RGO Composite for High

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Two-dimensional titanium carbide/RGO composite for high-performance supercapacitors Chongjun Zhao, Qian Wang, Huang Zhang, Stefano Passerini, and Xiuzhen Qian ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b04767 • Publication Date (Web): 03 Jun 2016 Downloaded from http://pubs.acs.org on June 4, 2016

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ACS Applied Materials & Interfaces

Two-dimensional titanium carbide/RGO composite for high-performance supercapacitors Chongjun Zhaoa*, Qian Wanga, Huang Zhangb,c**, Stefano Passerinib,c, Xiuzhen Qiana a

School of Materials Science and Engineering, East China University of Science and

Technology, Shanghai 200237, P.R. China. b

Helmholtz Institute Ulm, Helmholtzstrasse 11, D-89081 Ulm, Germany.

c

Karlsruhe Institute of Technology, PO Box 3640, D-76021 Karlsruhe, Germany.

Corresponding author

*Tel: +86-21-6425 0838; E-mail: [email protected] **Tel: +49 (0) 731 5034119; E-mail: [email protected]

ACS Paragon Plus Environment

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ABSTRACT Ti3C2Tx, a 2D titanium carbide in the MXenes family, is obtained from Ti3AlC2 through selectively etching of Al layer. Due to its good conductivity and high volumetric capacitance, Ti3C2Tx is regarded as one promising candidate for supercapacitors. In this paper, the fabrication of Ti3C2Tx/RGO composites with different proportions of Ti3C2Tx and RGO is reported, in which RGO act as conductive “bridge” to connect different Ti3C2Tx blocks, and matrix to alleviate the volume change during charge/discharge process. In addition, RGO nanosheets can serve as a second nanoscale current collector and support as well for the electrode. The electrochemical performance of the as-fabricated Ti3C2Tx/RGO electrodes, characterized by CV, GCD, and EIS, are also reported. A highest specific capacitance (Cs) of 154.3 F/g at 2 A/g is obtained at the Ti3C2Tx : RGO weight ratio of 7 : 1 combined with an outstanding capacity retention (124.7 F/g) after 6000 cycles at 4 A/g. KEYWORDS: Ti3C2Tx, MXene, 2D material, Reduced graphene oxide (RGO), Supercapacitors


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1. INTRODUCTION The rapid growth of energy demands and gradual attention to globally environmental issues are calling for a pressing exploration for new clean energies as well as the energy storage systems (ESS).1-4 Supercapacitors, known as electrochemical capacitors (EC), are among the ideal candidates for portable digital products and electric vehicles as the efficient energy storage and supply systems, owning to the high power density, fast recharge ability, long cycle-life, environment-friendliness and so on.5, 6 In view of the different working mechanisms, there are two types of ECs being distinguished, namely, electrical double-layer capacitor (EDLC) and pseudocapacitor. EDLC stores energies in the double layers by highly reversible and fast ion adsorption on the surface of electrodes, while the latter makes use of fast and reversible Faradic reactions.7-9 Both in these two systems, the electrode materials are key ingredients enabling the high performance of supercapacitors. In this case, many kinds of materials have been investigated as electrodes, such as activated carbon,10 metal oxides (hydroxide)/sulfide,11,

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conducting polymers13, etc, and extensive investigations have been devoted to exploiting new electrode materials to improve the specific capacitance performance of the EC systems. Recently, the importance of another group of 2D materials MXenes, viz. early transition metal carbides and/or carbonitrides, has been highly addressed in the application of energy storage systems, which benefit from the good electrical conductivities and hydrophilic surfaces.14-18 The MXenes can be achieved by selectively removing ‘A’ layers in MAX phases, where ‘M’ represents a group of early transition metals, ‘A’ is one of III or IV A-group elements and ‘X’ is carbon and/or nitrogen. This synthesis would yield electrically conductive MXenes with –F and –OH/=O terminated surface which can be formulated as Mn+1XnTx (T represents surface termination (=O, –OH, and/or –F) and x is the number of termination groups).16 So far, the


