Wearable Thermoelectric Devices Based on Au-Decorated Two

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Functional Inorganic Materials and Devices

Wearable Thermoelectric Device Based on Au Decorated Two-Dimensional MoS

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Yang Guo, Chaochao Dun, Junwei Xu, Peiyun Li, Wenxiao Huang, Jiuke Mu, Chengyi Hou, Corey A Hewitt, Qinghong Zhang, Yaogang Li, David L. Carroll, and Hongzhi Wang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b10720 • Publication Date (Web): 07 Sep 2018 Downloaded from http://pubs.acs.org on September 8, 2018

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ACS Applied Materials & Interfaces

Wearable Thermoelectric Device Based on Au Decorated Two-Dimensional MoS2 Yang Guo ac, Chaochao Dun c, Junwei Xu c, Peiyun Li d, Wenxiao Huang c, Jiuke Mu a, Chengyi Hou a, Corey A. Hewitt c, Qinghong Zhang b, Yaogang Li b*, David L. Carroll c*, Hongzhi Wang a

a

*

State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, College of

Materials Science and Engineering, Donghua University, Shanghai 201620, People’s Republic of China. b

Engineering Research Center of Advanced Glasses Manufacturing Technology, Ministry of

Education, Donghua University, Shanghai 201620, People’s Republic of China. c

Center for Nanotechnology and Molecular Materials, Department of Physics, Wake Forest

University, Winston-Salem, North Carolina 27109, United States. d

Department of Physics, Wake Forest University, Winston-Salem, North Carolina 27109, United

States. *Corresponding Author: Tel: +86-21-67792881; Fax: +86-21-67792855. E-mail address: [email protected] (H. Wang), [email protected] (D. Carroll), [email protected] (Y. Li).

ACS Paragon Plus Environment

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KEYWORDS: wearable, flexible thermoelectric, fabric-based device, two-dimensional MoS2, Au decoration ABSTRACT: Two-dimensional materials have recently opened a new avenue to flexible thermoelectric materials with enhanced performance due to their unique electronic transport properties. Here, we report a feasible approach to improve the thermoelectric performance of transition metal dichalcogenides by effectively decorating two-dimensional MoS2 with Au nanoparticles using in-situ growth. The present Au decorated MoS2 assembled heterojunction system shows a certain decoupled phenomenon, i.e., the Seebeck coefficient and conductivity increased simultaneously. This is due to the occurrence of p-type doping of the MoS2 2H phase and injection energy filtering of dopant-originated carriers around the local band bending at the interface. The composite flexible films can achieve a power factor value of 166.3 µWm−1K−2 at room temperature, which have great potential for harvesting human body heat. 1. INTRODUCTION Wearable electronics such as smart watches, Google glass, smart clothing, etc. have been increasingly ubiquitous in our lives performing various functions including monitoring, personal thermal management,1-5 entertainment, and healthcare etc.6,7 Powering them using renewable energy resources is a pressing need for eliminating frequent charging. As a continual heat source, the human body has a potential to be an energy source since heat loss accounts for 40-60% by infrared radiation even at rest.8 From this viewpoint, flexible thermoelectric (TE) materials present a desired solution for harvesting body heat.9-13 Two-dimensional (2D) materials have provide a new avenue to flexible TE materials as they can be easily assembled.14-16 Recently, 2D transition-metal dichalcogenides such as molybdenum disulphide (MoS2), have shown great promise in numerous applications including field effect


