Enhancing Electrochemical Performance of Graphene Fiber-Based

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Enhancing electrochemical performance of graphene fiber-based supercapacitors by plasma treatment Jie Meng, Wenqi Nie, Kun Zhang, Fujun Xu, Xin Ding, Shiren Wang, and Yiping Qiu ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b04438 • Publication Date (Web): 30 Mar 2018 Downloaded from http://pubs.acs.org on March 30, 2018

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ACS Applied Materials & Interfaces

Enhancing

electrochemical

performance

of

graphene

fiber-based

supercapacitors by plasma treatment Jie Meng1,2, Wenqi Nie1,2, Kun Zhang1,2*, Fujun Xu1,2, Xin Ding1,2, Shiren Wang3, Yiping Qiu1,2,4 1

Key Laboratory of Textile Science & Technology (Donghua University), Ministry of Education,

Shanghai 201620, PR China 2

3

College of Textiles, Donghua University, Shanghai 201620, PR China Department of Industrial and Systems Engineering, Texas A&M University, College Station, TX

77843, United States 4

College of Textiles and Apparel, Quanzhou Normal University, Fujian 362000, PR China

*Corresponding author. E-mail: [email protected]

Abstract Graphene fiber-based supercapacitors (GFSCs) hold high power density, fast charge/discharge rate, ultralong cycling life, exceptional mechanical/electrical properties and safe operation conditions, making them very promising to power small wearable electronics. However, the electrochemical performance is still limited by the severe stacking of graphene sheets, hydrophobicity of graphene fiber and complex preparation process. In this work, we develop a facile but robust strategy to easily enhance electrochemical properties of all-solid-state GFSCs by simple plasma treatment. We find that one-minute plasma treatment under ambient condition result in 33.1% enhancement of areal specific capacitance (36.25 mF/cm2) in comparison to the as-prepared GFSC. The energy density reaches 0.80 µWh/cm2 in PVA/H2SO4 gel 1

ACS Paragon Plus Environment

ACS Applied Materials & Interfaces 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

electrolyte and 18.12 µWh/cm2 in PVDF/EMIMBF4 electrolyte which is 22 times of that of as-prepared ones. The plasma treated GFSCs also exhibit ultrahigh rate capability (69.13% for 40 s plasma-treated ones) and superior cycle stability (96.14% capacitance retention after 20000 cycles for 1 min plasma-treated ones). This plasma strategy can be extended to mass-manufacture high-performance carbonaceous FSCs, such as graphene and carbon nanotube-based ones. Keywords: plasma, graphene fiber, supercapacitor, energy density, cycle stability Introduction In recent years, wearable energy conversion, storage devices and systems have attracted more and more attentions.1 Great efforts have been made in supercapacitors,2 solar cells,3 thermoelectric devices4-6 and rechargeable batteries.7 Among them, fiber-based supercapacitors (FSCs) are very promising due to their tiny volume, high power density, long cycle life, short charge/discharge time and safe operation conditions.8-11 In comparison to pseudocapacitors, carbonaceous FSCs (i.e. graphene based FSCs) possess high rate capability and ultralong cycle life thanks to the typical electrical double layer capacitive (EDLC) behavior. The ion transport and storage in FSCs are strongly associated with the specific surface area (SSA), accessible pore size distribution and the wettability of electrodes in electrolyte.12-13 Because of its extraordinary mechanical/electrical properties and high theoretical SSA (~2620 m2/g).14-15 graphene offers great potentials for FSCs. However, practical applications are still suffered from the ultralow specific capacitance and energy density. This is 2


