Facile Synthesis of Boron and Nitrogen Co-doped Porous Carbon

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Facile Synthesis of Boron and Nitrogen Co-doped Porous Carbon Foam for High Performance Supercapacitors Dong Guo, Bing Ding, Xin Hu, Yahui Wang, Fuqin Han, and Xiaoliang Wu ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/acssuschemeng.8b01435 • Publication Date (Web): 26 Jul 2018 Downloaded from http://pubs.acs.org on July 26, 2018

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Graphical abstract

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A simple and efficient strategy for the preparation of boron and nitrogen co-doped porous carbon foam (BNPC) is reported. The obtained BNPC sample exhibits high specific capacitance and energy density.

ACS Paragon Plus Environment

ACS Sustainable Chemistry & Engineering 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Facile Synthesis of Boron and Nitrogen Co-doped Porous Carbon Foam for High Performance Supercapacitors Dong Guo, Bing Ding, Xin Hu, Yahui Wang, Fuqin Han, Xiaoliang Wu* Department of Chemistry, College of Science, Northeast Forestry University, 26 Hexing Road, Harbin 150040, P. R. China *

Address correspondence to [email protected]

ABSTRACT: A facile and efficient method to prepare boron and nitrogen co-doped porous carbon foam (BNPC) derived from starch with urea as nitrogen source and boric acid as both boron source and templet is presented. The co-doping strategy can boost the synergistically doping amounts of boron and nitrogen, which can achieve a great increase in the doping efficiency of boron (three times higher than single boron doping) and nitrogen. Due to its hierarchical pore structure with moderate specific surface and relatively numerous nitrogen (9.38 at.%) and boron (3.87 at.%), the BNPC electrode exhibits outstanding electrochemical performances with an ultrahigh specific capacity of 402 F g−1 at a current density of 0.5 A g−1 and retains 266 F g−1 even at a current density of 20 A g−1 in 6 M KOH electrolyte. In addition, a symmetric device based on BNPC electrodes delivers a respectable energy density of 21.9 Wh kg−1 in 1 M Na2SO4 electrolyte. Therefore, this work provides a simple and efficient method to synthetize heteroatom doped hierarchical porous carbon materials for advanced energy storage systems. Keywords: Starch, Hierarchical porous carbon, Heteroatom doping, Energy density, Supercapacitors. 1


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Introduction Supercapacitors have great potential as high energy storage systems due to their ultrahigh

specific

power,

excellent

electrochemical

stabilization

and

rapid

charging/discharging rate.1-6 Because of the high surface area, extensive source, low cost and good electrochemical stability, carbon materials have been diffusely used as electrode materials for electrochemical double-layer capacitors (EDLCs).7-12 Nevertheless, traditional carbon-based supercapacitors show unsatisfactory energy density (mostly lower than 10 Wh kg-1), which seriously restrict their practical application. Consequently, the development and preparation of new carbon materials with high energy densities are very important and highly urgent for their practical application.13-16 Carbon-based supercapacitors store energy by ion adsorption at the interphase of the electrode and electrolyte. Thus, the electrochemical properties of carbon materials are mainly based on the pore structure and specific surface area, as well as the surface characteristics of carbon materials. Owing to their large surface areas, rich sources and moderate cost, activated carbon materials (ACs) have been used as the first candidate electrode material for commercial supercapacitor.13,17 Although ACs possess a large surface area up to 2000-3000 m2 g–1, the gravimetric specific capacity are usually under 250 F g−1 in aqueous electrolytes and the rate capability is also rather poor.13 The surface area of ACs is mostly contributed by micropore. However, such pore usually suffers from long diffusion paths and high internal resistance, which severely affect the specific capacitances and rate performances of supercapacitors.18-22 A three-dimensional (3D) interconnected hierarchical porous structure (micropore, 2



