Silicone-Based Triboelectric Nanogenerator for Water Wave Energy

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Silicone-Based Triboelectric Nanogenerator for Water Wave Energy Harvesting Tian Xiao Xiao, Tao Jiang, Jian Xiong Zhu, Xi Liang, Liang Xu, Jiajia Shao, Chunlei Zhang, Jie Wang, and Zhong Lin Wang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b17239 • Publication Date (Web): 02 Jan 2018 Downloaded from http://pubs.acs.org on January 3, 2018

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ACS Applied Materials & Interfaces

Silicone-Based Triboelectric Nanogenerator for Water Wave Energy Harvesting ⊥

Tian Xiao Xiao,†,‡, Tao Jiang,†,‡,

⊥

⊥

Jian Xiong Zhu,†,‡, Xi Liang,†,‡ Liang Xu,†,‡ Jia Jia Shao,†,‡ Chun Lei

Zhang,†,‡ Jie Wang*†,‡ and Zhong Lin Wang*†,‡,§

†

CAS Center for Excellence in Nanoscience, Beijing Institute of Nanoenergy and Nanosystems, Chinese

Academy of Sciences, Beijing 100083, P. R. China ‡

College of Nanoscience and Technology, University of Chinese Academy of Sciences, Beijing 100049, P. R.

China §

School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0245,

USA

KEYWORDS: Triboelectric nanogenerator, silicone rubber, spring-assisted, segmented electrode, water wave energy

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ACS Applied Materials & Interfaces 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

ABSTRACT: Triboelectric nanogenerator (TENG) has been proven to be efficient for harvesting water wave energy, which is one of the most promising renewable energy sources. In this work, a TENG with a silicone rubber/carbon black composite electrode was designed for converting the water wave energy into electricity. The silicone-based electrode with a soft texture provides a better contact with dielectric film. Furthermore, a spring structure is introduced to transform low-frequency water wave motions into high-frequency vibrations. They together improve the output performance and efficiency of TENG. The output performances of TENGs are further enhanced by optimizing the triboelectric material pair and tribo-surface area. A spring-assisted TENG device with the segmented silicone rubber-based electrode structure was sealed into a waterproof box, which delivers a maximum power density of 2.40 W m-3 as triggered by the water waves. The present work provides a new strategy for fabricating high-performance TENG device by coupling flexible electrodes and spring structure for harvesting water wave energy.


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1. INTRODUCTION With the gradual depletion of fossil fuels, energy crisis has become an egregious problem for human beings. Searching for other kinds of alternative energy sources toward the sustainable development of our society has attracted increasing attention.1,2 Water wave, solar and wind energies are all renewable and environmentally friendly energy sources.2,3 Especially, due to both the less dependence on ambient weather, climate or season condition, and the abundant reserves over other kinds of energy sources, water wave energy is one of the most promising energies for large-scale applications.4-8 Most demonstrated generators for harvesting water wave energy are based on the electromagnetic induction effect, and they must be huge, heavy, and particularly inefficient at ocean wave frequencies because of their working principle.9-11 Therefore, it is urgent to develop a new type of generator, which is lightweight, small-sized, cost-effective, and easy-fabricated, to harvest water wave energy more effectively. Recently, triboelectric nanogenerator (TENG) based on the coupling of triboelectrification effect and electrostatic induction has been invented as a brand-new technology that converts ambient mechanical energy into electricity.12-24 Different from conventional electromagnetic generators, which rely on a varying magnetic field to generate current, TENGs originated from the Maxwell’s displacement current are based on the varying polarization field induced by surface polarization charges.25,26 And with the development of TENG applications, flexible electrodes have been introduced into TENGs to replace hard metal, providing a better contact for harvesting human motion energy in some previous works.27,28 Because of the advantages of high efficiency, easy fabrication, low cost and typically high performance at low frequencies (< 5 Hz), TENGs have been effectively utilized to harvest water wave energy.29-35 Furthermore, a spring structure has been introduced into TENG devices to improve the output performance and efficiency of TENGs in water wave energy harvesting toward the blue energy dream.36,37 Herein, combining the advantages of flexible electrodes and spring structure, we fabricated a silicone-based and spring-assisted TENG for harvesting water wave energy. Such TENG is based on the contact-separation between the silicone rubber/carbon black electrode and the polytetrafluoroethylene (PTFE) thin film. Compared with conventional hard Cu electrode, the introduction of silicone rubber/carbon black electrode with a soft texture can bring 75.2%, 60.4%, and 103.9% enhancements in the transferred charge, output current and voltage of TENG, respectively. Then the influences of triboelectric material pairs and tribo-surface area as well as the segmentation on the silicone-based electrode on the TENG outputs were