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assigned to the low SSA and improper pore size distribution. Very limited amount of graphene layers in graphene fibers contributes to the ion transport and storage. Due to graphene stacking, the lamellar structure along radical direction makes ions inaccessible and results in ultralong ion transport path. The ion transport is further reduced as graphene fiber gets thicker. Moreover, the hydrophobicity of graphene fiber makes it unfavorable for electrolyte penetration and adsorption, greatly limiting the interface between active materials and solvent.16 Therefore, fabricating porous graphene fibers with good wettability can provide sufficient ion transport channels and improve the active interfacial area for enhanced electrochemical (EC) performance.17 Many efforts have been made toward high-EC-performance GFSCs. A type of sheath-core graphene sponge@graphene fiber was prepared by electrochemically electrolyzing graphene oxide (GO) on graphene fiber in aqueous GO suspension. The GFSC demonstrates areal specific capacitance up to 1.2-1.7 mF/cm2, with the areal energy and power density of 0.04–0.17 µWh/cm2 and 6–100 µW/cm2, respectively.18 Hydrothermally reduced graphene oxide (rGO) nanosheets based FSC using Na2MoO4/polymer gel electrolyte shows a areal capacitance of 38.2 mF/cm2 and areal energy density of 5.3 µWh/cm2, respectively.19 Graphene/active carbon based FSCs show volumetric specific capacitance of 27.6 F/cm3, good cyclability with 90.4% retention after 10,000 cycles and good bendability with 96.8% retention after bending 1,000 times.20 A conformal Ni layer and rGO film were successively coated on the surface of common polyester yarns, the resultant symmetric yarn supercapacitor 3



achieved the areal specific capacitance of 72.1 mF/cm2 and stable cycling performances (96% for 10 000 cycles).21 Hierarchically mesoporous structured MnO2 nanowire（40 wt%）graphene hybrid fibers were fabricated，the FSC exhibits a volumetric capacitance of 66.1 F/cm3，excellent cycling stability of 96% capacitance retention after 10,000 cycles, high energy and power density at 5.8 mWh/cm3 and 0.51 W/cm3, respectively.22 Although significant progress has been made, facile and strategy for mass production of FSCs are still highly in need. Herein, we develop a scalable, fast and green but robust plasma method to fabricate graphene fibers with high SSA, tunable pore size distribution and high hydrophilicity without deteriorating their tensile properties (similar tensile strength but large elongation). Plasma can tune the intrinsic properties of carbon materials by rapidly and uniformly modifying the surface energy and morphology of graphene layers under physical and chemical interactions,23-24 including CNTs,25-26 graphite27 and graphene.28-32 The plasma treatment can not only change the surface roughness,33-38 but also introduce additional oxygen-contained groups which should be favorable for better wettability.23, 39 In this work, we report that one-minute air plasma treatment on graphene fibers leads to enhanced areal specific capacitance (36.25 mF/cm2) and energy density (18.12 µWh/cm2) of graphene fiber based supercapacitors, which is 22 times of that of GFSCs based on as-prepared graphene fibers. Experimental Graphite was purchased from Nanjing Xianfeng Nano, China. Potassium 4


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permanganate (KMnO4), anhydrous ethanol, polyvinyl alcohol 1788 (PVA), hydrogen peroxide (H2O2) and calcium chloride (CaCl2) were purchased from Shanghai Lingfeng Chemical reagent Co., Ltd., China. Sulfuric acid (H2SO4, 98 wt%) and hydrochloric acid (HCl, 38 wt%) were purchased from Kunshan Jingke Microelectronics Material Co., Ltd., China. Phosphoric acid (H3PO4, 85 wt%), DMF (N,N-Dimethylformamide) were purchased from Sinopharm Chemical Reagent Co., Ltd., China. Polyvinylidene fluoride-co-hexafluoropropylene (PVDF) was purchased from Sigma-Aldrich. 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4) was purchased from Titan. The materials were used as received without further purification. Deionized (DI) water was made with Master-Q15 (Resistivity ~ 18.3 MΩ*cm). Preparation of graphene oxide and graphene fiber Graphene oxide was made according to the reported literature.40-41 Graphene oxide dispersion was injected into the coagulation bath by syringe with an inner diameter of 260 µm. The coagulation bath contains 5 wt% CaCl2 in ethanol (volume ratio of ethanol to water is 1:3). Then continuous GO fibers were drawn out from the coagulation with roller under the infrared drying condition, then washed by DI water and ethanol, and winded onto a PTFE winder. The obtained graphene oxide fibers were dried in tension, followed by drying at 60 oC for 4 h in a vacuum oven. Graphene oxide fibers were reduced by the thermal annealing method at the temperature of 800 oC. Graphene oxide fibers were heated from room temperature to 300 oC at a rate of 10 oC/min and kept at the temperature for 30 minutes to reduce the 5



