Band gap-Tunable Porous Borocarbonitride Nanosheets for High

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Energy, Environmental, and Catalysis Applications

Bandgap Tunable Porous Borocarbonitrides Nanosheets for High Energy-Density Supercapacitors Shouzhi Wang, Fukun Ma, Hehe Jiang, Yongliang Shao, Yongzhong Wu, and Xiaopeng Hao ACS Appl. Mater. Interfaces, Just Accepted Manuscript • Publication Date (Web): 18 May 2018 Downloaded from http://pubs.acs.org on May 18, 2018

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ACS Applied Materials & Interfaces

Bandgap Tunable Porous Borocarbonitrides Nanosheets for High Energy-Density Supercapacitors Shouzhi Wang†a, Fukun Ma†a,b, Hehe Jianga, Yongliang Shaoa, Yongzhong Wu*a and Xiaopeng Hao*a

a

State Key Lab of Crystal Materials, Shandong University, Jinan, 250100, China.

b

School of Materials Science and Engineering, Shandong Jianzhu University, Jinan, 250100,

China. †

Both authors contributed equally to this work.

*E-mail: [email protected]; [email protected]

Keywords: borocarbonitrides; porous nanosheets; tunable bandgap; energy density; supercapacitor

Abstract Bandgap tunable porous borocarbonitride (BCN) nanosheets were successfully fabricated with cheap and readily available precursors by annealing and exfoliating. The bandgap of the as-prepared BCN materials ranges from 5.5 eV to 1.0 eV, these samples exhibit beneficial structural features suitable for the application in supercapacitors (SCs). Especially, the BCN material with a bandgap of 1.0 eV exhibits great specific surface area (600.9 m2 g‒1), massive active sites and excellent conductivity (10.8 S m‒1). In addition, this example displays great specific capacitance (464.5 F g‒1), excellent cycle stability (98.5% performance retention after 10,000 cycles) and ultrahigh energy density (50.4 W h kg‒1, in 1 M Et4NBF4 1 ACS Paragon Plus Environment

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electrolyte). This excellent electrochemical performance and facile effective synthesis of bandgap tunable BCN materials will provide a promising strategy about configuring nanostructured multiple compounds electrode for other energy storage and conversion devices.

1. Introduction As a promising technology that meets the continuously increasing global demands for energy storage, supercapacitors (SCs) and Li-ion batteries are appealing.1 Supercapacitors, which are expected to bridge the gap between traditional capacitors and Li-ion batteries, have aroused attention owing to their fast charge/discharge rates, ultra-long cycling life, high power capacity and environmental friendliness.1–3 At present, advanced SC electrode materials include carbon materials2–3 conductive polymer4 and transition metal oxides.5 In particularly, porous carbon electrode materials with great specific surface areas, superb electrical conductivity, low cost, outstanding physical and chemical stability are widely investigated.6 Two-dimensional (2D) nanomaterials, like transition metal dichalcogenides and graphene (GN) , have been applied in energy storage and electrocatalysts extensively,7–8 because of their obvious electronic and physiochemical properties with luxurious planar geometry.9 As the structure of 2D hexagonal boron nitride nanosheet (BNNS) are similar to GN, BNNS has been arousing strong concern as well.10 As a typical semiconductor, BNNS exhibits outstanding thermal conductivity, mechanical properties, physical and chemical stability in the application of polymer composites,11 hydrogen storage12 and water cleaning.13 However, the wide bandgap and poor

2 ACS Paragon Plus Environment

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conductivity of BNNS hinder the electron transport during the charge/discharge proceeding, which has become the biggest obstacle of being applied in energy storage. So searching for an effective method to reduce the bandgap of BNNS is the first priority. Related to but different from GN or BNNS, ternary borocarbonitride (BCN) nanosheets are apt to maintain outstanding performances by integrating the excellence of both GN and BNNS. The BCN materials would have defect sites in the carbon net which can serve as active sites for electron transfer reactions.14 Furthermore, theoretical calculation predicted that the bandgap of BCN can be adjusted from 5.50 eV to 0.49 eV by controlling the content of carbon.14–16 However, the synthesis methods for BCN nanosheets are not on a good developing way. Chemical vapour deposition (CVD),17 laser ablation18 and pyrolysis are the methods reported up to present, and these require sophisticated instruments, high temperature and valuable chemicals. Furthermore, the low yields of BCN materials make these techniques unfeasible.18 Up to now, BCN nanosheets have accomplished value in Li-ion batteries,19 oxygen reduction reaction,20 hydrogen evolution reaction21 and SCs22. B/N co-doped GN23–24 have been used as the electrode in SCs and have obtained a series of results. BCN is better than B/N co-doped GN in some respects such as the conductivity and thermal stability, which is beneficial to its application in energy storage and conversion.21,25 A small quantity of B/N atoms in the BCN interface is contributed to their adsorption properties, but excess presence will impedes their electrochemical activity.21 However, there are few reports about the effect of adjusting the bandgap of BCN nanosheets on enhancing their conductivity



and electrochemical performances. Herein, we have designed and prepared bandgap tunable porous BCN nanosheets by a simple and efficient calcinating method, and then applied these materials in SCs. Several features about this strategy for obtaining porous BCN nanosheets: (1) Only cheap and readily available precursors are used, without catalyst, toxic solvents or pre-intercalation steps. (2) The bandgap of BCN materials can be adjusted by controlling the additive amount of carbon sources. (3) The porous BCN nanosheets exhibit highly specific surface areas, many outstanding conductive and active sites and show superior capacitive properties when being applied in SCs. Our study can guide the preparation of relevant multiple compounds with a certain bandgap and may increase the range of these materials as high performance electrodes in the energy conversion and storage fields.

2. Experimental section 2.1 Synthesis of BCN nanosheets In a typical solid-phase synthesis process, a certain proportion of boric acid, urea and glucose were dissolved in 80 mL deionised water, the total mass of the mixture was 10 g. The addition ratios for boric acid, urea and glucose were 4:4:2, 3:3:4, 2:2:6 and 1:1:8 corresponding to BCN-1, BCN-2, BCN-3 and BCN-4, respectively. Then, the obtained gel was freeze-dried. Subsequently, the resultant precursors were annealed at 900 °C with the heating rates of 10 °C min‒1 for 5 h under N2 atmosphere. Then, the fluffy BCN samples were exfoliated following our previous method.10 The supernatant was collected and dried in a vacuum oven. For comparison, the samples


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of BN were prepared without add glucose precursor, at the same experimental conditions; the samples of GN were prepared following previous report,3 respectively. 2.2 The electrochemical tests in the three-electrode mode The working electrode was prepared by coating a slurry containing the active materials (80 wt.%) poly(vinylidene fluoride) (10 wt.%), and Super-P (10 wt.%) on a stainless steel cloth (1× 1 cm2) and dried for 12 h. A platinum sheet (1 cm × 1 cm) was used as the counter electrode, Hg/Hg2SO4 as the reference electrode and a 1 M H2SO4 aqueous solution as the electrolyte. The thickness of the electrode film was approximately 30~45 μm. (Figure S1, Supporting Information) The area of the active material on each electrode was approximately 1 cm2 and the mass loading in each electrode was approximately 2 mg. 2.3 The electrochemical tests in the two-electrode system For the aqueous electrolyte, the cell was separated by a sulfonation film, which was soaked in 1 M H2SO4 and sandwiched between two polytetrafluoroethylene sheets with a peace of parafilm. For the ionic liquid electrolyte, the 1 M Et4NBF4 as electrolyte, the coin cell configuration (2025-type) was separated by the glass paper. The slurry of active materials was coated on the stainless steel cloth; the active materials loading on each electrode was about 2 mg.

