MXene-Bonded Activated Carbon as a Flexible Electrode for High

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MXene-Bonded Activated Carbon as a Flexible Electrode for High-Performance Supercapacitors Lanyong Yu, Longfeng Hu, Babak Anasori, Yi-Tao Liu, Qizhen Zhu, Peng Zhang, Yury Gogotsi, and Bin Xu ACS Energy Lett., Just Accepted Manuscript • DOI: 10.1021/acsenergylett.8b00718 • Publication Date (Web): 11 Jun 2018 Downloaded from http://pubs.acs.org on June 11, 2018

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ACS Energy Letters

MXene-Bonded Activated Carbon as a Flexible Electrode for High-Performance Supercapacitors Lanyong Yu, † Longfeng Hu, † Babak Anasori, ‡ Yi-Tao Liu, † Qizhen Zhu, † Peng Zhang, † Yury Gogotsi, *, ‡, § Bin Xu*, †

†

State Key Laboratory of Organic–Inorganic Composites, Beijing Key Laboratory of

Electrochemical Process and Technology for Materials, Beijing University of Chemical Technology, Beijing 100029, China ‡

Department of Materials Science and Engineering and A. J. Drexel Nanomaterials Institute,

Drexel University, Philadelphia, PA 19104, USA §

Key Laboratory of Physics and Technology for Advanced Batteries (Ministry of Education),

College of Physics, Jilin University, Changchun 130012, China

AUTHOR INFORMATION Corresponding Author *B. Xu. E-mail address: [email protected] Y. Gogotsi. E-mail address: [email protected]

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ABSTRACT: We report a strategy to employ 2D Ti3C2Tx MXene as a flexible, conductive, and electrochemically active binder, for one-step fabrication of MXene-bonded activated carbon as a flexible electrode for supercapacitors in organic electrolyte. In this electrode, the activated carbon particles are encapsulated between the MXene layers, eliminating the need for insulative polymer binders. MXene plays a multi-functional role in the electrode, including as a binder, a flexible backbone, a conductive additive and an additional active material. The synergetic effect of MXene and activated carbon constructs a 3D conductive network and enlarges the distance between the MXene layers, much enhancing the electrode capacitance and rate capability. In result, the flexible MXene-bonded activated carbon electrode exhibits a high capacitance of 126 F g–1 at 0.1 A g–1 and a retention of 57.9% at 100 A g–1 in organic electrolyte, which is required for developing high-performance, flexible supercapacitors.

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Recently, flexible supercapacitors have attracted great interest due to their ability to meet the requirement of modern wearable and portable electronic equipment.1-3 One of the key challenges for fabricating flexible supercapacitors is to manufacture electrodes with excellent mechanical flexibility.4,5 Although various carbon materials such as activated carbon fibers,6 carbon nanotubes,7 carbon aerogels,8 carbide derived carbon9 and graphene10,11 have been proposed as electrode materials for supercapacitors, activated carbons (ACs) are the most commonly used due to their large surface area, tunable pore size and moderate cost.12-14 However, fabricating electrodes with AC powder requires polymer binders, such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc., which usually occupy 10-25% of the electrode mass without much capacitance contribution, lowering the energy density of the devices.15,16 Moreover, the polymer binders are electrical insulators, which are adverse to the power density of supercapacitors due to the increased resistance, so the AC electrodes need a small amount of conductive additives to increase the electrical conductivity. Flexibility is another concern in the as-prepared carbon electrodes, since they are rather rigid and cannot be used in flexible supercapacitors.17-19 To compensate for this shortcoming, flexible substrates are often employed to add flexibility. The traditional flexible substrates are mainly carbon-based paper (including graphene and CNTs), textiles, sponges, and cable-type electrodes with thin conductive layers.1820

These additives have limitations, for instance, the carbon-based paper is lightweight, but

exhibits relatively low flexibility and occupies a large part of the electrode volume. In this regard, recently, we proposed a new strategy by exploring flexible binder other than flexible substrates to fabricate flexible electrodes for supercapacitors. We found reduced graphene oxide (rGO) can be used as a multi-functional conductive, flexible binder for manufacturing free-standing, flexible, high-performance supercapacitor electrodes from various


