supplementary materials for - science2020/07/22 · e+ and e-represent the electric field...
TRANSCRIPT
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science.sciencemag.org/content/369/6502/446/suppl/DC1
Supplementary Materials for
Anomalous absorption of electromagnetic waves by 2D transition metal
carbonitride Ti3CNTx (MXene)
Aamir Iqbal, Faisal Shahzad, Kanit Hantanasirisakul, Myung-Ki Kim, Jisung Kwon,
Junpyo Hong, Hyerim Kim, Daesin Kim, Yury Gogotsi*, Chong Min Koo*
*Corresponding author. Email: [email protected] (Y.G.); [email protected] (C.M.K.)
Published 24 July 2020, Science 369, 446 (2020)
DOI: 10.1126/science.aba7977
This PDF file includes:
Materials and Methods
Supplementary Text
Figs. S1 to S22
Table S1
References
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Materials and Methods
Materials
Ti3AlCN MAX powder with a particle size of < 38 µm was synthesized at the lab scale
following the procedure in our previous work (17). Ti3AlC2 MAX powder with a particle size of
< 38 µm was purchased from Carbon-Ukraine ltd. Lithium fluoride (LiF, 98.5%) and hydrochloric
acid (HCl, 37%) were purchased from Alfa Aesar. Polypropylene membrane (Celgard, pore size
0.064 µm) was used to obtain MXene films via vacuum-assisted filtration.
Synthesis of Ti3CNTx
Ti3CNTx was synthesized from Ti3AlCN MAX phase by following a similar route as for
Ti3C2Tx synthesis with minor modifications (1). In this synthesis protocol, Ti3AlCN was used
instead of Ti3AlC2. Briefly, 1 g of Ti3AlCN MAX was gradually added into a mixture of 20 mL
of 9 M HCl and 1.6 g of LiF in a 100 mL polypropylene bottle with continuous stirring at room
temperature for 24 h. The obtained mixture was washed with DI water 5-6 times by centrifugation
at 3500 rpm to reach pH value close to neutral. Finally, a stable well-dispersed suspension
containing single-to-few layer Ti3CNTx MXene flakes was obtained by collecting the supernatant
after centrifugation at 3500 rpm for 5 min. Free-standing films were fabricated by filtering a
measured volume of the MXene dispersion through a Celgard membrane. The thickness of the
films was controlled by the volume of the as-synthesized dispersion during vacuum filtration. The
films with different thicknesses were thermally treated in an inert environment of continuous argon
flow at different annealing temperatures of 150 °C, 250 °C, and 350 °C for 6 h.
Synthesis of Ti3C2Tx
Ti3C2Tx was synthesized from Ti3AlC2 after etching “Al” layers, as reported elsewhere (1).
All the conditions were the same as those reported for Ti3CNTx except the synthesis temperature.
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In this case, temperature was increased up to 35 °C to get higher yield from the reaction. The
obtained films (of comparable thickness) after vacuum filtration of the solution were annealed at
temperatures similar to that of Ti3CNTx.
Material Characterization
The structure and morphology of pristine and heat-treated Ti3CNTx and Ti3C2Tx films were
investigated by scanning electron microscopy (SEM, Inspect F50, FEI, USA) and transmission
electron microscopy (TEM, Tecnai F20 G2, FEI, at 200.0 kV voltage). SEM was also used to
verify the thickness measurements initially performed on a highly accurate length gauge (with a
tolerance factor of ± 0.1 µm) of Heidenhain instruments (Germany). A focused ion beam (FIB)
(Nova 600 Nanolab, FEI Company, Netherland) was used to cut the cross-section for analyzing
cross-sectional morphology of the samples with high resolution TEM images and elemental
mapping (HRTEM Talos, FEI Company, F200X). X-ray diffraction (XRD) patterns were obtained
using a D8 diffractometer with Cu-Kα radiation (40 kV and 44 mA) at a 2 theta range of 4°–70°
with a scanning step of 0.02°, a step time of 0.5 s, and a window slit of 10 × 10 mm2. Chemical
structural changes were examined using X-ray photoelectron spectroscopy (XPS, PHI 5000
VersaProbe, Ulvac-PHI, Japan) by Al Kα as the X-ray source with a power of 25 W. Simultaneous
thermogravimetric-mass spectrometry analysis (TGA-MS) was performed on a Discovery SDT
650 model connected to a Discovery mass spectrometer (TA Instruments, DE). Vacuum-filtered
films of MXenes were cut into small pieces and packed in a 90 μL alumina pan. Before heating,
the analysis chamber was flushed with helium gas at 100 mL min-1 for 1 h to reduce residual air.