3. Results and discussions 3.1 Morphology, composition and structure Scheme 1. Schematic illustration of the synthesis of porous BCN nanosheets: (a) precursor, (b) bulk BCN, (c) porous BCN nanosheets.



The porous BCN nanosheets were synthesised by combining freeze drying, annealing and exfoliating processes, as shown in Scheme 1. In detail, low-cost and massive boron acid, glucose and urea were used as B, C and N sources, respectively. These precursors were mixed in different proportions via string and freeze-drying processes. After annealing at 900 °C in nitrogen, the precursors were gradually switched into a stacked porous layered structure and C, B and N atoms were mutually bonded upon carbonization. During annealing, some gases like NH3, CO and CO2, were released from the spaces between BCN layers. Hence, massive of pores were finally obtained .20 Finally, the porous BCN nanosheets were generated using simple ultrasonic exfoliation.


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Figure 1. Morphologies of the BCN-4 samples: SEM images of before (a) and after (b) exfoliation; (c) AFM image and corresponding height profiles; (d) TEM image, the high-resolution TEM image revealing lattice fringes as shown in the inset; (e) SEM image and corresponding EDS mapping of B, C and N elements. The scanning electron microscopy (SEM) measurement was performed for the detailed morphological investigation, which was shown in Figures 1a, 1b and S2 (Supporting information). The SEM images show the formation of large and ultrathin nanosheets of BCN-4 before (Figure 1a) and after (Figure 1b) exfoliation.



Interestingly, the increased carbon atoms contained in the precursor made the BCN-1, BCN-2, BCN-3 and BCN-4 nanosheets thin, which is shown in Figure S2 (Supporting information). The atomic force microscopy (AFM) characterization further confirmed that the BCN-4 with layered structure has the homogeneous thickness of about 1.71 nm, conforming to three to four stacked layers,26 which is shown in the Figures 1c and S3 (Supporting information). The large size and average thickness in SEM and AFM characterisations proved the formation of few layer BCN nanosheets. Furthermore, the pores in the BCN-4 nanosheets can be well noticed from the AFM image, this characteristic was also proved in transmission electron microscopy (TEM) images, as shown in Figure 1d. Lattice fringes were visible upon high magnification TEM image (Figure 1d, inert). From the lattice fringes, the obtained d spacing was about 0.345 nm, which was well in accordance with the inter plane (002) spacing of BCN.20, 27 In Figure 2e, the elemental mapping images showing the N, B and C elementals and indicating the homogeneous distribution of N, B and C in the BCN nanosheets.


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Figure 2. Structure characterisations of BCN samples: (a) XRD patterns; (b) FTIR spectra; (c) Raman spectra; (d) nitrogen sorption isotherms of the BCN-4, inset shows PSD plots of the samples; XPS B 1s (e), C 1s (f) and N 1s (g) spectra of BCN-4. In Figure 2a, the X-ray diffraction (XRD) patterns of GN and BCN-based materials suggest two distinctive peaks at around 43° and 26°, exhibiting the (100) and (002) interlayer reflections of BCN, respectively.28 The peak around 26° shifted slowly towards lower 2θ values increasing by carbon atoms content compared to those of B and N atoms. This peak at 26.9°, 26.5°, 26.2°, 25.9°, 25.5° and 24.5° for GN, BN, BCN-1, BCN-2, BCN-3 and BCN-4, respectively, indicating that the interlayer spacing (d) of the BCN materials increases with increasing the proportion of carbon. In comparison with the referenced BN and GN, these intervenient shifting broad humps of (002) implied existence of defects.29 The presence of sp2-bonded conjugated graphitic carbons with some structural heteroatoms and some small stacks lead to those defects.30 Fourier transform infrared (FTIR) spectra (Figure 2b) of the GN, BN and BCN-based composites were collected. From Figure 1b, the presence of peaks at 1380 and 760 cm−1 in the BNNS, as well as in the BCN-based materials, which correspond to the out-of-plane and in-plane bending vibration of B−N.31 Simultaneously, the peaks around 1580 cm−1 appeared in the GN- and BCN-based materials due to the C=C stretching vibration. Furthermore, the areas of C=C peak increased from BCN-1 to BCN-4, indicating that the carbon contents increased in the BCN materials to a certain extent. Moreover, two new peaks at 661 and 1020 cm−1 only appeared in the



BCN materials owing to the production of the B−C and C=N bonds.31,32 All these investigations suggested the formation of hybrid structures for BCN materials.28 The Raman spectra (Figure 2c) showed the characteristic peaks of the G and D bands at around 1600 and 1360 cm−1, respectively.33 A characteristic shift of the G band (1609 cm−1) in BCN was indicated in comparison with GN (1580 cm−1) 24 and which was ascribed to the structural distortion of graphitic C atoms with inequable bond lengths of C=N and N−B.32 Moreover, the presence of a relatively weak 2D (2740 cm−1) band indicated the existence of few BCN nanosheet layers,26 thereby conforming to the XRD analysis and SEM images. Interestingly, the 2D peak of BCN-1, BCN-2, BCN-3 and BCN-4 are gradually clear, which indicate the carbon atoms content increasing. The ratio between the integral intensities of D and G bands (ID/IG) was considered by a measure of the degree of graphitisation in partially graphitic carbons; moreover, the ID/IG value decreased as the sp2 domain size increased.24 The ID/IG value of BCN-4 was 0.82, which indicated a high graphitic degree; moreover, the values of other BCN samples are shown in Table 1. A relatively higher degree of graphitization from BCN-1 to BCN-4 is beneficial for the materials improvement conductivity. From Table1, the electronic conductivity of the BCN-4 (10.8 S m−1) is higher than other obtained BCN materials, which plays a pivotal role in improved the performance of rate capability.4 This may be due to the balance of electroactive defects in the sample and conductive ordered domains being optimised, which promotes the electrochemical activity to some extent.34


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Thermogravimetric (TG) analysis of BCN-based materials achieved in oxygen atmosphere in Figure S4 (Supporting information). In the range of 500 °C to 700 °C, GN showed obvious weight loss, whereas BN showed hardly any weight loss; however, the BCN-based samples showed obvious weight losses. At 1000 °C, the residue contents were about 93.1%, 63.5%, 48.8%, 30.8%, 18.7% and 0.2% for BN, BCN-1, BCN-2, BCN-3, BCN-4 and GN, respectively. All these TG results revealed that the prepared BCN materials are relatively stable compounds.35 Table 1. Physicochemical properties of the as-obtained BCN samples Sample

SBET (m2 g‒1)

Vtotal (m3 g‒1)

N content (at. %)

C content (at. %)

