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Article Cite This: ACS Omega 2018, 3, 17276−17286
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Chemical Simultaneous Synthesis Strategy of Two Nitrogen-Rich Carbon Nanomaterials for All-Solid-State Symmetric Supercapacitor Rashmi Chandrabhan Shende,† Manoharan Muruganathan,‡ Hiroshi Mizuta,‡ Masashi Akabori,‡ and Ramaprabhu Sundara*,† †
Department of Physics, Alternative Energy and Nanotechnology Laboratory (AENL), Nano-Functional Materials Technology Centre (NFMTC), Indian Institute of Technology Madras, Chennai, Tamil Nadu 600036, India ‡ School of Material Science, Japan Advanced Institute of Science and Technology, Asahidai 1-1, Nomishi, Ishikawa 923-1292, Japan
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S Supporting Information *
ABSTRACT: Present work demonstrates a single step process for simultaneous synthesis of metal-nanoparticleencapsulated nitrogen-doped bamboo-shaped carbon nanotubes (M/N-BCNTs) and graphitic carbon nitride (G-C3N3). The synthesis of two different carbon nanostructures in a single step is recognized for the first time. This process involves the use of inexpensive and nontoxic precursors such as melamine as carbon and nitrogen sources for the growth of G-C3N3 and M/N-BCNTs. In this technique, the utilization of unwanted gases such as ammonia and hydrocarbons released during the decomposition of melamine is the key to grow M/N-BCNTs over the catalyst along with the formation of G-C3N4. The implementation of M/N-BCNTs as the electrode material for all-solid-state symmetric supercapacitor results in a maximum specific capacitance of ∼368 F g−1 with excellent electrochemical stability with 97% capacity retention after 10 000 cycles. Furthermore, fabricated symmetric supercapacitor shows maximum high energy and power density up to 10.88 W h kg−1 and 2.06 kW kg−1, respectively. The superior electrochemical activity of M/N-BCNTs can be attributed to its high surface to area volume ratio, unique structural characteristics, ultrahigh electrical conductivity, and carrier mobility. appealing electronic structure.14 These unique features make G-C3N4 a very effective material as visible light photocatalyst to split water.15−19 In addition, G-C3N4 finds specific interest in fuel cells and solar cells because of its excellent oxidation reduction reaction attributed to high nitrogen content.17,18 Until the present, several methods have been developed for the separate synthesis of N-CNTs and G-C3N4. In general, GC3N4 is synthesized by the polymerization of different solid precursors such as cyanamide, dicyandiamide, guanidine hydrochloride, melamine, thiourea, and urea at a temperature range of 450−700 °C.17−23 Moreover, nitrogen-doped carbon nanotubes can be synthesized by a chemical vapor deposition technique using various metal catalyst particles and carbon precursor gases including methane and acetylene. In most of the synthesis, NH3 gas or nitrogen-rich compounds are used as the precursor for nitrogen.4,24−28 However, the synthesis temperature is very high (800−1050 °C) and the procedure is tedious. Above all, there are few reports available demonstrating the encapsulation of transition metal nanoparticles inside the nitrogen-doped carbon nanotubes.29−31 Nevertheless,
1. INTRODUCTION Carbon, the fourth most abundant element in earth, forms various allotropes owing to its unique electronic configuration. Among all, carbon nanotubes, graphene, and graphitic carbon nitride (G-C3N4) are mostly studied allotropes for various applications.1,2 Moreover, nitrogen-doped carbon nanotubes (N-CNTs) are emerged as one of the most promising materials for energy applications such as fuel cells,3,4 secondary batteries,5 solar cells, and supercapacitors.6 Their unique properties such as excellent electrical and thermal conductivity, high surface area to volume ratio, superior mechanical strength, and good thermal and chemical stability make them an ideal material for the aforementioned applications.4,6−9 In addition, N-CNTs when integrated with metal nanoparticles improve the electrochemical performance of nanomaterial and are wellexplored for energy applications.10−13 For example, Li et al. demonstrated N-CNTs as a promising anode material for sodium-ion batteries and achieved the specific capacity of 270 mA h g−1 at 50 mA g−1. Liu et al. reported the transition metal (Fe, Co, and Ni)-encapsulated nitrogen-doped carbon nanotubes as the highest efficient bifunctional catalyst for oxygen electrode reactions. Besides, G-C3N4 is the most stable allotrope with excellent physicochemical stability, versatile optical properties, excellent photocatalytic activity, and © 2018 American Chemical Society
Received: October 16, 2018 Accepted: November 30, 2018 Published: December 13, 2018 17276
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However, the growth of M/N-BCNTs did not occur in the second boat. This indicates that 600 °C temperature was insufficient for the growth of N-BCNTs. The reason for this can be explained from a vapor−liquid−solid (VLS) growth mechanism. It is already established that carbon nanotubes (CNTs) follow VLS growth mechanism, where hydrocarbon vapors interact with molten catalysts to form CNTs.36 Low temperature (600−650 °C) is not suitable to achieve the molten state of the catalyst to undergo VLS mechanism, and thus the growth of N-BCNTs was not observed at low temperatures. Next, the temperature of the furnace was increased to 700 °C. At this temperature, G-C3N4 and M/NBCNTs were obtained in separate boats, as shown in Figure 1b. As explained earlier, polymerization of melamine leads to the formation of G-C3N4. Interestingly, during polymerization, vapors consisting of ammonia and hydrocarbons were released as byproducts (Figure S1), which further undergo catalytic decomposition at the surface of molten catalyst particles and results in the growth of M/N-CNTs. Next, the increase in temperature up to 800 °C results in the growth of M/NBCNTs in a second boat; however, G-C3N4 was decomposed completely (this is further confirmed using thermogravimetric analysis (TGA) of G-C3N4 (Figure S2) and no residue was seen in the first boat (Figure 1b). Figure 2 represents the powder X-ray diffraction (XRD) pattern for G-C3N4, Ni/N-BCNTs, Co/N-BCNTs, and Fe/N-
these synthesis methods are suitable for the growth of either metal-encapsulated N-CNTs or G-C3N4. There are no reports available combining these two separate methods to achieve NCNTs and G-C3N4 in a single step, thereby resulting in cost reduction and scalability. Present work reveals a single-step process for the simultaneous synthesis of metal nanoparticle-encapsulated nitrogen-doped bamboo-shaped carbon nanotubes (M/NBCNTs) and G-C3N4 using nontoxic and inexpensive precursors at low temperature. Present approach is the simplistic way to synthesize metal-encapsulated N-CNTs and G-C3N4 in a single step. Electrochemical studies reveal that novel M/N-BCNTs is a promising electrode material for allsolid-state symmetric supercapacitor with excellent rate capability and cyclic stability. Because the photocatalysis,17,32 electrocatalysis,33 and electrochemical34,35 assets of G-C3N4 is already reported and eventually confirmed that G-C3N4 is a promising material for water splitting, fuel cells, solar cells, and actuator; present work is focused on the electrochemical aspect of M/N-BCNTs for symmetric supercapacitors.
2. RESULTS AND DISCUSSION Here, the simultaneous synthesis of M/N-BCNTs and G-C3N4 was achieved through a single step using single-furnace chemical vapor deposition (CVD) unit at a specific temperature. The schematic representation of the synthesis method is shown in Figure 1a. Two ceramic boats containing melamine
Figure 2. X-ray diffraction pattern G-C3N4, Ni/N-BCNTs, Co/NBCNTs, and Fe/N-BCNTs.