investigated. The segmented electrode structure can further increase the output power density by 23.5%. Finally, we packaged the spring-assisted TENG with segmented silicone rubber/carbon black electrode into a sealed box to harvest water wave energy. Driven by the water waves, the TENG device can produce a high power density of 2.40 W m-3, demonstrating the capacity of the as-fabricated device for efficient water wave energy harvesting.

2. RESULTS AND DISCUSSION A vertical contact-separation mode TENG consisting of two silicone rubber/carbon black composite electrodes and a PTFE thin film was designed and fabricated. And as shown in Figure S1, the thickness of fabricated silicone rubber/carbon black electrode is 764.0 µm. The schematic diagram of the silicone-based TENG and photographs of its two parts are shown in Figure 1a. The TENG is based on the contact electrification between one silicone rubber/carbon black electrode and a PTFE film that is attached on another composite electrode, whose triboelectric material pair is denoted by C/PTFE-C. The detailed fabrication process can be found in the Experimental section. Figure 1b shows the working principle of the TENG. First, under an external triggering, the PTFE thin film and the bottom silicone rubber/carbon black electrode get contacts and create positive triboelectric charges on the electrode and negative ones on the PTFE surface (state i). Then the separation between the PTFE and bottom electrode produces an electric potential difference between the two electrodes, which drives free electrons flowing from the top electrode to the bottom one (state ii). The current is generated until they arrive at the maximum separation (state iii). When the two surfaces of PTFE and bottom electrode get close to each other again until complete contact, free electrons flow back from the bottom electrode to the top one, generating reversed current flow (state iv). The periodic contact and separation between two parts of TENG produce periodic electric output signals. Figure 1c-d present the typical output profiles of such TENG with the tribo-surface area of 6 cm2 under a linear motor triggering at a maximum separation of 5 mm. The maximum output current reaches 22.3 µA, and the maximum output voltage is 630.7 V. For a comparison between the flexible silicone-based electrode and hard metal electrode, the influence of triboelectric material pair adopted in the contact-separation mode TENG on the output performance of TENG was investigated. Besides the former C/PTFE-C tribo-material pair, we chose other four tribo-material pairs to fabricate the corresponding TENG devices, i.e., Cu/PTFE-Cu, Cu/PTFE-C, Cu/SR-C, and C/PTFE-Cu