B content (at. %)

Conductivity (S m‒1)

ID/IG

BCN-1

71.8

0.17

26.5

25.4

29.8

0.05

1.01

BCN-2

108.3

0.23

21.0

43.0

15.8

0.71

0.98

BCN-3

388.8

0.35

16.2

61.2

9.5

2.4

0.87

BCN-4

600.9

0.52

8.5

82.1

5.4

10.8

0.82

The Brunauer−Emmett−Teller (BET) and pore size disposition (PSD) of the BCN samples have been evaluated in Figures 2d and Figure S5 (Supporting information). In comparison with BCN-1 and BCN-2, the nitrogen sorption isotherms of BCN-3 and BCN-4 exhibited an apparent microporous characteristic reflected by the type-I sorption curves, with an abrupt adsorption plateau in the low relative-pressure field (P/Po < 0.4).36 This characteristic can be ascribed to the microporous BCN nanosheets and some packing pores, as seen in AFM images (Figure 1c). The BET surface area of the BCN-4 was calculated to be 600.9 m2 g‒1 and its total pore volume was 0.52 cm3 g‒1, both of which are shown in Table 1. The



PSD of BCN-4 exhibited in the Figure 2d inset revealed a multiple pore structures and the average pore size was approximately 2.1 nm. These results indicated that the BCN nanosheets with porous structure and relatively great specific surface area can as function of an electrolyte container that allows ion adsorption and quick motion under the charge/discharge processes.37 The chemical composition of the BCN nanosheets was further analysed by X-ray photoelectron spectroscopy (XPS), as shown in Figures 2e–f and Figure S6 (Supporting information). The peaks related to B, N, O and C are marked out in the survey spectra (Figure S6a). The percentages of C, B and N calculated from the XPS spectra in the as-obtained samples are displayed in Table 1; the highest carbon content is BCN-4 (82 %), which is comparable to the result of previous FTIR and TG tests. Furthermore, the elements content of the BCN-based materials also characterized from corresponding energy dispersive X-ray spectroscopy (EDS) analyses, as shown in Figure S7 and Table S1 (Supporting information). The carbon atoms content trends of the BCN-based materials also can be seen in the XPS analysis results, which indicates BCN materials with certain content of carbon atoms can be synthesized successfully. The B1s spectra (Figures 2e and S6b, Supporting information) of BCN materials can be fitted to three different peaks at about 190.6, 191.8 and 192.5 eV, demonstrating the coexistence of B−C, B−N and B‒O bonds, respectively.24,38 The C1s spectra in Figures 2f and S6c (Supporting information) highlighted that the sp2 C=C bonding (∼284.8 eV) dominated the whole BCN-conjugated framework. The


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extra three smaller C1s peaks at around 288.6, 286.0 and 284.3 eV corresponded to C‒O, C‒N and C‒B bonds, respectively.24,28 The asymmetric N1s XPS peak of BCN (Figures 2g and S6d, Supporting information) can be fitted to four peaks of pyridinic N (N-6) (398.4 eV), pyrrolic N (N-5) (398.7 eV), quaternary N (N-Q) (400.1 eV) and N–B (397.9 eV).39–40 Moreover, the areas of B‒O and N‒B peaks decreased gradually from BCN-1, BCN-2 and BCN-3; in particular, these peaks disappeared in the N1s and B1s spectra of the BCN-4 sample. All these indicate that the oxygen and boron contents decreased as the carbon atoms content increased in the BCN samples. The contents of N-Q and N-5 increased as the carbon increased, as shown the in N1s spectrum in Figures 2g and S6d (Supporting information). Functional groups N-6 and N-5 had high binding ability with the electrolyte ions and N-Q improved the electronic conductivity of the material.39, 41



Figure 3. The bandgap characterisation of GN and BCN-based materials: Mott–Schottky plots (a), (αhν)2 versus hν plot (b), carbon content versus bandgap (c) and conductivity (d). The BN and C materials have superiority in energy conversion and storage device because of their abundance reserves and superior physicochemical stability. However, the intrinsic bandgaps limit their applications. Based on first principle calculations, the predicted BCN monolayers have direct bandgaps and the bandgap values can be adjusted to any desirable value by tuning the absorption of carbon atoms or B/N atoms.16 The electronic band structure of the resulting BCN nanosheets was studied using the Mott–Schottky (M–S) plots and UV–visible absorption spectra (Figure S8, Supporting information) to ensure the possibility of the BCN materials as electrode for energy storage. Distinctly, the Mott–Schottky plots of BCN-based materials at diverse frequencies display the typical n-type characteristic of inorganic semiconductors due to the positive slope of the linear plots, which was shown in Figure 3a.42 Increasing the carbon content of the BCN-based materials, the slop of the M-S plots becomes smaller, suggesting an increase of carrier density, which is consistent with the four probe test result.43 Bandgaps of the BCN materials were calculated according to Taucs’ equation: αhν = (hν − Eg)1/2, where α is the absorption coefficient, hν is the energy of the photon and Eg represents the optical bandgap.26 The extrapolation of the straight portion of the plot of (αhν)2 versus hν to α = 0 determines the bandgap, as shown in Figure 3b.31


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Interestingly, the bandgaps of BN (5.50 eV), BCN-1 (3.52 eV), BCN-2 (2.51 eV), BCN-3 (1.61 eV), BCN-4 (1.01 eV) and GN (0 eV) gradually decreased with the rising of the carbon contents in the BCN samples (Figure 3c). The bandgaps were almost linear with the carbon contents in the BCN samples and it provides a guide for the preparation of BCN materials with a certain bandgap by adjusting the carbon content. The conductivity of the BCN basedsamples were tested by a four-probe technique, as seen in Table 1; moreover, as the bandgap decreases, the conductivity of the BCN material increases, as shown in Figure 3d. With the increase of carbon atoms, the mobility of electron and hole of BCN materials was adjusted, and the carrier transport ability and conductivity were further enhanced.16 In all, the as-prepared BCN materials had direct bandgaps and their bandgap values can be adjusted to desirable values by tuning the carbon precursor contents. 3.2 Three-electrode electrochemical properties of the BCN based materials



Figure 4. The electrochemical performance of BN, GN and BCN-based materials under three-electrode mode. (a) Cyclic voltammograms performance of the electrode under 50 mV s‒1. (b) Galvanostatic charge−discharge curves of electrodes at 1 A g‒1. (c) The bandgaps versus the specific capacitances of the electrodes at 0.1 A g‒1. (d) Nyquist plots of the electrodes; inset displays the enlarged high-frequency region. In order to demonstrate the excellent capacitive properties of BCN materials for SCs, the electrochemical properties of the samples were studied in a three-electrode system in H2SO4 electrolyte and analysed by cyclic voltammetry (CV), galvanostatic charge/discharge (GCD) experiments and electrochemical impedance spectroscopy (EIS) (see Experimental section for details, Supporting information). Figure 4a displays the CV curves for BN, GN and BCN-based electrodes at 50 mV s‒1. After being introduced a large number of carbon atoms from BN to BCN-4 16 ACS Paragon Plus Environment