Figure 1. (a) Schematic representation of the experimental setup used for the synthesis of M/N-BCNTs and G-C3N4. (b) Effect of temperature on the growth of M/N-BCNTs and G-C3N4.
BCNTs. Powder XRD pattern of G-C3N4 shows a very sharp characteristic peak at ∼27.8° corresponding to the C(002) graphite plane with the d-spacing of ∼0.32 nm for the interlayer stacking of aromatic systems. A small peak at 13° can be indexed to the C(100) plane corresponding to the in-planer structural repeat unit with a period of 0.68 nm.37−39 Powder XRD pattern of G-C3N4 confirms the complete decomposition of melamine and formation of G-C3N4. The as-grown M/NBCNTs show C(002) peak at ∼26° corresponding to the hexagonal graphite along with the metal peaks. Ni/N-BCNTs
in one boat and catalyst in another boat were kept at the center of the CVD unit. The temperature of the furnace was raised to the required temperature in the inert atmosphere of argon/ nitrogen. Initially, optimization was carried out to obtain M/ N-BCNTs and G-C3N4 in a single step by performing the synthesis at different temperatures ranging from 600 to 800 °C. At 600−650 °C, melamine from first boat undergoes polymerization and results in the formation of G-C3N4. 17277
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disorder nature of N-BCNTs. Typically, there are two major factors that could increase the intensity of D band; one is the introduction of heteroatoms such as nitrogen in the carbon network, and the other is curvatures and the edges of the NBCNTs. Thermal stability of G-C3N4 was studied using TGA in air and nitrogen atmosphere. Initial weight loss up to 150 °C can be attributed to the adsorbed water molecules on the surface of G-C3N4. The nature of the TGA curve is similar in air and nitrogen atmosphere. However, the complete decomposition occurs at ∼770 °C in air atmosphere and 790 °C in nitrogen atmosphere. Thus, it can be inferred that the thermal stability of G-C3N4 is slightly more in nitrogen atmosphere relative to air atmosphere. TGA of Ni/N-BCNTs, Co/N-BCNTs, and Fe/N-BCNTs is shown in Figure S3. TGA plots of nanocomposites show no major weight loss until ∼550 °C indicating the absence of amorphous carbon in as-grown M/NBCNTs. Thus, this technique avoids the formation of unwanted amorphous carbon in nanocomposites. The major weight loss taking place above 500 °C is ascribed to the complete decomposition of carbon−nitrogen network from M/N-BCNTs. The residue left above 600 °C for Ni/NBCNTs, Co/N-BCNTs, and Fe/N-BCNTs is 22.1, 12.2, and 14.4%, confirming the presence of metal nanoparticles in the composite, respectively. The amount of metal content in M/ BCNTs was calculated using the following equation
nanocomposite illustrates the major peaks between 20° and 70° which can be indexed to a cubic structure of Ni (ref. no. 00-001-1258, Fm3m (225), a = b = c = 0.354 nm). The intense peaks at 44.6°, 51.6°, and 76.1° correspond to (111), (200), and (220) planes of cubic Ni, respectively. Powder XRD pattern of Co/N-BCNTs shows intense peaks at 44.2°, 51.5°, and 75.8° which can be indexed to (111), (200), and (220) planes of the cubic Co structure (ref. no. 00-015-0806, Fm3m (225), a = b = c = 0.354 nm), respectively. For Fe/N-BCNT nanocomposite, powder XRD pattern shows a small peak at 44.3° corresponding to the (110) plane of cubic Fe (ref. no. 01-085-1410, Im3m (229), a = b = c = 0.288 nm) along with the C(002) peak of N-BCNTs. Figure 3 represents the Raman spectrum for G-C3N4. Two dominant peaks, peak A and B, at 706 and 1232 cm−1 obtained
%M =
atomic weight of metal × weight of the residue molecular weight of metal oxide × initial weight of the sample
The calculated metal content for Ni/N-BCNTs, Co/NBCNTs, and Fe/N-BCNTs is 17.7%, 11.6%, and 4.4%, respectively. The morphologies, structure, and the presence of metal nanoparticles were examined from scanning electron microscopy (SEM) images. SEM images shown in Figure 4a,b depict the sheetlike porous morphology of G-C3N4. SEM images of Ni/N-BCNTs (Figure 4c,d), Co/N-BCNTs (Figure 4e,f), and Fe/N-BCNTs (Figure 4g,h) demonstrate that the large quantity of nanotubes was formed with several micrometer lengths. Further, elemental analysis of G-C3N4, Ni/N-BCNTs, Co/N-BCNTs, and Fe/N-BCNTs was carried out using energy-dispersive X-ray spectroscopy (EDX) and presented in Figure 2i. EDX measurement of G-C3N4 confirms that the carbon and nitrogen are main constitution elements. EDX analysis of Ni/N-BCNTs, Co/N-BCNTs, and Fe/N-BCNTs exhibits the dominant constitution of carbon along with nitrogen, oxygen, and metals (Ni, Co, and Fe). Transmission electron microscopy (TEM) images of Ni/NBCNTs (Figure 5a−c), Co/N-BCNTs (Figure 5d−f), and Fe//N-BCNTs (Figure 5g−i) reveal the bamboolike hollow structure of nanotubes with metal nanoparticles encapsulated within the tube, the presence of which is confirmed from powder XRD. The nanotubes are composed of several compartments, which result in the bamboo-shaped morphology. Ni/N-BCNTs and Fe/N-BCNTs show a similar structure with wall thicknesses of ∼13 nm (Figure 5c) and ∼14 nm (Figure 5i) with noticeable compartments. In cases of Co/NBCNTs, the thickness of the wall is more (∼16 nm) and compartments are small (Figure 5f) and not prominent. Bamboo-shaped morphology and compartment formation are mainly because of the incorporation of nitrogen atom in carbon lattices. Thus, the structure is dependent on the
Figure 3. Raman spectra of G-C3N4, Ni/N-BCNTs, Co/N-BCNTs, and Fe/N-BCNTs.
in the Raman spectrum are ascribed to different kinds of striazine ring breathing mode present in the G-C 3 N 4 structure.40 Peak C located at 1310 cm−1 correspond to the stretching mode of s-triazine ring.40,41 Moreover, a small peak at 978 cm−1 correspond to the symmetric breathing mode of striazine ring in G-C3N4 lattice.2 In addition, Raman spectra depicted in Figure 3 act as a tool for determining the relative defect concentrations present in carbon-based nanocomposites. G band is the characteristic band for all graphitic systems, arising because of the stretching vibration of C−C bonds in sp2 hybridization. The presence of defects in sp2 hybridized carbon network gives rise to D band in Raman spectrum. 2D band at ∼2635 cm−1 arises because of the stacking order of graphite planes. The ratio of intensity of the characteristic D band and G band provides the information of defect content in the system. Raman spectra of Ni/N-BCNTs, Co/N-BCNTs, and Fe/N-BCNTs are depicted in Figure 3 and show distinct G and D bands at 1318 and 1585 cm−1, respectively. A large defect ratio of Ni/N-BCNTs (ID/IG = 1.25), Co/N-BCNTs (ID/IG = 1.19), and Fe/N-BCNTs (ID/IG = 1.25) confirms the 17278
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Figure 4. SEM images of (a,b) G-C3N4, (c,d) Ni/N-BCNTs, (e,f) Co/N-BCNTs, and (g,h) Fe/N-BCNTs. (i) EDX of G-C3N4, Ni/N-BCNTs, Co/N-BCNTs, and Fe/N-BCNTs.