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triboelectric material pairs, as schematically shown in Figure 2a. The TENG with the Cu/SR-C tribo-material pair consists of the silicone rubber/carbon black electrode coated by a silicone rubber dielectric layer and the copper electrode. The tribo-surface areas of these TENGs were all fixed at 6 cm2, and the maximum separation distance was fixed as 5 mm. Figure 2b-d show the transferred charge, output current and output voltage of these TENGs with different triboelectric material pairs. As can be seen, the outputs of the TENG with the Cu/PTFE-Cu tribo-material pair are the lowest, where a charge of 33.1 nC, a current of 13.9 µA, and a voltage of 309.3 V were obtained. By contrast, the TENG with the C/PTFE-C tribo-material pair exhibits the highest output performance, and there are 75.2%, 60.4%, and 103.9% enhancements in the transferred charge, output current and voltage (58.0 nC, 22.3 µA, 630.7 V). The outputs of TENG with the C/PTFE-Cu tribo-material pair are roughly the same as the C/PTFE-C one. In these two structures, the Cu and silicone rubber/carbon black electrodes adhered on the acrylic blocks are both coated by the PTFE film as a whole. The PTFE film contacts with another silicone-based electrode directly, and the contact intimacy is almost unaffected by the coated Cu or silicone-based electrode. The improvement of the silicone rubber/carbon black electrode on the TENG performance over the Cu electrode is because that the flexible silicone-based electrode could provide a better contact with PTFE thin film, which can improve the area for charge transfer to enhance the triboelectric charge density on the material surfaces.28 For the TENG with the Cu/PTFE-C tribo-material pair, the charge, current and voltage are higher than those of the Cu/PTFE-Cu one, but lower than those of the C/PTFE-Cu. That implies when the Cu electrode deposited on PTFE film is replaced by the flexible silicone-based electrode, the contact between PTFE and Cu can also be improved to some extent. However, the contact completeness between the flexible electrode and PTFE is the best, and the area for charge transfer is most improved. For the Cu/SR-C tribo-material pair, both the transferred charge and output voltage are higher than those of the Cu/PTFE-C one, because of the soft texture of the silicone rubber layer. Nevertheless, in the TENGs with the C/SR-C or C/SR-Cu tribo-material pair, the surface viscosities of both silicone rubber and silicone rubber/carbon black electrode make the two parts of TENG difficult to separate, therefore they cannot be adopted for practical applications. In order to investigate the effect of the tribo-surface area on the output performance of TENGs, we fabricated the TENGs with the C/PTFE-C and Cu/PTFE-Cu tribo-material pairs in an area of 1-16 cm2 and measured the electric outputs. The transferred charge density, output current density and peak power density of the C/PTFE-C TENGs as functions of the tribo-surface area are shown in Figure 3a-c. It is apparent that as the tribo-surface area increases, the peak values of charge density and current density both decrease, and the



maximum power density at a matched resistance also decreases. At the smallest experimental area of 1 cm2, the TENG can produce the highest outputs of 205.0 µC m-2, 70.0 mA m-2 and 6.25 W m-2. When the tribo-surface area is smaller, the two parts of TENG can contact more sufficiently under the same pressing (generating higher tribo-surface charge density), and the charge transfer becomes more favorable, especially for smaller areas, leading to the higher transferred charge density, current density and power density. In Figure 3c, with increasing the trio-surface area, the value of matched resistance also decreases due to larger capacitance for TENG. Although the current density decreases with the increasing tribo-surface area, the output current increases with the area as well as the voltage (Figure S2a-b). The gradual decrease of increasing slope is ascribed to the drop of charge density. In addition, we carried out the finite element simulations on the open-circuit voltage for the TENGs with different tribo-surface areas and obtained the consistent result that the voltage increases with the tribo-surface area (Figure S3). The dimensions adopted in the simulations were close to those of real devices. Under an ideal condition, the open-circuit voltage is independent of the tribo-surface area,38 but the more obvious edge effect at the smaller area can lead to a lower voltage. In fact, in the experiments, besides the edge effect, the voltage increase with the area has another contribution from measurement principle of digital oscilloscope. The digital oscilloscope applied the relative magnitude of the waveform amplitude displayed on the oscilloscope to reflect the relative magnitude of the maximum voltage upon the Y deflection pole of the oscilloscope, which can measure the voltage provided by the TENG. It has an internal resistance, and the extracted voltage is the voltage at a large resistance (100 MΩ) rather than the real open-circuit voltage. Therefore, the voltage increases with the area partly due to the increasing of current. The average peak values of charge density, current density and the maximum value of peak power density were also extracted and compared for the TENGs with the C/PTFE-C and Cu/PTFE-Cu tribo-material pairs, as shown in Figure 3d-f. Besides the dependency of the TENG performance on the tribo-surface area, we can also view that the C/PTFE-C TENG delivers higher outputs than the Cu/PTFE-Cu TENG for a constant tribo-material area, validating the advantages of silicone rubber/carbon black composite electrode again. Taking the area of 16 cm2 for example, there are 122.8%, 67.9%, and 62.9% enhancements in the transferred charge, output current and power density. Note that the higher transferred charge density, current density and power density for the Cu/PTFE-Cu TENG at smaller area are also contributed to the higher tribo-surface charge density caused by the more sufficient contact at a smaller area. In addition, the current and voltage of the C/PTFE-C TENG are also higher than those of the Cu/PTFE-Cu TENG (Figure S2c-d).