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electrode, a quasi-rectangular and enlarged CV curve area (Figure 4a) was noticed and these results indicated a remarkably enhanced capacitance due to the efficient charge transfer within the electrode.31 Furthermore, the significantly enhanced specific capacitance of the BCN-4 can be attributed to the great surface areas and the active site in the pores of BCN nanosheets, which can enhance the absorption of electronic and ion in electrolyte. The CV curves of BCN-4 materials at different scan rates are displayed in Figure S9a‒b (Supporting information), the CV curves retain a relatively rectangular shape without a diagonal angle even at100 mV s−1, indicating the outstanding electrochemical capacitive behaviour. The specific capacitances of the BCN-based materials were investigated by means of GCD measurements using a series of BCN electrodes under the same current density (1 A g‒1), which was shown in Figure 4b. From the GCD curves, the best performance was achieved for the BCN-4 sample; the curves of BCN-1, BCN-2, BCN-3 and BN have an obvious voltage drop, which indicates these materials have worse conductivities in comparison with BCN-4 and GN electrodes. The specific capacitances for BN, BCN-1, BCN-2, BCN-3, BCN-4 and GN under the given current density of 1A g‒1 were 2.2, 69.8, 306.9, 313.3, 410.2 and 64.5 F g‒1, respectively. The correlation of the capacitances with the increasing current density is shown in Figure S9 (Supporting information); the capacitance of BCN-4 electrode was superior to other electrodes at any current density for GCD characteristics. The highest capacitance of the BCN-4 electrode was 464.5 F g‒1 at 0.1 A g‒1, which iss shown in Figure S9 c–d (Supporting information). The results of capacitance are in



correspondence with the results of CV tests. Moreover, even up to 1 A g‒1, the capacitance of the BCN-4 (410.2 F g‒1) materials also was the highest compared with those recently reported B/N co-doped materials and BCN materials, such as B/N co-doped carbon nanosheets (358 F g‒1 at 0.1 A g‒1),22 B/N co-doped graphene (239 F g‒1 at 1 mV s‒1)23 B/N co-doped porous carbon (304 F g‒1 at 0.1 A g‒1),44 graphene-like BNC (130 F g‒1 at 0.2 A g‒1), 38 BCN nanotubes (312 F g‒1 at 0.2 A g‒1),27 BCN nanosheets (244 F g‒1 at 1 A g‒1)25 and BCN-PANI (340 F g‒1 at 0.4 A g‒1)45. In addition, even up to 10 A g‒1 (261.5 F g‒1), the BCN-4 materials also showed excellent rate performance; the materials also had 64% capacitance retention compared with the capacitance at the current density of 1 A g‒1. In Figure 4c, the specific capacitance of the BN, BCN-1, BCN-2, BCN-3 and BCN-4 are 4.2, 162.5, 330.3, 411.2 and 464.1 F g‒1, respectively; the bandgaps are 5.5, 3.5, 2.5, 1.6 and 1.0 eV, respectively. Figure 4c shows that the bandgaps are negative correlated with specific capacitances and this result is in accordance with the theoretical prediction on the BCN materials.15 The narrowing of the bandgap brings the superior electrochemical performance of the BCN samples; this observation can be ascribed to the fact that the increased carbon content can generate bonding and anti-bonding bands related with the hybridization of occupied and empty defect states, which brings more π electrons and benefits the conductivity.14 In turn, the excellent conductivity can accelerate the transport and transfer of electrons or electrolyte ions in the BCN nanosheets during the charging–discharging process. Moreover, the outstanding performance of the BCN-4 can be ascribed to the abundance of defects on


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the nanosheet surface which enhance the diffusion rate of ion electrolytes, participates in the pseudocapacitance and thus remarkably enhances the electrochemical performance of the SC electrodes.24 The EIS measurements were further evaluated to investigate the ion transport kinetics and charge transfer resistance within the BCN-based electrodes (Figure 4d). In the high frequency regions, the charge transfer resistances of the BCN-based electrodes were calculated to be 75, 29.4, 10.5, 3.0 and 1.9 Ω for the BCN-1, BCN-2, BCN-3, BCN-4 and GN respectively, all of these values were calculated from the intercepts of a quasi-semicircle in the X-axis, as shown in Figure 4d inset. With the bandgap decrease, the electrical conductivity increases for the BN, BCN-1, BCN-2, BCN-3 and BCN-4 electrode; these results are in accordance with the results of conductivity measurements.25 Furthermore, in the low-frequency region, the curves of the BCN-4 electrodes were more perpendicular than other lower carbon-containing electrodes; these results indicated that the bandgap-adjusted BCN materials can enhance the diffusion of ions and specific capacitance (Figure S10, Supporting information).46 The superior performance of the BCN-4 was explored using a cycling lifespan test. As shown in Figure S11 (Supporting information), with 98.5% capacitance retention even after 10,000 cycles at the current density of 10 A g‒1, the electrode shows superior electrochemical cycle stability. 3.3 The mechanism of the charge/discharge proceeding for porous BCN nanosheets



Figure 5. The proposed pseudocapacitive mechanism for charging/discharging of BCN-based electrodes in SCs To understand the sharp rising in capacitance for BCN-4, several factors should be considered, the possible pseudocapacitive mechanism was proposed as shown in the Figure 5. Firstly, we think that the free π electrons and the change in the oxidation state of the N and B atoms are conducive to the additional capacitance of the BCN samples. The formation of these BCN nanosheets results in an improvement in capacitance through Faradaic contributions which are usually given the credit to the chemical actives of boron in H+ chemisorptions and reactions, especially from the pyridinic sites.47 The nitrogen atoms in BCN-4, especially N-6 and N-5 at basal planes, have great binding energy with H+, thus, they promote positively to the increase of pseudocapacitance.4 The possible pseudo-Faradaic reactions may occur on the surface of BCN nanosheets as follows:4, 47


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The nitrogen atoms in BCN-4 have been shown to enhance the electronic conductivity owing to the absorption of electrons from the electron-rich N-atoms48 and produce holes in GN that improve electrolyte wetting and accelerate the transfer of ions to form the double layer.24,43,49 Furthermore, the defects (e.g. sp3–C, Stone–Wales defects)21 and grain boundaries produced by the porous structure act as superb redox centres for charge separation that further contribute to the increment in pseudocapacitance.4,50 Moreover, the porous open structure in BCN materials facilitates the transport/diffusion of electrolyte ions and significantly shortens the diffusion paths, resulting in a high-rate performance.4, 51 3.4 Two-electrode electrochemical properties

Figure 6. The two-electrode electrochemical performance of BCN-4 in aqueous electrolytes: (a) CV curves tested at scan rates of 1–100 mV s−1. (b) GCD curves tested at 0.1–20 A g−1. (c) Specific capacitance as a function of scan rate and current density. (d) Cycling performance of the SC at 10 A g–1, the inset displays the GCD curve at the initial stage and after 10,000 cycles. (e) Nyquist plots of initial and after 21 ACS Paragon Plus Environment