mesopore, macropore) is desirable for the high-performance electrode materials.23-25 The mesopores can facilitate rapid ion diffuse and macropores can regarded as ion-buffering reservoirs to offer short transport channel in the interior of porous carbon, which will enhance the utilization efficiency of micropores, resulting in not only high specific capacitance, but also outstanding rate performance.26-28 Furthermore, recent researches have shown that heteroatoms doping (e.g. N, S, B, and etc.) can ameliorate the performances of carbon-based electrode materials through increasing the surface Faradaic reaction, while maintaining the excellent characteristics (excellent electrochemical stability and good rate capability) of carbonaceous materials at the same time.29-33 Consequently, the development and preparation of hierarchical porous carbon materials with suitable content of heteroatom functional groups are highly beneficial for high performance supercapacitors. Herein, we develop a sample and efficient way for the preparation of boron and nitrogen co-doped porous carbon foam (BNPC) derived from starch with urea as the nitrogen source and boric acid as both boron source and templet. Benefiting from its hierarchical pore architecture with moderate specific surface area and relatively numerous nitrogen (9.38 at.%) and boron (3.87 at.%), the BNPC electrode shows a specific capacity of 402 F g−1 at 0.5 A g−1, and the specific capacity keeps 266 F g−1 even at 20 A g−1 in 6 M KOH. More interestingly, the assembled BNPC//BNPC symmetric supercapacitor achieves an energy density of 21.9 Wh kg−1 according to the gross weight of electroactive materials on two electrodes in 1 M Na2SO4 electrolyte. Experimental sections Material preparation Boric acid (2 gram) and urea (2 gram) were dissolved in distilled water at 80 °C, and 3


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then starch (2 gram) and ZnCl2 (2 gram) were added under stirring. Next, the obtained product was dried at 85 °C overnight. The obtained mixture was heated at 700 °C for 2h in the nitrogen flow. Then, the obtained sample was washed with dilute HCl solution and distilled water, and dried at 85 °C overnight. The as-obtained samples were denoted as BNPC. For comparison, samples were prepared according to the BNPC without urea or boric acid, and the obtained samples were denoted as BPC and NPC, respectively. In addition, sample was prepared according to the BNPC without urea and boric acid, and the product was denoted as PC. Material Characterization The morphology of the as-prepared materials was checked through scanning electron microscopy (SEM, JEOL JSM-7500F) and transmission electron microscopy (TEM, JEOL JEM2010). The crystallographic characteristics of the obtained samples were determined by X-ray diffraction equipped with Cu Kα radiation. Raman spectra were checked by Jobin-Yvon HR800 spectrometer at an excitation wavelength of 458 nm. The surface area was measured by N2 adsorption/desorption by the BET method and pore size distribution were computed by the density functional theory (DFT) model. X-ray photoelectron spectroscopy analysis was collected on a PHI5700ESCA spectrometer using a monochromatic (Kα radiation) source. Electrochemical characterization 75 wt% electroactive material, 20 wt% carbon black and 5 wt% polytetrauoroethylene added into ethanol, then pressed onto the Ni foam (1 cm × 1 cm) and dried under vacuum. Ni foam loaded with electroactive materials, Hg/HgO electrode and platinum foil were served as the working electrode, reference and counter electrodes, respectively. The electrochemical properties of the single electrode were tested in a three-electrode system in 6 M KOH aqueous electrolyte. CV tests of the single electrode were recorded between -1 and 0 V (vs. Hg/HgO) at various scan rates. Galvanostatic charge-discharge was tested in the same voltage window 4



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of CV at the current densities ranging from 0.5 to 20 A g-1. Electrochemical impedance spectra (EIS, Nyquist plots) were carried out at an open circuit potential of 5 mV at a frequency range of 0.01 Hz to 100 kHz. The symmetrical supercapacitor device was fabricated with two BNPC electrodes with the equal loaded mass (both positive and negative electrodes are made of the BNPC electrode materials) and separated by a glassy fibrous separator. The whole system was immersed in 1 M Na2SO4 aqueous electrolyte for electrochemical measurements. All electrochemical tests were checked by a CHI 660E electrochemical workstation. The gravimetric specific capacity of the individual electrode was computed through the formula:

C

It m V

(1)

Where I is the current density, Δt is the discharge time, ΔV is the discharge potential, and m is the weight of the electroactive material. The gravimetric specific capacity, energy density (E) and power density (P) of the symmetric system were computed by the formula: C

 IdV

(2)

mV

E=0.5CV2

(3)

P = E/Δt

(4)

Where I is the current density, V is the working range, ν is the scan rate, m is the weight of the active materials of the two electrodes and Δt is the discharge time (s). Results and discussion The microstructures of the obtained samples were checked by scanning electron 5