Figure 5. TEM images for (a−c) Ni/N-BCNTs, (d−f) Co/N-BCNTs, and (g−i) Fe/N-BCNTs at different magnifications.
very few nanoparticles are observed outside the tube and can be assigned to unreacted catalysts. Figure S4d−f clearly depicts that the tip of the nanotubes is encapsulated with metal nanoparticles. X-ray photoelectron spectroscopy was performed to examine the chemical composition and electronic states of elements in M/N-BCNTs and G-C3N4. The survey spectrum was recorded as a function of binding energy ranging from 0 to 1050 eV. Figure S5 shows the survey spectrum recorded for M/NBCNTs and G-C3N4 confirming the presence of carbon, nitrogen, and oxygen. Additionally, survey spectra of Ni/NBCNTs, Co/N-BCNTs, and Fe/N-BCNTs depict the peaks for Ni, Co, and Fe, respectively. The prepared nanomaterials, that is, Ni/N-BCNTs, Co/N-BCNTs, and Fe/N-BCNTs have a high nitrogen content (∼5 at. %). The high-resolution
amount of nitrogen doping in nanotubes. It is reported that the solubility of nitrogen is maximum in Ni, followed by Fe and Co.42,43 Also, EDX measurements show that the nitrogen content is less in Co/N-BCNTs compared to Ni/N-BCNTs and Fe/N-BCNTs. Thus, the structural variation in Co/NBCNTs can be attributed to a lesser amount of incorporated nitrogen atoms in carbon lattice. High-resolution TEM images reveal that the wall of nanotubes is composed of several layers of wrinkled lamellate graphene having 0.34 nm d-spacing. The unique arrangement of these graphene layers, similar to the herringbone pattern, results in the variation in the wall thickness from ∼14 nm to as thin as ∼3 nm. Figure S4a−c shows the TEM image at low magnification, and it is observed that the length of the nanotubes is several micrometers with most of the nanoparticles encapsulated inside the tubes. Also, 17279
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Figure 6. High-resolution (a−c) C 1s, (d−f) N 1s, and (g−i) Ni 2p, Co 2p, and Fe 2p X-ray photoelectron spectroscopy (XPS) spectra for Ni/NBCNTs, Co/N-BCNTs, and Fe/N-BCNTs, respectively.
spectra of C 1s for Ni/N-BCNTs (Figure 6a), Co/N-BCNTs (Figure 6b), and Fe/N-BCNTs (Figure 6c) are deconvoluted into four major peaks corresponding to sp2 CC (284.5 eV), C−N (285.5 eV), CO (286.4 eV), and N−CO (290.1 eV). Figure 6d,e, respectively, represents the high-resolution spectra of N 1s for Ni/N-BCNTs, Co/N-BCNTs, and Fe/NBCNTs. The deconvoluted spectra of N 1s show the four distinct peaks attributed to pyridinic N (398.4 eV), pyrrolic N (400.1 eV), graphitic N (401.4), and oxidized N (404.0 eV). The schematic representation of aforesaid nitrogen types is depicted in Figure S6. Meanwhile, the high-resolution deconvoluted spectra of Ni 2p (Figure 6g) exhibit two peaks at 852.9 and 870.1 eV corresponding to Ni0, and peaks at 854.7 and 872.3 eV assigned to Ni 2p3/2 and Ni 2p1/2 reveal the presence of Ni2+ because of surface oxidation of Nickel.44,45 Figure 6h presents the deconvoluted spectra for Co 2p having peaks at 778.0 and 793.6 eV related to Co0. Peaks at 780.9 and 795.7 eV are, respectively, assigned to Co 2p3/2 and Co 2p1/2, which is due to the surface oxidation of elemental Co.46,47 Similarly, the spectrum of Fe 2p (Figure 6i) deconvoluted into three peaks at 707.6, 709.5, and 719.3 eV are ascribed to Fe0, whereas two peaks located at 711.6 and 722.1 eV, respectively, belong to Fe 2p3/2 and Fe 2p1/2.45,48,49 Moreover, the presence of satellite peaks in deconvoluted spectra indicates the oxidized element. The deconvoluted C 1s spectrum for G-C3N4 (Figure 7a) shows major two peaks assigned to sp2-bonded N−CN and graphitic carbon. The N 1s spectrum can be fitted to four distinct peaks, as shown in Figure 7b. Peaks located at 398.4 and 399.0 eV are assigned to C−NC and N−C(3) arising because of the graphitic nature of G-C3N4, respectively. The peak at 400.6 eV corresponds to nitrogen bonded with three carbon atoms in the aromatic ring. The schematic representation of carbon and nitrogen species in G-C3N4 is
Figure 7. High-resolution (a) C 1s and (b) N 1s spectra for G-C3N4.
shown in Figure S7. A small peak located at 404.4 eV is attributed to π-excitations and charging effect.50 The Brunauer−Emmett−Teller (BET) surface area (Figure 8a−d) and Barrett−Joyner−Halenda (BJH) pore size and pore volume (Figure 8e−h) analyses indicate that M/N-BCNTs and G-C3N4 exhibit high surface and porous structure. The nitrogen adsorption−desorption isotherms and pore-size distribution curves indicate that M/N-BCNTs and G-C3N4 show type-IV characteristics confirming the mesoporous structure. The specific surface area, pore size, and pore volume for M/N-BCNTs and G-C3N4 are listed in Table 1. The specific area of the as-grown M/N-BCNTs and G-C3N4 obtained by this method is nearly three times more than the previously reported values.15,51,52 These data exemplify that the nanostructures obtained using this optimized technique introduce porous structures with high surface area, enhanced pore volume, and narrow pore-size distribution. Cyclic voltammetry (CV) curves for Ni/N-BCNTs-, Co/NBCNTs-, and Fe/N-BCNTs--based solid-state supercapacitors at different scan rates are displayed in Figure 9a−c. An almost rectangular shape of CV curves confirms the good capacitive behavior. The weak redox peak in CV profiles is the 17280
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Figure 8. N2 adsorption−desorption isothermal curves for (a) Ni/N-BCNTs, (b) Co/N-BCNTs, and (c) Fe/N-BCNTs and (d) G-C3N4. Poresize distribution curves for (e) Ni/N-BCNTs, (f) Co/N-BCNTs, and (g) Fe/N-BCNTs and (h) G-C3N4.