The samples were heated to 350 °C at a constant heating rate of 10 °C min-1 in a He atmosphere
(100 mL min-1). Electrical conductivity of the samples was measured using an advanced four probe
(MCP-TP06P PSP) connected with Loresta-GP meter (Model MCP-T610, Mitsubishi Chemical,
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Japan). The density and porosity were calculated experimentally using the mass and volume of the
films. EMI shielding efficiencies of all the samples were measured by WR-90 rectangular
waveguide using a 2-port network analyzer (ENA5071C, Agilent Technologies, USA) after
standard calibration (using short offset, short and load on both ports) in the frequency range of 8.2-
12.4 GHz (X-band). Pristine and annealed samples were cut into rectangular dimensions of 25×12
mm2, slightly larger than that of sample holder’s opening 22.84×10.14 mm2. Samples were
mounted carefully to avoid any leakage from the edges of the waveguide and screwed tightly
before taking the final measurements.
Supplementary Text
Electromagnetic Interference (EMI) Shielding Measurements
EMI SE is the material’s ability to attenuate the energy of the incident electromagnetic waves.
When the electromagnetic radiations interact with material under test (shield), the shielding
phenomenon is governed by reflection (R), absorption (A), and transmission (T), collectively must
add up to 1, that is,
𝑅 + 𝑇 + 𝐴 = 1 (1)
The reflection (R) and transmission (T) coefficients are obtained from the network analyzer in
the form of scattering parameters, (S11, S12, S21, S22), which can be used to find the R and T
coefficients as:
𝑅 = |𝑆11|2 = |𝑆22|2 (2)
𝑇 = |𝑆21|2 = |𝑆12|2 (3)
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The total EMI SE (EMI SET) is the sum of the contributions from reflection (SER), absorption
(SEA) and multiple internal reflections (SEMR). The total SET can be written as;
𝑆𝐸𝑇 = 𝑆𝐸𝑅 + 𝑆𝐸𝐴 + 𝑆𝐸𝑀𝑅 (4)
For calculations, SEMR is generally considered negligible when SET is higher than 15 dB. SER and
SEA can be expressed in terms of reflection and absorption coefficient considering the power of
the incident electromagnetic waves inside the shielding material as;
𝑆𝐸𝑅 = 10 log (1
1−𝑅) = 10 log (
1
1−|𝑆11|2) (5)
𝑆𝐸𝐴 = 10 log (1−𝑅
𝑇) = 10 log (
1−|𝑆11|2
|𝑆21|2 ) (6)
Assuming propagation of EM waves in a nonmagnetic and highly conducting medium, the
Fresnel formula for reflection, absorption and multiple reflections, using equation 4, can be given
as (11, 31, 32):
𝑆𝐸𝑇 = 10 𝑙𝑜𝑔 (1
𝑇) = 10 𝑙𝑜𝑔 (
𝐸𝑖
𝐸𝑡)
2= 20 𝑙𝑜𝑔 |
(1+𝑁)2
4𝑁 𝑒−𝑘𝑑[1 − (
1−𝑁
1+𝑁)2 𝑒2𝑖𝑘𝑑] | (7)
where Ei and Et are incident and transmitted intensities of electric field of the EM waves,
respectively; N is the complex refractive index of the shield, k is the imaginary part of refractive
index, and d is the shield thickness. For MXenes, the complex refractive index (Nm) is given by;
𝑁m = √σ
2ωε0(1 + i), due to their excellent conductivity (5,000-10,000 S cm-1) (33).
From equation 7, the quantitative contributions from SER, SEA, and SEMR are expressed as:
𝑆𝐸𝑅 = 20 𝑙𝑜𝑔((1+𝑁)2
4|𝑁| ) = 50 + 10 𝑙𝑜𝑔(
𝜎
𝑓 ) (8)
𝑆𝐸𝐴 = 20 𝑙𝑜𝑔 𝑒−𝑘 𝑑 = 20 𝑙𝑜𝑔 𝑒𝛼𝑑 = 8.686 𝛼 𝑑 = 1.7𝑑√𝜎𝑓 (9)
𝑆𝐸𝑀𝑅 = 20 𝑙𝑜𝑔 |1 − 𝑒(2𝑖𝑘𝑑) (1−𝑁)2
(1+𝑁)2 | (10)
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In equation 9, 𝛼 is the attenuation constant indicating the ability of a material to absorb the
associated energy of the incident EM waves. Neglecting the role of multiple reflection for total
shielding efficiency higher than 15 dB, using eq. 4, 8, and 9, SET can be written as:
𝑆𝐸𝑇 = 50 + 10 𝑙𝑜𝑔 (
𝜎
𝑓) + 1.7𝑑√𝜎𝑓 (11)
This famous equation is known as Simon’s formula.