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microscopy (SEM). As shown in Figure 1a, the PC displays block structure without obvious pores. A similar morphology can be observed for NPC (Figure 1b). In contrast, BPC and BNPC (Figure 1c, d) show porous structure with substantial macropores. The enlarged resolution SEM of BNPC exhibits an interconnected porous framework with a large number of macropores. Furthermore, through transmission electron microscopy (TEM) image observation, the PC and NPC samples exhibit substantial micropores the surface of carbon wall (Figure S1a, b). The BNPC (Figure 1f) samples exhibit an interconnected porous structure with substantial mesopores and macropores in the surface of carbon wall, which is favorable the fast ion diffusion during the chage/dischage process. Meanwhile, the enlarged resolution TEM image of BNPC (Figure S1d) can observe massive micropores in the surface of carbon wall. In order to research the reasons for the difference in the morphology, the mixture of boric acid and starch were pyrolyzed according to the BNPC (named as BC). The BC displays a similar morphology with BPC (Figure S2a). According to the above analysis, it can be concluded that the porous framework in BNPC and BPC are related to the boric acid. As the increase of heating temperature, the boric acid would decompose to produce boron trioxide and it embedded in the carbonaceous materials. Porous structures are created in BNPC after washing with dilute hydrochloric acid in which boron trioxide species are removed.16 In addition, the homologous element mapping images of BNPC show the homogeneous distribution of B, N, O, and C element (Figure S2c-f). The structural features of the as-prepared materials were confirmed by X-ray powder diffraction (XRD) and Raman spectra. Figure 2a exhibits the XRD patterns of the obtained materials, two broad and weak diffraction peaks at around 2θ = 25°and 44°can be observed, 6



which are corresponding to the graphite (002) and (100) plane, respectively. The broad (002) and (100) XRD peaks indicate amorphous state in these samples. In Raman spectra (Figure 2b), all materials show two characteristic peaks located at 1339 and 1586 cm-1 which attribute to typical D and G bands of carbon. The D peak (1339 cm-1) and G peak (1586 cm-1) are assigned to disordered graphite structure and graphitic carbon. The ID/IG of BNPC (0.95) is higher than PC (0.86), NPC (0.89) and BPC (0.92), meaning that the BNPC sample possesses more defects and disordered graphite. Furthermore, the pore textures of the porous carbon materials were checked by N2 adsorption-desorption isotherms (Figure 2c) and the obtained data are showed in Table 1. The PC and NPC samples show typical type I adsorption-desorption isotherm. In contrast, the adsorption-desorption isotherms of BPC and BNPC materials show the combined features of type I and IV isotherms, indicating the existence in micropore and mesopore structure. The BNPC material exhibts a specific surface area of 933 m2 g-1, lower than other samples. It is noted that the Smic value (provided by micropores) of BNPC is lower than those of PC, NPC and BPC, but the Sme value (provided by mesopores) of BNPC is higher than those of PC, NPC and BPC, which indicates that part of micropores in BNPC disappear during B, N co-doping process. Figure 2d exhibits the pore size distribution of the as-prepared materials, the PC and NPC samples possess pores most less than 4 nm calculated by DFT method, which is the same as the traditional activated carbon.34 The pore size distribution of BPC and BNPC is much broader than those of PC and NPC, which is more favorable for rapid ion transport. The surface properties of the obtained samples were checked by X-ray photoelectron spectroscopy. As shown in Figure 3a, the XPS survey of BNPC has four peaks at 191.0, 284.5, 7


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398.7, and 531.7 eV are assigned to the B1s, C1s, N1s and O1s, demonstrating the successful B and N co-doping for BNPC. The chemical compositions of the obtained materials are listed in Table 2. The doping content of N for BNPC (9.38 at.%) is higher than that of NPC (7.22 at.%). Moreover, The doping content of B for BNPC is 3.87 at.%, which is almost three times higher than that of BPC (1.22 at.%). These results indicate that B and N co-doping method could boost the synergistically doping amounts of B and N, which can achieve a great increase in the doping efficiency of boron and nitrogen. Furthermore, the high resolution C1s spectra of BNPC can be assigned to C-B (283.9 eV), C=C (284.5 eV), C-C/C-N (285.3 eV), C=O (286.3 eV) and O-C=O (288.7 eV).35 The B1s spectra (Figure 3c) can be fitted as four peaks centering at 190.1, 191.0, 191.8 and 192.6 eV, corresponding to BC2O, BN, BCO2 and B2O3, respectively.30 The increased doping amount of boron is resulted from the generation of B-N bonds. In addition, the high resolution N1s spectra can be fitted as four peaks (Figure 3d), corresponding to pyridinic-N (398.1 eV), C-N-B (399.2 eV), pyrrolic-N (400.4 eV) and quaternary-N (404.1 eV), respectively.36,37 It has been reported that pyridinic-N and pyrrolic-N can offer pseudocapacitance by redox reactions, while quaternary-N can increase the electroconductivity of carbon materials. 38-39 Owing to its hierarchical porous architecture with moderate specific surface area and massive boron and nitrogen functional groups, the BNPC is expected to be an outstanding electrode material for supercapacitors. The electrochemical performances of the obtained materials were tested in 6.0 M KOH electrolyte using a three-electrode system. Cyclic voltammetry (CV) tests were firstly performed at various scan rates between -1 and 0 V. Compared with PC, the CV curve of NPC electrode exhibits slightly faradaic humps due to 8