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porous carbons, through vacuum-assisted filtration of the mixture of porous carbons and graphene oxide (GO), followed by thermal reduction.21 Besides the excellent flexibility, the synergetic effect of rGO with porous carbons produces a 3D conductive network and enlarges the electrode/electrolyte interface, enhancing electrode capacitance and rate performance of the rGO-bonded film electrodes. MXenes are a large family of 2D transition metal carbides and nitrides that have been gaining a lot of interest in a variety of applications.22-26 They exhibit high electrical conductivity and flexibility, so they can compete with graphene as a flexible substrate used in both batteries27,28 and supercapacitors.29-32 Here we report a novel strategy to employ 2D Ti3C2Tx MXene as a flexible and conductive binder, thus fabricating MXene-bonded flexible carbon electrodes for supercapacitors in organic electrolyte. In this flexible electrode, the AC particles are encapsulated between the MXene layers. In this unique structural arrangement, the MXene layers provide flexibility, which is critical to the formation of the flexible electrode, and construct a 3D conductive network to facilitate the electron transport. The AC particles enlarge the distance between the MXene layers, thus ensuring easy ion and electrolyte infiltration. The resulting flexible AC/MXene electrode exhibits both high capacitance and attractive rate performance in organic electrolyte as it will discuss in this paper. Figure 1 illustrates the fabrication of AC electrode using Ti3C2Tx MXene as a flexible and conductive binder. The synthesis of Ti3C2Tx MXene flakes was described elsewhere,23 which results in a colloidal solution in water. To fabricate the free-standing, flexible film, we mixed the water-based colloidal solution of MXene flakes and AC particles uniformly and vacuum-filtered the mixture by using Celgard 3501 membranes. This procedure is simpler than the conventional paste electrode fabrication method with PVDF as the binder, which needs mixing the active


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material, conductive agent, and PVDF in an organic solvent, then coating the slurry onto aluminum foil current collectors.16 It is also simpler than our previous rGO-bonded electrode fabrication method, in which additional thermal treatment is required to reduce GO to rGO.21 As shown below, Ti3C2Tx MXene plays a multi-functional role in the MXene-bonded AC electrode, including as a binder, a flexible backbone, a conductive additive and an additional active material, thanks to its unique 2D morphology, excellent conductivity and good hydrophilicity.25

Figure 1. Schematic diagram for the fabrication of MXene-bonded AC films, including mixing MXene flakes and AC particles in water, vacuum-assistant filtration, peeling off and drying.

We used commercial AC Maxsorb-3 (Kansai Thermochemical Co., Japan) as the active material. SEM image and nitrogen sorption indicate the AC has a powdery morphology with particle size of 10-20 µm, and a developed porous structure with a surface area of 2786 m2 g–1 and pore volume of 1.64 cm3 g–1 (Figure S1). These AC particles are large and relatively rigid, and very difficult to shape into a flexible film. The Ti3C2Tx MXene has 2D nanosheet morphology with lateral size of 1~3 um, and can form densely stacked, lamellar films by


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vacuum-assistant filtration as shown in Figure S2. We prepared a series of MXene-bonded AC films by varying the mass ratio of AC to Ti3C2Tx MXene. The films mass ratios were 1:1, 2:1 and 4:1 (AC:MXene), and they were denoted as AC/MXene-1:1, AC/MXene-2:1 and AC/MXene-4:1 films, respectively, hereafter. The mass of all the films was 10 mg. As shown in Figure 2a, the MXene-bonded AC films are freestanding, flexible, and can be directly used as electrodes for supercapacitors without the metal current collector. The cross-sectional SEM images (Figure 2b-d) indicate the AC/MXene films have a lamellar structure, in which the AC particles are evenly encapsulated in a continuous MXene network with excellent conductivity and open structure to facilitate transport of electrons and ions. Figure 2e and 2f show the higher magnification cross-sectional SEM image and the corresponding EDS mapping of Ti of AC/MXene-2:1, indicating the encapsulation structure of the AC particle and MXene flakes in the AC/MXene films. Different from the densely stacked morphology of pure MXene film (Figure S2c), the AC/MXene films show much increased thickness due to their loose structure as well as the low density of the porous carbon. The film thickness increases with the increasing AC content, being ~20 µm for AC/MXene-1:1, ~26 µm for AC/MXene-2:1, and ~30 µm for AC/MXene-4:1. For comparison, the conventional PVDF-bonded electrode (AC-PVDF) was also prepared by coating the slurry of AC, carbon black (CB) conductive agent and PVDF binder with a mass ratio of 8:1:1 on aluminum foil current collectors. The mass of the AC-PVDF was controlled to the same with the AC/MXene films. The cross-sectional SEM image of the ACPVDF electrode (Figure S3) shows the AC particles and CB are glued together by the PVDF binder. However, the nano-sized CB particles are difficult to disperse evenly in the micrometersized AC particles, and can only provide point-to-point conductive contact. Moreover, the ACPVDF also shows a much closer packed structure with a thickness of ~24 µm, which is much


