Facile fabrication of cross-linked carbon nanofiber via directly carbonizing electrospun polyacrylonitrile nanofiber as high performance scaffold for supercapacitors

Accepted Manuscript Title: Facile fabrication of cross-linked carbon nanofiber via directly carbonizing electrospun polyacrylonitrile nanofiber as high performance scaffold for supercapacitors Author: Guobin Xue Jiang Zhong Yongliang Cheng Bo Wang PII: DOI: Reference:

S0013-4686(16)31773-X http://dx.doi.org/doi:10.1016/j.electacta.2016.08.063 EA 27841

To appear in:

Electrochimica Acta

Received date: Revised date: Accepted date:

5-6-2016 12-8-2016 15-8-2016

Please cite this article as: Guobin Xue, Jiang Zhong, Yongliang Cheng, Bo Wang, Facile fabrication of cross-linked carbon nanofiber via directly carbonizing electrospun polyacrylonitrile nanofiber as high performance scaffold for supercapacitors, Electrochimica Acta http://dx.doi.org/10.1016/j.electacta.2016.08.063 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Facile fabrication of cross-linked carbon nanofiber via directly carbonizing electrospun polyacrylonitrile nanofiber as high performance scaffold for supercapacitors

Guobin Xue,a Jiang Zhong,a Yongliang Cheng,*ab Bo WangError! Bookmark not defined.a

a

Key laboratory of Nuclear Solid Physics, School of Physics and Technology, Wuhan

University, Wuhan, 430072, China, and

b

Wuhan National Laboratory for

Optoelectronics, Huazhong University of Science and Technology, Wuhan, 430074, China.

a

Key laboratory of Nuclear Solid Physics, School of Physics and Technology, Wuhan University, Wuhan, 430072, China. E-mail: [email protected] , [email protected] b Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan, 430074, China. E-mail: [email protected].

Corresponding Author *Address correspondence to mail: [email protected] , [email protected] , [email protected]. 1

ABSTRACT Cross-linked carbon nanofiber (CLCNF) was successfully prepared by directly carbonizing

electrospun

polyacrylonitrile

(PAN)

nanofiber.

Comparing

to

non-cross-linked carbon nanofiber (NCLCNF) obtained via carbonizing of pre-oxidation PAN nanofiber, CLCNF shows better conductivity owing to its cross-linked structure. Then CLCNF was used as scaffold to support polyaniline (PANi)

nanorods

for

supercapacitor

electrode

material.

The

hierarchical

CLCNF/PANi composite displays a capacity of 206 C g-1 at 0.5 A g-1 with excellent rate capability (remains 49% even at 800 A g-1), which is much higher than that of NCLCNF/PANi composite (17%). More interestingly, supercapacitor device based on CLCNF/PANi

composite

achieves

75.3%

capacity

retention

after

10000

charge-discharge cycles at 10 A g-1, suggesting excellent cycle stability. All these experimental results indicate that this method for fabricating CLCNF is a substantial advancement towards the practical applications of carbon nanofiber in energy conversion and storage field.

Keywords: carbon nanofibers；supercapacitor；positron

1. Introduction Carbon-based materials have always been the most attractive hotspot for electrochemical applications, especially for the energy storage, because of their

2

excellent electrical conductivity, mechanical strength, chemical and thermal stabilities.[1-4] Owing to their rich allotropes (graphite, diamond, fullerene, nanotube, graphene), various microtextures (more or less ordered depended on the degree of graphitization), variety of dimensionalities from 0 to 3 dimension and ability for existence under different forms (powder, fiber, foam, fabric and composite), engineering carbon materials for different applications has achieved great progress.[5-10] Among various kinds of carbon materials, electrospun carbon nanofiber (CNF) exhibits outstanding advantages, such as high specific surface area, easy preparation, commercial viability and flexibility to tailor its structure.[11, 12] The preparation of CNF usually involves electrospinning polymer with high carbon yield, pre-oxidation and carbonization process.[13] So far, many polymers have been used as precursor to fabricate CNF with various morphologies and structures for different application in supercapacitor or Li-ion battery electrode.[14, 15] It should be noticed that the contact point between nanofibers in CNF is sufficient physical contact, causing large contact resistance. Especially when coating CNF with other low conductivity materials for supercapacitor, original contacted nanofibers are separated by the coating, which limits electron conduction though whole electrode and leads to low rate capability. Therefore it is desirable to create ‘true’ junction between nanofibers by formation of cross-linked structure.[16-18] As a well-known polymer with good stability, mechanical strength and high carbon yield, polyacrylonitrile (PAN) has been widely used as one dominating precursor to synthesize carbon fibers.[12] The fabricating process usually involves