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nitrogen doping can provide Faradic reaction (Figure S3a). Compared with PC, the CV curve of BPC electrode shows a larger rectangular-like shape due to boron doping is an effective strategy to improve the specific capacity of carbon materials, including electric double layer capacity and pseudocapacitance (Figure S3b).15, 32 As shown in Figure 4a, the BNPC electrode exhibits a larger area of CV curve than PC, NPC and BPC electrodes, corresponding to a larger specific capacitance. This is due to the boron and nitrogen co-doped strategy can boost the synergistically doping amounts of boron and nitrogen (as analyzed by XPS). It is thus reasonable to obtain a higher redox capacitance for BNPC. The possible related redox reactions can be expressed as follows40: H N

N + H2O + e-

+ OH-

(5) HN

N + H2O + e-

+ OH-

(6) O

N

N + e-

H + OH-

(7)

Moreover, even at 100 mV s-1, the CV profile of BNPC maintains a rectangular-like shape (Figure S3c), meaning a good rate performance. The galvanostatic charge-discharge profiles of BNPC show a little distorted triangular shape (Figure 4b), further confirming that the specific capacitance originates from the combined contribution of electric double layer capacitance and pseudocapacitance. In accordance with the CV results, the BNPC electrode exhibits a longer charge-discharge time than PC, NPC and BPC electrodes (Figure S3d). The BNPC electrode shows a ultrahigh specific capacity of 402 F g–1 at 0.5 A g–1 (Figure 4c), which is higher than those of PC electrode (256 F g–1 at 0.5 A g–1), NPC electrode (316 F g–1 9


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at 0.5 A g–1), BPC electrode (367 F g–1 at 0.5 A g–1) and other previously published heteroatoms doped porous carbon materials (Table 3). Furthermore, even at a high current density of 20 A g–1, the BNPC electrode retains a high specific capacity of 266 F g–1, meaning a good rate performance. From the Nyquist plots (Figure 4d), the BNPC shows a lower equivalent series resistance (0.38 Ω) than PC (0.58 Ω), NPC (0.41 Ω) and BPC (0.43 Ω), which indicates a better conductivity for BNPC. Moreover, the surface charge-transfer resistance of BNPC electrode is lower than that of other samples, which means that the BNPC electrode has a faster charge-transfer process. The cycling stability of BNPC was evaluated by CV measurements at 200 mV s-1 (Figure S3e). The specific capacity of BNPC remains 87% of its initial capacity after 10,000 cycles, indicating good electrochemical stability. The reduced capacity is mainly attributed to the partial decomposition of surface heteroatom functional groups during charge-discharge measurement. To further evaluate the practical electrochemical performance, a symmetric supercapacitor was assembled based on the BNPC electrodes with a two-electrode system. Considering that the energy density is not only interrelated to the specific capacity of electrode materials, but also related to the working voltage range. Therefore, strenuous efforts were made to choose the optimized electrolytes for the carbon-based symmetric supercapacitors. As reported by Béguin, due to the balanced H+/OH- and strong solvation of both alkali metal cation and sulfate anions, Na2SO4 aqueous solutions can achieve a wide working voltage up to 1.6 V.45,47 Therefore, the BNPC//BNPC symmetric supercapacitor was developed in 1 M Na2SO4 electrolyte. Figure 5a shows the CV curves of the BNPC//BNPC symmetric supercapacitor were measured in various working voltage range at 50 mV s-1. As 10