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MXenes family includes Ti2CTx, (Ti0.5, Nb0.5)2CTx, Nb2CTx, Ti3CNTx, V2CTx, Ti3C2Tx, (V0.5, Cr0.5)3C2Tx, Ta4C3Tx, and Nb4C3Tx, among which Ti3C2Tx is the most intensively studied.15 Some theoretical and experimental studies have already demonstrated that this kind of materials are potentially promising as electrode materials for batteries, metal ion (Li+, Na+) capacitors and supercapacitors.18-22 Lukatskaya et al. reported that binder-free Ti3C2Tx paper showed a capacitance in excess of 300 F/cm3 at 20 mV/s in potassium hydroxide (KOH) aqueous electrolyte.18 Ghidiu et al. also tested the electrochemical performance of rolled Ti3C2Tx clay as electrode in 1 M sulfuric acid (H2SO4). Capacitance value of 900 F/cm3 at 2 mV/s and superior rate capability were observed.23 Meanwhile, Ling et al. showed that Ti3C2Tx/polymer films exhibit intriguing volumetric capacitance in KOH electrolyte, specifically, 528 F/cm3 at a scan rate of 2 mV/s, and 306 F/cm3 at 100 mV/s.24 Zhao et al. proposed a facial approach to fabricate flexible MXene/CNT composites with sandwich structure, which possess a high capacitance of 150 F/g at 2 mV/s, and 117 F/g at 200 mV/s. The latter value is about 130% higher than that offered by Ti3C2Tx paper at the same rate.25 However, there are still some challenges in the application of Ti3C2Tx. For instance, the contact between the Ti3C2Tx blocks is loose due to the uneven size caused by the different numbers of titanium carbide layers, which compromises its electrochemical performance because of the incomplete utilization of Ti3C2Tx blocks. In addition, the volume changes of Ti3C2Tx during the charge/discharge process in alkali hydroxide electrolyte also will limit the cycling stability of as-fabricated electrode. Graphene, another important 2D material, due to its intrinsic features of high electronic conductivity (~16000 S/m), large specific surface area (~2630 m2/g) and superior mechanical properties, is often considered as an important coadjutant to achieve higher performance of electrode materials.26-28 In previous works, we have found that reduced graphene oxide (RGO)


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acts as an important component in strengthening the electrochemical performance of transition metal oxides (hydroxides)/sulfides (Cu2O, Co3O4, MnO2, Ni(OH)2, Ni3S2).12, 29-34 Hence, it is expectable that introducing RGO into pure Ti3C2Tx can improve the electrochemical performance of as-fabricated electrodes. In this paper, Ti3C2Tx/RGO composite electrodes were fabricated by introducing RGO into MXenes with the hope that RGO nanosheets would act as conductive “bridges” to connect different blocks of Ti3C2Tx. The undersized Ti3C2Tx in composite without adding RGO leads to low utilization. However, Ti3C2Tx lying on the introduced soft and flexible RGO nanosheets can improve contact and thus smooth electronic transfer process to the current collector, which significantly improves supercapacitor performance of the electrode. Also, flexible graphene may serve as matrix for alleviating potential volume changes from intercalation of cations, particularly in the long-term cycling test. Besides, RGO nanosheets could also act as a second nanoscale current collector supporting electronic conductivity in electrodes. As a matter of this fact, we demonstrate that the Ti3C2Tx/RGO composite electrode (Ti3C2Tx: RGO = 7 : 1) shows a highest specific capacitance and best cycle stability.