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transistors,17,18 electrochemical storage in supercapacitors19 and lithium-ion batteries,20 photoluminescence,21,22 electrochemical catalysis,23,24 sensors,25,26 etc. due to the fact that it is as modifiable as graphene.27 The crystal structure of MoS2 has a semiconducting 2H phase and a metallic 1T phase, where the latter possesses a high conductivity (σ) and has potential to be used in TE applications. For preparing macroscopic metallic 1T phase films, however, the 2H phase (a semiconducting polymorph with a high resistance of almost 107 times the 1T phase) was inevitably introduced and accounted for about 30% of the film.27,28 Therefore, only a few works related to the thermal energy harvesting potential of 2D MoS2 have been reported due to the low σ of the 2H phase.28,29 Herein, we report an approach for improving the related TE performance by effectively decorating 2D MoS2 with Au nanoparticles using in-situ growth and the prototype of a TE device used for wearable human body energy harvesting. The device construction is a wrist band which is based on fabric and consists of five p-type strips. Compared to the intrinsic MoS2, the Au decorated MoS2 (Au-MoS2) composite films can achieve a power factor (σS2) of 166.3 µW m−1 K−2 at room temperature, which is mainly attribute to the synchronously enhanced σ and Seebeck coefficient (S). This work using metal nanoparticle decorated 2D MoS2 (which could be extended to other 2D transition metal dichalcogenides) is utilized to improve the performance of flexible TE materials. 2. EXPERIMENTAL SECTION Synthesis of Au-MoS2 hybrid nanomaterials: Typically, the 2D MoS2 nanosheets were prepared by lithium intercalation using 400 mg bulk MoS2 powder with 8 mL n-Butyl Lithium, which diluted by 25 mL n-hexane in a flask reactor with reflux and reacted at 70 °C for 48 h to obtain Li-intercalated MoS2. The resulting gray brown dispersions were centrifuged and washed


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with n-hexane at least six times. The precipitates of LixMoS2 were dispersed in 50 mL deionized water and sonicated for 1 h. Subsequently, the resultant was centrifuged to remove the unexfoliated powder at 2000 rpm for 15 min and then a taupe dispersion of HxMoS2 nanosheets was obtained. The dispersion of HxMoS2 nanosheets was diluted by 200 mL deionized water and sonicated for 3 h for the following experiments. Au-MoS2 hybrid nanosheets were fabricated according to previous report.30 Briefly, 50 mL dispersion was added to a glass vial containing 5 mL of 1 mM ascorbic acid aqueous solution. The mixed dispersion was sonicated for 15 min, and a gradient volume of HAuCl4·4H2O was added to obtain the Au decorated 2D MoS2 nanosheets with gradient increases of Au concentrations (nominal amount 0, 5.6 wt%, 16.7 wt%, and 27.9 wt %). Assembly of Au-MoS2 hybrid composites into macroscopical films: The resulting solution of Au-MoS2 was filtered under vacuum to form a homogeneous flexible film over cellulose membranes with pores of 0.22 µm. The films thickness can be controlled by adjusting the solution volume of Au-MoS2 nanosheets. Fabrication of the flexible TE device: The fabric was made with five rectangular holes with the size of 6 mm × 1 mm. The Au-MoS2 hybrid film was cut into strips of 5 mm × 45 mm, crossed into the holes in the fabric, and fixed on two sides with copper adhesive tape. The strips were connected by commercial metal yarn. All the joints were connected by silver gel to enforce the connection. Characterization and measurements: X-ray diffraction (XRD) was performed on a Bruker D2 Phaser with Cu Kα radiation (λ=1.54178 Å). Transmission electron microscopy (TEM) images were obtained on a JEOL-2100 transmission electron microscope at an accelerating voltage of 100 kV. High resolution transmission electron microscopy (HRTEM) images and the


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selected area electron diffraction (SAED) images were taken on a JEM 2010F microscope. The scanning electron microscope (SEM) images of Au-MoS2 nanocomposites based flexible films were obtained on a JEOL JSM-6330F. X-ray photoelectron spectroscopy (XPS) measurements were acquired on a Perkin-Elmer XPS system. The hall measurement was determined on an HMS-3000. The S was measured by using a custom-built apparatus. The σ was carried out with a typical 4-probe technique, which is based on the formula: σ= L (RSπ)-1 ln2, where R is the resistance, L and S are the length and cross section of the samples respectively. The factor (π1

ln2) is the standard correction term for the 4-probe technique.

