1 for 10000 cycles (inset: first and last 5th charge–discharge cycles) To further study the electrochemical performance of the N,P,S-HCS, all the samples were tested in 3-electrode system in 6M KOH. The N,P,S-HCS was conducted by galvanostatic charge-discharge (GCD) at 0.5 A g-1 through the controlling of annealing temperature as shown in Fig. 4a-b. It is worth noting that although the N,P,S-HCS annealed at 800 oC has relatively low specific surface area compared with the samples annealed above 900 oC, both well gravimetric (Cg) and volumetric capacitance (Cv) were obtained (Table S1). The specific capacitance of N,P,S-HCS at 0.5 A g-1 was 274 F g-1 with 219 F cm-3. Moreover, the rate capability of N,P,S-HCS-800 maintained well as compared



with other synthesis conditions (Fig. S8). The reason can be ascribed to the well-maintained heteroatom doping and high density which indicated that annealed at mild temperature can prevent the excessive multiple element losses via decomposing into gas and thus keep the structure in high density with less pores generated.28 In order to verify the synergistic effects of N,P,S-HCS, samples with different heteroatom doping were evaluated by cyclic voltammograms (CV) in Fig. 4c. The qusi-rectangle shape was observed in all the three samples, indicating the typical EDLC capacitive behavior of carbon materials, except the slight distortion in the range of -0.8 to -0.6 V which stand for the pseudo-capacitive behavior due to the redox reactions by heteroatom. Regardless of the relatively low specific surface area, the N,P,S-HCS as discussed before, have the maximum area of the CV curves proving that the synergistic effect of ordered structure and abundant multi-element doping improve the specific capacity than the no-PA-HCS and out-PA-HCS. In addition, in order to study the effect of silica template, the electrochemical properties of N-PC and N,P,S-PC have been studied in Fig. S8 and S10-11. Without adding silica template, the N-PC and N,P,S-PC show the poor rate capability and cycling stability owing to its disordered structure (Fig. S5 and S9). Furthermore, the N,P,S-HCS with the density of 0.8 mg mL-1, which have surpassed conventional carbon materials (ρ < 0.75 mg mL-1), obtained the well-balanced between Cg and Cv than other heteroatom doped porous carbon, carbon spheres and graphene (Fig. 4d).30,43-46 The ionic transport research of different element doped HCS electrodes in 6 M KOH was evaluated by electrochemical impedance spectroscopy (EIS) with the frequency range from 0.01 to 100000 Hz. The curves clearly manifested that all samples reflect the nearly vertical line in the low frequency region as the carbon materials behaved (Fig. 4e). Among them, the N,P,S-HCS shows the lower internal resistance and the equivalent series resistance (ESR) of N,P,S-HCS were 0.56 Ω obtained by extrapolating the real axis with the vertical lines. The cycling stability is another important parameter to estimate the performance of the supercapacitors. The cycling test was performed at 10 A g-1 in 6M KOH by galvanostatic charge/discharge (Fig. 4f). After 10000 cycles, the N,P,S-HCS samples retained 95 % with the coulombic efficiency of nearly 100 % performing the excellent stability. That may be owing to the ordered structure of the carbon spheres which produce the fast ion pathway during the charge/discharge process.


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Figure 5. (a) the equipment drawing of the all-solid-state device, (b) the CV curves of N,P,S-HCS device at different potential windows at 10 mV s-1, (c) the GCD curves of the N,P,S-HCS device at different current densities with the voltage window of 1.2 V, (d) the EIS spectra (inset: magnified 0.5-2.0 Ω region and equivalent circuit of the device) of the N,P,S-HCS device and (e) Ragone plots of the N,P,S-HCS device. Another reports’ data are added for comparison. Finally, in order to evaluate the feasibility of the N,P,S-HCS electrode, we assembled it into symmertic all-solid state supercapacitors (ASSCs) and tested its electrochemisty properties (Fig. 5a). It can be seen that the shape of CV curves became more distorted due to the oxygen evolution reaction by electrolysis of water as shown in the CV curves of the device at different voltage ranges (Fig. 5b). Among them, the voltage of 1.2 hold the qusi-rectangle shape with the maxmium value of voltage window. The GCDs of the ASSCs device at different current densities are displayed in Fig. 5c and it presents the highest capacitance of 31.3 F g-1 and 20.8 F cm-3 at the current density of 0.5 A g-1. The nearly symmertic and linear charge/discharge curves expalin the superior capacitive characters of our ASSCs device. Furthermore, the small charge transfer resistance and the vertical tail can be found in the EIS plot which indicated the good conductivity of the N,P,S-HCS devices (Fig. 5d). The maxmium energy density is 4.2 Wh L-1 and still maintains 3.4 Wh L-1 with the power density of 804 W L-1. Due to the ordered structure, high density and well-dispered heteroatom, the



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as-achieced device is superior to many other carbon based devices, such as graphene film (2.78 Wh L-1 with 40.3 W L-1),47 N,O-codoped ordered carbon//MnO2 (1.1 Wh L-1 with 429 W L-1),48 CNT/MoO3-x//CNT (1.5 Wh L-1 with 420 W L-1)49 and PPy@CNTs@3DGA//MnO2@CNTs @3DGA (2.01 Wh

L-1

with

630

W

L-1),50

RGO/GO/RGO

(1.24

Wh

L-1

with

890

W

L-1),51

3DHPC-NiCo2S4//3DHPC-Fe2O3 (1.71 Wh L-1 with 62.9 W L-1),52 RGO/Mn3O4//RGO/Mn3O4 (1.91 Wh L-1 with 268 W L-1),53 which confirms the possbility of volumetric capacitance improvement by heteroatom doping and structure tuning (Fig. 5e).

CONCLUSIONS In summary, by using polyaniline as both nitrogen and carbon source, phytic acid as phosphorus source, ammonium persulfate as sulfur source, silica colloids as template, heteroatom doped hierarchically porous carbon spheres have been synthesized and measured its electrochemical properties in SCs. The resulting N,P,S-HCS have high density with abundant multiple element doping and thus show the superior balance between gravimetric and volumetric capacitance. The optimized electrode of the N,P,S-HCS delivered 274 F g-1 corresponding to 219 F cm-3 at the current density of 0.5 A g-1, and long-term cycling stability retaining 95 % of the initial values after 10000 cycles. To further assembling into ASSCs device, the symmetric SCs achieved high energy density of 4.2 Wh L-1 with the potential window of 1.2 V in KOH-PVA electrolyte. The N,P,S-HCS may shed a light on tuning the well ordered structures and introducing abundant heteroatom doping to solve the mismatching of gravimetric and volumetric capacitance.

ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website at DOI: XX.XXXX.

TEM

and

SEM

images,

FTIR

spectrum,

XRD,

Raman

spectrum,

nitrogen

adsorption–desorption isotherms, PSD, CV, GCD, EIS, rate capability, cyclic stability curves and Table.

AUTHOR INFORMATION ACS Paragon Plus Environment

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Corresponding Author *E-mail: [email protected], Fax: +86 21 66137152 Conflicts of interest

There are no conflicts to declare.

ACKNOWLEDGEMENTS This work was supported by the National Key R&D Program of China (2017YFB0102200), the National Natural Science Foundation of China (21722704), Science and Technology Commission of Shanghai Municipality (16JC1401700 and 16DZ1204300).

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TOC

Synopsis The carbon materials with well balanced gravimetric and volumetric capacitance for supercapacitors have been demostrated.


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N,P,S-codoped Hierarchically Porous Carbon ... - ACS Publications

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