2. EXPERIMENTAL SECTION 2.1 Synthesis of graphene oxides and MAX phase Ti3AlC2 Graphene oxides (GO) were synthesized via a modified Hummers method using pristine graphite powders as raw materials.35, 36 Detailed preparation process was given in supporting information. The MAX phase Ti3AlC2 was synthesized by mixing commercial Ti2AlC (Kanthal Corporation, Sweden) powders with TiC (Sigma-Aldrich, Belgium) in a 1 : 1 molar ratio followed by


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calcination at 1350 °C for 2 h under flowing argon. After ball-milling for 4 h in ethanol, the Ti3AlC2 powders were obtained (after drying). 2.2 Synthesis of RGO and Ti3C2Tx RGO was reduced from GO by a simple hydrothermal process. Typically, 50 mg GO powders were dispersed in 50 mL deionized water and ultrasonicated for 1 h to obtain a transparent suspension. After aging for 30 min under magnetic stirring, the suspension was transferred into a stainless steel Teflon-lined autoclave (100 ml) and heated at 180 °C for 8 h. The final product was obtained after repeatedly washing with water and ethanol followed a vacuum drying at 80 °C for 10 h. The MXene materials were obtained by etching the Al from the above synthesized MAX phase materials.14, 23 In a typical single-step process, stoichiometric amount of MAX phase material (Ti3AlC2 powder) was dispersed in 6 M HCl (Merck, Belgium) solution, and then the LiF (Sigma-Aldrich, Belgium) powder was slowly added into the suspension until the white LiF powders totally dissolved. After that, the black suspension was moved into a plastic bottle, sealed and heated in a water bath at 50 °C for 48 h under magnetic stirring. At last, the product was collected by centrifuging and repeatedly washing with deionized water till the pH value of supernatant reached around 5. The final MXene powder was obtained after dried at 80 °C for 10 h. 2.3 Preparation of Ti3C2Tx, RGO and Ti3C2Tx/RGO composite electrodes The typical synthesis procedure of Ti3C2Tx/RGO composite electrode is as it follows: RGO powder was firstly dispersed in ethanol (30 mL) by ultrasound. A selected amount of Ti3C2Tx powder was then mixed with RGO solution. After 1h, the composite was separated from the solvent through filtration, and then washed thoroughly with water, filtered and dried at 80 °C for


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12 h. Different composites were obtained by adjusting the weight ratio of Ti3C2Tx/RGO to 3, 5, 7, and 9, denoted as Ti3C2Tx/RGO-3, Ti3C2Tx/RGO-5, Ti3C2Tx/RGO-7, and Ti3C2Tx/RGO-9, respectively. For the fabrication of electrode, the as-prepared samples as active materials were mixed with conductive carbon black (Super P, Imerys, France), and polyvinylidene fluoride (PVDF, Arkema Inc., Philadelphia, USA) at a weight ratio of 8 : 1 : 1. The resulting slurries were pasted on stainless steel mesh current collectors with an area of 1× 1 cm2 and dried in a vacuum oven at 80 °

C for 8 h. Different electrodes were obtained with the different Ti3C2Tx/RGO ratios. Pure

Ti3C2Tx and RGO electrodes were also accordingly prepared. Mass loading is 3.2, 3.7, 2.0, 2.2, 2.1 and 1.5 mg for Ti3C2Tx, Ti3C2Tx/RGO-9, Ti3C2Tx/RGO-7, Ti3C2Tx/RGO-5, Ti3C2Tx/RGO-3 and pure RGO electrode respectively. 2.4 Materials characterization XRD patterns of all samples were measured on an X-ray diffractometer ( Cu Kα, λ = 0.15406 nm, RIGAKU, D/MAX 2550V, Japan). Raman spectra were performed using an Raman microprobe (inVia, Renishaw Instruments, Wotton under Edge, England) with a 514 nm laser excitation line. The morphology was monitored by FESEM (Hitachi, S-4800, Japan), and the structure was confirmed by TEM (JEOL, JEM-2100, Japan). The elementary compositions of the composites were characterized by EDS (Bruker AXS, Quantax 400-30, Germany). 2.5 Electrochemical measurements All the electrochemical performances were measured in typical three-electrode cells in 2 M KOH electrolyte using the as-prepared electrodes as working electrode, a Pt foil (2 × 3 cm2) as counter electrode and a commercial SCE as reference electrode, respectively. Before the electrochemical measurements, a pretreatment process was carried out by immersing working