seen, the stability potential window for the BNPC//BNPC symmetric supercapacitor is 0-1.6 V. Therefore, the electrochemical performances of BNPC//BNPC symmetric supercapacitor were tested in the voltage window of 0-1.6 V. Figure 5b exhibits the CV curves of the BNPC//BNPC symmetric supercapacitor were tested at various scan rates. Even at 200 mV s–1, the CV profile display rectangular-like shape indicating good rate capability. The calculated specific capacity based on charge-discharge profiles is shown in Figure 5c. The specific capacity of the BNPC//BNPC symmetric supercapacitor is calculated to be 61.5 F g-1 at 0.2 A g-1. Furthermore, Ragone plots of the BNPC//BNPC symmetric supercapacitor are shown in Figure 5d. The BNPC//BNPC symmetric supercapacitor shows a high energy density of 21.9 Wh kg-1, comparable with those of other reported carbon based symmetric supercapacitor, for instance, N-doped 3D-graphitic foams (8.4 Wh kg-1),37 nitrogen-doped porous carbon (9.58 Wh kg-1),38 nitrogen-rich porous carbons (12 Wh kg-1),48 heteroatom-doped carbon nanofiber networks (7.76 Wh kg-1),49 seaweed biopolymer derived carbon (7.5 Wh kg-1).50 The specific capacitance of BNPC//BNPC symmetric supercapacitor remains 88% of its initial capacity after 10,000 cycles in 1 mol L-1 Na2SO4 electrolyte (Figure S4), suggesting good electrochemical stability. As a contrast, the electrochemical performances of BNPC//BNPC symmetric supercapacitor were also checked in 6 M KOH electrolyte. Even at 100 mV s-1, the CV profile of BNPC//BNPC symmetric supercapacitor still maintains a rectangular-like shape (Figure S5a), revealing a good rate performance. The energy density of BNPC//BNPC symmetric supercapacitors in 6 M KOH (Fig. S5b) is smaller than that in 1 M Na2SO4 owing to its narrow voltage range. The outstanding electrochemical properties of the BNPC material can be ascribed to its 11


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interconnected hierarchical pore architecture with moderate specific surface area and massive nitrogen and boron. Firstly, interconnected hierarchical porous architecture with moderate specific surface area can provide substantial accessible active sites to store a great deal of charges and accordingly will be conducive to a high specific capacity. Secondly, the macropores can serve as ion buffering reservoirs, which can greatly shorten the ion transport distance to the interior surfaces. Finally, massive B and N functional groups can not only increase the surface hydrophilicity of electrode material, but also offer some pseudocapacitance, thus a substantial enhanced capacitance performance. Conclusions In our study, we reported a facile, effective way to synthesize boron and nitrogen co-doped hierarchical porous carbon foam (BNPC) derived from starch with urea as the nitrogen source and boric acid as both boron source and templet. The co-doping strategy can boost the synergistically doping of boron and nitrogen, which can achieve a great increase in the doping efficiency of boron and nitrogen. The obtained BNPC material exhibits an interconnected hierarchically pore architecture with moderate specific surface area and massive heteroatom contents. Consequently, the BNPC material shows high specific capacity and good rate capability. Furthermore, the assembled BNPC symmetric supercapacitor achieves a high energy density of 21.9 Wh kg−1 according to the gross weight of the electroactive materials on two electrodes.

ASSOCIATED CONTENT

Supporting Information Supplementary data associated with this article can be found in the online. 12



AUTHOR INFORMATION Corresponding Author [email protected] ORCID Xiaoliang Wu: 0000-0002-9297-0922 Notes The authors declare no competing financial interest

Acknowledgment This work was supported by National Natural Science Foundation of China (51702043) and Fundamental Research Funds for the Central Universities (2572017BB18).

13


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[23] Wang, D.W.; Li, F.; Liu, M.; Lu, G.Q.; Cheng, H.M. 3D aperiodic hierarchical porous graphitic carbon material for high-rate electrochemical capacitive energy storage, Angew. Chem. Int. Ed. 47 (2008) 373-376. [24] Sun, L.; Zhou, H.; Li, L.; Yao, Y.; Qu, H.N.; Zhang, C.L.; Liu, S.H.; Zhou, Y.M. Double soft-template synthesis of nitrogen/sulfur-codoped hierarchically porous carbon materials derived from protic ionic liquid for supercapacitor, ACS Appl. Mater. Interfaces 9 (2017) 26088-26095. [25] Sun, K.L.; Yu, S.S.; Hua, Z.L.; Li, Z.H.; Lei, G.T.; Xiao, Q.Z.; Ding, Y.H. Oxygen-containing hierarchically porous carbon materials derived from wild jujube pit for high-performance supercapacitor, Electrochim. Acta 231 (2017) 417-428. [26] Yu, S.; Wang, H.R.; Hu, C.; Zhu, Q.Z.; Qiao, N.; Xu, B. Facile synthesis of nitrogen-doped, hierarchical porous carbons with a high surface area: the activation effect of a nano-ZnO template, J. Mater. Chem. A 4 (2016) 16341-16348. [27] Wang, H.R.; Yu, S.K.; Xu, B. Hierarchical porous carbon prepared using nano-ZnO as template and activation agent for ultrahigh power supercapacitors, Chem. Commun. 52 (2016) 11512-11515. [28] Wang, Q.; Yan, J.; Wang, Y.; Wei, T.; Zhang, M.; Jing, X.; Fan, Z.J. Three-dimensional flower-like and hierarchical porous carbon materials as high-rate performance electrodes for supercapacitors, Carbon 67 (2014) 119-127. [29] Park, S.K.; Kwon, S.H.; Lee, S.G.; Choi, M.S.; Suh, D.H.; Nakhanivej, P.; Lee, H. Park, H.S. 105 cyclable pseudocapacitive Na-ion storage of hierarchically structured phosphorus incorporating nanoporous carbons in organic electrolytes. ACS Energy Lett. 17