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Subsequently, we studied the impact of the segmentation of silicone rubber/carbon black electrode on the TENG performance. The laser cutting machine was applied to segment the composite electrode on an acrylic substrate to get the segmented structure. The photographs and optical microscope images for the non-segmented and segmented electrode structures are illustrated in Figure 4a. In the segmented electrode, five slim visible stripes can be observed, and the strip width is about 300 µm from the optical microscope image. Figure 4b-d shows the comparison of output performances between the non-segmented and segmented TENGs. The areas of 4 cm2 and 16 cm2 were chosen for example. The transferred charge density, output current density and maximum peak power density are all enhanced by the segmented structure on the electrode regardless of the tribo-surface area. Note that in this experiment, the current densities of non-segmented and segmented TENGs were obtained by dividing the currents by the total area of the triboelectric surfaces. In fact, the segmentation on the silicone-based electrode can improve its contact with the PTFE film to raise the triboelectric surface charge density, similar to the decrease of the tribo-surface area of TENG. For the output voltage as shown in Figure S4, at the area of 4 cm2, the voltage is enhanced by the segmentation, which is dominated by the increased surface charge density. However, at the area of 16 cm2, the voltage is weakened slightly, under the competition action between the increased charge density and the increased edge effect created by the segmentation. The slight decrease of voltage can be also revealed in the finite element simulations (Figure S5). For the applications of water wave energy harvesting, a silicone-based and spring-assisted TENG device was fabricated by using the segmented silicone rubber/carbon black electrode and the PTFE film on Cu electrode, as schematically shown in Figure 5a. Two spring-connected acrylic blocks attached by the PTFE-Cu films can collide with the silicone-based electrode on the internal wall of the outer acrylic box. The detailed fabrication process of the TENG device can be found in the Experimental section. First, we measured the output performances of the silicone-based and spring-assisted TENGs with non-segmented structure and segmented structure, respectively, and then compared them. The maximum displacement of the linear motor, i.e., maximum displacement of external box, was fixed as 7.0 cm, and the maximum reached speed of the motor was 1 m s−1. As shown in Figure 5b-c, the output current and transferred charge of the non-segmented TENG both increase gradually with increasing the motor acceleration from 2.5 to 10 m s-2. The current and charge of segmented TENG have the similar tendency with respect to the motor acceleration, but they are higher than those of non-segmented TENG (Figure 5d-e), which is still the enhancement of segmented structure. The output voltage also has a slight improvement by the segmented electrode, but it is not obvious



compared to the charge and current (Figure S6). Then the resistance dependencies of output power are compared between the non-segmented and segmented TENGs, as shown in Figure 5f. The non-segmented TENG produces a maximum output power of 10.1 mW (power density: 2.81 mW m-2) at the matched resistance of 20 MΩ, while the maximum output power for the segmented TENG reaches 12.5 mW (power density: 3.47 mW m-2) at the same matched resistance (enhanced by 23.5%). In addition, the enhancement in the peak current at different load resistances can be viewed in Figure S7. To demonstrate the application capacity of such silicone-based and spring-assisted TENG in harvesting water wave energy, we sealed the segmented TENG with the C/PTFE-Cu tribo-material pair into a waterproof acrylic box, and connected the two TENG units in parallel through two rectifier bridges. A photo of the sealed TENG device floating on water in a pool connected with scores of LEDs is shown in Figure 6a. Note that to simulate the real ocean water environment, enough salts were added into the water of the pool to make the mass density of the water close to that of the seawater. In the present work, the corrosion of acrylic box by the seawater is not considered. However, in the further investigations, the corrosion issue and life time of the TENG device will be addressed carefully. Driven by the water wave motion, 65 LEDs with a pattern “TENG” can be lightened up by the fabricated device (see the inset of Figure 6a and Video S1). Then the rectified output characteristics were measured at different frequencies of water waves, and the results are shown in Figure 6b-d. With increasing the frequency of water waves, the output current, output voltage and maximum peak power density all increase due to the higher velocity of contact. The integrated device can deliver a maximum current of 42.7 µA, a maximum voltage of 524.8 V, and a maximum power density of 2.40 W m-3 (4.41 mW in the box of 0.00184 m3) at 2.0 Hz. The typical outputs, current-resistance and power density-resistance relationships for the TENG device driven by the water waves of 1.25 Hz are presented in Figure S8a-c. In addition, the matched resistance of the two TENG units connected in parallel is not much lower than that of one unit in the linear motor test, which results from the competition action between the increase of the capacitance and the decrease of motion velocity for the motion part of TENG triggered by the water waves.