Theoretical Calculation of EMI Shielding Effectiveness
Theoretical EMI SET, SER, and SEA for Ti3CNTx, and Ti3C2Tx MXenes were calculated by transfer
matrix method (27, 28). The transfer matrix method considers analytical solution for calculating
transmission, reflection, and absorption of EM waves propagating through 2D infinite plane
interfaces and layers of known thickness. This method allows to provide an exact solution for
multiple reflections between the layers whose thickness is even much smaller than the wavelength
of the incident wave. The transfer equation for the propagation through thin N multiple layers is
expressed as follows:
(𝐸𝑡+
𝐸𝑡−) = [𝑀2 . 𝑀1]𝑁 (𝐸𝑖
+
𝐸𝑖−) = (
𝑎 𝑏𝑐 𝑑
) (𝐸𝑖+
𝐸𝑖−) (12)
where M1 and M2 are the transfer matrices for the propagation through an interface and propagation
within a layer, respectively. E+ and E- represent the electric field amplitudes of the forward and
backward EM waves in a medium, respectively.
For a homogeneous and isotropic media, M1 and M2 are expressed as:
𝑀1(𝑖,𝑗) = 1
𝑡𝑖𝑗 (
1 −𝑟𝑖𝑗
−𝑟𝑖𝑗 1), and 𝑀2 (𝑛,𝑙) = (
ɸ−1 00 ɸ
) (13)
Here, rij and tij are the complex Fresnel coefficients of reflection and transmission,
respectively, where the EM wave propagates through interface from the layer i to j. ɸ is
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represented as ɸ = 𝑒−𝑖 2𝜋
𝜆 𝑛𝑙
, where n, l are the complex refractive index and the thickness of the
layer, respectively, and λ is the wavelength of propagating EM wave in free space.
From equation (12), the reflection and transmission coefficients are calculated by:
𝑅 = −𝑐
𝑑 and 𝑇 = 𝑎 −
𝑏𝑐
𝑑 (14)
Therefore, using equation (14), SET, SER, and SEA can be expressed as:
𝑆𝐸𝑇 = 10 𝑙𝑜𝑔 (1
𝑇) = 10 𝑙𝑜𝑔 (
1
|𝑡|2) (15)
𝑆𝐸𝑅 = 10 𝑙𝑜𝑔 (1
1−𝑅) = 10 𝑙𝑜𝑔 (
1
1−|𝑟|2) (16)
𝑆𝐸𝐴 = 𝑆𝐸𝑇 − 𝑆𝐸𝑅 (17)
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Fig. S1: TEM image of monolayer Ti3CNTx MXene flake. SAED pattern in the inset confirms
the hexagonal structure.
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Fig. S2: XRD patterns of Ti3C2Tx at different annealing temperatures. Ti3C2Tx maintains the
laminate structure with decreasing d-spacing after annealing without formation of TiO2
nanocrystal.
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Fig. S3: Comparison of d-spacing values of Ti3CNTx and Ti3C2Tx MXene at different
annealing temperatures. Ti3CNTx MXene shows higher d-spacing than its counterpart due to
absorbing/desorbing more water molecules.
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Fig. S4: TGA-MS thermogram of Ti3C2Tx MXene. Thermal removal of intercalated or adsorbed
water on the surface of Ti3C2Tx MXene films.
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Fig. S5: TEM images of Ti3CNTx MXene as a function of annealing temperature. (A-C) TEM
images and (D-F) SAED patterns of the as-synthesized and annealed Ti3CNTx MXene films at
different annealing temperatures of 250 °C and 350 °C, respectively. The Ti3CNTx is resistive to
oxidation up to 250 °C. However, surface oxidation begins from 350 °C, confirmed by the
formation of TiO2 peaks in SAED pattern at 350 °C. It can be caused by water evolving from the
MXene surface.
