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: gogotsi@drexel.edu (Y.G.); koo@kist.re.kr (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

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.

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,

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)

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)

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

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)

Fig. S1: TEM image of monolayer Ti3CNTx MXene flake. SAED pattern in the inset confirms

the hexagonal structure.

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.

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.

Fig. S4: TGA-MS thermogram of Ti3C2Tx MXene. Thermal removal of intercalated or adsorbed

water on the surface of Ti3C2Tx MXene films.

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.

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 ℃.

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.

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.

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

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.

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 ℃.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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)

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

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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