3. RESULTS AND DISCUSSION Figure 1a shows a schematic illustration of the preparation process of the flexible TE device, including preparation of Au-MoS2 nanomaterials, fabrication of TE films, and assembly of the device. Specifically, MoS2 nanosheets were obtained by chemical exfoliation of an intermediate precursor Li-intercalated MoS2 (LixMoS2) through a forced hydrogen incorporation process.31 After the dispersion of 2D MoS2 in deionized water, Au nanocrystals were synthesized in-situ on surface of the 2D MoS2. The Au-MoS2 hybrid nanomaterials with gradient Au concentrations were selectively controlled by the different volume of gold (III) chloride tetrahydrate (HAuCl4·4H2O) to obtain the decorated 2D MoS2 with nominal Au amounts of 0, 5.6 wt%, 16.7 wt%, and 27.9 wt%, which are denoted as MoS2, Au-MoS2-5.6 wt%, Au-MoS2-16.7 wt%, and Au-MoS2-27.9 wt%, respectively. The Au-MoS2 hybrid flexible films were prepared by restacking the suspended decorated 2D MoS2 using a vacuum filtration technique. The details of the fabrication of the flexible TE device mainly included three steps: I) Making rectangular holes in the substrate of the fabric; II) fixing


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the active materials of Au-MoS2 strips with copper adhesive; III) connecting the strips with commercial metal yarn, as shown in Figure 1b.

Figure 1. Fabrication of the flexible TE device. (a) Bulk MoS2 was first Lithium intercalated into LixMoS2. HxMoS2 was then formed by an ultrasonication process after immersion in deionized water, where the 2D MoS2 was stably dispersed in water. Au-MoS2 hybrid nanomaterials were formed by growing Au nanoparticles on 2D MoS2. The Au-MoS2 hybrid nanomaterials act as building blocks to prepare TE thin films by vacuum filtration. (b) Illustration of the TE wrist band fabrication. The as-prepared TE film can be easily bent, showing its flexibility (as shown in Figure 2a). Figure S1 displays the dispersions of un-doped 2D MoS2 and Au-MoS2 nanocomposites, which are stable for hours. The dispersion color changes due to the surface plasmon resonance SPR


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phenomena, which causes the absorption of light in the blue-green region and the reflection of red light.32 The film also shows a hierarchical structure and an average thickness about 3 µm as shown in SEM images (Figure 2b and c), which can be controlled by the volume of the dispersions.

Figure 2. Characterization of MoS2 and Au-MoS2 hybrid nanosheets. (a) A flexible Au-MoS2 hybrid TE film. (b) and (c) Side view of the TE film observed by SEM showing the layered nature of the film made by restacking Au-MoS2 nanosheets. (d) XRD of the restacked films consisting of Au-MoS2 nanocomposites compared with intrinsic 2D MoS2. (e) TEM image of MoS2 nanosheets. (f) High-magnification image of MoS2 nanosheets. (g) and (h) Highmagnification image of Au-MoS2 hybrid nanosheets. (i) HRTEM image of the Au-MoS2 hybrid nanosheets. (j) SAED pattern of an Au-MoS2 hybrid nanosheet. (k) High-resolution XPS from Mo3d peak of as-prepared 2D MoS2. (l) XPS survey spectrum of the original 2D MoS2 and Au-


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MoS2 nanocomposites. The microstructure of the hybrid thin films is demonstrated by XRD analysis, which provides direct phase information for the Au-MoS2 hybrid nanocomposites. The chemically exfoliated 2D MoS2 was shown in the up curve of Figure 2d, while the diffraction peaks of (002) at 2θ ≈ 14.7° and (001) at 2θ ≈ 8.9° match the pristine 2H MoS2 and 1T MoS2 phases, respectively.28,30 Similar to previous reports, both the (001) and (002) peaks are much broader than the pristine 2H MoS2 phase, which reveals that the nanosheets in the film are thin layers and randomly arranged by restacking during filtration.27,30 After the 2D MoS2 were decorated by Au nanoparticles, diffraction peaks emerge at 38.5°, 44.6°, 64.8°, and 77.7°, which can be assigned to the (111), (200), (220), and (311) planes of cubic Au, respectively, indicating the successful formation of Au-MoS2 hybrid nanomaterials. The peak intensity of the (001) plane of Au-MoS2 hybrid nanomaterials is much weaker than that of the pristine 2D MoS2, which indicates that decoration by Au nanoparticles can effectively separate the 2D MoS2 layers and suppress the ordered restacking process of the nanosheets.30 Additionally, the diffraction Au peaks gradually become stronger with increasing Au volume. The size of the as-prepared 2D MoS2 nanosheets is 1-2 µm, illustrating by the TEM images as shown in Figure 2e and f. The Au-MoS2 hybrid nanocomposites were formed by reducing HAuCl4 with ascorbic acid. The introduced Au nanoparticles, with size of about 5-10 nm, are found to spread randomly across the surface of the 2D MoS2, which can be seen in Figure 2g and h. We verified the structure of Au-MoS2 hybrid nanocomposites by using HRTEM (Figure 2i and Figure S2), which shows clear lattice, as well as the boundary of Au and MoS2. The lattice fringes with inter-planar spacings of 0.27 nm and 0.23 nm are assigned to the (100) plane of MoS2 and (111) plane of Au, respectively, which are also in agreement with the SAED pattern as shown in Figure 2j. The diffraction patterns have