graphene oxide fibers partly. The partly reduced graphene oxide fibers were heated up to 800 oC at a rate of 4 oC/min and maintained at this temperature for 3 h. It is noted that the thermal annealing process was under the protection of high-purity nitrogen. The reduced graphene oxide fibers were washed by DI water and dried at room temperature. Plasma treated with reduced graphene fiber The graphene fibers were straightened on a self-made glass support, which was placed in the middle of the plasma chamber (Harrick plasma, Ithaca, NY) at 20W RF power, so that the fibers can be treated comprehensively with the plasma. Graphene fibers were treated with air plasma in ambient condition for a series of duration times (10 s, 20 s, 40 s, 1 min, 2 min, 3 min and 5 min). Preparation of all-solid-state GFSCs The PVA/H2SO4 gel electrolyte was prepared with the following method. Briefly, 1 g of PVA powder was added to mixture of 10 mL of deionized water. Subsequently, the mixture was heated to 90 oC under vigorous stirring for 30 min until the solution clarified. After cooling down to room temperature, 1 g of H2SO4 solution was added and stirred thoroughly. The organic electrolyte was prepared with the following steps: 189 mg polyvinylidene fluoride-co-hexafluoropropylene (PVDF) was added into 10 ml DMF and stirred for 1 hour, then 1.98 g 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4) was added in. The assembled GFSC on flexible PET substrate consists of two parallel graphene fiber electrodes and electrolyte in between. Characterizations 6


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Scanning electron microscope (SEM) of graphene fibers were obtained with low-/high-resolution scanning electron microscope (SEM, HITACHI, TM3000 and SU5000). Fourier transform infrared spectroscopy (FTIR) was tested with a Nicolet NEXUS-670. The wettability and contact angles of graphene fibers were conducted with a video-based optical contact angle measurement system (OCA 40 Micro, DataPhysics, Germany). The mechanical properties were recorded using the single fiber tension tester (XQ-2, Shanghai New Fiber Instrument). The electrical conductivities were measured with Keithley 2400 source-meter. The plasma treatment was performed on a Harrick cleaner (PDC-32G-2, Ithaca, NY). Raman spectra were collected with a Raman spectrometer using an excitation wavelength of 532 nm (inVia-Reflex). Electrochemistry test and BET results were calculated according to the paper as our group published before.42 Results and discussion

7



Figure 1. Schematic illustration exhibits the preparation method of graphene fiber and plasma treatment.

Figure 1 shows the roadmap of fabricating plasma-treated graphene fibers. The graphene oxide fiber (GOF) was wet-spun with the large graphene oxide (LGO) dispersion, and subsequently reduced by thermal annealing at high temperature. The resultant graphene fibers (GF) were straightened and placed on a glass support for further plasma treatment. Finally, two plasma treated graphene fibers (PGF) were placed in parallel and the PVA/H2SO4 gel electrolyte was casted between the fiber electrodes to form the GFSC.

8


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Figure 2. SEM images of graphene fiber and plasma-treated graphene fiber. (a) The cross-sectional image of as-prepared graphene fiber. (b) The surface image of as-prepared graphene fiber. (c) The cross-sectional image of plasma-treated graphene fiber (1 min). (d) The surface image of plasma-treated graphene fiber. The as-prepared graphene fiber and plasma-treated graphene fiber were first characterized by scanning electron microscopy (SEM). Figure 2a and 2c are typical cross-sectional images of as-prepared and 1 min plasma-treated graphene fiber, respectively. The fiber is formed with graphene layers closely wrapped and stacked together with a diameter of ~31 µm. Figure 2b and 2d exhibit the surface image of control and plasma-treated graphene fibers, respectively. Typical rough and winkled surface in graphene fiber can be seen in both types, which may contribute to the SSA 9



of graphene fibers. Moreover, it is hard to detect significant differences of their surface morphology between as-prepared and plasma-treated graphene fibers.