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smaller than that of ~30 µm for AC/MXene-4:1 with the same AC content (80%) in the film. Note that the 3D conductive network and open structure of the AC/MXene films, as well as the developed porosity of ACs are favorable for electron transfer and electrolyte infiltration, resulting in enhanced capacitive performance.

Figure 2. Digital photos of the AC/MXene-2:1 film (a), SEM images of AC/MXene-1:1 (b), AC/MXene-2:1 (c) and AC/MXene-4:1 (d) films; high-magnification SEM image of AC/MXene-2:1 film (e) and corresponding EDS mapping of Ti (f).

Figure S4 shows the XRD patterns of the AC particles, MXene film and AC/MXene films. The XRD pattern of the AC particles has a wide peak located at about 2θ = 22-26° representing the (002) diffraction and a peak at 2θ = 43° corresponding to the (100) diffraction, characteristic of amorphous carbon. The (002) peak of the MXene film appears at 2θ = 7.24°. 29 After the two components are mixed, the (002) peak of MXene in AC/MXene films becomes broad and shifts


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to smaller angles, as the AC content increases, showing that the order between the Ti3C2Tx MXene flakes is interrupted. Besides, all AC/MXene films have the broad (002) peak of AC particles. This confirms manufacturing of MXene-bonded AC films. The nitrogen (77K) adsorption/desorption test was employed to characterize the porosity of the AC/MXene films and the AC-PVDF, and the results are given in Figure S5 and Table S1. The AC particles exhibit type I adsorption/desorption isotherms indicating microporous carbon,33 while the wide knee in p/p0=0-0.3 indicates the existence of some small mesopores of ~2-3 nm, as observed in the pore size distribution curves (Figure S1c). The BET surface area and pore volume of AC particles are 2786 m2 g-1 and 1.64 cm3 g-1, respectively. Due to the dense stacking of the MXene nanosheets, the specific surface area of the MXene film is only 4.66 m2 g–1. All AC/MXene films display type I adsorption/desorption isotherms with pores distributed in 1-3 nm, very similar to the AC particles. These indicate the Ti3C2Tx MXene binder has a minimal influence on the porosity of AC. With the increase of the AC content, the BET surface area of the AC/MXene film increases, reaching up to 2090 m2 g-1 for AC/MXene-4:1. In contrast, the BET surface area of AC-PVDF is only 1607 m2 g-1, much lower than that of AC/MXene-4:1 with the same AC content (80%), confirming the pore blocking effect of PVDF binder as reported previously.15, 21 The MXene-bonded AC films possess high surface area and abundant pores within 1–3 nm. Due to the larger surface areas and abundant micropores, the capacitance and rate performance of the MXene-bonded AC films are greatly improved. The electrochemical performances of MXene-bonded AC films were evaluated in a symmetrical two-electrode capacitor. The conventional AC-PVDF electrode was also tested under the same conditions for comparison. In order to determine the working voltage window of MXene-bonded AC films in 1 mol.L-1 tetraethylammonium tetrafluoroborate/acetonitrile


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(Et4NBF4/AN) electrolyte, cyclic voltammetry (CV) curves of AC/MXene-1:1 film in different voltage ranges were measured, as shown in Figure S6a. The CV curves in 0-1 V, 0-1.5 V and 02 V show perfect rectangle shapes, indicating the AC/MXene films are electrochemical stable in the voltage range of 0-2 V. However, when the voltage cutoff increases to 2.5 V, the oxidation peak appears. In contrast, the PVDF-bonded AC electrode shows rectangular CV curves in 0-2.7 V (Figure S6b), indicating AC is stable in this voltage range. As a result, the oxidation peak in 2-2.5 V for AC/MXene-1:1 film may originate from Ti3C2Tx MXene, which cannot endure such a high voltage.34,35 Therefore, all tests were performed within a voltage window of 0-2 V to avoid oxidation reactions. The CV curves of the AC/MXene films and the AC-PVDF electrode at a scan rate of 10 mV s– 1