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3 (2018) 724-732. [30] Chen, H.; Xiong, Y.C.; Yu, T.; Zhu, P.F.; Yan, X.Z.; Wang, Z.; Guan, S.Y. Boron and nitrogen co-doped porous carbon with a high concentration of boron and its superior capacitive behavior, Carbon 113 (2017) 266-273. [31] Xu, B.; Duan, H.; Chu, M.; Cao, G.P.; Yang, Y.S. Facile synthesis of nitrogen-doped porous carbon for supercapacitors, J. Mater. Chem. A 1 (2013) 4565-4570. [32] Wang, D.W.; Li, F.; Chen, Z.G.; Lu, G.Q.; Cheng, H.M. Synthesis and electrochemical property of boron-doped mesoporous carbon in supercapacitor, Chem. Mater. 20 (2008) 7195-7200. [33] Park, S.K.; Lee, H.; Min Sung Choi, Suh, D.H.; Nakhanivej, P.; Park, H.S. Straightforward and controllable synthesis of heteroatom-doped carbon dots and nanoporous carbons for surface-confined energy and chemical storage. Energy Storage Mater. 12 (2018) 331-340. [34] Wang J.; Kaskel S. KOH activation of carbon-based materials for energy storage, J. Mater. Chem., 22 (2012) 23710-23725. [35] Hao, F.; Yao, Y.; Li, Y.P.; Tian, C.X.; Zhang, X.H.; Chen, J.H. Synthesis of high-concentration B and N co-doped porous carbon polyhedra and their supercapacitive properties, RSC Adv. 5 (2015) 77527- 77533. [36] Xia, Q.Y.; Yang, H.; Wang, M.; Yang, M.; Guo, Q.B.; Wan, L.M.; Xia, H.; Yu, Y. High energy and high power lithium-ion capacitors based on boron and nitrogen dual-doped 3D carbon nanofibers as both cathode and anode, Adv. Energy Mater. DOI: 10.1002/aenm.201701336. 18



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[37] M.J. Kwak, A. Ramadoss, K.Y. Yoon, J. Park, P. Thiyagarajan, J.H. Jang, Single-step synthesis of N-doped three-dimensional graphitic foams for high-performance supercapacitors, ACS Sustainable Chem. Eng. 5 (2017) 6950-6957. [38] Sun, L.; Tian, C.; Fu, Y.; Yang, Y.; Yin, J.; Wang, L.; Fu, H. Nitrogen-doped porous graphitic carbon as an excellent electrode material for advanced supercapacitors, Chem. Eur. J. 20 (2014) 564-574. [39] Li, Z.; Xu, Z.W.; Tan, X.H.; Wang, H.L.; Holt, C.M.B.; Stephenson, T.; Olsen, B.C.; Mitlin, D. Mesoporous nitrogen-rich carbons derived from protein for ultra-high capacity battery anodes and supercapacitors, Energy Environ. Sci. 6 (2013) 871-878. [40] Liu, H.; Song, H.; Chen, X.; Zhang, S.; Zhou, J.; Ma, Z. Effects of nitrogen- and oxygen-containing functional