Figure 3. Electrochemical performance of as-prepared graphene fiber and plasma-treated graphene fibers with different treated time. (a) CV curves at a scan rate of 5 mV/s. (b) The GCD curves at a current density of 0.1 mA/cm2. (c) Specific capacitance of as-prepared graphene fiber and plasma-treated graphene fiber at different current densities obtained from GCD tests. (d) Ragone plot of GFSCs under different plasma treatments. The electrochemical properties of resultant GFSCs are summarized in Figure 3. As shown in Figure 3a, all the CV curves demonstrate rectangular-like shape and a rapid current response to voltage reversal at each end potential, indicating the typical behavior of electrical double layer capacitor.43 Among them, the plasma-treated

10


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graphene fibers with 40 s and 1 min show the largest CV areas compared with other graphene fibers (10 s, 20 s, 2 min, 3 min and 5 min), confirming the fiber electrode has better charge storage capability. Figure 3b shows the galvanostatic charge-discharge (GCD) behaviors of all samples at current density 0.1 mA/cm2. It is obvious that all curves show triangular shape with negligible electrode-potential drop (IR drop) for as-prepared graphene fiber (37.7 mV) and plasma-treated graphene fiber electrodes (9.2 mV, 10.2 mV, 8.1 mV, 18.8 mV, 17.5 mV, 33.8 mV, 27.6 mV for 10 s, 20 s, 40 s, 1 min, 2 min, 3 min and 5 min, respectively). This is probably owing to the low ion-transport resistance and short diffusion distance, which is beneficial to the charge storage capability for FSCs.44 The discharge time for as-prepared graphene fiber and plasma-treated graphene fibers are 106 s, 114.6 s, 119.6 s, 143.1 s, 144.9 s, 73.8 s, 49.3 s and 32.5 s for 10 s, 20 s, 40 s, 1 min, 2 min, 3 min and 5 min treatment, respectively. It is noteworthy that 1 min-plasma-treated graphene fiber possesses excellent symmetry and the longest discharge time which may result in higher CA than others. In addition, the charge curves of plasma-treated graphene fibers are symmetric to their corresponding discharge counterparts, demonstrating the high reversibility of GFSCs and the rapid charge transport between fiber electrodes. Figure 3c shows the areal specific capacitance CA based on GCD curves relative to the current density from 0.1 to 1 mA/cm2. The as-prepared graphene fiber based supercapacitors exhibit 26.55 mF/cm2 at 0.1 mA/cm2 which is comparable to reported values in literature.21, 45-46 Plasma treatment leads to higher CA up to 36.25 mF/cm2 for 11



1 min plasma treatment. This areal CA is 21 folds of that of sheath-core graphene sponge@graphene fiber (1.2-1.7 mF/cm2),18 41.8% higher than the as-prepared graphene fiber (21.1 mF/cm2),42 10.1% higher than that of hybrid GFSC based on MnO2/graphene core–sheath fiber and CNT/graphene fiber (32.6 mF/cm2),45 22 folds of that of FSC based on ZnO nanowires and graphene (1.6 mF/cm2),47 82 times of CVD graphene fiber (443 µF/cm2).15 However, longstanding plasma treatment can deteriorate the electrochemical performance of graphene fiber. For instance, 5 min plasma-treated graphene fiber-based supercapacitors shows the lowest specific capacitance of 8.13 mF/cm2, which is even much lower than that of as-prepared graphene fiber based ones. Moreover, it can be found that the plasma treatment can also enhance the rate capability of graphene fiber based supercapacitors. The 40 s plasma-treated sample holds the highest the capacitance retention of 69.18%, while further increasing the plasma treatment time dramatically deteriorates the capacitance retention. Figure 3d displays the Ragone plots for all GFSCs. The areal energy density increases to 0.80 µWh/cm2 for 1 min plasma-treated graphene fiber-based supercapacitor in PVA/H2SO4 gel electrolyte, which is 29% higher than that of as-prepared graphene fiber based supercapacitor (0.62 µWh/cm2). The energy density of all GFSCs follows a downtrend with respect to the power density. Interestingly, the 40 s plasma-treated GFSCs shows relatively flat EA-PA curve with the best energy density retention of 69.18%, while the rate capability of as-prepared GFSC (21.70%) is much worse than it. 12


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Figure 4. (a) Nitrogen adsorption–desorption isotherm and (b) pore-size distribution of as-prepared graphene fiber and 1 min plasma-treated graphene fiber. (c) Different pore volume percentages of as-prepared graphene fiber and 1 min plasma-treated graphene fiber. (d) Optical microscopic images of water droplet on graphene fibers to determine contact angles. (left) the as-prepared graphene fiber; (right) plasma-treated graphene fiber. (e) Electrical conductivities of graphene fiber with different plasma treated times. (f) Nyquist plots from the EIS test for graphene fiber and plasma-treated graphene fiber. 13