in 0-2 V are shown in Figure 3a, all of which have almost rectangular profiles, typical for

double layer capacitors. The galvanostatic charge–discharge (GCD) curves at 0.1 A g–1, as shown in Figure 3b, have triangular profiles without obvious voltage drop at the beginning of charge and discharge, indicating the ideal electric double layer behavior of the AC/MXene films. The specific capacitances of AC-PVDF, neat MXene film and AC/MXene films were calculated from the discharge curves at 0.1 A g–1 (Table S1). The capacitance of AC particles is 155 F g-1, which is a high value for AC due to its extremely large surface area. Since the active material AC accounts for 80 wt% of the AC-PVDF, the capacitance of the AC-PVDF electrode (excluding the mass of the Al foil current collector) is lowered to 124 F g-1. The capacitance of neat MXene film is only 17 F g-1 due to the restacked MXene layer. The capacitance of MXene-bonded AC films calculated based on the total mass of the AC/MXene films are listed in Table S1, which increases with the AC content due to the increasing BET surface area and pore volume of the AC/MXene films, i.e., 88 F g–1 for AC/MXene-1:1, 126 F g–1 for AC/MXene-2:1, and 138 F g–1


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for AC/MXene-4:1. As MXene binder has a minimal influence on the porosity of AC, the capacitance of AC in the AC/MXene films can be supposed to have no change. Therefore, the capacitances of MXene in the AC/MXene films are calculated to be 21, 68 and 70 F g-1 in the AC/MXene-1:1, AC/MXene-2:1 and AC/MXene-4:1, respectively. The much increased capacitance of MXene in the AC/MXene films can be ascribed to the enlarged distance between the MXene layers opened by AC particles. This result indicates that the MXene binder can also act as “active material”. The specific capacitance (138 F g–1) of the AC/MXene-4:1 film is the highest among the electrodes made in this study, much higher than previously reported MXene or MXene-based hybrid materials in non-aqueous electrolyte.34,35 Moreover, it is also 11.3% higher than that of the conventional PVDF-bonded AC electrode, confirming the synergistic contribution of MXene as a better binder, conductive additive and active material for improving the energy density of supercapacitor. Volumetric capacitance is also an important parameter for supercapcitors. The electrode density of AC-PVDF is 0.318 g cm-3, a common value for porous carbon with high surface area, resulting in a volumetric capacitance of 39 F cm-3. Due to the high density of MXene (3.06 g cm-3), the AC/MXene-1:1 has a much higher electrode density of 0.398 g cm-3. When the mass ratio of AC to MXene increases to 2:1 and 4:1, the electrode density of AC/MXene films decreases to 0.306 and 0.265 g cm-3 due to their loose structures as shown in Figure 2. Although the AC/MXene-2:1 and AC/MXene-4:1 films have a little lower electrode densities than that of AC-PVDF, they show comparable volumetric capacitances (38, 37 F cm-3) to that of AC-PVDF (39 F cm-3) due to their larger gravimetric capacitances. Furthermore, unlike the conventional PVDF-bonded electrode, MXene-bonded electrodes do not need metal foil current collector. By eliminating the need for a current collector, more active


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materials can be used in the whole capacitor device, making further improvement of the energy density of supercapacitors. The most important superiority of MXene-bonded electrodes lies in excellent rate performance, as MXene has metal-like conductivity. As listed in Table S1, the conductivity of pure MXene film is as high as 2500 S cm-1, while the AC-PVDF fabricated with insulative polymer PVDF as binder is only 0.3 S cm-1 even with the addition of 10% CB conductive agent. Using conductive MXene as binder, the conductivity of AC/MXene films shows increasing tendency with MXene content and reaches as high as 29-166 S cm-1, 100-500 times larger than that of AC-PVDF. Benefiting from the 3D conductive network constructed by Ti3C2Tx MXene flakes, all AC/MXene films show much enhanced rate capabilities and can withstand a high current density of 50 A g–1, better than those of the electrically insulative PVDF-bonded AC electrode, as shown in Figure 3c. The AC/MXene-2:1 film shows the best rate performance, although its capacitance (126 F g–1) is a bit lower than that of the AC/MXene-4:1 film. As the current density increases from 0.1 to 50 A g–1, the capacitance retention of the AC/MXene-2:1 film is 65.4%, which is higher than those of AC/MXene-1:1 (55.1%) and AC/MXene-4:1 (54.0%). However, since Ti3C2Tx MXene also acts as the conductive agent, one would expect that the AC/MXene-1:1 film with the higher conductivity should have better rate capability than the AC/MXene-2:1 film. This can be explained by the fact that in the AC/MXene-1:1 film the AC content is lower, which results in more restacked Ti3C2Tx MXene layers. The compact and restacked MXene layers with insufficient AC particles in between are not favorable for ion transport and electrolyte infiltration and although MXene layers have higher conductivity, this structure results in poor rate capabilities. All the AC/MXene films exhibit better rate performance than the PVDF-bonded AC electrode, which can only deliver very low capacitance at high rates (Figure 3c). The improved