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two series, including Au nanoparticles and 2D MoS2. The diffraction rings of Au (111), (200), and (220) planes, marked by the yellow arrows, are observed. The diffraction spots are indexed to (100) and (110) planes of MoS2, respectively. We further identified the two polymorphs of the pristine 2D MoS2 and the Au nanoparticles in the hybrid nanocomposites using XPS. As shown in Figure 2k, the 1T phase of 2D MoS2 appears at a binding energy that is about 0.9 eV lower than the 2H phase. The two polymorphs of 2D MoS2 can be distinguished from the high-resolution XPS spectrum of Mo 3d region. Regarding the 1T phase concentration of 2D MoS2, the calculated deconvolution result of the Mo3d peaks is about 68%. The spectrum of the as-prepared 2D MoS2 and the Au-MoS2 hybrid nanocomposites is shown in Figure 2l. The Mo 3d shows a broad peak at 229.3 eV, which can be attributed to 3d5/2 and 3d3/2. The Mo 3p shows two peaks at 410.7 and 394.9 eV, which can be attributed to the doublet of Mo 3p1/2 and 3p3/2, respectively. The binding energy for S 2p is 161.8 eV. Here, all the binding energies of Mo and S are in good agreement with previous reports, indicating that the decorating of Au does not affect the crystallinity of 2D MoS2, and the 2D MoS2 are chemically stable in the HAuCl4 aqueous solutions. Peaks located at 84.2, 87.8, 334.7, and 352.6 eV can be ascribed to Au 4f7/2, 4f5/2, 4d5/2, and 4d3/2, respectively. This suggests the successful deposition of Au nanoparticles onto the surface of the 2D MoS2. Comparing with the spectrum of 2D MoS2, no obvious shift in the binding energies of Mo3p, Mo3d, and S2p can be seen in the spectrum of Au-MoS2 hybrid nanocomposites.


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Figure 3. TE properties of flexible thin films based on 2D MoS2 and Au-MoS2 hybrid nanocomposites. Temperature dependent S (a), σ (b), and σS2 (c). To systematically study the effect of Au-decoration on 2D MoS2, the related temperature dependent electrical and TE performance from room temperature down to 150 K were performed (Figure 3a and b). First of all, decreasing σ with the declining temperature for un-doped 2D MoS2 films and Au-MoS2 hybrid nanomaterials was observed, suggesting a semiconductor behavior. Meanwhile, it is noteworthy that all the S are almost steady during a large temperature range between 290 to 190 K, demonstrating the great advantage of using 2D MoS2 as a TE material near the region of room temperature. The positive values of the S indicate a p-type semiconductor of the un-doped 2D MoS2 and Au-MoS2 hybrid nanomaterials. In detail, un-doped 2D MoS2 film showed a low σ of about 88.7 S cm−1 at 290 K, which caused by the increased carrier scattering in the grain boundaries of restacked MoS2 nanosheets. On the contrary, AuMoS2 hybrid nanomaterials, especially the one with gold (III) chloride trihydrate contents of 16.7 wt%, possess higher σ around 177.1 S cm−1 at 290 K, which is about two times that of the MoS2 film. Meanwhile, the S also increases slightly from 84.6 to 96.9 µV K−1 at 290 K after decoration. As a result, Au-MoS2 hybrid nanocomposites give an optimal σS2 of 166.3 µW m−1 K−2 at room temperature due to the enhanced σ and improved S, which is more than two times of the original 2D MoS2 film (as shown in Figure 3c).