To uncover the effect of plasma on the electrochemical enhancement of graphene fiber based supercapacitors, we conducted a series of characterizations, including BET, contact angle, electrical conductivity measurements and EIS test. The pore characteristics of plasma-treated graphene fibers were characterized by N2 absorption/desorption isotherm test. Figure 4a shows typical Type IV isotherms and mesoporous structures. The specific surface area (SSA) of 1 min plasma-treated graphene fiber is 253.32 m2/g, which is higher than that of as-prepared graphene fiber (221.05 m2/g). It should be notified that the 1 min plasma-treated graphene fibers are from the same batch as as-prepared graphene fibers. So, it suggests that the 1 min plasma treatment indeed increases the SSA of graphene fibers. Further analysis by plotting the pore size distribution (Figure 4b) and pore volume percentages (Figure 4c) provides more detailed information. As shown in Figure 4b, the 1 min plasma-treated graphene fiber shows a pore size distribution with 20.75% micropores, 70.66% mesopores and 10.84% macropores, while the as-prepared graphene fiber consists of 13% micropores, 86.14% mesopores and 3.1% macropores. It is clearly that the micro-porosity (20.75%) in 1 min plasma-treated graphene fiber is significantly improved as compared to as-prepared graphene fibers (13%). As we know, nanoporous carbons including micropores (0-2 nm) to mesopores (2-50 nm) are essential to the ion storage in carbonaceous materials.13 Micropores enhance the ion storage while mesoporous walls shorten ion pathways.48-49 More importantly, subnanometer pores (1 min) further increases, the electrochemical 15



performance of GFSCs (Figure 3) decreases dramatically, this should be related with the impropriate pore size distribution and suppressed electrical conductivity of graphene fiber electrodes probably due to the destruction of graphene fibers. Long plasma exposure will damage the graphitization of graphene layers, leading to reduced electrical conductivity and mechanical properties (Figure S1a). In Figure 4e, as the plasma treatment time is less than 1 min, the electrical conductivity slightly decreases from 35 S/cm (as-prepared graphene fiber) to ~25-30 S/cm for 1 min plasma treated graphene fiber. As the plasma treatment time further increases, the electrical conductivity is severely reduced to ~5-10 S/cm. Additionally, the mechanical properties of plasma treated graphene fibers (Figure S1a) are well retained after 40 s and 1 min plasma exposure, however, overlong exposure damages the tensile properties of graphene fibers. Figure S1e shows the Raman spectra of graphene fiber as control and 1 min plasma treated graphene fiber. Two obvious peaks at 1350 cm-1 and 1582 cm-1 characteristic of D and G bands coming from carbon materials clearly appear for both control graphene fiber and 1 min plasma treated graphene fiber. The D band intensity demonstrates the defect of the crystalline region. The G band stands for the regular sp2 carbon networks. The intensity ratio ID/IG is widely used for characterizing the defect quantity in graphitic materials.51-52 The intensity ratio ID/IG was increased from 1.013 to 1.203 after plasma treatment, demonstrating that the graphene fiber was effectively etched by plasma. Consequently, it can be stated that the plasma treatment has a synergistic effect on improving the electrochemical properties of graphene fiber-based supercapacitors 16


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by tuning the pore size distribution with higher micro-porosity and enhancing the wettability in PVA/H2SO4 gel electrolyte.

Figure 5. Comparison of the areal (a) and volumetric (b) Ragone plots of our GFSCs with other fiber-based supercapacitors. Figure 5a shows the comparison of the areal energy densities and power densities of GFSCs in our work with other fiber-based supercapacitors based on SWCNTs/PANi, GF/3D-G and SWCNTs. 1 min plasma-treated GFSC exhibits the energy density of 0.80 µWh/cm2 in PVA/H2SO4 gel electrolyte as the areal power density is 0.02 mW/cm2. It is 9 times of that of SWCNTs yarn based FSC (0.09 µWh/cm2), 2 folds of SWCNTs/PANi based FSC (0.4 µWh/cm2),53 80 times of CVD-grown graphene fiber (0.0039 to 0.010 µWh/cm2),15 4 times of GF@3D-G supercapacitor

(0.04-0.17

µWh/cm2).18

We

further

applied

1

M

1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4)/polyvinylidene fluoride (PVDF)/N, N-dimethylformamide (DMF) gel electrolyte) to further increase the energy density by enlarging the working voltage.42 It shows high energy density (18.12 µWh/cm2) in organic gel electrolyte at a scanning rate of 5 mV/s, which is 22