3

pre-oxidation in air at 200-300oC and then carbonation above 600oC in inert atmosphere. During the pre-oxidation process, PAN fiber undergoes cyclization of nitrile groups (C≡N) and crosslinking of the chain molecules, resulting in the formation of ladder structure, which prevents the fusion during subsequent high temperature carbonization.[13, 19] Therefore, CNF with cross-linked structure may be obtained if the PAN nanofiber was directly carbonized at high temperature without pre-oxidation. On the other hand, Polyaniline (PANi) is considered to be one of the most promising active electrode material for electrochemical supercapacitor, because of its high specific capacity, facile synthesis, good environmental stability and low cost.[20, 21] However, long term charge/discharge processes lead to the swelling/shrinkage of PANi, causing volume changes and destroying the backbone of polymer and thus resulting in poor cycle life and rate capability. Coating PANi on excellent conducting carbon materials has been proved an efficient way to enhance the cycle stability and rate capability of PANi.[7, 16, 20, 22] Herein, stimulated by the above concerns, we demonstrate the fabrication of cross-linked CNF via directly carbonizing electrospun PAN nanofiber. Compared with our previous work [16] and traditional CNF preparation method, this method avoids the pre-oxidation process and simplifies complicated parameters for forming cross-linked structure. To verify its advantage working as scaffold, we coated PANi nanorods on the surface of CLCNF as supercapacitor electrode material. The cross-linked structure effectively ensures rapid electron transfer through whole

4

electrode, leading to an obvious improvement in rate capability. The CLCNF/PANi composite exhibits excellent rate capability of 49% with the current density increasing from 0.5 A g-1 to 800 A g-1, which is much higher than that of NCLCNF/PANi composite (17%). Meanwhile, the CLCNF/PANi composite was assembled into a supercapacitor device, which also exhibited excellent power density and cycle stability. 2. Experimental section 2.1. Synthesis of CNF network PAN (2.0 g) was dissolved into N,N-dimethylformamide (DMF, 20.0 mL) to form a transparent solution after magnetically stirring for several hours. This solution was then ejected from the stainless steel capillary with a feeding rate of 2.0 mL h-1 and one horizontal stainless steel plate (ground conductor) was used as the collector. The distance and voltage between the capillary and collector were 20 cm and 25 kV, respectively. The temperature and relatively humidity of the electrospinning chamber were controlled at 30oC and 30-40% respectively. The as collected PAN precursor nanofiber was then carbonized at 1100oC for 2 h in Ar atmosphere to obtain CLCNF. NCLCNF was attained by being pre-oxidation at 260oC for 2 h in air and then carbonization at 1100oC for 2 h in Ar atmosphere. 2.2. Preparation of CNF/PANi composites As a typical procedure, CNF was firstly immersed in 7 M HNO3 solution for 6 h to increase its hydrophilicity and then washed with deionezed water. Aniline (Ani, 84 μL) was added into 1 M HClO4 solution (30 mL) and stirred to form uniform mixture.

5

Then acid-treated CNF (10 mg) was immersed into above solution for 30 min to ensure sufficient adsorption of ANi. Subsequently, another 1 M HClO4 solution (30 mL) containing ammonium peroxydisulfate (APS) was rapidly added into above mixture. The molar ratio of ANi/APS was 1.5. The polymerization reaction was carried out at 5oC. After reacting for 6 h, the CNF/PANi composite was moved out and washed with deionized water for several times. Comparing the weight difference between CNF and CNF/PANi, we got the weight ratio of CNF to PANi is about 1:1 in the resulting composites. 2.3. Calculation of capacity, energy and power density On the basis of the galvanostatic charge-discharge (GCD) curves, the capacity of electrode materials was calculated using the following equation: Cq = 2im  Vdt / ΔV Where Cq (C g-1) represents the capacity, im=I/m (A g-1) is the current density (I is the current and m is the mass of the electrode),

 Vdt is the integral voltage area, ΔV is the

potential after the IR drop. Energy and power densities of supercapacitor devices were estimated using the following equations: E = 0.5 Cqm ΔV P = E/Δt Where E (Wh kg-1) and P (W kg-1) are the specific energy and power densities, Cqm represents the capacity (C g-1) of the supercapacitor device, and Δt is the discharge time (s).