10,000 cycles, inset shows the high-frequency region and the equivalent circuit model of the investigated system. (f) Ragone plots of the SC devices, the values reported for other SC devices are added for comparison. The high-capacitance performance of the BCN-4 samples inspired us to study its practical application in SCs; hence, symmetrical cells were assembled with two identical BCN-4 electrodes. As shown in Figure 6a, the rectangular shape of the CV curves was substantially maintained even at 100 mV s−1, which indicate the excellent rate capability. Similarly, the GCD curves of the BCN-4-based symmetric SC still maintained a linear form at 20 A g−1, which demonstrate the high-rate capability again (Figure 6b). Furthermore, without visibly IR drop was observed for these GCD curves at high current density; this result suggests the small internal resistance and well conductivity of the BCN-4 samples.24 The specific capacitances of the SCs are 108 F g‒1 at 0.1 A g‒1. Even up to 20 A g‒1, the specific capacitance also maintains at 51 F g‒1 (Figure 6c). These results are in according with the specific capacitance obtained from the CV test; the capacitance contained 112 F g‒1 at 1 mV s‒1, as shown in Figure 6c. The high performances of BCN-4-based SC are similar to the relevant B/N co-doping carbon and BCN materials such as B/N-carbon nanosheets (57.5 F g‒1 at 0.1 A g‒1),22 B/N-graphene (62 F g‒1 at 10 mV s‒1),23 B/N co-doping graphene (80 F g‒1 at 1 A g‒1),24 BCN@MnO2 (14.5 F g‒1 at 0.25 A g‒1)52 and B/N co-doped porous carbon (67 F g‒1 at 0.1 A g‒1)53. These results suggest that abundant porous structure and nanosheets in the BCN electrode material can benefit the formation of an efficient electrical double layer capacitance (EDLC) during the fast transport of ions.20


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The cycling lifespan of the BCN-4-based SC was finally investigated in a two-electrode system at 10 A g−1. As shown in Figure 6d, the specific capacitance of symmetric SC (61 F g‒1) decreased only by 3.8% after 10,000 charge/discharge cycles, suggesting magnificent electrochemical cycling stability. After 10,000 cycles, the BCN-4 materials still maintain well nanosheet structure as seen from Figure S12 (Supporting information). Typical Nyquist plots of the symmetric SC for the initial cycle and after 10,000 cycles were further utilised to study the ion/electron-transport kinetics and rate capability, as shown in Figure 6e. At low frequencies, the imaginary part of the impedance increases sharply and the plots are nearly vertical lines, which are the characteristic of a capacitive behaviour. A comparatively small semi-circle can be noticed at high frequencies, indicating that series resistance (Rs) is low (about 0.8 Ω), which suggests the low ionic diffusion resistance.24 The fitting of impedance data to the equivalent circuit model is shown in Figure 6e inset (origin and fitting data, see Table S2 in supporting information), where Rs represents the total of the electrolyte, active materials resistance and contact resistance between current collector and active material; Rct represents the charge transfer resistance at the interface of electrode materials and electrolyte; W1 represents the Warburg impedance, Cdl is the capacitance associated with EDLC and Cps is related to the pseudocapacitance.54 After 10,000 cycles, the ESR reached approximately 3 Ω, as manifested by the excellent ionic conductivity of the electrolyte and the low internal resistance of electrodes.



The power density and energy density of the device were obtained from the GCD test based on the Ragone plot (Figure 6f). The SC exhibited outstanding electrochemical performance with a maximum energy density of 14.8 W h kg‒1 and a power density of 5.2 kW kg‒1. As far as we know, the performance of the device in terms of its electrochemical energy storage is higher than that of mostly BCN-based or B/N co-doping carbon-based SCs reported in the scientific literatures, which is shown in Figure 6f and Table S3 (Supporting information).23,24,55−58

Figure 7. The two-electrode electrochemical performance of BCN-4 in 1M Et4NBF4: (a) CV curves. (b) GC discharge curves. (c) Specific capacitance as a function of scan rate and current density. (d) Ragone plots in aqueous and ionic liquids electrolytes together with the ranges for common classes of energy storage devices.


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To estimate the performance of BCN-4 based actual device and obtain a high-energy density, a two-electrode symmetrical SC was constructed in a coin cell configuration (2025-type) that used ionic liquid (Et4NBF4–propylene carbonate, 1M) electrolytes; the voltage window was up to 3 V. The energy density (E) of a device depends on the operating voltage (V) and specific capacitance (C): E = 1/2CV2. A higher capacitance was obtained using aqueous rather than ionic liquid; however, a major advantage of SC with ionic liquids can deliver a high energy density due to a wider voltage window (3.0 V). Figures 7a and S13a (Supporting information) exhibit CV curves with the scan rates from 1–200 mV s‒1 that display a typical quasi-rectangular type. Even up to a high scan rate, the CV curves manifested favourable quasi-rectangular shape with no obvious hump, implying the excellent rate capability of the BCN samples. As shown in the Figure 7b (the other GCD curves are shown in Figure S13b, Supporting information), the GCD curves of BCN-4-based device exhibited symmetric triangular shapes, which are the characteristic of ideal EDLCs. The highly enhanced electrochemical performance of BCN samples can be ascribed to the porous structure with a great specific surface area that favours fast charge and ion transfer by providing short and extended electron pathways. The capacitances at the increasing current densities and scan rates are shown in Figure 7c; the specific capacitances of the cell was 40.4 F g‒1 at the current density of 0.1 A g‒1, which correspond to the capacitance calculated by CV test (47 F g‒1 at 1 mV s‒1) and even up to 20 A g‒1. The capacitance contained 10 F g‒1, which indicates



the excellent rate capability. Depending on the above electrochemical results, the electrochemical properties of BCN-4 are comparable to that of the commercial and previously reported B/N co-doped carbon electrodes in organic electrolytes, like B/N-carbon (49 F g‒1 at 1 A g‒1),24 bio-derived carbon (34.5 F g‒1 at 0.2A g‒1)57 and heteroatom-doped carbon (54.4 F g‒1 at 0.5A g‒1).58 The BCN-4 electrode achieving an excellent rate capability performance and electrochemical stability is ascribed to its good conductivity and the porous nanosheet structure that benefits the transport of electrons. The energy density and power densities are essential parameters for evaluating the electrochemical performance of a SC, which were calculated from GCD curves at increasing current density, as shown in Figure 7d. The BCN-4 SC shows a maximum energy density of 50.4 W h kg‒1 and the device delivered a high power density of 3 kW kg‒1. The energy density of the devices is superior to many BCN and heteroatom-doped carbon materials, as shown in Table S4 (Supporting information). The presence of nitrogen and boron species in BCN materials improved their wettability and electrical conductivity and resulted in high pseudocapacitance for BCN-based electrodes. These results ensure high power and energy densities.

4. Conclusion Porous BCN nanosheets were fabricated by the direct pyrolysis and exfoliation methods using the simple and low-cost precursor and the bandgaps of BCN nanosheets were tuned successfully by controlling the carbon contents. The as-synthesised BCN nanosheets had a porous nanostructure with a great specific


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surface area, abundant active sites and great conductivities. Such an amazing structure is favourable for ion/electron transport and the B and N atoms in BCN strongly changed the electron-acceptor/donor characteristics of carbons. These superior features result in the great gravimetric capacitance (464.5 F g−1 at 0.1 A g−1) and the excellent rate capability of BCN nanosheets. Moreover, the symmetric SC based on the sample with a bandgap of 1.0 eV offered a high-energy density (50.4 W h kg−1), as well as a high stability (about 96.2% of capacitance retention after 10,000 cycles at 10 A g−1). Hence, the strategy for obtaining bandgap tunable BCN materials activates the motivation about exploiting multiple compounds materials with a certain bandgap to be applied in the field of electrochemical energy conversion and storage devices.