17



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times higher than that in PVA/H2SO4 electrolyte. In figure 5b, the volumetric energy density was 0.895 mWh/cm3 in PVA/H2SO4 electrolyte, which is even comparable to RGO/MnO2/PPy

yarn

based

supercapacitor

(1.1

mWh/cm3),54

similar

to

PPy/RGO/MWCNT fiber based supercapacitor (0.94 mWh/cm3),55 lower than rGO/CNC hybrid fiber based supercapacitor (5.1 mWh/cm3),56 194 folds of wire shaped supercapacitor with CVD growth of graphene (0.0046 mWh/cm3).15 Specifically, it is worthy noted that the 1 min plasma treated GFSC exhibits extraordinary volumetric energy density of 10.296 mWh/cm3 in organic electrolyte.

Figure 6. (a) CV curves of the 1 min plasma-treated GFSC under bending. (b) GCD curves of the 1 min plasma-treated GFSC under different bending angles. (c) Digital photos of four pieces of 1 min plasma-treated GFSCs connected in-series after connected to LED. (d) Cycle stability of the 1 min plasma-treated GFSC.

18


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To verify the feasibility of our GFSCs in practice, we tested a GFSC system by assembling four pieces of 1 min plasma-treated GFSCs in-series. It was found that the CV (Figure 6a) and GCD (Figure 6b) curves of the as-assemble 1 min-GFSC under different bending angles are well maintained with very similar shape, suggesting its excellent flexibility. As shown in Figure 6c, the integrated GFSC can successfully power up a single piece of LED (Figure 6c), which has never been done by as-prepared GFSC. In Figure 6d, the assembled GFSC also exhibits excellent cycling performance with 96.1% capacitance retention after 20,000 GCD cycles, suggesting its outstanding stability with a long cycle life. Conclusions In summary, we report a very simple, green, fast but robust plasma treatment method to manufacture graphene fiber-based supercapacitors with high energy density (0.80 µWh/cm2 in PVA/H2SO4 gel electrolyte, 18.12 µWh/cm2 in PVDF/EMIMBF4 based gel electrolyte) in large scale. The ultrafast plasma treatment is found to enhance the electrochemical performance of GFSCs by simultaneously tuning the pore size distribution with high micro-porosity and enhancing hydrophilicity of graphene fiber electrodes. Compared to as-prepared GFSCs, the 1 min plasma-treated GFSC shows 33.1% higher specific capacitance (36.25 mF/cm2) at a current density of 0.1 mA/cm2 in PVA/H2SO4 electrolyte and very stable tensile property. The plasma-treated GFSCs also exhibit excellent cycling stability and flexibility. Acknowledgements We are grateful to the funding supports from the “DHU Distinguished Young 19



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Professor Program”, Key Laboratory of Textile Science & Technology (Donghua University), Ministry of Education (KLTST201606), the National Natural Science Foundation

of

China

(No.51603036),

and

Young Elite Scientists Sponsorship Program by CAST (2017QNRC001). We also acknowledge Prof. Ying Ma at the Donghua University for her technical support and helpful discussion on plasma treatment. Supporting Information Supporting Information Available: Typical stress–strain curve and FTIR spectra of as-prepared graphene fiber and plasma-treated graphene fiber. Digital photos of four pieces of 1 min plasma-treated GFSCs connected in-series. CV curves of GFSC devices in PVDF/EMIMBF4 electrolyte. Raman spectra of graphene fiber as control and 1 min plasma treated graphene fiber. XPS spectra of GOF (graphene oxide fiber) and 300-GOF (the graphene oxide fiber after 300 oC thermal reduction). References (1) Hu, Y.; Cheng, H.; Zhao, F.; Chen, N.; Jiang, L.; Feng, Z.; Qu, L. All-In-One Graphene

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Wet spinning

LGO PGF

Electrolyte Assembly

Plasma treatment

Silver PET substrate

PGF

Thermal annealing

GF


GOF

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b

a

20 μm

c

30 μm

d

30 μm

20 μm


ACS Applied Materials & Interfaces 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


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Porous graphene fiber


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Enhancing Electrochemical Performance of Graphene Fiber-Based

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