nanoparticles present in nanocomposites. Once the system attains stability, all metal atoms can contribute to the electrochemical reaction, and the reaction during charge− discharge (CD) can be given as: Ni(II) ↔ Ni(III), Co(II) ↔ Co(III), and Fe(II) ↔ Fe(III). The detailed pseudocapacitive mechanism is explained in the Supporting Information Even at high scan rates, CV curves retain the shape without any distortion implying the desirable quick CD property of the supercapacitor. Further, CD studies at different current densities were carried out in the potential window of 0−1 V. Figure 9d−f shows that CD curves are nearly symmetric, thereby further confirming the typical capacitive characteristics coupled with fast CD behavior of the solid-state supercapacitor. Specific capacitance was calculated using the relation,
Table 1. Summary of BET Surface Area and BJH Pore Size and Volume sample name Ni/N-BCNTs Co/N-BCNTs Fe/N-BCNTs G-C3N4 purified CNTs51 partially unzipped CNTs53 H2SO4-treated G-C3N415 G-C3N415
BET surface area (m2 g−1)
pore volume (cm3 g−1)
pore size (nm)
204.1 191.6 190.6 82.3 41.45 124
0.86 0.64 0.62 0.39
16.7 13.1 12.8 18.5 2.4
15.6 8.6
consequence of the pseudocapacitive behavior of quasireversible faradic reactions occurring on the surface metal
Figure 9. Cyclic voltammetry curves at different scan rates for (a) Ni/N-BCNTs, (b) Co/N-BCNTs, and (c) Fe/N-BCNTs. Charge−discharge curves at various current densities for (d) Ni/N-BCNTs, (e) Co/N-BCNTs, and (f) Fe/N-BCNTs. 17281
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It mΔV
based on yogurt-derived nitrogen-doped carbon.64 Thus, the fabricated solid-state supercapacitors are promising devices with superior energy and power density. Table 2 gives the comparison of electrochemical properties of different electrode materials for the supercapacitor. It is very clear that most of the N-doped structures are activated to increase the porosity and thus follows multistep. The key difference between these materials and M/N-BCNTs is that no extra precursors for nitrogen are required, and the synthesis strategy is cost-effective, facile, and scalable. The symmetric supercapacitor based on Ni/N-BCNTs shows better electrochemical performance compared to the various mentioned electrode materials. This can be attributed to the synergistic effect of various aspects. Commonly, electrochemical supercapacitors are divided into two types based on the energystorage mechanism and the electrode material: electric doublelayer capacitors (EDLCs) and the pseudocapacitors. The EDLCs store energy through electrostatic electric charge accumulation at the electrode−electrolyte interfaces, which is solely a physical process. In contrast, the pseudocapacitors store energy through a faradic process, which includes fast and reversible redox reactions on the surface of electrodes. These two mechanisms can work distinctly or can be merged together in a single device, and purely based on the electrode materials used in the supercapacitors. In general, carbon-based materials exhibit EDLC mechanism, whereas metal, metal oxides/ hydroxides/sulfides show pseudocapacitance. In the present study, M/N-BCNTs lead to the synergistic effect of EDLC and pseudocapacitor energy-storage mechanisms, thereby resulting in faster kinetics and enhanced electrochemical capacitive performance. Additionally, the superior electrochemical performance of Ni/N-BCNTs can be attributed to several factors which include: (i) high electrical conductivity and carrier mobility, (ii) more nitrogen and elemental Ni content, and (iii) high surface area and pore volume resulting into easy access of electrolyte ions into the structure relative to Co/NBCNTs and Fe/N-BCNTs. Electrical conductivity and carrier mobility of nanomaterials are evaluated using Hall effect measurements (van der Pauw method) performed at room temperature and tabulated in Table 3. Thus, the level of nitrogen doping, surface area, pore volume, electrical conductivity, and carrier mobility play a vital role in determining the electrochemical performance of nanomaterials. Long-term cyclic stability is an essential requirement for energy-storage devices. Hence, the cyclic stability test for Ni/ N-BCNTs-, Co/N-BCNTs-, and Fe/N-BCNTs-based solidstate supercapacitor was performed by repeating CD measurements 10 000 times in the potential window of 1 V at a constant current density of 5 A g−1. Figure S8g−i represents the capacitance retention of the supercapacitor as a function of cycle number. Fabricated solid-state supercapacitor exhibits ∼97% of capacity retention at the end of 10 000 cycles, confirming excellent cyclic stability and reversibility. The excellent cyclic stability of Ni/N-BCNTs-, Co/N-BCNTs-, and Fe/N-BCNTs-based supercapacitors is attributed to the unique structure of M/N-BCNTs where metal nanoparticles are encapsulated within the carbon network. Encapsulation of nanoparticles constrains the volume expansion because the redox reaction occurs during CD and eventually leads to excellent stability of the electrode material. Thus, M/NBCNTs are a promising electrode material for supercapacitors owing to their unique structure, electrical conductivity, high
(1)
where Cs is the specific capacitance; I, t, m, and ΔV are the applied current, discharge time, active mass of one electrode, and potential window, respectively. Ni/N-BCNTs-, Co/NBCNTs-, and Fe/N-BCNTs-based supercapacitors show maximum specific capacitance of 368, 358, and 236 F g−1 at a current density of 2 A g−1, respectively. CD profiles at different current densities show a very small IR drop confirming the low equivalent series resistance attributed to good electrical conductivity of the electrode. Figure S8 summarizes the results obtained from CD curves at different current densities. As illustrated in Figure S8a−c, the specific capacitance declines with the increasing current density. This can be explained as: at low current density, the ample time facilitates complete access of the active ions to the electrode. Whereas at high current density, because of fast CD, active ions did not have enough time to access the electrode.54 The fabricated solid-state supercapacitors retain ∼87% of the specific capacitance even at a high current density of 10 A g−1 indicating high rate capability. The energy density (Es) and power density (Ps) were calculated using the following equations69 Es =
∫0
Ps =
1 t
t
∫0
IV dt m t
IV dt m
(2)
(3)
The Ragone plot presented in Figure S8d clearly shows that Ni/N-BCNT-based solid-state supercapacitor delivers an energy density of 9.5 W h kg−1 corresponding to a power density of 2.63 kW kg−1 and remains 7.98 W h kg−1 at a high power density of 8.8 kW kg−1. Similarly, Co/N-BCNT and Fe/ N-BCNT solid-state supercapacitors exhibit maximum energy density of 10.88 and 6.4 W h kg−1 at 2.06 and 1.99 kW kg−1 power densities (Figure S8e,f), respectively. It is noteworthy that the fabricated symmetric all solid-state supercapacitors exhibit high energy and power density compared to previous reports on the symmetric supercapacitor, as shown in Figure 10.63−68,70,71 For example, Chen et al. obtained a maximum energy density of 6.07 W h kg−1 for activated nitrogen-doped carbon nanofiber-based symmetric supercapacitor.63 Wahid et al. reported the maximum energy density of 7 W h kg−1 at a high power density of 5000 W kg−1 for the supercapacitor
Figure 10. Comparison of Ragone plot for fabricated symmetric solidstate supercapacitor with extant literature. 17282
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Table 2. Comparison of Different Electrode Materials for Supercapacitors sample
specific capacitance
N-doped porous carbon from polyaniline nanotubes N-doped graphene/carbon nanotubes composite porous nitrogen-doped hollow carbon spheres from polyaniline graphene/MnO2/CNTs CNT@PANI composite yarn N-doped carbon nanocages carbon nanotubes/nitrogen-doped carbon polyhedra hybrids N,S-doped activated carbon from Elm flower N-doped carbon nanofiber N-doped porous carbon from yogurt porous 3D interconnected carbon framework MoS2 hierarchical nanospheres activated carbon nanotubes ultrafine Co3O4 nanocrystal electrodes Ni/N-BCNTs Co/N-BCNTs Fe/N-BCNTs
energy density
electrolyte
365.9 F g−1 at 10.3 W h kg−1 at 0.1 A g−1 45 W kg−1 −1 −1 213 F g at 1 A g
6 M KOH
213 F g−1 at 0.5 A g−1 61 F g−1 at 0.1 A g−1 8.9 W h kg−1 at 106 W kg−1 −2 38 mF cm at 0.01 mA cm−2 313 F g−1 at 1 A g−1 10.9 W h kg−1 at 250 W kg−1 135 F g−1 at 12 W h kg−1 at 5 mV s−1 250 W kg−1 62 F g−1 at 10 A g−1 12.4 W h kg−1 at 12 kW kg−1 −1 6.07 W h kg−1 at 195.44 F g at 1 A g−1 ∼200 W kg−1 −1 −1 225 F g at 2 A g 7 W h kg−1 at 5 kW kg−1 65 F g−1 at 0.2 A g−1 12 W h kg−1 at 400 W kg−1 368 F g−1 at 5.42 W h kg−1 at 5 mV s−1 128 W kg−1 −1 −1 145 F g at 1 A g 4.7 W h kg−1 at 1.3 kW kg−1 −1 172 F g at 3.01 W h kg−1 at 0.9 A g−1 560 W kg−1 368 F g−1 at 2 A g−1 9.5 W h kg−1 at 2.63 kW kg−1 358 F g−1 at 2 A g−1 10.88 W h kg−1 at 2.06 kW kg−1 −1 −1 236 F g at 2 A g 6.4 W h kg−1 at 1.99 kW kg−1
6 M KOH
electrical conductivity (S cm−1)
carrier mobility (cm2 V−1 s−1)
Ni/N-BCNTs Co/N-BCNTs Fe/N-BCNTs
4.27 × 104 6.99 × 103 4.05 × 103
3.4 × 104 4.9 × 103 2.8 × 103
system 3 electrodes
55
3 electrodes
56
3 electrodes
57
2 electrodes
58
2 electrodes
59
2 electrodes
60
2 electrodes
61
2 electrodes
62
2 electrodes
63
2 electrodes
64
2 electrodes
65
2 electrodes
66
2 electrodes
67
2 electrodes
68
2 electrodes
This work
1 M Na2SO4 PVA/H2SO4 6 M KOH 1 M H2SO4 6 M KOH PVA/H2SO4 1 M H2SO4 1 M Na2SO4 PVA/LiCl 1 M H2SO4 PVA/H3PO4
PVA/H2SO4
91% retention after 800 cycles 98% retention after 20 000 cycles ∼100% retention after 5000cycles 87.2% retention after 20 000 cycles 95.9% retention after 5000 cycles 91% retention after 5000 cycles 100% retention after 3000 cycles 96.5% retention after 5000 cycles 97.1% retention after 20 000 cycles 100% retention after 20 000 cycles
97% retention after 10 000 cycles
refs
conductivity, and carrier mobility. The synergistic effect of the aforementioned merits results in a high specific capacitance (∼368 F g−1) accompanied by a good rate capability and excellent cyclic stability over 10 000 cycles. Fabricated all-solidstate symmetric supercapacitors using Co/N-BCNTs show the maximum energy density of 10.88 W h kg−1 at 2.06 kW kg−1, demonstrating excellent supercapacitor performance.