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rate performances of the MXene-bonded AC films are ascribed to the 3D conductive network constructed by Ti3C2Tx MXene which has high conductivity.36 The electrochemical impedance spectroscopy (EIS) test (Figure 3d) shows a vertical line in the low frequency, indicating a capacitive behavior.37 At the high frequency, the AC-PVDF electrode exhibits the highest Ohmic resistance, and the MXene film shows the lowest Ohmic resistance, proving the excellent conductivity of the later. With MXene as conductive binder, the conductivities of the AC/MXene films are improved and the Ohmic resistance reduced. Besides, the radius of the semicircle representing the charge-transfer resistance also becomes smaller. However, the lengthened and more gradual sloping line in the high-to-medium frequency range implies a larger diffusion resistance due to the restacked MXene layers. As such, the AC/MXene-2:1 film shows relatively low Ohmic resistance and fast ion diffusion for high capacitance and good rate performance. It can be understood that MXene has excellent conductivity and the rate performance of AC electrode can be significantly improved using conductive MXene instead of electrically insulative PVDF as the binder for electrode molding.


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Figure 3. Electrochemical performance comparison of AC/MXene films and the AC-PVDF electrode in 1 mol L–1 Et4NBF4/AN. (a) CV curves at 10 mV s–1. All the plots keep a nearrectangular shape at a scan rate of 10 mV s-1, indicating double layer capacitor behavior. (b) V-t curves at 100 mA g–1..All the plots keep a triangle shape. (c) Rate capabilities. All the AC/MXene films present much better rate capability than the AC-PVDF electrode. (d) Nyquist plots with the inset of the equivalent circuit. All the AC/MXene films have much lowered Ohmic resistance and lowered charge transfer resistance than those of the AC-PVDF electrode. All the data are based on the total mass of the electrodes, excluding the aluminum foil current collector in AC-PVDF electrode.


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Further CV and GCD tests were performed to demonstrate the outstanding rate capabilities of the AC/MXene-2:1 film. As shown in Figure 4a, the AC/MXene-2:1 film can withstand ultrafast charge–discharge at a current density of 100 A g–1, and even at 400 A g–1 (Figure S7a). In contrast, the PVDF-bonded AC electrode suffers from a large voltage drop when the current density is only 75 A g–1 (Figure S7c). Although the charge–discharge time is shortened to 1.668 s, the V–t curve of the AC/MXene-2:1 film still maintains a triangular profile and the capacitance remains 71 F g–1 at the current density of 100 A g–1 with a retention ratio of 57.9% (Figure 4b), and 25.8 F g–1 at 400 A g–1 (Figure S7b), much better than that of the previously reported MXene-based materials in organic electrolytes, which could only operate at current densities below 10 A g–1.34,35 Note that the rate capability of the AC/MXene-2:1 film is also superior to some advanced flexible carbon electrode for supercapacitors, such as few-layer graphene paper,38 and the printed-reduced graphite oxide film.39 The outstanding rate capability of AC/MXene-2:1 film can be further proved by the rectangular-like CV curves at ultrafast scanning rates (Figure 4c). It is known that 1000 mV s-1 is a challenge scan rate for carbon electrodes in non-aqueous electrolytes.40 The PVDF-bonded AC electrode changes its CV curves from rectangle to spindle at a scan rate of 1000 mV s–1 (Figure S7d), although the Maxsorb-3 AC used here has developed porosity. In contrast, the CV curve of the AC/MXene-2:1 still keep a rectangle profile with a capacitance as high as 73 F g–1 when the scan rate increases to an ultrahigh value of 4000 mV s–1 (Figure 4d). To our knowledge, this is an outstanding result for a porous carbon-based electrode in organic electrolyte, superior to some carbons for high-rate supercapacitors, such as mesoporous carbon sphere arrays (71 F g-1 at 200 mV s-1) ,41 hierarchical macropore-rich activated carbon