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Fig. S6: TEM images of Ti3C2Tx MXene as a function of annealing temperature. (A-C) TEM
images and (D-F) SAED patterns of the pristine and annealed Ti3C2Tx MXene films at different
annealing temperatures of 250 ℃ and 350 ℃, respectively. The Ti3C2Tx is strongly resistive to
oxidation up to 350 ℃.
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Fig. S7: Structural morphology of Ti3CNTx MXene as a function of annealing temperature.
Cross-sectional SEM images of a 40-μm-thick Ti3CNTx MXene of (A) as-synthesized, and
annealed at different temperatures of (B) 150, (C) 250, and (D) 350 ℃. Nano to micro sized pores
are generated after annealing, which become larger as a result of increasing temperature providing
much open structure.
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Fig. S8: Structural morphology of Ti3C2Tx MXene as a function of annealing temperature.
Cross-sectional SEM images of (A) as-synthesized and annealed Ti3C2Tx MXene at different
annealing temperatures of (B) 150, (C) 250, and (D) 350 °C. The structure remains compacted
without generating significant porosity in Ti3C2Tx MXene after different annealing conditions.
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Fig. S9: Structural morphology of annealed Ti3CNTx MXene as a function of initial
thickness. Cross-sectional SEM images of Ti3CNTx MXene films annealed at 350 °C with
different initial thicknesses of (A) 10, (B) 20, (C) 30, and (D) 40 µm. It depicts that the formation
of porosity and the pore volume increases with increasing initial thickness.
Fig. S10: Dimensional stability and mechanical properties of Ti3CNTx films. (A and B) Dimensional
stability of Ti3CNTx film before and after annealing at 350 ℃ for 6 h, respectively. (C and D) Spray coated
Ti3CNTx film before and after annealing, respectively. (E and F) Flexibility of Ti3CNTx film before and
after annealing, respectively. It shows that annealed Ti3CNTx MXene films offer sufficient mechanical
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robustness along with their light weight and superb EMI SE. Dimensional stability and good adhesion allow
post-processing of MXene films on thermally stable substrates, such as glass or Si wafer. Good flexibility
makes Ti3CNTx films promising for shielding flexible portable electronics.
Fig. S11: Chemical composition analysis of the as-prepared Ti3CNTx and Ti3C2Tx MXenes.
XPS survey spectra of (A) Ti3CNTx and (B) Ti3C2Tx. The Ti3CNTx has a strong N 1s peak, unlike
the Ti3C2Tx.
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Fig. S12: Chemical composition analysis of Ti3CNTx MXene as a function of annealing
temperature. High resolution XPS spectra of (A) Ti 2p, and (B) O 1s of Ti3CNTx films annealed
at different temperatures. It confirms that the surface oxidation starts at 350 ℃.
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Fig. S13: Chemical composition analysis of Ti3C2Tx MXene as a function of annealing
temperature. High resolution XPS spectra of (A) Ti 2p, and (B) O 1s of Ti3C2Tx films annealed
at different temperatures. No oxidation is observed in the examined temperature range.
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Fig. S14: High resolution structural morphology and composition of annealed Ti3CNTx
MXene. (A) Cross-sectional TEM image of Ti3CNTx film annealed at 350 ℃ and corresponding
HRTEM images of (B) partially-oxidized surface with TiO2 formation, and (C) un-oxidized inner
part of the film.
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Fig. S15: EMI shielding measurements of Ti3CNTx and Ti3C2Tx films at different annealing
temperatures. EMI SER and SEA of (A-B) 40-μm-thick Ti3CNTx, and (C-D) Ti3C2Tx MXene films
at different annealing temperatures. It shows that SER remains constant irrespective of the
annealing temperature whereas SEA increases with the temperature for both Ti3CNTx and Ti3C2Tx
MXenes.
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Fig. S16: EMI shielding measurements of annealed Ti3CNTx and Ti3C2Tx films with
different initial thickness. EMI SET, SER, and SEA of (A-C) Ti3CNTx and (D-F) Ti3C2Tx annealed
at 350 °C with different thicknesses. It shows that SER remains constant irrespective of the initial
thickness while SET and SEA increase linearly with thickness for both Ti3CNTx and Ti3C2Tx
MXenes, the former holds dominant increment.