Table 3. Electrical Conductivity and Carrier Mobility for Ni/N-BCNTs, Co/N-BCNTs, and Fe/N-BCNTs sample name
6 M KOH
cyclic stability 86% retention after 10 000 cycles 96.5% retention after 200 cycles 91.1% retention after 5000 cycles
4. EXPERIMENTAL METHODS 4.1. Material Synthesis. M/N-BCNTs and G-C3N4 were synthesized simultaneously using the CVD system (Figure 1a). It consists of a single tubular furnace with a quartz tube mounted inside. Two alumina boats are kept at the center of the furnace. Melamine (4 g), as carbon and nitrogen source, was kept in one boat, and the catalyst MCl2·6H2O (M = Fe, Co, and Ni, 400−500 mg) was kept in the other boat. The quartz tube was closed at both ends using aluminum end couplers, which have the inlet and outlet for the argon/ nitrogen gas. At first, argon gas (160 sccm) was purged inside the chamber for 10 min to create the inert atmosphere and continued throughout the experiment. Next, the temperature of the furnace was raised to 700 °C with a heating rate of 10 °C min−1. The temperature of the furnace was maintained at 700 °C for 30 min and then allowed to cool down naturally. The as-grown products were labeled as M/N-BCNTs and GC3N4. The experiment was repeated by replacing melamine with dicyandiamide and a catalyst with conventional Ni(OH)2 under similar parameters. Interestingly, in this case also, the growth of M/NBCNTs and G-C3N4 was observed with a similar morphology. The formation and the structure of
specific capacitance, good power, and energy density accompanied by excellent cyclic stability. Moreover, supercapacitors are restricted toward commercialization because of high cost per unit of energy stored, which are mainly due to electrode material and fabrication process. The present technique can reduce the cost of electrode material by ∼90%, thereby proposing a promising step toward commercialization.
3. CONCLUSIONS The present study demonstrates the simultaneous synthesis of M/N-BCNTs and G-C3N4 in a single step using nontoxic and inexpensive precursors. Formation, structure, and surface morphology of samples were successfully illustrated using different techniques. The BET surface area studies show that M/N-BCNTs and G-C3N4 exhibit remarkable surface area and highly mesoporous structure which provides the platform for fast diffusion of electrolyte ions. The as-grown M/N-BCNTs integrate unique assets for electrochemical process, such as encapsulation of metal nanoparticles within the bamboolike carbon−nitrogen-rich network, extremely high electrical 17283
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samples were confirmed from the XRD pattern (Figure S9), SEM, and TEM (Figure S10). Thus, it can be proved that this method is clearly generic and applicable to most of the solid precursors such as dicyandiamide, thiourea, urea, and guanidine hydrochloride. Moreover, the synthesis process allows the use of metal precursors (MCl2·6H2O; M = Fe, Co, and Ni), metal nanoparticles (Fe, Ni, and Co), metal oxides (Fe3O4, NiO, and CoO), and metal hydroxides [Fe(OH)3, Co(OH)2, and Ni(OH)2] as a catalyst for the growth of M/N-BCNTs. 4.2. Material Characterization. The formation of M/NBCNTs and G-C3N4 was studied through an XRD pattern recorded from 2θ = 5° to 2θ = 90° using PANalytical X’pert Pro powder X-ray diffractometer using a nickel-filtered Cu Kα radiation (λ = 0.154 nm) source. Raman spectroscopic measurements were carried out using LabRAM HP800 UV Raman equipped with a He−Ne laser of 632 nm excitation. Inspect F50 high-resolution SEM and FEI Tecnai T20 highresolution TEM were used to study the surface morphology and structure of M/N-BCNTs and G-C3N4. EDX measurements were carried out using Inspect F50 SEM. The TA instrument (SDT Q600) equipped with a microbalance system was used to carry out the TGA. XPS analysis was carried out using SPECS X-ray photoelectron spectrometer equipped with a Mg K X-ray source and a PHOIBOS 100MCD semicircular analyzer at ultrahigh vacuum, that is, 10−10 mbar. Recorded spectra were analyzed using CasaXPS software. The BET surface area and BJH pore volume and size analysis were carried out in N2 atmosphere72 using Micromeritics-ASAP2020 instrument. Hall effect measurements were carried out using Resi Test 8400 Hall effect measurement analyzer by employing a dc Hall effect measurement method. The electrochemical performance of the electrode material was characterized by cyclic voltammetry and chronopotentiometry techniques on BioLogic BCS810 electrochemical workstation. 4.3. Electrochemical Measurements. The electrochemical studies were carried out on two-electrode solid-state system using a solid electrolyte PVA/H2SO4. Initially, the solid electrolyte was prepared using polyvinyl alcohol (PVA) and H2SO4. For this purpose, 1 g of PVA was added slowly in 10 mL of deionized water under vigorous stirring at 80 °C. Once the homogeneous and clear mixture forms, conc. H2SO4 (1 g) was added and stirring was continued to obtain the clear solution. The slurry was prepared by uniformly mixing the active material (75%), conducting graphite (15%), and polyvinylidene fluoride (10%) in N-methyl-2-pyrrolidone. Next, electrodes were prepared by coating the slurry on copper foil using the doctor blade technique. After coating, electrodes were dried at 120 °C in a vacuum oven for 8 h. The all solid-state supercapacitor cells were assembled from two pieces of electrodes separated by a filter paper and a solid electrolyte.