6

2.4. Characterizations The morphology and structure of CNF and CNF/PANi composite were analyzed using field emission scanning electron microscope (FESEM, FEI Nova 450 Nano) and transmission electron microscope (TEM, Tecnai G20). The positron annihilation lifetime spectroscopy (PALS) measurement was carried out using a conventional fast-fast coincidence system with a time resolution of about 270 ps. A 20 μCi

22

Na

source was sandwiched between two identical samples. Electrical conductivity was measured by a standard four-probe configuration (RTS-8). All samples were tested as a free standing film with a thickness about 0.125 mm. The resistivity is calculated by ρ=R□d, where ρ is the resistivity, R□ is the square resistance got from the RTS-8, and d is the thickness of the film. The resulted resistivity was the average value from 8 samples. Raman spectra measurement was performed on a Renishaw inVia Raman spectrometer using the 514.5 nm line of an Ar+ laser. Fourier transmission infrared spectra (FTIR) were measured on a Bruker Vertex 70 FTIR spectrometer. X-ray photoelectron spectroscopy (XPS) analyses were performed using a GENESIS spectrometer (EDAX Inc, USA), employing an Al Ka X-ray source with a 500 mm electron beam spot. The measurements of cyclic voltammetry (CV) and GCD were carried out using VMP-300 electrochemical station. For the typical three electrode measurement, a piece of CNF/PANi film with a diameter of 5 mm and weight about 0.4 mg was used as working electrode, Hg/HgSO4 (CHI, USA) and Celgard (Celgard, USA) was used as reference electrode and separator, respectively. The counter electrodes were prepared by mixing active carbon (YP-50, Kuraray Chemical, Japan) and polytetrafluoroethylene emulsion with a mass ratio of 90:10. Then, the mixture was pressed into films and cut into rounds with diameter of 1cm. Two-electrode symmetric device was constructed based on two piece of CNF/PANi composite with same area and mass as electrode. All the electrochemical tests were conducted in Swagelok cells (Swagelok, USA). Electrochemical impedance was measured from 10 mHz to 200 kHz with a potential amplitude of 10 mV using Autolab PGSTAT302N and 44 points were collected. 7

3. Results and discussion Fig. 1a shows the preparation process of CLCNF. Briefly, the precursor PAN/DMF solution was first electrospun into a nanofiber membrane. Then the as-spun nanofiber network was directly carbonized at 1100oC for 2 h in Ar atmosphere. The advantage of this method is that during the carbonization process, individual nanofiber would fuse and interconnect with each other to form cross-linked structure. The detailed morphology and structural features of PAN nanofiber, NCLCNF and CLCNF were characterized by scanning electron microscope (SEM) and transmission electron microscope (TEM). Fig. 1b and 1c show the SEM images of PAN nanofiber and NCLCNF, which present the similar morphology. This is because that the non-plastic cyclic or ladder structure formed during pre-oxidation process hinder the fusion of PAN nanofiber and stabilize the structure of NCLCNF.[12, 13] The average diameter of PAN nanofiber and NCLCNF is around 310 nm and 200 nm, respectively. The decrease of diameter could be attributed to the decomposition of PAN during pre-oxidation and carbonization process. When it comes to CLCNF (Fig. 1d), cross-linked structure between the adjacent nanofiber is clearly observed (marked by red circle) and no obvious interface between two adjacent nanofiber can be observed (insert of Fig. 1d), suggesting that nanofiber is really cross-linked. The average diameter of CLCNF decreases to about 140 nm and becomes inhomogeneous, which may be also attributed to the decomposition and melt of PAN nanofiber. Raman spectroscopy was applied to study the as-prepared CLCNF and NCLCNF. As shown in Fig. 2, both samples show two broad-band peaks located at 1329 cm-1

8

(D band) and 1566 cm-1 (G band). The relatively intensity of the D band is slightly higher than that of the G band, indicating highly defected nanofiber.[23] The in-plane crystallite size La can be obtained from the equation:



La nm   2.4  10

10

I  λ  D   IG 



1

4

where ID and IG are the intensity of the D and G peaks, respectively, and λ is the wavelength of the laser. The calculated crystal size of NCLCNF and CLCNF is approximately 15.86 nm and 14.62 nm respectively, indicating that pre-oxidation process can not only decrease the amount of amorphous carbon and numbers of defects but also improve crystalline structure of the CNF. Positron annihilation spectroscopy (PALS) is a commonly used technique for the investigation of the electronic properties of condensed matter and for study on the open volume defects. It is due to the fact that thermalized positrons are localized in lattice defects in the bulk and at the surface. To study the difference between CLCNF and NCLCNF, we performed the PALS measurement. Positron lifetime spectra give a best fit for two-lifetime components resolved from PATFIT: a short-lived component (about 0.16 ns) due to positrons in the bulk and a component (about 0.35 ns) due to surface-trapped positrons.[24, 25] Table 1 displays the comparison of positron lifetime and intensity of CLCNF and NCLCNF. Clearly, the second position intensity (I2) of CLCNF is bigger than that of NCLCNF, suggesting that CLCNF owns more trapped states. The average positron lifetime (a) was also calculated using the result.

a of CLCNF (about 0.271 ns) is obviously longer than that of NCLCNF (0.241 ns), again demonstrating the richer defect in CLCNF. As discussed above, CLCNF 9

contains more amorphous form and defects, which all harm to the conductivity. However, CLCNF still has a resistivity about (6.48±0.05)10-4 m, slightly smaller than NCLCNF (about (9.57±0.06)10-4 m). This may be contributed to the formation of cross-link structure, which will reduce the interface contact resistance and be benefit to the electron conducting. To explore the advantage of CLCNF, we fabricated CNF/PANi composite to study its potential application as effective scaffold. The PANi was synthesized through a chemical oxidation polymerization method based on previous report.[26-28] The average thickness of NCLCNF and CLCNF film is 0.124 mm and 0.130 mm, respectively. After growing PANi nanorods, no obvious change of thickness is observed with micrometer. As shown in Fig. 3a and 3b, the PANi nanorods are uniformly aligned in the direction perpendicular to the CNF surface. The strong anchoring of PANi nanorods on the fiber surface enables fast electron transport through the underlying CNF, resulting in the improvement in the electrochemical performance of PANi. It is obvious that contact joint in NCLCNF were separated by PANi (Fig. 3a), while the cross-linked joint in CLCNF guarantees the connection of carbon fiber (Fig. 3b). The chemical structure of composite was characterized by Fourier transform infrared spectra (FTIR). As shown in Fig. 3c, compared with pure CLCNF, several typical peaks at 1087 cm-1, 1240 cm-1, 1302 cm-1, 1490 cm-1 and 1571 cm-1 can be observed for CLCNF/PANi, which are attributed to CH stretching vibrations, aromatic C=N stretching vibrations, CN stretching, CC stretching in the benzenoid ring and CC stretching in the quinoid ring of PANi, respectively.[22]

10

Meanwhile, the XPS spectrum reveals four bands at 531 eV, 398 eV, 284 eV and 207 eV, corresponding to O, N, C, Cl, respectively (Fig. 3d).[29] The existence of chlorine element indicated that PANi was doped with ClO4 － .[30] Furthermore, the deconvoluted profile fit of the XPS for C1s showed the presence of CC (284.9 eV), COC/CN (285.9 eV), CO/CCl (287.6 eV) as shown in Fig. 3e. The high resolution N1s spectrum can be deconvoluted into three individual peaks which located at 398.8 eV, 400.1 eV and 401.3 eV, corresponding to quinoid-imine (NH), the benzenoid-amine (NH) and positively charged nitrogen (NH+), respectively (Fig. 3f).[22, 31, 32] Based on the above detailed results, it can be confirmed the successfully grown PANi on the surface of CLCNF. In order to demonstrate the electrochemical performance, CV and GCD measurements which conducted in three-electrode configuration with 1 M H2SO4 as electrolyte were performed. As shown in Fig. 4a, each CV curve of CLCNF/PANi under the potential ranging from -0.6 to 0.2 vs (Hg/HgSO4)/V exhibit a quasi-rectangular shaped baseline current and two pairs of redox waves, which are attributed

to

the

leucoemeraldine/emeraldine

and

emeraldine/pernigraniline

transformations of PANi, revealing the electroactive behavior of PANi.[16, 26, 33-35] The CV curves of pure CLCNF exhibits a much smaller area in comparison with that of CLCNF/PANi due to the absence of electroactive (Fig. S1). The shape of CV curves for CLCNF/PANi composite is well maintained even at 1000 mV s-1, however, the shape of CV curves for NCLCNF/PANi composite has severely distorted from its original shape at the same sweep rate (Fig. S2a), implying its excellent rate capability