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Figure 4. (a) The σ and S of the Au-MoS2 nanocomposites film versus the volume of Au precursors. (b) Sketch of the distribution of the 1T phase and 2H phase nanosheets in the laminar Au-MoS2 nanocomposites film. (c) The energy band diagram of 2H phase MoS2 and Au showing band bending after the contact is established, with which electron transfer occurs from MoS2 to Au causing p-type doping. Traditionally, the S is interdependent with the σ of the system by the carrier characteristics and tends to decrease as the increasing carrier concentrations, which is mainly due to the reduced average energy of carriers. For as-prepared Au-MoS2 assembled heterojunction system, the S and σ simultaneously increased (as shown in Figure 4a). This is due to the occurrence of p-type doping of the MoS2 2H phase and injection energy filtering of dopant-originated carriers around the local band bending at the interface. This functions in a way similar to that of “modulation doping” proposed by Chen et.al.33 In detail, for most of the chemical-exfoliated 2D MoS2, the asprepared nanosheets consist of certain amount of 2H phase while the main body is 1T phase. Here, as shown in Figure 4b and Figure 2k, the amount of 2H phase in the prepared 2D MoS2 ink accounts for a substantial proportion around 32%. As is well known, the 2H phase of MoS2 shows a semiconductor behavior with a high resistance of almost 107 times that of the 1T


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phase,27 which hinders charge transfer kinetics. On one hand, the introduction of Au nanoparticles significantly improves the σ of the 2H phase even in a low percolation threshold. On the other hand, Figure 4c shows the band bending after the contact is established between the 2H phase MoS2 and the Au nanoparticles when the Au nanoparticles were introduced by in-situ growth. Therefore, electrons transfer from 2H phase MoS2 to Au, which caused p-type doping to 2H MoS2 and the increasing of carrier concentrations.34,35 This is also in agreement with the hall measurement results (as shown in Table S1). Another possible reason is that the local band bending across the interface may also act as an injection energy filter for dopant-originated carriers, which is favorable to improvement of the S of hybrid films. To illustrate the potential of the flexible films for harvesting human body heat, we further designed a fabric-based wrist band with five rectangular ribbons of the TE thin films as shown in Figure 5a. The working mode of the wrist band was shown in Figure 5b, and the thermal voltage response curve was measured by wearing it on wrist. As can be seen in Figure 5c, the voltage of the wrist band was about 2.4 mV for a temperature gradient (∆T) of about 5 K. From the curve, we can observe that the thermal voltage dropped off gradually when we disengaged the wrist band from the skin (as shown in the red curve). The thermal voltage stayed steady except a few drops as it trended to the equilibrium state of the temperature in the device.


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Figure 5. Demonstration and performance of a flexible TE device. (a) Prototype of a fabricbased TE wrist band. (b) TE wrist band under working mode of as worn on wrist. (c) The thermal voltage output of the TE wrist band under various circumstances. The red curve: the wrist band was disengaged when the voltage reached to maximum; the blue curve: the wrist band was kept on wrist (All legs have a temperature gradient of about 5 K). (d) The σS2 of Au-MoS2based film against the bending test with radius around 5 mm, where Pf and Pf0 mean the σS2 after and before bending test (scale bar: 1 cm). Basically, the output voltage is consistent with the voltage calculated by combining the S. Moreover, the generated voltage can be increased by a higher ∆T or a series and parallel circuit, which has the potential of powering wearable devices in the future. In addition, the present TE films also exhibit high stability in σ and S against the mechanical bending, which is characterized by a combined σS2. It shows that the σS2 retains by 97% after bending for 500 cycles with a


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bending radius of 5 mm, demonstrating the high reliability of the TE films (as shown in Figure 5d). 4. CONCLUSIONS In conclusion, we have shown a feasible method for improving the TE performance of the 2D MoS2 film by effectively decorating Au nanoparticles on the nanosheets. It was found that the present composites show a certain decoupling phenomenon of the enhancement of σ and S within a certain range. This is due to the occurrence of p-type doping of the MoS2 2H phase and injection energy filtering of dopant-originated carriers around the local band bending at the interface. The TE performance of the Au-MoS2 hybrid film can achieve a σS2 value of 166.3 µW m−1 K−2 at room temperature, which has great potential for harvesting human body heat. We believe that our results will provide the possibility to explore the properties and applications of other 2D transition-metal dichalcogenides other than 2D MoS2.