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BCNTs; charge-storage mechanism; rate capability; Ragone plot and cyclic stability plot; XRD; and SEM and TEM images (PDF)
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected] (R.S.). ORCID
Manoharan Muruganathan: 0000-0001-5421-5160 Masashi Akabori: 0000-0001-6346-3676 Ramaprabhu Sundara: 0000-0002-7960-9470 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS Authors thank the Indian Institute of Technology, Madras, and the Japan Advanced Institute of Science and Technology, Japan, for the financial support.
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REFERENCES
(1) Zhang, W.; Zhu, S.; Luque, R.; Han, S.; Hu, L.; Xu, G. Recent Development of Carbon Electrode Materials and Their Bioanalytical and Environmental Applications. Chem. Soc. Rev. 2016, 45, 715−752. (2) Miller, T. S.; Jorge, A. B.; Suter, T. M.; Sella, A.; Corà, F.; McMillan, P. F. Carbon Nitrides: Synthesis and Characterization of a New Class of Functional Materials. Phys. Chem. Chem. Phys. 2017, 19, 15613−15638. (3) Cheng, Y.; Zhang, H.; Varanasi, C. V.; Liu, J. Highly Efficient Oxygen Reduction Electrocatalysts Based on Winged Carbon Nanotubes. Sci. Rep. 2013, 3, 3195. (4) Gong, K.; Du, F.; Xia, Z.; Durstock, M.; Dai, L. Nitrogen-Doped Carbon Nanotube Arrays with High Electrocatalytic Activity for Oxygen Reduction. Science 2009, 323, 760−764. (5) Shin, W. H.; Jeong, H. M.; Kim, B. G.; Kang, J. K.; Choi, J. W. Nitrogen-Doped Multiwall Carbon Nanotubes for Lithium Storage with Extremely High Capacity. Nano Lett. 2012, 12, 2283−2288. (6) Wang, L.; Gao, Z.; Chang, J.; Liu, X.; Wu, D.; Xu, F.; Guo, Y.; Jiang, K. Nitrogen-Doped Porous Carbons as Electrode Materials for High-Performance Supercapacitor and Dye-Sensitized Solar Cell. ACS Appl. Mater. Interfaces 2015, 7, 20234−20244. (7) Bulusheva, L. G.; Okotrub, A. V.; Kurenya, A. G.; Zhang, H.; Zhang, H.; Chen, X.; Song, H. Electrochemical Properties of Nitrogen-Doped Carbon Nanotube Anode in Li-Ion Batteries. Carbon 2011, 49, 4013−4023. (8) Shende, R.; Sundara, R. Nitrogen Doped Hybrid Carbon Based Composite Dispersed Nanofluids as Working Fluid for LowTemperature Direct Absorption Solar Collectors. Sol. Energy Mater. Sol. Cells 2015, 140, 9−16. (9) Li, B.; Dai, F.; Xiao, Q.; Yang, L.; Shen, J.; Zhang, C.; Cai, M. Nitrogen-Doped Activated Carbon for High Energy Hybrid Supercapacitor. Energy Environ. Sci. 2016, 9, 102−106. (10) Xing, Y.; Zheng, X.; Wu, Y.; Li, M.; Zhang, W.-H.; Li, C. Nitrogen-Doped Carbon Nanotubes with Metal Nanoparticles as Counter Electrode Materials for Dye-Sensitized Solar Cells. Chem. Commun. 2015, 51, 8146−8149. (11) Song, J.; Zhu, C.; Fu, S.; Song, Y.; Du, D.; Lin, Y. Optimization of cobalt/nitrogen embedded carbon nanotubes as an efficient bifunctional oxygen electrode for rechargeable zinc-air batteries. J. Mater. Chem. A 2016, 4, 4864−4870. (12) Wu, Z.-Y.; Xu, X.-X.; Hu, B.-C.; Liang, H.-W.; Lin, Y.; Chen, L.F.; Yu, S.-H. Iron Carbide Nanoparticles Encapsulated in Mesoporous Fe-N-Doped Carbon Nanofibers for Efficient Electrocatalysis. Angew. Chem., Int. Ed. 2015, 54, 8179−8183. (13) Jiang, Y.; Zhou, C.; Liu, J. A Non-Polarity Flexible Asymmetric Supercapacitor with Nickel Nanoparticle@ Carbon Nanotube Three-
ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsomega.8b02835. Schematic demonstration of growth mechanism for GC3N4 and M/N-BCNTs; TGA curves; low- and highmagnified TEM images; XPS survey spectrum; schematic of nitrogen species exist in G-C3N4 and M/N17284
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Dimensional Network Electrodes. Energy Storage Mater. 2018, 11, 75−82. (14) Hu, S.; Ma, L.; Li, F.; Fan, Z.; Wang, Q.; Bai, J.; Wu, G. Construction of G-C3N4/S-g-C3N4 Metal-Free Isotype Heterojunctions with an Enhanced Charge Driving Force and Their Photocatalytic Performance under Anoxic Conditions. RSC Adv. 2015, 5, 90750−90756. (15) Yan, H.; Chen, Y.; Xu, S. Synthesis of graphitic carbon nitride by directly heating sulfuric acid treated melamine for enhanced photocatalytic H2 production from water under visible light. Int. J. Hydrogen Energy 2012, 37, 125−133. (16) Yan, H. Soft-Templating Synthesis of Mesoporous Graphitic Carbon Nitride with Enhanced Photocatalytic H2 Evolution under Visible Light. Chem. Commun. 2012, 48, 3430. (17) Zheng, Y.; Liu, J.; Liang, J.; Jaroniec, M.; Qiao, S. Z. Graphitic Carbon Nitride Materials: Controllable Synthesis and Applications in Fuel Cells and Photocatalysis. Energy Environ. Sci. 2012, 5, 6717. (18) Zhu, J.; Xiao, P.; Li, H.; Carabineiro, S. A. C. Graphitic Carbon Nitride: Synthesis, Properties, and Applications in Catalysis. ACS Appl. Mater. Interfaces 2014, 6, 16449−16465. (19) Zhang, Y.; Liu, J.; Wu, G.; Chen, W. Porous Graphitic Carbon Nitride Synthesized via Direct Polymerization of Urea for Efficient Sunlight-Driven Photocatalytic Hydrogen Production. Nanoscale 2012, 4, 5300. (20) Yaddanapudi, H. S.; Tian, K.; Teng, S.; Tiwari, A. Facile Preparation of Nickel/Carbonized Wood Nanocomposite for Environmentally Friendly Supercapacitor Electrodes. Sci. Rep. 2016, 6, 33659. (21) Sun, H.; Cao, Y.; Feng, L.; Chen, Y. Immobilizing Photogenerated Electrons from Graphitic Carbon Nitride for an Improved Visible-Light Photocatalytic Activity. Sci. Rep. 2016, 6, 22808. (22) Tahir, M.; Mahmood, N.; Zhu, J.; Mahmood, A.; Butt, F. K.; Rizwan, S.; Aslam, I.; Tanveer, M.; Idrees, F.; Shakir, I.; et al. One Dimensional Graphitic Carbon Nitrides as Effective Metal-Free Oxygen Reduction Catalysts. Sci. Rep. 2015, 5, 12389. (23) Pawar, R. C.; Kang, S.; Park, J. H.; Kim, J.