Supporting information Supporting Information Available: SEM, AFM, XPS, TG, BET, EDS, UV, CV, GCD data and some electrochemical performance comparison with similar materials reported. Notes The authors declare no competing financial interest.

Acknowledgements This work was supported by NSFC (No. 51572153, 51602177) and the Major Basic Program of the Natural Science Foundation of Shandong Province (No. ZR2017ZB0317).

References 27 ACS Paragon Plus Environment


(1) Miller, J. R.; Simon, P. Electrochemical Capacitors for Energy Management. Science 2008, 321, 651−652. (2) Chmiola, J.; Yushin, G.; Gogotsi, Y.; Portet, C.; Simon, P.; Taberna, P. L. Anomalous Increase in Carbon Capacitance at Pore Sizes Less Than 1 Nanometer. Science 2006, 313, 1760−1763. (3) Zhu, Y.; Murali, S.; Stoller, M. D.; Ganesh, K.; Cai, W.; Ferreira, P. J.; Pirkle, A.; Wallace, R. M.; Cychosz, K. A.; Thommes, M. Carbon-Based Supercapacitors Produced by Activation of Graphene. Science 2011, 332, 1537−1541. (4) Wang, S.; Gai, L.; Zhou, J.; Jiang, H.; Sun, Y.; Zhang, H. Thermal Cyclodebromination of Polybromopyrroles to Polymer with High Performance for Supercapacitor. J. Phys. Chem. C 2015, 119, 3881−3891. (5) Lang, X.; Hirata, A.; Fujita, T.; Chen, M. Nanoporous Metal/Oxide Hybrid Electrodes for Electrochemical Supercapacitors. Nat. Nanotechnol. 2011, 6, 232−236. (6) Shan, D.; Yang, J.; Liu, W.; Yan, J.; Fan, Z. Biomass-Derived Three-Dimensional Honeycomb-Like Hierarchical Structured Carbon for Ultrahigh Energy Density Asymmetric Supercapacitors. J. Mater. Chem. A 2016, 4, 13589−13602. (7) Liu, C.; Yu, Z.; Neff, D.; Zhamu, A.; Jang, B. Z. Graphene-Based Supercapacitor with an Ultrahigh Energy Density. Nano lett. 2010, 10, 4863−4868. (8) Peng, X.; Peng, L.; Wu, C.; Xie, Y. Two Dimensional Nanomaterials for Flexible Supercapacitors. Chem. Soc. Rev. 2014, 43, 3303−3323. (9) Kong, D.; Cha, J. J.; Wang, H.; Lee, H. R.; Cui, Y. First-Row Transition Metal


Page 28 of 45

Page 29 of 45 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


Dichalcogenide Catalysts for Hydrogen Evolution Reaction. Energy Environ. Sci. 2013, 6, 3553−3558. (10) Zhao, G.; Wu, Y.; Shao, Y.; Hao, X. Large-Quantity and Continuous Preparation of Two-Dimensional Nanosheets. Nanoscale 2016, 8, 5407−5411. (11) Liu, D.; He, L.; Lei, W.; Klika, K. D.; Kong, L.; Chen, Y. Multifunctional Polymer/Porous Boron Nitride Nanosheet Membranes for Superior Trapping Emulsified Oils and Organic Molecules. Adv. Mater. Interfaces, 2015, 2, 1500228. (12) Lei, W.; Zhang, H.; Wu, Y.; Zhang, B.; Liu, D.; Qin, S.; Liu, Z.; Liu, L.; Ma, Y.; Chen, Y. Oxygen-Doped Boron Nitride Nanosheets with Excellent Performance in Hydrogen Storage. Nano Energy 2014, 6, 219−224. (13) Lei, W.; Portehault, D.; Liu, D.; Qin, S.; Chen, Y. Porous Boron Nitride Nanosheets for Effective Water Cleaning. Nat. Commun. 2013, 4, 1777. (14) Shirodkar, S. N.; Waghmare, U. V.; Fisherb, T. S.; Grau-Crespo, R. Engineering the Electronic Bandgaps and Band Edge Positions in Carbon-Substituted 2D Boron Nitride: a First-Principles Investigation. Phys. Chem. Chem. Phys. 2015, 17, 13547−13552. (15) Zhang, M.; Gao, G.; Kutana, A.; Wang, Y.; Zou, X.; Tse, J. S.; Yakobson, B. I.; Li, H.; Liu, H.; Ma, Y. Two-Dimensional Boron-Nitrogen-Carbon Monolayers with Tunable Direct Band Gaps. Nanoscale 2015, 7, 12023−12029. (16) Banerjeea, S.; Pati, S. K.; Criticality of Surface Topology for Charge-Carrier Transport Characteristics in Two-Dimensional Borocarbonitrides: Design



Principles

for

an

Efficient

Electronic

Page 30 of 45

Material.

Nanoscale

2014,

6,

13430−13434. (17) Yin, L. W.; Bando, Y.; Golberg, Gloter, D. A.; Li, M. S.; Yuan, X.; Sekiguchi, T. Porous

BCN

Nanotubular

Fibers:

Growth

and

Spatially

Resolved

Cathodoluminescence. J. Am. Chem. Soc. 2005, 127, 16354−16355. (18) Enouz-Védrenne, S.; Stéphan, O.; Glerup, M.; Cochon, J. L.; Colliex, C.; Loiseau, A. Interactions Between Bacteriophage DNA and Cationic Biomimetic Particles. J. Phys. Chem. C 2008, 112, 16422−16430. (19) Lei, W.; Qin, S.; Liu, D.; Portehault, D.; Liu, Z.; Chen, Y.; Large Scale Boron Carbon Nitride Nanosheets with Enhanced Lithium Storage Capabilities. Chem. Commun. 2013, 49, 352−354. (20) Wang, J.; Hao, J.; Liu, D.; Qin, S.; Portehault, D.; Li, Y.; Chen, Y.; Lei, W. Porous Boron Carbon Nitride Nanosheets as Efficient Metal-Free Catalysts for the Oxygen Reduction Reaction in Both Alkaline and Acidic Solutions. ACS Energy Lett. 2017, 2, 306−312. (21) Chhetri, M.; Maitra, S.; Chakraborty, H.; Waghmare, U. V.; Rao, C. N. Superior Performance of Borocarbonitrides, BxCyNz, as Stable, Low-Cost Metal-Free Electrocatalysts For the Hydrogen Evolution Reaction. Energy Environ. Sci. 2016, 9, 95−101. (22) Ling, Z.; Wang, Z.; Zhang, M.; Yu, C.; Wang, G.; Dong, Y.; Liu, S.; Wang, Y.; Qiu, J. Sustainable Synthesis and Assembly of Biomass-Derived B/N Co-Doped Carbon Nanosheets with Ultrahigh Aspect Ratio for High-Performance