Supporting Information. Aqueous dispersions of intrinsic 2D MoS2 and Au-MoS2 nanocomposites (Figure S1). HRTEM image of the Au nanoparticle on MoS2 nanosheets (Figure S2). Hall measurement results of the TE films at 290 K (Table S1). This material is available free of charge via the Internet at http://pubs.acs.org. Notes The authors declare no completing financial interest. ACKNOWLEDGMENTS


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Yang Guo and Chaochao Dun contributed equally to this work. The authors gratefully acknowledge the financial supports by STC of Shanghai (16JC1400700, 16XD1400100) ， SMEC (2017-01-07-00-03-E00055), MOE of China (No.111-2-04, IRT_16R13), Eastern Scholar, and the financial supports by the U. S. Air Force Office of Scientific Research Grant FA955016-1-0328, and NASA/Streamline 1123-SC-01-R0 NASA #NNX16CJ30P. Yang Guo thanks the China Scholarship Council financial support and Ph.D. Innovation Funds by DHU (201706630056, 16D310612), the Fundamental Research Funds for the Central Universities (18D110308), and the use of equipment from the Center of Nanotechnology and Molecular Materials at Wake Forest University. This work was also partially supported by NSF grant DMR-1507942.

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Page 20 of 25

The table of contents


20

Page 21 of 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


a Intercalation

Ultrasonication

n-BuLi

DI water

Bulk MoS2

HxMoS2

LixMoS2

HAuCl4

Vacuum filtration

In-situ growth

Au3+

Au-MoS2 film

Au-MoS2

b Textile


Cl-


a

c

d

(001) (002)

Intensity (a.u.)

b

1 cm

1 μm

MoS2 (111) (200)

500 nm

g

i

200 nm

(111)Au

(100) MoS2 0.27 nm

30

40

50

60

70

80

2 (degree) 1T MoS2

Mo 3d5/2

Intensity (a.u.)

Au NPs

1 μm

20

k 0.23 nm

(311)

Au-16.7 wt% 10

e

(220)

Au-5.6 wt%

2H MoS2

Mo 3d3/2

5 nm 234

232

230

228

226

224

500 nm

50 nm

(200)Au

(220)Au

500

400

Au 4f5/2 Au 4f7/2

Au 4d3/2 Au 4d5/2 600

300

1T MoS2

Mo 3d

(100)MoS2

Au-MoS2

S 2p

(110)MoS2

l

C 1s

(111)Au

Mo 3p1/2 Mo 3p3/2

j

h

O 1s

f

Intensity (a.u.)

Binding energy (eV)

Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 25

200

Binding energy (eV)


100

Page 23 of 25

105

MoS2

Au-MoS2-16.7 wt%

Au-MoS2-5.6 wt%

Au-MoS2-27.9 wt%

b

c 250

100

200

Conductivity (S/cm)

200

95 90 85

Power factor (W/mK2)

a

Seebeck (V/K)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


150 100 50

150

100

50

80 140 160 180 200 220 240 260 280 300

0 140 160 180 200 220 240 260 280 300

0 140 160 180 200 220 240 260 280 300

Temperature (K)

Temperature (K)

Temperature (K)



b 300

Conductivity

Vacuum

100

200

Vacuum

50 100

CB

qVbi

EF,MoS2

75

150

Au

Au

Au

VB

25

50 0

c

Au-MoS2 film

Seebeck

250

Seebeck (V/K)

Conductivity (S/cm)

1 a 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 25

-5

0

5

10

15

20

Percent (wt.%)

25

30

0

2H MoS2 1T MoS2

Au nanoparticle

2H MoS2


Au

2H MoS2

Built-in potential

-4.3 EF,Au

-5.9

Page 25 of 25

a

b

c

d

120

On Disengaged

97%

100

Pf/Pf0 (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


80 Normal

Bending

60 40 20

On

0

0


100

200 300 400 Bending cycles

500

Wearable Thermoelectric Devices Based on Au-Decorated Two

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