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Fig. S17: Comparison of change in EMI shielding effectiveness of Ti3CNTx and Ti3C2Tx films
as a function of annealing temperature. Comparison of ΔSET, ΔSER, and ΔSEA of Ti3CNTx and
Ti3C2Tx films with different thicknesses after heat treatment. (A) 10, (B) 20, and (C) 30 μm. The
absolute values for ΔSET and ΔSEA are much higher for Ti3CNTx compared to Ti3C2Tx. It
manifests that the improved EMI shielding capability is governed by improved absorption ability.
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Fig. S18: Structural analysis of Ti3CNTx films annealed at 350 °C for different annealing
time. (A) XRD patterns, and (B) porosity of 40-μm-thick Ti3CNTx films annealed at 350 °C for
different annealing times.
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Fig. S19: EMI shielding measurements of Ti3CNTx films annealed at 350 °C for different
annealing time. EMI SE: (A) SET, (B) SER, and (C) SEA, of 40 μm thick Ti3CNTx films annealed
at 350 °C for different annealing times, respectively.
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Fig. S20: Comparison between experimental and theoretical EMI SET for the as-synthesized
Ti3CNTx and Ti3C2Tx. It shows that the theoretically calculated SET values at different electrical
conductivities are consistent with the experimental measured results at room temperature. It
manifests that our simulation results are acceptable for comparison purpose.
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Fig. S21: Comparison of experimental and theoretical EMI values of Ti3CNTx films annealed
at different temperatures as a function of porosity values. EMI SE: (A) SER and (B) SEA values
for Ti3CNTx annealed at different temperatures with different conductivity and porosity. Herein,
experimental SER is consistent with the calculated values, while similar to SET in Fig. 2F, SEA is
not following the conventional shielding behavior, suggesting some other possible mechanism.
Fig. S22: Comparison of experimental and theoretical EMI values of Ti3C2Tx films annealed
at different temperatures as a function of porosity values. EMI SE: (A) SET, (B) SER, and (C)
SEA for Ti3C2Tx annealed at different temperatures with different conductivity and porosity. The
experimental data matches well with the conventional theoretical calculations.
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Table S1. EMI SE of various shielding materials. T
yp
e
Filler Filler
Matrix Thickness EMI SE
Ref [wt.%] [cm] [dB]
Gra
ph
ene
and
gra
ph
ite
Graphene Bulk / 0.005 60 (34)
Graphene Bulk / 8.40 10-4 20 (3)
Graphene(annealed) Bulk / 0.006 90 (35)
Graphene /CNTs Bulk / 0.16 38 (36)
Graphene /CNTs Bulk / 0.16 36 (37)
rGO 7 PS 0.25 45.1 (38)
rGO 30 PS 0.25 29 (39)
rGO 25 PEDOT:PSS 0.08 70 (40)
rGO 3.07 PDMS 0.2 54.2 (41)
Graphene 0.8 PDMS 0.1 20 (6)
rGO/ Fe3O4 10 PEI 0.25 18 (42)
rGO 10 PEI 0.23 12.8 (43)
rGO 16 PI 0.08 21 (44)
rGO 1 PU 0.25 23 (45)
rGO 3 Epoxy 0.1 38 (46)
rGO/ Fe3O4 Bulk / 0.03 24 (47)
PEDOT:PSS 4.6 rGO 0.15 91.9 (48)
EG 98
HANF 0.006 60.4
(49) 90 0.006 47.4
Car
bo
n (
fib
res
/ n
ano
tubes
)
Carbon / Bulk 1 51 (50)