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[44] Zhu, H.; Wang, X.L.; Yang, F.; Yang, X.R. Promising carbons for supercapacitors derived from fungi, Adv. Mater. 23 (2011) 2745-2748. [45] Bichat, M.P.; Raymundo-Piñero, E.; Béguin, F. High voltage supercapacitor built with seaweed carbons in neutral aqueous electrolyte, Carbon 48 (2010) 4351-4361. [46] Elmouwahidi, A.; Zapata-Benabithe, Z.; Carrasco-Marí n, F.; Moreno-Castilla, C. Activated carbons from KOH-activation of argan (Argania spinosa) seed shells as supercapacitor electrodes, Bioresour. Technol. 111 (2012) 185-190. [47] Demarconnay, L.; Raymundo-Piñero, E.; Béguin, F. A symmetric carbon/carbon supercapacitor operating at 1.6 V by using a neutral aqueous solution, Electrochem. Commun. 12 (2010) 1275-1278. [48] Gao, F.; Shao, G.; Qu, J.; Lv, S.; Li, Y.; Wu, M. Tailoring of porous and nitrogen-rich carbons derived from hydrochar for high-performance supercapacitor electrodes, Electrochim. Acta 155 (2015) 201-208. [49] Chen, L.F.; Huang, Z.H.; Liang, H.W.; Gao, H.L.; Yu, S.H. Three-dimensional heteroatom-doped carbon nanofiber networks derived from bacterial cellulose for supercapacitors, Adv. Funct. Mater. 24 (2014) 5104-5111. [50] Piñero, E.; Leroux, F.; Béguin, F. A high-performance carbon for supercapacitors obtained by carbonization of a seaweed biopolymer, Adv. Mater. 18 (2006) 1877-1882.

20



Page 22 of 29

(b)

(a)

1 µm

500 nm

(c)

(d)

500 nm

2 µm

(e)

(f)

500 nm

200 nm

Figure 1. (a) SEM image of PC. (b) SEM image of NPC. (c) SEM image of BPC. (d, e) SEM images of BNPC. (f) TEM image of BNPC.

21


Page 23 of 29

(a)

20

30

40

50

2 (degree)

60

70

Intensity (a.u.) 500

80

1000

1500

2000

2500

3000

3500

Raman shift (cm ) -1

(d)

1.2

(c)

PC NPC BPC BNPC

-1

1.0 0.8

3

-1

800

dV/dD (cm g nm

-1 3

PC NPC BPC BNPC

)

1000

(b)

PC NPC BPC BNPC

Intensity (a.u.) 10

Quantity Adsorbed (cm g STP)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


600 400 PC NPC BPC BNPC

200 0 0.0

0.2

0.4

0.6

0.8

0.6 0.4 0.2 0.0 0

1.0

Relative pressure (p/p0)

4

8

Pore size (nm)

12

16

Figure 2. (a) XRD patterns of PC, NPC, BPC and BNPC. (b) Raman spectrum of PC, NPC, BPC and BNPC. (c) N2 adsorption/desorption isotherms of PC, NPC, BPC and BNPC. (d) Pore size distribution of PC, NPC, BPC and BNPC.

22



Page 24 of 29

Table 1. Porosity parameters of the as-prepared carbon materials SBET(m2 g-1)a

Smic(m2 g-1)b

Sme(m2 g-1)c

Sme/ Smic

Vtotal(cm3 g-1)d

D (nm)e

PC

1158

1022

136

0.11

0.598

2.1

NPC

1402

1150

252

0.22

0.846

2.4

BPC

1458

1166

292

0.23

1.563

4.3

BNPC

933

618

315

0.51

1.034

4.4

Samples

a

Specific surface area (SBET) was calculated with modifie Brunauer-Emmett-Teller (BET) method.

b

Micropore surface area (Smic) was obtained from t-plot method.

c

Mesopore surface area (Sme) was obtained from t-plot method

d

Total pore volume (Vtotal) was estimated from the adsorbed amount at a relative pressure of

0.99. e

Average pore diameter (D) was obtained from D = 4Vtotal/SBET.

23


Page 25 of 29

C

O

Intensity(a.u.)

(b)

PC NPC BPC BNPC

N

Intersity (a.u.)

(a)

B

200

400

600

Raw Sum C-B C=C C-C/N C=O O-C=O

280

800

284

(c)

186

B2O3

192

194

296

Raw Sum Pyridinic-N C-N-B Pyrrolic-N Quaternary-N

Intersity (a.u.)

BN BCO2

190

292

(d)

Raw Sum BC2O

188

288

Binding energy (eV)

Binding energy (eV)

Intersity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


196

392

396

400

404

408

Binding energy (eV)

Binding energy (eV)

Figure 3. (a) XPS survey spectrum of PC, NPC, BPC and BNPC, high-resolution spectrum of BNPC (b) C1s, (c) B1s and (d) N1s.