11

of CLCNF/PANi. In addition, it also can be seen that the peaks potentials shifted towards more positive and negative values for oxidation and reduction process, respectively, with increasing sweep rate, due to the internal resistance.[22] All these results suggest that the capacity of the CLCNF/PANi electrode is primarily derived from PANi. Fig. 4b displays the GCD curves of CLCNF/PANi at three different high current densities. It can be seen that the GCD curves of CLCNF/PANi exhibits smaller voltage drop than NCLCNF/PANi (Fig. S2b), suggesting its rapid I-V response. Rate capability is an important factor for the power application of supercapacitors. A good electrochemical energy storage device is required to provide larger capacity at a high charge/discharge rate. Fig. 4c shows the capacity of CLCNF/PANi and NCLCNF/PANi composite at various current densities. We used the capacity in C g-1 as the metric here.[36,37] CLCNF/PANi composite obviously exhibits better rate capability than NCLCNF/PANi. The capacity of CLCNF/PANi is about 206 C g-1 at current density of 0.5 A g-1 (based on the total electrode mass). This value is much higher than that of CLCNF (Fig. S3), indicating that the capacity of CLCNF/PANi is mainly attributed to the PANi. When increasing the current density to 800 A g-1, the CLCNF/PANi still have a capacity about 101.3 C g-1 (about 49% of the capacity at 0.5 A g-1), while the rate capability of NCLCNF/PANi is only about 17% (192.9 C g-1 at 0.5 A g-1 and 33.0 C g-1 at 800 A g-1). The superior rate capability in CLCNF/PANi electrode can be attributed to the unique structure of CLCNF.[38, 39] During the charge/discharge process, PANi will transform in different redox state with different electrical conductivity. In fully oxidation/reduction state, PANi is

12

non-conductive and hinders electron transport between carbon nanofibers. The ‘true’ connect joints ensure good connection of carbon nanofibers and hence improve the rate capability. Comparing to other reported carbon/PANi composite electrode, such as graphitized carbon nanofiber/PANi (52% capacity retention with the current density increasing from 0.4 A g-1 to 50 A g-1),[28] graphene/PANi (50% of capacity retention with the current density increasing from 1 A g-1 to 10 A g-1),[40] graphene/CNT/PANi (50% capacity retention with the current density increasing from 0.3 A g-1 to 3.1 A g-1),[41] the rate capability of CLCNF/PANi is obviously higher, as 82% when current density ranging from 0.5 A g-1 to 50 A g-1 (Fig. S4 and Table S1). Electrochemical impedance spectroscopy (EIS) measurement was further performed to investigate charge-transfer characteristics (Fig. 4d). The diameter of semicircle for CLCNF/PANi in high frequency range is slightly smaller than that of NCLCNF/PANi, indicating a smaller charge-transfer resistance (1.4  for CLCNF/PANi and 2.1  for NCLCNF/PANi). All these results reveal that the formation of cross-linked structure is beneficial to electron transfer, resulting in a faster electronic response and the improvement in rate capability. Two-electrode cells allow a good estimation of materials performance in electrochemical capacitors. For application consideration, two-electrode symmetrical supercapacitor device was fabricated here to evaluate electrochemical performance of CLCNF/PANi in 1 M H2SO4 electrolyte. Fig. 5a shows the CV curves of symmetrical device based on CLCNF/PANi at different sweep rates ranging from 20 to 1000 mV s-1 in voltage range of 0-0.8 V. The indistinctly change of area of CV curves suggesting a good rate capability. The GCD curves at high current density (Fig. 5b) exhibits small voltage drop, indicating a rapid I-V response owing to its cross-linked 13