3. CONCLUSIONS In summary, we fabricated a kind of silicone-based and spring-assisted TENG based on the silicone rubber/carbon black electrode and spring structure for harvesting water wave energy. Two PTFE-Cu-covered


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acrylic blocks connected by a spring are placed between two silicone-based electrodes anchored on two internal walls of the box-like device. Compared with other studies, the introduction of flexible electrodes can improve the material contact and enhance the TENG outputs especially under the random motion of water waves, while the spring structure can transform low-frequency water wave motions into high-frequency vibrations, raising the energy harvesting efficiency. The output performance of such TENG was measured under the regular action of linear motor, and the influences of the triboelectric material pair, tribo-surface area and the segmented electrode structure were investigated. The TENG with the C/PTFE-C tribo-material pair can produce 75.2%, 60.4%, and 103.9% enhancements in the transferred charge density, output current density and voltage over the Cu/PTFE-Cu one, and a smaller tribo-surface area can bring a higher charge density and current density. Then the segmentation on the silicone rubber/carbon black electrode can further increase the output power of the silicone-based and spring-assisted TENG by 23.5%. Furthermore, the silicone-based and spring-assisted TENG with the segmented electrode structure sealed into a waterproof box has been demonstrated to successfully harvest water wave energy, delivering a maximum power density of 2.40 W m-3

as triggered by the water waves. This work could provide the guides for improving the

performance of TENGs by coupling the flexible electrodes and spring structure in efficiently harvesting water wave energy.

EXPERIMENTAL SECTION Fabrication of the Segmented Silicone Rubber/Carbon Black Electrode. The part A and part B of silicone rubber (Ecoflex 00-30) were mixed in the volume ratio of 1:1. Then conductive carbon black (TIMCAL Super P Li), with the same volume as the silicone rubber was added into the liquid mixture, and fully stirred until they were well-distributed. Next, the mixture was dried in a bake oven lasting for 4 hours at 60 °C. After that, the laser cutting machine was applied to segment the baked mixture on an acrylic substrate to get the segmented silicone rubber/carbon black electrode. Fabrication of the Silicone-Based and Spring-Assisted TENG. First, two 80 µm-thick PTFE films with the dimension of 6 cm × 6 cm were deposited by copper on one side as the electrode. The copper sides of the two PTFE-Cu films were attached to two acrylic blocks with a size of 7 cm × 7 cm. Second, the two acrylic blocks were connected by using a spring with a moderate rigidity (the compression rate and the maximum load are 0.2 kg cm-1 and 0.7 kg, respectively) and a length of about 3.5 cm. Note that a circular iron



with a diameter of 5.5 cm was sandwiched between an acrylic block bonded with PTFE-Cu film and another pristine acrylic block to increase the total mass. Third, an open acrylic box with an outside dimension of 10.5 cm × 8.5 cm × 8.0 cm was fabricated, and its inside has the space of 9.5 cm × 7.5 cm × 7.5 cm to hold the two spring-connected acrylic blocks. And two silicone rubber/carbon black electrodes with segmented structure or non-segmented structure were attached onto two internal walls of the box. At last, two TENG units with the C/PTFE-Cu triboelectric material pair were electrically connected in parallel by using two rectifier bridges which were attached to the outer wall of the box. After that, the silicone-based and spring-assisted TENG device was obtained. For the water wave energy harvesting, the fabricated TENG with the segmented electrodes was sealed into a waterproof acrylic box with an outside dimension of 15.5 cm × 12.5 cm × 9.5 cm. Electric Measurements of the TENG Device. The basic electric outputs of the TENGs were first measured under regular triggering provided by the linear motor (LINMOT 1100) at different accelerations. And the water wave response tests of the device performance were carried out in the water waves generated by using a series of wave pumps (rw-20 JEPOWER TECHNOLOGY Inc.) controlled by a function generator (AFG3011C Tektronix Inc.). The output current and transferred charge of the TENGs were measured by a current preamplifier (Keithley 6514 System Electrometer), while the output voltage was measured by a digital oscilloscope (Agilent InfiniiVision 2000X).

ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website. Comparison of output performance of the designed TENGs with different triboelectric material pairs, the non-segmented and segmented TENGs, and FEM simulations utilizing COMSOL software, as well as typical output characteristics of the TENG device driven by the water waves of 1.25 Hz. (PDF) A video showing dozens of serially connected LEDs being lighted up driven by water wave motions. (AVI)

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] (J. Wang); *E-mail: [email protected] (Z. L. Wang).


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ORCID Zhong Lin Wang: 0000-0002-5530-0380 Tao Jiang: 0000-0001-7941-7703

Author Contributions ⊥

T.X., T.J., and J.Z. contributed equally to this work.

Notes The authors declare no competing financial interest.

ACKNOWLEDGMENTS Support from the National Key R & D Project from Minister of Science and Technology (2016YFA0202704), the Beijing Municipal Science & Technology Commission (Z171100000317001), National Natural Science Foundation of China (Grant No. 51432005, 51702018, and 51561145021), Project funded by China Postdoctoral Science Foundation (2016M590070), and the “thousands talents” program for the pioneer researcher and his innovation team are appreciated.

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Page 14 of 21

Page 15 of 21 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


Figures

Figure 1. (a) Schematic diagram and photographs of a silicone-based TENG (C/PTFE-C) consisting of the silicone rubber/carbon black electrode and PTFE thin film. (b) Working principle of the TENG. (c-d) Typical output current and output voltage under a linear motor triggering at a maximum separation of 5 mm.



(a)

(b)

60

Cu/SR-C C/PTFE-Cu

C/PTFE-C

Cu/PTFE-Cu

Cu/PTFE-C

Cu/SR-C

C/PTFE-Cu

Silicone rubber

PTFE

Charge (nC)

Cu/PTFE-C

Cu

40

Cu/PTFE-Cu

20

0

Silicone rubber/carbon black

0

(c)

5

(d) Cu/PTFE-C

Cu/SR-C C/PTFE-Cu

C/PTFE-Cu

600

20

C/PTFE-C

Cu/SR-C Cu/PTFE-C

Voltage (V)

Cu/PTFE-Cu

10

300

0 -10 -20 0

10 15 Time (s)

C/PTFE-C

20 Current (µA)

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 16 of 21

Cu/PTFE-Cu

0

-300 5

10 15 Time (s)

20

0

5

10 15 Time (s)

20

Figure 2. (a) Schematic diagrams of the TENGs with different triboelectric material pairs. (b) Transferred charge, (c) output current, and (d) output voltage of TENGs with different triboelectric material pairs under a linear motor triggering at a maximum separation of 5 mm. The tribo-surface area was fixed at 6 cm2.


2

2 cm

160

2

4 cm

6 cm

2

9 cm

80

2

16 cm

0 5

10 15 Time (s)

20

25

2

2 cm

40

2

4 cm

2

6 cm

2

9 cm

2

16 cm

0

0 80

C/PTFE-C Cu/PTFE-Cu

200

5

10 15 Time (s)

(e)

20

50

2 0 5

6

7

8

10 10 10 Resistance (Ω)

(f)

9

10

C/PTFE-C Cu/PTFE-Cu

6 2

40

100

4

10

Ppeak (W/m )

60

150

2

1 cm 2 2 cm 2 4 cm 2 6 cm 2 9 cm 2 16 cm

6

25

C/PTFE-C Cu/PTFE-Cu

2

(d)

(c)

2

2

1 cm

-40

0

2

2

(b)

80

Power density (W/m )

2

2

Average Jpeak (mA/m )

2

Charge density (µ C/m )

240 (a)1 cm

Average σ peak (µ C/m )

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


Current density (mA/m )

Page 17 of 21

4

2

20

0

4

8 12 2 Area (cm )

16

0

4

8 12 2 Area (cm )

16

0

0

4

8 12 2 Area (cm )

16

Figure 3. (a) Transferred charge density, (b) output current density, (c) peak power density of the TENGs with the C/PTFE-C triboelectric material pair for different tribo-surface areas. (d) Average peak charge density, (e) average peak current density, and (f) maximum peak power density with respect to the tribo-surface area for two TENGs with the C/PTFE-C and Cu/PTFE-Cu triboelectric material pairs under a linear motor triggering at a maximum separation of 5 mm.