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electrodes in the KOH solution for 24 h. CV, GCD, and EIS were conducted on an electrochemical workstation (CHI660e, Chenhua Instruments, Shanghai, China). EIS were carried out in 100 KHz ~ 0.01 Hz using a sinusoidal signal of 5 mV at open circuit potential. The discharge specific capacitances of tested electrodes were calculated via eq 1,37

∆

(1)

∆

where Cs is specific capacitance (F/g), m is mass of active materials in electrode (g), ∆U is actual potential window in the discharge process (V), I is applied current (A) and ∆t is the discharge time (s).

3 RESULTS AND DISCUSSION

Figure 1. XRD patterns of Ti3AlC2, Ti3C2Tx and Ti3C2Tx/RGO-7 composite Figure 1 presents the XRD patterns of Ti3AlC2, Ti3C2Tx and Ti3C2Tx/RGO-7 composite. Peaks at 2θ values of 9.5°, 19.2°, 34.0°, 36.8°, 39.0°, 41.8°, 44.9°, 48.5°, 52.4°, 56.5° and 60.3° are


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assigned to the (002), (004), (101), (103), (104), (105), (106), (107), (108), (109) and (110) planes of pure Ti3AlC2 respectively, according to JCPDS No. 52-087516, 38. It can be seen in the XRD patterns that the crystallinity and structural order of Ti3AlC2 decrease after LiF/HCl treatment. As reported, the characteristic (002) peak at 9.5° 2θ in the Ti3AlC2 is broadened and obviously shifted to a much lower value, which results from the larger d-spacing and can be explained by the structural expansion from etching and substitution of Al with –F and –OH/=O terminating groups. The most intense peak at 2θ=39° nearly disappeared, confirming the removal of Al layers from Ti3AlC2 in a more convincible way.38, 39 In the Ti3C2Tx/RGO-7 pattern, there is a weak peak at 24.8°, which belongs to RGO.

Figure 2. Raman spectra of GO, Ti3AlC2, Ti3C2Tx and Ti3C2Tx/RGO-7 composite Raman spectra recorded for selected samples are presented in Figure 2. The peaks between 200 and 700 cm-1 almost vanished after LiF/HCl treatment, which results from the structural deterioration and loss of crystallinity already evidenced from the XRD results.16,

40

In the

spectrum of Ti3C2Tx/RGO-7 composite, two legible Raman scattering peaks at 1358 cm-1 (D


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band) and 1597 cm-1 (G band) can be observed, which is always regarded as an evidence of graphene existence. Accordingly, ID : IG is usually calculated to semi-quantitatively illustrate the reduction level of graphene oxides.41 Compared with pure GO (0.81), a high D/G ratio (1.1) is obtained for the Ti3C2Tx/RGO-7 composite, indicating that RGO was in a deeply reduced state from the hydrothermal method.

Figure 3. EDS images of Ti3C2Tx: (a) C, (b) Al, (c) O, (d) Cl, (e) Ti, (f) F, (g) overlay of C, Al, O, Cl, Ti and F.


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The EDS mapping of Ti3C2Tx (Figure 3) confirms that the Al atoms are mostly etched and substituted by the introduced O, F and Cl groups. The presence of the latter can be explained by the termination of exposed Ti-surfaces groups after the removal of Al.42 Figure 4a exhibits FESEM image of Ti3AlC2, having smooth surfaces, but uneven sizes. The larger Ti3AlC2 is about 14 µm while the smaller one is only about 1 µm. After LiF/HCl treatment, a layered structure due to the removal of Al from Ti3AlC2 is evident. Most delightful, the 2D structure of Ti3C2Tx (Figure 4b) looks pretty much like that of exfoliated transition metal oxides or, even, graphite.