Page 31 of 45 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


Supercapacitors. Adv. Funct. Mater. 2016, 26, 111−119. (23) Wu, Z-S.; Winter, A.; Chen, L.; Sun, Y.; Turchanin, A.; Feng, X.; Müllen, K. Three-Dimensional

Nitrogen

and

Boron

Co-Doped

Graphene

for

High-Performance All-Solid-State Supercapacitors. Adv. Mater. 2012, 24, 5130−5135. (24) Sun, L.; Fu, Y.; Tian, C.; Yang, Y.; Wang, L.; Yin, J.; Ma, J.; Wang, R.; Fu, H. Isolated Boron and Nitrogen Sites on Porous Graphitic Carbon Synthesized from Nitrogen-Containing Chitosan for Supercapacitors. ChemSusChem 2014, 7, 1637−1646. (25) Karbhal, I.; Devarapalli, R. R.; Debgupta, J.; Pillai, V. K.; Ajayan, P. M.; Shelke, M. V. Facile Green Synthesis of BCN Nanosheets as High-Performance Electrode Material for Electrochemical Energy Storage. Chem. Eur. J. 2016, 22, 7134−7140. (26) Ci, L.; Song, L.; Jin, C.; Jariwala, D.; Wu, D.; Li, Y.; Srivastava, A.; Wang, Z. F.; Storr, K.; Balicas, L.; Liu, F.; Ajayan. P. M. Atomic Layers of Hybridized Boron Nitride and Graphene Domains. Nat. Mater. 2010, 9, 430−435. (27) Moses, K.; Kiran, V.; Sampath, S.; Rao, C. N. Few-Layer Borocarbonitride Nanosheets: Platinum-Free Catalyst for the Oxygen Reduction Reaction. Chem.-Asian J. 2014, 9, 838−843. (28) Lei, W.; Portehault, D.; Dimova, R.; Antonietti, M. Boron Carbon Nitride Nanostructures from Salt Melts: Tunable Water-Soluble Phosphors. J. Am. Chem. Soc. 2011, 133, 7121−7127.



(29) Kumar, N.; Moses, K.; Pramoda, K.; Shirodkar, S. N.; Mishra, A. K.; Waghmare, U. V.; Sundaresan, A.; Rao, C. N. Borocarbonitrides, BxCyNz. J. Mater. Chem. A 2013, 1, 5806−5821. (30) Liu, X.; Antonietti, M. Moderating Black Powder Chemistry for the Synthesis of Doped and Highly Porous Graphene Nanoplatelets and Their Use in Electrocatalysis. Adv. Mater. 2013, 25, 6284−6290. (31) Gao, G.; Gao, W.; Cannuccia, E.; J.Tijerina, T.; Balicas, L.; Mathkar, A.; Narayanan, N. T.; Liu, Z.; Gupta, K. B.; Peng, J.; Yin, Y.; Rubio, A.; Ajayan, M. P. Artificially Stacked Atomic Layers: Toward New Van Der Waals Solids. Nano Lett. 2012, 12, 3518−3525. (32) Xue, Y.; Yu, D.; Dai, L.; Wang, R.; Li, D.; Roy, A.; Lu, F.; Chen, H.; Liu, Y.; Qu, J.; Three-dimensional B, N-Doped Graphene Foam as a Metal-Free Catalyst for Oxygen Reduction Reaction. Phys. Chem. Chem. Phys. 2013, 15, 12220−12226. (33) Qin, L.; Yu, J.; Kuang, S.; Xiao, C.; Bai, X. Few-Atomic-Layered Boron Carbonitride Nanosheets Prepared by Chemical Vapor Deposition. Nanoscale 2012, 4, 120−123. (34) Bayatsarmadi, B.; Zheng, Y.; Jaroniec, M.; Qiao, S. Z. Soft-Templating Synthesis of N-Doped Mesoporous Carbon Nanospheres for Enhanced Oxygen Reduction Reaction. Chem.-Asian J. 2015, 10, 1546−1553. (35) Rao, C. N. R.; Gopalakrishnan, K.; Borocarbonitrides, BxCyNz: Synthesis, Characterization, and Properties with Potential Applications. ACS Appl. Mater. Interfaces 2016, 9, 19478−19494.


Page 32 of 45

Page 33 of 45 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


(36) Guo, D. C.; Mi, J.; Hao, G. P.; Dong, W.; Xiong, G.; Li, W. C.; Lu, A. H. Ionic Liquid C16mimBF4 Assisted Synthesis of Poly(benzoxazine-co-resol)-Based Hierarchically Porous Carbons with Superior Performance in Supercapacitors. Energy Environ. Sci. 2013, 6, 652−659. (37) Zhao, Y.; Liu, B.; Pan, L.; Yu, G.; 3D Nanostructured Conductive Polymer Hydrogels for High-Performance Electrochemical Devices. Energy Environ. Sci. 2013, 6, 2856−2870. (38) Dou, S.; Huang, X.; Ma, Z.; Wu, J.; Wang, S. A Simple Approach to the Synthesis of BCN Graphene with High Capacitance. Nanotechnology 2015, 26, 045402. (39) Wen, Y.; Rufford, T. E.; Hulicova-Jurcakova, D.; Wang, L. Nitrogen and Phosphorous

Co-Doped

Graphene

Monolith

for

Supercapacitors.

ChemSusChem 2016, 9, 513−520. (40) Yang, S. B.; Feng, X. L.; Wang, X. C.; Müllen, K. Graphene-Based Carbon Nitride Nanosheets as Efficient Metal-Free Electrocatalysts for Oxygen Reduction Reactions. Angew. Chem. Int. Ed. 2011, 50, 5339−5343. (41) Su, F.; Poh, C. K.; Chen, J. S.; Xu, G.; Wang, D.; Li, Q.; Lin, J.; Lou, X. W. Nitrogen-Containing

Microporous

Carbon

Nanospheres

with

Improved

Capacitive Properties. Energy Environ. Sci. 2011, 4, 717−724. (42) Zhang, J. S.; Chen, X. F.; Takanabe, K.; Maeda, K.; Domen, K.; Epping, J. D.; Fu, X. Z.; Antonietti, M.; Wang, X. C. Synthesis of a Carbon Nitride Structure for Visible-Light Catalysis by Copolymerization. Angew. Chem. Int. Ed. 2010, 49,



441−444. (43) Wang, Z.; Yang, C.; Lin, T.; Yin, H.; Chen, P.; Wan, D.; Xu, F.; Huang, F.; Lin, J.; Xie, X.; Jiang, M.