Carbon / PN resin 0.2 51.2 (51)
Carbon foam / Bulk 0.2 40 (52)
CB 15 ABS 0.11 20 (8)
SWCNT 30 MWCNT 0.013 65 (53)
SWCNT 15 Epoxy 0.1 20 (9)
SWCNT 7 PS 0.12 18.5 (54)
MWCNT 25 MCMB 0.06 56 (55)
MWCNT 15 ABS 0.11 50 (8)
MWCNT 20 PC 0.21 39 (56)
MWCNT 20 PS 0.2 30 (57)
MWCNT 76.2 WPU 0.1 21.1 (58)
CNT 20 rGO 0.0015 57.6 (59)
CNT sponge 1 PDMS 0.18 54.8 (60)
Met
als
Al Foil Bulk /
0.80 10-3 66 (1)
Cu Foil 0.001 70
CuNi Bulk /
0.15 25 (61)
CuNi-CNT 0.15 54.6
Copper Bulk / 0.31 90 (62)
Cu coated beads / PCL 0.2 110 (63)
Ni filament 7 PES 0.285 86.6 (64)
Ag nanowire 67 Carbon 0.3 70.1 (65)
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Ag nanowire 28.6 WPU 0.23 64 (66)
Ag nanowire 4.5 PI 0.5 35 (67)
Ag nanowire 4.5 PI 0.5 35 (34)
Ag nanofiber / Bulk 0.01 76
(68) 0.10 10-3 20
SS Bulk / 0.4 89 (64)
SS 1.1 PP 0.31 48 (62)
Oth
ers
Carbon Foam Bulk / 0.2 51.2 (51)
Carbon Foam Bulk / 0.2 40 (52)
Flexible graphite Bulk / 0.31 130
(69) 0.079 102
MoS2 30 Glass 0.15 24.2 (70)
rGO/γ-Fe2O3 75 PANI 0.25 51 (71)
rGO/Fe3O4 66 PANI 0.25 30 (72)
rGO/Fe3O4 Bulk / 0.025 24 (47)
rGO/CNT/Fe3O4 Bulk / 0.2 37.5 (73)
rGO-BaTiO3 Bulk / 0.15 41.7 (74)
MX
enes
(li
tera
ture
dat
a)
Ti3C2Tx film Bulk /
0.15 10-3 48
(1)
0.25 10-3 54
0.60 10-3 59
1.12 10-3 68
2.15 10-3 78
4.0 10-3 87
4.50 10-3 92
Ti3C2Tx film 90 SA 0.80 10-3 57 (1)
Mo2Ti2C3Tx film Bulk /
0.25 10-3 26 (1)
Mo2TiC2Tx film 0.25 10-3 23
MXene foam Bulk /
6.00 10-3 70
(12) 1.80 10-3 50
0.60 10-3 32
Ti3C2Tx
50
cellulose
16.7 10-3 25
(4) 80 7.40 10-3 26
90 4.70 10-3 24
TiO2-Ti3C2/graphene / /
9.17 10-4 27
(75) 7.82 10-4 23.4
5.59 10-4 23.3
5.25 10-4 18
Ti3C2/SWCNT / PVA/PSS
2.07 10-5 3.39 (5)
Ti3C2/MWCNT 1.70 10-5 2.81
Ti3C2Tx aerogel
Bulk /
0.10 44.8
(14) Ti2CTx aerogel 0.10 48.5
Ti3CNTx aerogel 0.10 42.3
Ti2CTx
Bulk
/ 1.1 10-3 50
(2) V2CTx / 1.2 10-3 46
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Nb2CTx / 1.0 10-3 15 TiyNb2-yCTx / 1.4 10-3 50
NbyV2-yCTx / 1.2 10-3 36
Ti3C2Tx / 1.4 10-3 70
Ti3CNTx / 1.0 10-3 55
Mo2TiC2Tx / 1.0 10-3 21
Nb4C3Tx / 1.1 10-3 26
Mo2Ti2C3Tx / 1.3 10-3 37
Ti3C2Tx ultrathin film Bulk / 5.5 10-6 20 (7)
MX
enes
(th
is w
ork
)
*Pristine Ti3C2Tx Bulk /
0.001 66.5
This
work
0.002 74.6
0.003 77.9
0.004 83.5
*Heat-treated Ti3C2Tx Bulk /
0.001 74.1
0.002 81.1
0.003 85.2
0.004 93.0
*Pristine Ti3CNTx Bulk /
0.001 43.5
0.002 47.9
0.003 53.3
0.004 61.4
*Heat-treated Ti3CNTx Bulk /
0.001 75.1
0.002 83.0
0.003 97.1
0.004 116.2
* CNT: carbon nanotube; rGO: reduced graphene oxide; EG: expanded graphite; CB: carbon black;
SWCNT: single-wall carbon nanotube; MWCNT: multi-wall carbon nanotube; PS: polystyrene;
PEDOT:PSS: poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate); PEI: polyethylenimine; PI:
polyimide; PU: polyurethane; WPU: water-borne polyurethane; HANF: hydrated aramid nanofiber;
MCMB: meso-carbon microbead; ABS: acrylonitrile-butadiene-styrene; PDMS; polydimethylsiloxane;
PCL: poly(ε-caprolactone); PES: polyethersulfone; PP: polypropylene; PANI: polyaniline; PN resin:
phthalonitrile resin; PC: polycarbonate; PVA/PSS: poly(vinyl alcohol)/poly(sodium 4-styrene sulfonate);
SS: stainless steel; SA: sodium alginate.
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