Figure 4. FESEM images of (a) Ti3AlC2, (b) Ti3C2Tx, (c) enlarged view of (b), (d) Ti3C2Tx/RGO-7 composite. Figure 4c is a high magnification FESEM image of Figure 4b. Such typically layered structure could improve the contact of electrode with electrolyte and be beneficial to the ion transport,


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resulting in better pseudocapacitance performance.43 The introduction of RGO further modifies the composite sample morphology. As shown in Figure 4d, in fact, the RGO nanosheets in the composite act as conductive “bridge” and nanoscale collector for electron transfer.30, 34 TEM was used to further investigate the microstructure of the as-synthesized composite in detail (Figure 5a and b). The result in Figure 5a shows that some smaller Ti3C2Tx are loaded on the large graphene sheets and a structure of restacked Ti3C2Tx MXene sheets can be recognized from Figure 5b, which is in good accordance with the FESEM images.

Figure 5. HRTEM (a) and TEM (b) images of Ti3C2Tx/RGO-7 composite Figure 6a and b show the CV and GCD curves of all electrodes, respectively. The almost rectangular shape of the CV profiles (Figure 6a) for all electrodes indicates a high reversibility of capacitive behavior.44 All the CV curves in Figure 6a show no peaks, which reveal that the electrodes performed as pseudocapacitances over the complete voltammetric cycle. The faradaic process of layered Ti3C2Tx in potassium hydroxide solution can be described as eq 2,37 Ti C T K e K Ti C T

(2)


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Figure 6. Electrochemical performance of RGO,Ti3C2Tx and Ti3C2Tx/RGO electrodes. (a) CV curves at 20 mV/s; (b) GCD curves at 2 A/g As show in Figure 6b, the charge and discharge profiles of all electrodes at 2 A/g are nearly linear with minor IR drop (Table S1), demonstrating the excellent capacitive performance of the composite material and concerting well with the CV curves. As the pure Ti3C2Tx electrode exhibits a higher specific capacitance than pure RGO, it is easy to understand that the specific capacitances of Ti3C2Tx/RGO composite increase with adding some Ti3C2Tx in the composite (from 3:1 to 7:1). However, with much more Ti3C2Tx (Ti3C2Tx:RGO/9:1), the specific capacitance of Ti3C2Tx/RGO composite drops. It is comprehensive that the RGO, acting as support and bridge for active materials, is inadequate to prevent all Ti3C2Tx from aggregation, which may induce more inefficient utilization of active materials and thus lower the electrochemical capacity. Therefore, the Ti3C2Tx/RGO-7 electrode exhibits the best performance, corresponding to the highest specific capacitance (154.3 F/g at 2 A/g). Table 1 lists the specific capacitances of all electrodes as obtained at various current densities. From the table it is seen that the Ti3C2Tx/RGO-7 composite offers always the best performance independent on the applied current density. Effect of Ti3C2Tx content on the capability in our work is consistent with


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Yan’s.38 Performance comparisons of Ti3C2Tx/RGO-7 electrode with other work is listed in Table S2. It is worth to note that ultrasonic treatment (1h) during the preparation process also plays a key role to fabricate high performance materials, and the Ti3C2Tx/RGO mixture prepared only by grinding at the same ratio with Ti3C2Tx/RGO-7 exhibits a smaller specific capacitance than the ultrasonic one which is similar to the pure Ti3C2Tx, as shown in Figure S1. Table 1. Cs at various current densities Specific capacitance (F/g)