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microspheres (30 F g-1 at 1000 mV s-1) 42 and graphene-like carbide derived carbon (59 F g-1 at 3000 mV s-1).43 Figure 4e presents a Ragone plot of the AC/MXene-2:1 film. The energy density of AC/MXene-2:1 film can reach 17.5 Wh kg–1 and can output an ultrahigh power density of 207 kW kg–1. The outstanding rate capability of the AC/MXene-2:1 film can be understood from the following two aspects: First, MXene nanosheets serving as the conductive binder can construct a 3D conductive network to facilitate quick electron transfer, while the enlarged distance between the MXene layers opened by AC particles and the 3D connected structure ensure easy ion and electrolyte infiltration, resulting in excellent rate performance. Second, the AC particles with extremely large specific surface area and the additional active material MXene with opened structure can offer a high capacitance. In addition, the AC/MXene-2:1 film exhibits a good longterm cycling stability with 92.4% capacitance retention after 10, 000 cycles at a current density of 10 A g–1 (Figure 4f). The CV curves of the AC/MXene-2:1 film at a scan rate of 20 mV s–1 after 10,000 charge-discharge cycles at 10 A g–1 (inset of Figure 4f) show only a little capacitance loss compared to the initial CV curves, confirming the excellent cycling stability of the AC/MXene-2:1 film.


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Figure 4. Electrochemical performance testing results for AC/MXene-2:1 film. (a) V-t curves at enhanced current densities. The AC/MXene-2:1 film can withstand ultrafast charge–discharge at a current density of 100 A g–1 with a very small voltage drop. (b) Rate capabilities. The AC/MXene-2:1 film presents excellent rate performance with a capacitance of 71 F g-1 at 100 A


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g-1.

(c) CV curves. The CV curves of the AC/MXene-2:1 film can maintain rectangle-like

characteristics even at an ultrahigh scan rate of 4000 mV s-1. (d) Capacitance at different scan rates. The AC/MXene-2:1 film presents a high capacitance of 73.8 F g-1 at 4000 mV s-1. (e) Ragone plots. The AC/MXene-2:1 film can output an ultrahigh power density of 207 kW kg-1 with a maximum energy density of 17.5 Wh kg-1. (f) Cyclic performance at 10 A g–1. The inset in (f) is the CV curves at a scan rate of 20 mV s–1 at initial and after 10,000 cycles at 10 A g–1. The capacitance retention of the AC/MXene-2:1 film is as high as 92.4% after 100,000 cycles at a current density of 10 A g-1, indicating good cyclic stability. All the data are based on the total mass of the AC/MXene-2:1 film.

In summary, we have demonstrated a possibility to use 2D Ti3C2Tx MXene as a flexible and conductive binder for carbon electrode fabricating for supercapacitors. In this flexible electrode, the AC particles are encapsulated between the MXene layers. On the one hand, the MXene nanosheets serving as the flexible and conductive binder provide excellent mechanical flexibility and electrical conductivity, which are critical to the formation of the flexible electrode material with superior rate performance. On the other hand, the AC particles with extremely large specific surface area and the additional active material MXene with opened structure can offer a high capacitance. As a result, the MXene-bonded flexible AC electrode exhibits a high capacitance of 126 F g–1 and excellent rate performance with 57.9% capacitance retention at 100 A g–1 in organic electrolyte, which exceed that of both pure MXene and polymer-bonded carbon films.


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ASSOCIATED CONTENT Supporting Information. Experimental methods, SEM, XRD, nitrogen adsorption and additional electrochemical data. AUTHOR INFORMATION Corresponding Authors * E-mail address: [email protected] * E-mail address: [email protected] ORCID Babak Anasori: 0000-0002-1955-253X Yury Gogotsi: 0000-0001-9423-4032 Bin Xu: 0000-0001-5177-8929 Notes The authors declare no competing financial interest. ACKNOWLEDGMENT This work was financially supported by the National Key Research and Development Program of China (2017YFB0102204) and the National Natural Science Foundation of China (NSFC, 51572011 and 21073233). YG acknowledges the Thousand Talents Program (China) (WQ20152200273)

REFERENCES


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MXene-Bonded Activated Carbon as a Flexible Electrode for High

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