-h.; Ahn, S.; Lee, C. S. Room-Temperature Synthesis of Nanoporous 1D Microrods of Graphitic Carbon Nitride (g-C3N4) with Highly Enhanced Photocatalytic Activity and Stability. Sci. Rep. 2016, 6, 31147. (24) Van Dommele, S. Nitrogen Doped Carbon Nanotubes: Synthesis, Characterization and Catalysis; Utrecht University, 2008. (25) Yao, Y.; Zhang, B.; Shi, J.; Yang, Q. Preparation of NitrogenDoped Carbon Nanotubes with Different Morphologies from Melamine-Formaldehyde Resin. ACS Appl. Mater. Interfaces 2015, 7, 7413−7420. (26) John, A. R.; Arumugam, P. Open Ended Nitrogen-Doped Carbon Nanotubes for the Electrochemical Storage of Energy in a Supercapacitor Electrode. J. Power Sources 2015, 277, 387−392. (27) Liu, H.; Zhang, Y.; Li, R.; Sun, X.; Désilets, S.; Abou-Rachid, H.; Jaidann, M.; Lussier, L.-S. Structural and Morphological Control of Aligned Nitrogen-Doped Carbon Nanotubes. Carbon N. Y. 2010, 48, 1498−1507. (28) Xiong, C.; Wei, Z.; Hu, B.; Chen, S.; Li, L.; Guo, L.; Ding, W.; Liu, X.; Ji, W.; Wang, X. Nitrogen-Doped Carbon Nanotubes as Catalysts for Oxygen Reduction Reaction. J. Power Sources 2012, 215, 216−220. (29) Deng, D.; Yu, L.; Chen, X.; Wang, G.; Jin, L.; Pan, X.; Deng, J.; Sun, G.; Bao, X. Iron Encapsulated within Pod-like Carbon Nanotubes for Oxygen Reduction Reaction. Angew. Chem., Int. Ed. 2012, 52, 371−375. (30) Liu, Y.; Jiang, H.; Zhu, Y.; Yang, X.; Li, C. Transition Metals (Fe, Co, and Ni) Encapsulated in Nitrogen-Doped Carbon Nanotubes as Bi-Functional Catalysts for Oxygen Electrode Reactions. J. Mater. Chem. A 2016, 4, 1694−1701. (31) Song, A.; Yang, W.; Yang, W.; Sun, G.; Yin, X.; Gao, L.; Wang, Y.; Qin, X.; Shao, G. Facile Synthesis of Cobalt Nanoparticles Entirely Encapsulated in Slim Nitrogen-Doped Carbon Nanotubes as Oxygen Reduction Catalyst. ACS Sustainable Chem. Eng. 2017, 5, 3973−3981.
(32) Wang, X.; Maeda, K.; Chen, X.; Takanabe, K.; Domen, K.; Hou, Y.; Fu, X.; Antonietti, M. Polymer Semiconductors for Artificial Photosynthesis: Hydrogen Evolution by Mesoporous Graphitic Carbon Nitride with Visible Light. JACS 2009, 131, 1680−1681. (33) Feng, L.; Yang, L.; Huang, Z.; Luo, J.; Li, M.; Wang, D.; Chen, Y. Enhancing Electrocatalytic Oxygen Reduction on Nitrogen-Doped Graphene by Active Sites Implantation. Sci. Rep. 2013, 3, 3306. (34) Wu, G.; Hu, Y.; Liu, Y.; Zhao, J.; Chen, X.; Whoehling, V.; Plesse, C.; Nguyen, G. T. M.; Vidal, F.; Chen, W. Graphitic Carbon Nitride Nanosheet Electrode-Based High-Performance Ionic Actuator. Nat. Commun. 2015, 6, 7258. (35) Ma, T. Y.; Tang, Y.; Dai, S.; Qiao, S. Z. Proton-Functionalized Two-Dimensional Graphitic Carbon Nitride Nanosheet: An Excellent Metal-/Label-Free Biosensing Platform. Small 2014, 10, 2382−2389. (36) Reddy, A. L. M.; Shaijumon, M. M.; Ramaprabhu, S. Alloy Hydride Catalyst Route for the Synthesis of Single-Walled Carbon Nanotubes, Multi-Walled Carbon Nanotubes and Magnetic MetalFilled Multi-Walled Carbon Nanotubes. Nanotechnology 2006, 17, 5299−5305. (37) Liu, J.; Zhang, T.; Wang, Z.; Dawson, G.; Chen, W. Simple Pyrolysis of Urea into Graphitic Carbon Nitride with Recyclable Adsorption and Photocatalytic Activity. J. Mater. Chem. 2011, 21, 14398−14401. (38) Wang, X.; Maeda, K.; Thomas, A.; Takanabe, K.; Xin, G.; Carlsson, J. M.; Domen, K.; Antonietti, M. A Metal-Free Polymeric Photocatalyst for Hydrogen Production from Water under Visible Light. Nat. Mater. 2008, 8, 76. (39) Fina, F.; Callear, S. K.; Carins, G. M.; Irvine, J. T. S. Structural Investigation of Graphitic Carbon Nitride via XRD and Neutron Diffraction. Chem. Mater. 2015, 27, 2612. (40) Zinin, P. V.; Ming, L.-C.; Sharma, S. K.; Khabashesku, V. N.; Liu, X.; Hong, S.; Endo, S.; Acosta, T. Ultraviolet and near-infrared Raman spectroscopy of graphitic C 3 N 4 phase. Chem. Phys. Lett. 2009, 472, 69−73. (41) Liu, S.; Ke, J.; Sun, H.; Liu, J.; Tade, M. O.; Wang, S. Size Dependence of Uniformed Carbon Spheres in Promoting Graphitic Carbon Nitride toward Enhanced Photocatalysis. Appl. Catal., B 2017, 204, 358−364. (42) Kowanda, C.; Speidel, M. O. Solubility of nitrogen in liquid nickel and binary Ni-Xi alloys (Xi=Cr, Mo,W, Mn, Fe, Co) under elevated pressure. Scr. Mater. 2003, 48, 1073−1078. (43) Chesnokov, V. P.; Linchevskij, B. V. Nitrogen Diffusion in Liquid Nickel and Its Melts with Chromium, Molybdenum and Tungsten. Izv. Akad. Nauk SSSR, Met. 1977, 5, 75−77. (44) Kumar, R.; Singh, R. K.; Dubey, P. K.; Singh, D. P.; Yadav, R. M.; Tiwari, R. S. Freestanding 3D Graphene-Nickel Encapsulated Nitrogen-Rich Aligned Bamboo Like Carbon Nanotubes for HighPerformance Supercapacitors with Robust Cycle Stability. Adv. Mater. Interfaces 2015, 2, 1500191. (45) Nurmi, J. T.; Tratnyek, P. G.; Sarathy, V.; Baer, D. R.; Amonette, J. E.; Pecher, K.; Wang, C.; Linehan, J. C.; Matson, D. W.; Penn, R. L.; et al. Characterization and Properties of Metallic Iron Nanoparticles: Spectroscopy, Electrochemistry, and Kinetics. Environ. Sci. Technol. 2005, 39, 1221−1230. (46) Liu, B.; Jin, L.; Zheng, H.; Yao, H.; Wu, Y.; Lopes, A.; He, J. Ultrafine Co-Based Nanoparticles @ Mesoporous Carbon Nanospheres toward High-Performance Supercapacitors. ACS Appl. Mater. Interfaces 2016, 9, 1746−1758. (47) Zheng, Y.; Lin, Z.; Chen, W.; Liang, B.; Du, H.; Yang, R.; He, X.; Tang, Z.; Gui, X. Flexible, Sandwich-Like CNTs/NiCo2O4 Hybrid Paper Electrodes for All-Solid State Supercapacitors. J. Mater. Chem. A 2017, 5, 5886−5894. (48) Li, X.-q.; Zhang, W.-x. Sequestration of Metal Cations with Zerovalent Iron NanoparticlesA Study with High Resolution X-Ray Photoelectron Spectroscopy (HR-XPS). J. Phys. Chem. C 2007, 111, 6939−6946. (49) Zhang, X.; Lin, S.; Chen, Z.; Megharaj, M.; Naidu, R. KaoliniteSupported Nanoscale Zero-Valent Iron for Removal of Pb2+ from 17285