24



Page 26 of 29

Table 2. The atomic percentages of C, O, N and B of PC, NPC, BPC and BNPC from the XPS results Sample

C at%

O at%

N at%

B at%

PC

87.76

12.24

0

0

NPC

80.16

12.62

7.22

0

BPC

85.93

12.85

0

1.22

BNPC

75.21

11.54

9.38

3.87

25


(a)

4

0

-4

-1.0

-0.8

-0.6

-0.4

-0.2

0.2

Potential (V) vs Hg/HgO

-1

8

PC NPC BPC BNPC

-8

(c)

1Ag

-1

10 A g

-1

20 A g

-1

-0.8 -1.0 0

400

800

Time (s)

1200

1600

(d)

6

200

-1

5Ag

-0.6

0.0

300

-1

-1

2Ag

-0.4

PC NPC BPC BNPC

400

0.5 A g

-0.2

-Z''(ohm)

-1

500

(b)

0.0

Potential (V) vs Hg/HgO

Special Capacitance (F g )

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Current density (A g )

Page 27 of 29

4

PC NPC BPC BNPC

2

100

0 0

5

10

15

-1

0

20

2

4

6

8

Z'(ohm)


Figure 4. (a) CV curves of PC, NPC, BPC and BNPC electrodes at the scan rate of 20 mV s-1. (b) Galvanostatic charge/discharge curves of the BNPC at various current densities. (c) Specific capacitances of PC, NPC, BPC and BNPC electrodes based on galvanostatic charge/discharge curves from 0.5 to 20 A g-1. (d) Nyquist plots of PC, NPC, BPC and BNPC electrodes.

26



Page 28 of 29

Table 3. Comparison of electrochemical performance of heteroatoms doped porous carbon materials. Sample

C (F g-1)

Electrolyte

Ref

B,N-codoped chitosan derived porous carbon

306（0.1 A g-1）

1 M H2SO4

16

N,P-codoped glucose derived porous carbon

265（0.5 A g-1）

6 M KOH

20

Soybean root-derived hierarchical porous carbon

276（0.5 A g-1）

6 M KOH

21

Boron and nitrogen co-doped porous carbon

304（0.1 A g-1）

1 M H2SO4

30

B,N-codoped agarose derived porous carbon

242（0.1 A g-1）

6 M KOH

39

N-doped glucose derived porous carbon

293（1.0 A g-1）

6 M KOH

38

B,N-codoped porous graphitic carbon

313（1.0 A g-1）

6 M KOH

41

Lignin-derived hierarchical porous carbon

165（0.05 A g-1）

1 M H2SO4

42

Chicken eggshell membranes derived carbon

297（0.2 A g-1）

1 M KOH

43

Auricularia derived activated carbon

196（5.0 mV s-1）

6 M KOH

44

244（2.0 mV s-1） 1 M H2SO4

45

Argan seed shell derived activated carbon

355 (0.125 A g-1)

1 M H2SO4

46

BNPC

402（0.5 A g-1）

6 M KOH

This work

Seaweed derived nanotextured carbon

27


Page 29 of 29

10

(a)

(b)

-1


-1


4

2

0

1.0 V 1.2 V 1.4 V 1.6 V 1.8 V

-2

-4 0.0

0.5

1.0

1.5

2.0

5

0 -1

20 mV s -1 50 mV s -1 100 mV s -1 200 mV s

-5

-10

0.0

0.5

Potential (V)

100

10

0

5

10

15

-1


20

1.0

Potential (V)

1.5

2.0

(d)

-1

Energy density (Wh kg )

(c)

-1

Special Capacitance (F g )

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


10

Ref 37 Ref 48 Ref 50

1

1

10

100

Ref 38 Ref 49 BNPC

1000

10000 -1

Power density (W kg )

Figure 5. Electrochemical measurements of as-assembled BNPC//BNPC symmetric supercapacitor in 1 M Na2SO4 electrolyte: (a) CV curves of the BNPC//BNPC symmetrical supercapacitor in different operation voltages at the scan rate of 50 mV s−1. (b) CV curves of the BNPC//BNPC symmetrical supercapacitor at different scan rates in the voltage window of 0-1.6 V. (c) Specific capacitance of the as-assembled BNPC//BNPC symmetrical supercapacitor based on total weight of electroactive materials in two electrodes at different current densities. (d) Ragone plots of the BNPC//BNPC symmetrical supercapacitor and other previously reported carbon based symmetrical supercapacitors.

28


Facile Synthesis of Boron and Nitrogen Co-doped Porous Carbon

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