(a)

Segmented

2

Charge density (µ C/m )

(b) 120

200 µm

2 cm Non-segmented

200 µm

2 cm

Non-segmented Non-segmented

40 0 2

2

4 cm

16 cm

60

2

Segmented Non-segmented Non-segmented

30


(d)

(c) 2

Segmented

80

Segmented

Current density (mA/m )

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 18 of 21

Segmented

0

4

2

4 cm

Non-segmented Segmented

3 2

16 cm


2 1 0

-30

5

2

4 cm

2

16 cm

10

6

7

8


9

10

Figure 4. (a) Photographs and optical microscope images of the structures for the non-segmented and segmented silicone-based electrodes. (b-d) Comparison of output performances between the non-segmented and segmented TENGs: (b) transferred charge density, (c) output current density, and (d) peak power density at different resistances. The areas of 4 cm2 and 16 cm2 were chosen for example.


Page 19 of 21

(a)

(c)

(b) 60

2

160

2

a=10.0 m/s

a=10.0 m/s

2

Spring PTFE

2

a=7.5 m/s 2

a=5.0 m/s

20

2

a=3.75 m/s 2

a=2.5 m/s

0

-20


0

6

12 Time (s)

18

2

a=7.5 m/s

150

2

Charge (nC)

a=7.5 m/s

2

a=5.0 m/s a=3.75 m/s

a=2.5 m/s

2

6

12 18 Time (s)

24

12 18 Time (s)

24


12

2

2

2

a=3.75 m/s

a=2.5 m/s

50 0

0

6

a=5.0 m/s

0

-30

0

a=10.0 m/s

100

2

2

40

(f)

(e) 200 2

a=10.0 m/s

30

80

24

Power (mW)

(d) 90 60

a=5.0 m/s 2

a=3.75 m/s 2

a=2.5 m/s

0

Acrylic

Cu

2

120

40

Charge (nC)

Current (µ A)

a=7.5 m/s

Current (µ A)

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


9 6 3 0

0

6

12 18 Time (s)

24

10

5

10

6

7

8


9

10

10

Figure 5. (a) Schematic illustration of the silicone-based and spring-assisted TENG device with segmented silicone rubber/carbon black electrodes. (b-c) Output current and transferred charge at various linear motor accelerations for the non-segmented silicone-based and spring-assisted TENG. (d-e) Output current and transferred charge versus the acceleration for the segmented silicone-based and spring-assisted TENG. (f) Comparison of output power-resistance relationship between the non-segmented and segmented TENGs.



(a)

Current (µ A)

(b)

45

0.75 Hz 1.25 Hz 2.0 Hz

30 15 0

5 cm

0

(c)

6

(d) 3


0.75 Hz 1.25 Hz 2.0 Hz

450 Voltage (V)

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 20 of 21

300 150 0

12 Time (s)

18

0.75 Hz 1.25 Hz 2.0 Hz

2.4 1.8 1.2 0.6 0.0

0

6

12 Time (s)

18

5

10

6

10

7

8

10 10 Resistance (Ω)

9

10

Figure 6. (a) Photograph of the silicone-based and spring-assisted TENG device floating on water for water wave energy harvesting and optical image of 65 LEDs with a “TENG” pattern driven by the water waves. (b) Output current, (c) output voltage, and (d) peak power density as a function of the resistance for the integrated TENG device under different frequencies of the water waves.


Page 21 of 21

TOC

Spring Cu

PTFE

Acrylic

5 cm

9 6 3

3


12



Power (mW)

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


0.75 Hz 1.25 Hz 2.0 Hz

2.4 1.8 1.2 0.6 0.0

0 5

10

6

10

7

8

9


10

10

5

10

6

10


7

8

10 10 Resistance (Ω)

9

10

Silicone-Based Triboelectric Nanogenerator for Water Wave Energy

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