DOI: 10.1021/acsomega.8b02835 ACS Omega 2018, 3, 17276−17286
ACS Omega
Article
Aqueous Solution: Reactivity, Characterization and Mechanism. Water Res. 2011, 45, 3481−3488. (50) Bao, Y.; Chen, K. AgCl/Ag/g-C3N4 Hybrid Composites: Preparation, Visible Light-Driven Photocatalytic Activity and Mechanism. Nano-Micro Lett. 2016, 8, 182−192. (51) Shaijumon, M. M.; Ramaprabhu, S. Synthesis of Carbon Nanotubes by Pyrolysis of Acetylene Using Alloy Hydride Materials as Catalysts and Their Hydrogen Adsorption Studies. Chem. Phys. Lett. 2003, 374, 513−520. (52) Li, Y.; Wang, J.; Li, X.; Liu, J.; Geng, D.; Yang, J.; Li, R.; Sun, X. Nitrogen-Doped Carbon Nanotubes as Cathode for Lithium-Air Batteries. Electrochem. Commun. 2011, 13, 668−672. (53) Shende, R. C.; Ramaprabhu, S. Thermo-Optical Properties of Partially Unzipped Multiwalled Carbon Nanotubes Dispersed Nanofluids for Direct Absorption Solar Thermal Energy Systems. Sol. Energy Mater. Sol. Cells 2016, 157, 117−125. (54) Xu, P.; Kang, J.; Choi, J.-B.; Suhr, J.; Yu, J.; Li, F.; Byun, J.-H.; Kim, B.-S.; Chou, T.-W. Laminated Ultrathin Chemical Vapor Deposition Graphene Films Based Stretchable and Transparent High-Rate Supercapacitor. ACS Nano 2014, 8, 9437−9445. (55) Zhu, T.; Zhou, J.; Li, Z.; Li, S.; Si, W.; Zhuo, S. Hierarchical Porous and N-Doped Carbon Nanotubes Derived from Polyaniline for Electrode Materials in Supercapacitors. J. Mater. Chem. A 2014, 2, 12545. (56) Lin, T.-T.; Lai, W.-H.; Lü, Q.-F.; Yu, Y. Porous NitrogenDoped Graphene/Carbon Nanotubes Composite with an Enhanced Supercapacitor Performance. Electrochim. Acta 2015, 178, 517−524. (57) Han, J.; Xu, G.; Ding, B.; Pan, J.; Dou, H.; MacFarlane, D. R. Porous Nitrogen-Doped Hollow Carbon Spheres Derived from Polyaniline for High Performance Supercapacitors. J. Mater. Chem. A 2014, 2, 5352. (58) Cheng, Y.; Lu, S.; Zhang, H.; Varanasi, C. V.; Liu, J. Synergistic Effects from Graphene and Carbon Nanotubes Enable Flexible and Robust Electrodes for High-Performance Supercapacitors. Nano Lett. 2012, 12, 4206−4211. (59) Wang, K.; Meng, Q.; Zhang, Y.; Wei, Z.; Miao, M. HighPerformance Two-Ply Yarn Supercapacitors Based on Carbon Nanotubes and Polyaniline Nanowire Arrays. Adv. Mater. 2013, 25, 1494−1498. (60) Zhao, J.; Lai, H.; Lyu, Z.; Jiang, Y.; Xie, K.; Wang, X.; Wu, Q.; Yang, L.; Jin, Z.; Ma, Y.; et al. Hydrophilic Hierarchical NitrogenDoped Carbon Nanocages for Ultrahigh Supercapacitive Performance. Adv. Mater. 2015, 27, 3541−3545. (61) Xu, X.; Wang, M.; Liu, Y.; Li, Y.; Lu, T.; Pan, L. In Situ Construction of Carbon Nanotubes/Nitrogen-Doped Carbon Polyhedra Hybrids for Supercapacitors. Energy Storage Mater. 2016, 5, 132−138. (62) Chen, H.; Yu, F.; Wang, G.; Chen, L.; Dai, B.; Peng, S. Nitrogen and Sulfur Self-Doped Activated Carbon Directly Derived from Elm Flower for High-Performance Supercapacitors. ACS Omega 2018, 3, 4724. (63) Chen, L.-F.; Huang, Z.-H.; Liang, H.-W.; Yao, W.-T.; Yu, Z.-Y.; Yu, S.-H. Flexible All-Solid-State High-Power Supercapacitor Fabricated with Nitrogen-Doped Carbon Nanofiber Electrode Material Derived from Bacterial Cellulose. Energy Environ. Sci. 2013, 6, 3331−3338. (64) Wahid, M.; Parte, G.; Phase, D.; Ogale, S. Yogurt: A Novel Precursor for Heavily Nitrogen Doped Supercapacitor Carbon. J. Mater. Chem. A 2015, 3, 1208−1215. (65) Bello, A.; Barzegar, F.; Momodu, D.; Dangbegnon, J.; Taghizadeh, F.; Manyala, N. Symmetric Supercapacitors Based on Porous 3D Interconnected Carbon Framework. Electrochim. Acta 2015, 151, 386−392. (66) Javed, M. S.; Dai, S.; Wang, M.; Guo, D.; Chen, L.; Wang, X.; Hu, C.; Xi, Y. High Performance Solid State Flexible Supercapacitor Based on Molybdenum Sulfide Hierarchical Nanospheres. J. Power Sources 2015, 285, 63−69.
(67) Chen, W.; Rakhi, R. B.; Hedhili, M. N.; Alshareef, H. N. ShapeControlled Porous Nanocarbons for High Performance Supercapacitors. J. Mater. Chem. A 2014, 2, 5236. (68) Liu, X. Y.; Gao, Y. Q.; Yang, G. W. A Flexible, Transparent and Super-Long-Life Supercapacitor Based on Ultrafine Co3O4 Nanocrystal Electrodes. Nanoscale 2016, 8, 4227−4235. (69) Lai, H.; Wu, Q.; Zhao, J.; Shang, L.; Li, H.; Che, R.; Lyu, Z.; Xiong, J.; Yang, L.; Wang, X.; et al. Mesostructured NiO/Ni Composites for High-Performance Electrochemical Energy Storage. Energy Environ. Sci. 2016, 9, 2053−2060. (70) Chen, H.; Jiang, J.; Zhang, L.; Qi, T.; Xia, D.; Wan, H. Facilely Synthesized Porous NiCo2O4 Flowerlike Nanostructure for HighRate Supercapacitors. J. Power Sources 2014, 248, 28−36. (71) Yang, P.; Mai, W. Flexible Solid-State Electrochemical Supercapacitors. Nano Energy 2014, 8, 274−290. (72) Zhao, J.; Niu, W.; Zhang, L.; Cai, H.; Han, M.; Yuan, Y.; Majeed, S.; Anjum, S.; Xu, G. A Template-Free and Surfactant-Free Method for High-Yield Synthesis of Highly Monodisperse 3Aminophenol-Formaldehyde Resin and Carbon Nano/Microspheres. Macromolecules 2013, 46, 140−145.
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