The content of RGO

1 A/g

2 A/g

3 A/g

4 A/g

5 A/g

Ti3C2Tx

0%

135.5

123.0

115.5

108.0

101.7

Ti3C2Tx/RGO-9

10.0 %

142.7

141.7

137.0

132.0

126.7

Ti3C2Tx/RGO-7

12.5 %

154.3

154.3

151.0

146.7

141.7

Ti3C2Tx/RGO-5

16.7 %

142.9

142.7

138.0

133.3

128.3

Ti3C2Tx/RGO-3

25.0 %

129.0

128.0

126.0

122.0

116.7

RGO

100.0 %

129.5

99.7

87.0

76.0

45.8

Samples

Figure 7. Electrochemical performances of Ti3C2Tx/RGO-7 electrodes. (a) CV curves at various scan rates; (b) GCD curves at various current densities


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Figure 7a presents the CV curves of Ti3C2Tx/RGO-7 electrode at different scan rates. When the scan rate is higher than 50 mV/s, the curves remain no longer the standard rectangular shape, possibly because the diffusion of K+, especially inside the MXene structure according to eq 2, is limited. In addition, an immersion process in electrolyte is necessary before measurement, for those electrodes without immersion process possess a low electrochemical capacitance and an improvement during the initial cycles, e.g., 50 cycles, as shown in Figure S2. Figure 7b shows the GCD curves at different current densities. Even at a higher current density of 6 A/g, the coulombic efficiency remains 96.5%.

Figure 8. Rate (a) and cycling performance (b) of RGO and Ti3C2Tx-based electrodes The specific capacitance change with increasing scan rates is shown in Figure 8a, from which it can be observed as the capacitance retention is significantly improved with the introduction of RGO. The best performance is achieved using the Ti3C2Tx/RGO-7 electrode, offering the outstanding Cs of 138 F/g at 6 A/g. Cyclic stability curves at constant current density of 4 A/g are illustrated for all the samples in Figure 8b. After 6000 cycles the Ti3C2Tx/RGO-7 electrode still maintains a Cs of 124.7 F/g (corresponding to 85% of capacity retention).


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To further elucidate the electrochemical performance of these composite materials, EIS was performed. Figure 9 presents the Nyquist plot of all electrodes. All the electrodes’ spectra are consisted of a semicircle and a straight line in the high-middle frequency and low frequency regions, respectively, which correspond to the charge-transfer process (Rct) at the electrode/electrolyte interface and charge-accumulation in the electrode solid phase of Ti3C2Tx, respectively. The intercept of this last feature with the real axis (Zˈ) is regarded as equivalent series resistance (ESR, Table S1), including intrinsic resistance of the active material and current collector (Re), the diffusion resistance of the electrolyte (Rdiff), and the contact resistance at the interface of electrode and electrolyte (Rcont).37, 42

Figure 9. EIS spectra of all electrodes (100 kHz ~ 0.01 Hz). Inset is the magnification of the high frequency region.


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From the incorporation of large specific surface area of RGO and electric active sites of MXene in the composite, the obtained material exhibited highly enhanced electronic/ionic transport abilities and super-capacitance from the synergetic contribution of both double-layer and faradaic capacitances.45 It can be observed in the spectra that all the samples have a nearly vertical line in the low-frequency region, reflecting the fast ion diffusion in Ti3C2Tx/RGO bulk phase and ideally capacitive behavior of the electrodes.30,32 Ti3C2Tx/RGO-7 electrode has a relatively low ESR and Rct value (0.81 and 2.08 Ω, respectively), implying that the charge transfer and ion diffusion are much easier than other electrodes during the electrochemical reactions.

Figure 10. Plots of imaginary capacitance versus frequency for all electrodes Figure 10 presents the imaginary capacitance vs. frequency plot. The imaginary capacitance was calculated based on eq 3,46


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C'' =

Z'

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(3)