Visible-Light Photocatalytic, Solar Thermal and

Photoelectrochemical Properties of Aluminium-Reduced Black Titania. Energy Environ. Sci. 2013, 6, 3007–3014. (44) Chen, H.; Xiong, Y.; Yu, T.; Zhu, P.; Yan, X.; Wang, Z.; Guan, S. Boron and Nitrogen Co-Doped Porous Carbon with a High Concentration of Boron and Its Superior Capacitive Behavior. Carbon 2017, 113, 266−273. (45) Gopalakrishnana, K.; Sultana, S.; Govindarajb, A.; Rao, C. N. R. Supercapacitors Based on Composites of PANI with Nanosheets of Nitrogen-Doped RGO, BC1.5N, MoS2 and WS2. Nano Energy 2015, 12, 52−58. (46) Saha, S.; Jana, M.; Khanra, P.; Samanta, P.; Koo, H.; Murmu, N. C.; Kuila, T. Band Gap Engineering of Boron Nitride by Graphene and Its Application as Positive Electrode Material in Asymmetric Supercapacitor Device. ACS Appl. Mater. Interfaces 2015, 7, 14211−14222. (47) Guo, H.-L.; Su, P.; Kang, X.; Ning, S.-K. Synthesis and Characterization of Nitrogen-Doped Graphene Hydrogels by Hydrothermal Route with Urea as Reducing-Doping Agents. J. Mater. Chem. A 2013, 1, 2248−2255. (48) Wang, S.; Gai, L.; Jiang, H.; Guo, Z.; Bai, N.; Zhou, J. Reduced Graphene Oxide Grafted by the Polymer of Polybromopyrroles for Nanocomposites with Superior Performance for Supercapacitors. J. Mater. Chem. A 2015, 3, 21257−21268. (49) Wu, J.; Rodrigues, M.-T. F.; Vajtai, R.; Ajayan, P. M. Tuning the Electrochemical


Page 34 of 45

Page 35 of 45 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


Reactivity of Boron-and Nitrogen-Substituted Graphene. Adv. Mater. 2016, 28, 6239−6246. (50) Wang, S.; Zhang, L.; Sun, C.; Shao, Y.; Wu, Y.; Lv, J.; Hao, X. Gallium Nitride Crystals: Novel Supercapacitor Electrode Materials. Adv. Mater. 2016, 28, 3768−3776. (51) Wang, S.; Zhu, J.; Shao, Y.; Li, W.; Wu, Y.; Zhang, L.; Hao, X. Three-Dimensional

MoS2@CNT/RGO

Network

Composites

for

High-Performance Flexible Supercapacitors. Chem. Eur. J. 2017, 23, 3438−3446. (52) Tomko, T.; Rajagopalan, R.; Aksoy, P.; Foley, H. C. Synthesis of Boron/Nitrogen Substituted Carbons for Aqueous Asymmetric Capacitors. Electrochimica Acta 2011, 56, 5369−5375. (53) Riedel, R.; Bill, J.; Passing, G. A Novel Carbon Material Derived from Pyridine-Borane. Adv. Mater. 1991, 3, 551−552. (54) Anothumakkool, B.; Soni, R.; Bhange, S. N.; Kurungot, S. Novel Scalable Synthesis of Highly Conducting and Robust PEDOT Paper for a High Performance Flexible Solid Supercapacitor. Energy Environ. Sci. 2015, 8, 1339−1347. (55) Romero, J.; Rodriguez-San-Miguel, D.; Ribera, A.; Mas-Balleste, R.; Otero, T. F.; Manet, I.; Licio, F.; Abellan, G.; Zamora, F.; Coronado, E. Metal-Functionalized Covalent Organic Frameworks as Precursors of Supercapacitive Porous N-Doped Graphene. J. Mater. Chem. A 2017, 5, 4343−4351. (56) Chen, L.-F.; Huang, Z.-H.; Liang, H.-W.; Yao, W.-T.; Yua, Z.-Y.; Yu, S.-H.



Flexible

All-Solid-State

High-Power

Supercapacitor

Page 36 of 45

Fabricated

with

Nitrogen-Doped Carbon Nanofiber Electrode Material Derived from Bacterial Cellulose. Energy Environ. Sci. 2013, 6, 3331−3338. (57) Mao, X.; Yang, X.; Wu, J.; Tian, W.; Rutledge, G. C.; Hatton, T. A. Microwave-Assisted Oxidation of Electrospun Turbostratic Carbon Nanofibers for Tailoring Energy Storage Capabilities. Chem. Mater. 2015, 27, 4574−4585. (58) Zhao, Y.-Q.; Lu, M.; Tao, P.-Y.; Zhang, Y.-J.; Gong, X.-T.; Yang, Z.; Zhang, G.-Q.; Li, H.-L. Hierarchically Porous and Heteroatom Doped Carbon Derived from Tobacco Rods for Supercapacitors. J. Power Sources 2016, 307, 391−400.


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Scheme 1. Schematic illustration of the synthesis of porous BCN nanosheets: (a) precursor, (b) bulk BCN, (c) porous BCN nanosheets. 113x88mm (300 x 300 DPI)

ACS Paragon Plus Environment

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Figure 1. Morphologies of the BCN-4 nanosheets: SEM images of (a) before and (b) after exfoliation; (c) AFM image and corresponding height profiles; (d) TEM image, the high-resolution TEM image revealing lattice fringes as shown in the inset; (e) SEM image and corresponding EDS mapping of B, C and N elements. 219x226mm (298 x 298 DPI)



Figure 2. Structure characterisations of BCN samples: (a) XRD patterns; (b) FTIR spectra; (c) Raman spectra; (d) nitrogen sorption isotherms of the BCN-4, inset shows PSD plots of the samples; XPS B 1s (e), C 1s (f) and N 1s (g) spectra of BCN-4.


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Figure 3. The bandgap characterisation of GN and BCN-based materials: Mott–Schottky plots (a), (αhν)2 versus hν plot (b), carbon content versus bandgap (c) and conductivity (d). 144x111mm (298 x 298 DPI)



Figure 4. The electrochemical performance of BN, GN and BCN-based materials under three-electrode mode. (a) Cyclic voltammograms performance of the electrode under 50 mV s‒1. (b) Galvanostatic charge−discharge curves of electrodes at 1 A g‒1. (c) The bandgaps versus the specific capacitances of the electrodes at 0.1 A g‒1. (d) Nyquist plots of the electrodes; inset displays the enlarged high-frequency region. 142x113mm (298 x 298 DPI)


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Figure 5. The proposed pseudocapacitive mechanism for charging/discharging of BCN-based electrodes in SCs 232x89mm (300 x 300 DPI)



Figure 6. The two-electrode electrochemical performance of BCN-4 in aqueous electrolytes: (a) CV curves tested at scan rates of 1–100 mV s−1. (b) GCD curves tested at 0.1–20 A g−1. (c) Specific capacitance as a function of scan rate and current density. (d) Cycling performance of the SC at 10 A g–1, the inset displays the GCD curve at the initial stage and after 10,000 cycles. (e) Nyquist plots of initial and after 10,000 cycles, inset shows the high-frequency region and the equivalent circuit model of the investigated system. (f) Ragone plots of the SC devices, the values reported for other SC devices are added for comparison.


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Figure 7. The two-electrode electrochemical performance of BCN-4 in 1M Et4NBF4: (a) CV curves. (b) GC discharge curves. (c) Specific capacitance as a function of scan rate and current density. (d) Ragone plots in aqueous and ionic liquids electrolytes together with the ranges for common classes of energy storage devices. 142x114mm (298 x 298 DPI)


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