structure. The device exhibits a capacity of 33.0 C g-1 even at a high current density of 200 A g-1 (Fig. 5c). Energy and power densities are two crucial parameters determining the ultimate performance of supercapacitor. The SC device has a highest energy density of 5.13 Wh kg-1 with a power density of 579 W kg-1. Furthermore, the device can deliver a high power density of 12682 W kg-1 with an energy density of 3.62 Wh kg-1 (Fig. S5). The cycle performance is an important index for supercapacitor application. GCD technique was further performed to evaluate the cycle stability of this device at a high current density of 10 A g-1 (Fig. 5d). CLCNF/PANi presents excellent cycle stability and capacity retained 75.3% after 10000th cycles, revealing good cycle stability. The reduction in capacity can be attributed to deterioration of the PANi after many swelling and shrinking cycles. 4. Conclusions In summary, we have developed a convenient strategy to prepare CLCNF via directly carbonizing electrospun PAN nanofiber. This method ensures the better conductivity of CLCNF owing to the formation of cross-linked structure. Acting as scaffold to support PANi, CLCNF/PANi composite exhibits an excellent rate capability of 49% with the current density increasing from 0.5 A g-1 to 800 A g-1, which is much higher than that of NCLCNF/PANi composite (17%). This is because that the existence of cross-linked structure allows electron quickly transport through whole electrode during the rapid charge-discharge process. Moreover, supercapacitor device based on CLCNF/PANi also presents excellent cycle stability, as 75.3% of initial capacity can be achieved after 10000 charge-discharge cycles. Above excellent electrochemical performance suggests that this facile synthesis process has important potential in fabricating other CNF-based composite materials for energy conversion and storage application. 14

Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.

Acknowledgments

This work was financially supported by the National Natural Science Foundation of China (11175134，51322210, 61434001), a Foundation for the Author of National Excellent Doctoral Dissertation of PR China (201035), the China Postdoctoral Science Foundation (2014M552033), the Fundamental Research Funds for the Central Universities (HUST: 2012YQ025, 2013YQ049, 2013TS160) and Director Fund of WNLO. The authors thank to the facility support of the Center for Nanoscale Characterization & Devices, WNLO-HUST and the Analysis and Testing Center of Huazhong University of Science and Technology.

Supporting Information Available The supporting information contains CV curves of CLCNF and NCLCNF with sweeping rate from 20mV s-1 to 1000 mV s-1; CV curves of CLCNF/PANi with sweeping rate from 20mV s-1 to 1000 mV s-1; GCD curves of CLCNF/PANi at three high current densities; gravimetric capacitance as a function of current density for CLCNF and NCLCNF; Ragone plot of supercapacitor device based on CLCNF/PANi.

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Fig. 1 (a) Schematic illustration of the preparation of CLCNF, (b) SEM image of PAN nanofiber, (c) SEM image of NCLCNF and (d) SEM image of CLCNF, the insert shows the TEM image of a cross-linked site.

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Fig. 2 Raman spectra of NCLCNF and CLCNF.

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Fig. 3 Characterization of CNF/PANi composites. (a) SEM image of NCLCNF/PANi, (b) SEM image of CLCNF/PANi, (c) FTIR spectra of CLCNF and CLCNF/PANi, (d) XPS survey spectra of CLCNF/PANi, (e) C1s spectra of CLCNF/PANi and (f) N1s spectra of CLCNF/PANi.

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Fig. 4 Electrochemical performance with three-electrode configuration in 1 mol L-1 H2SO4. (a) CV curves of CLCNF/PANi with sweeping rate ranging from 20 mV-1 s to 1000 mV s-1, (b) GCD curves of CLCNF/PANi at three high current densities, (c) gravimetric capacity as a function of current density for CLCNF/PANi and NCLCNF/PANi, and (d) EIS analysis of CLCNF/PANi and NCLCNF/PANi.

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Fig. 5 Electrochemical performance of supercapacitor device based on CLCNF/PANi in 1 mol L-1 H2SO4. (a) CV curves with sweeping rate ranging from 20 mV s-1 to 1000 mV s-1, (b) GCD curves at different current densities, (c) gravimetric capacity as a function of current density, and (d) cycle performance at a current density of 10 A g-1.

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Table 1

Positron Lifetime and Intensity for CLCNF and NCLCNF τ1 (ns)

τ2 (ns)

I1 (%)

I2 (%)

τa (ns)

CLCNF

0.1709

0.3492

41.9334

57.2083

0.2714

NCLCNF

0.1576

0.3352

50.5232

48.2724

0.2414

24