2πf |Z|2

where Cʺ means the imaginary part of the capacitance, f is the frequency, Zʹ is the real part of the impedance, Z is the electrochemical impedance. The imaginary part of the capacitance reaches a maximum value at a frequency f0, defining a time constant as τ0 = 1/f0.47 As seen in the inset of Figure 10, τ0 are 6.8s, 12.9s, 8.2s, 10s, 8.2s, 82.5s for Ti3C2Tx, Ti3C2Tx/RGO-9, Ti3C2Tx/RGO-7, Ti3C2Tx/RGO-5, Ti3C2Tx/RGO-3 and pure RGO electrode, respectively. This means that Ti3C2Tx/RGO-7 electrode can deliver its stored energy faster than other composite electrodes except the pure Ti3C2Tx. In other words, it makes Ti3C2Tx/RGO-7 electrode more appropriate for power capacitor. Phase angle versus frequency plot was given in Figure S3. It can be clearly seen that in low frequency, the phase angles of all electrodes are close to 90°, which indicates an ideal capacitor at low frequency range.48

4 CONCLUSIONS Composite Ti3C2Tx/RGO electrodes comprising 2D highly conductive Ti3C2Tx nanosheets, prepared by a LiF/HCl treatment, and various amounts of RGO were synthesized and tested as supercapacitor electrode materials. Ti3C2Tx/RGO-7 electrodes deliver the highest capacitance of 154.3 F/g at 2 A/g and 138 F/g at a rate as high as 6 A/g. In addition, the fabricated electrodes exhibit superior cyclability, with capacity retention of 85% after 6,000 cycles. We believe that these results represent a breakthrough in MXene-based materials, which can significantly prompt their rapid development and applications in supercapacitors.


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ACKNOWLEDGEMENT: We are grateful for the Shanghai Natural Science Foundation (13ZR1411900). H.Z. acknowledges the financial support from Chinese State Scholarship Fund (201408310121). SUPPORTING INFORMATION Materials and reagents; synthesis of graphene oxides; CV curves for Ti3C2Tx/RGO-7, Ti3C2Tx/RGO-7-grind and Ti3C2Tx electrodes; cycling performance of Ti3C2Tx/RGO-7 and Ti3C2Tx/RGO-7-no immersion electrodes; phase angle Bode plot of all electrodes; ESR values from Nyquist plots and IR drop of all the electrodes; performance comparisons with other work. "This material is available free of charge via the Internet at http://pubs.acs.org." REFERENCES (1) Zhang, L. L.; Zhao, X. S. Carbon-Based Materials as Supercapacitor Electrodes. Chem. Soc. Rev. 2009, 38, 2520-2531. (2) Zhai, Y. P.; Dou, Y. Q.; Zhao, D. Y.; Fulvio, P. F.; Mayes, R. T.; Dai, S. Carbon Materials for Chemical Capacitive Energy Storage. Adv. Mater. 2011, 23, 4828-4850. (3) Liu, C.; Li, F.; Ma, L. P.; Cheng, H. M. Advanced Materials for Energy Storage. Adv. Mater.2010, 22, E28-62. (4) Wang, G. P.; Zhang, L.; Zhang, J. J. A Review of Electrode Materials for Electrochemical Supercapacitors. Chem. Soc. Rev. 2012, 41, 797-828. (5) Miller, J. R.; Simon, P. Electrochemical Capacitors forEnergy Management. Science 2008, 321, 651-652. (6) Simon, P.; Gogotsi, Y.; Dunn, B. Where Do Batteries Endand Supercapacitors Begin? Science 2014, 343, 1210-1211. (7) Wei, W. F.; Cui, X. W.; Chen, W. X.; Ivey, D. G. Manganese Oxide-Based Materials as Electrochemical Supercapacitor Electrodes. Chem. Soc. Rev. 2011, 40, 1697-1721. (8) Inagaki, M.; Konno, H.; Tanaike, O. Carbon Materials for Electrochemical Capacitors. J. Power Sources 2010, 195, 7880-7903.


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For Table of contents use only

Ti3C2Tx/RGO composite electrode was successfully synthesized through a facile method. A highest specific capacitance of 154.3 F/g at 2 A/g was obtained when the weight ratio of Ti3C2Tx to RGO is 7 : 1, and it still retained 124.7 F/g even after 6000 cycles at 4 A/g.


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RGO Composite for High

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