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Stacked pendulum-structured triboelectric nanogenerators for effectively harvesting low-frequency water wave energy
Nano Energy 66 (2019) 104108
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Stacked pendulum-structured triboelectric nanogenerators for effectively harvesting low-frequency water wave energy
T
Wei Zhonga,b,1, Liang Xua,b,1, Haiming Wanga,b,1, Ding Lia,b, Zhong Lin Wanga,b,c,∗ a
CAS Center for Excellence in Nanoscience, Beijing Key Laboratory of Micro-nano Energy and Sensor, Beijing Institute of Nanoenergy and Nanosystems, Chinese Academy of Sciences, Beijing, 100083, PR China b School of Nanoscience and Technology, University of Chinese Academy of Sciences, Beijing, 100049, PR China c School of Material Science and Engineering, Georgia Institute of Technology, Atlanta, GA, 30332, USA
A R T I C LE I N FO
A B S T R A C T
Keywords: Triboelectric nanogenerator Water wave energy Pendulum structure Disk-track structure Blue energy
The invention of triboelectric nanogenerators (TENGs) provides an effective approach for harvesting water wave energy that is clean and renewable. Here, stacked pendulum-structured triboelectric nanogenerators for harvesting low-frequency water wave energy is proposed. The device works based on a pendulum-like principle through a compact disk-track structure that enables area contact instead of point contact while maintaining the susceptible rolling motion. Thus the tribo-electrification and the output are greatly enhanced in slow water waves. While only considering the volume of the TENG units, charge output density of 4622 μC m−3 can be achieved, which is more than 13.2 times of a typical ball-shell structured device. A peak power density of 14.71 W m−3 and an average power density of 1.05 W m−3 are obtained in low-frequency water waves below 0.5 Hz. The device shows great potential of the rolling area-contact design to enhance the output of TENG-based wave energy harvester with excellent low-frequency performance, which is crucial to the development of TENGs for effectively exploiting abundant water wave energy.
1. Introduction The ocean, which covers more than 70% of the surface of the earth, contains huge amounts of clean and renewable energy in the form of wave energy, tidal energy and thermal energy etc. [1–3]. Under the concern for environment protection and clean energy, to exploit the ocean energy has drawn worldwide attention [1,4]. Among different forms of ocean energy, the wave energy is one of the most focused due to its large reserves and vast distribution [2,3]. However, although efforts have been made for several decades on the research of wave energy, there are still many obstacles for its commercialization [2,5–7]. The current technologies are mainly based on electromagnetic generators (EMGs) which usually lead to cumbersome and expensive machines [6,7]. Very recently, another approach based on triboelectric nanogenerators (TENGs) has emerged, bringing new opportunities for this field [8–10]. The TENG works based on the effects of tribo-electrification and electrostatic induction [11]. It has merits of lightweight, low cost, versatile choices of structures and materials etc. [12]. Since its invention in 2012, the TENG has demonstrated its great potential in
harvesting various low-frequency mechanical energies for self-powered systems, such as wind, water flow, human motion and vibration [8,12–19]. The idea of using TENG to harvest wave energy was brought out in 2014 [10], and several prototypes have proved the feasibility of this approach [15,18,20–28]. Among all the wave energy harvesting devices, the ball-shell structure is one of the most common types, where a solid ball is adopted to roll in a spherical shell [21,23,25]. Several designs have improved the output, especially the transferred charges, which are the basis for the performance of the device [29,30]. A fully enclosed TENG that encapsulated a hard rolling ball inside a spherical shell was proposed in 2015 with a transferred charge density of 212.39 μC m−3 in water [21]. The work using soft silicone rubber ball improved the value to about 350 μC m−3 in 2018 [23]. Another design adopted highly soft silicone rubber ball and produced a charge density of 361.11 μC m−3 in water in 2019 [25]. For the ball-shell structure, the contact is essentially point contact with small contact area which limits the tribo-electrification. For further improving the output performance, designs that enable area contact with easy rolling abilities are highly desired.
∗
Corresponding author. CAS Center for Excellence in Nanoscience, Beijing Key Laboratory of Micro-nano Energy and Sensor, Beijing Institute of Nanoenergy and Nanosystems, Chinese Academy of Sciences, Beijing, 100083, PR China. E-mail address: [email protected] (Z.L. Wang). 1 These authors contributed equally to this work. https://doi.org/10.1016/j.nanoen.2019.104108 Received 14 August 2019; Received in revised form 2 September 2019; Accepted 7 September 2019 Available online 09 September 2019 2211-2855/ © 2019 Elsevier Ltd. All rights reserved.
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Fig. 1. Structure and working principle of the PS-TENG device. (a) Schematic explosive view of the device. (b) Photograph of the rolling disk (Scale bar: 3 cm). Inset: Photograph of the surface of wrinkled aluminum foil (Scale bar: 1 mm). (c) The operation principle of the TENG like a pendulum. (d) Basic working mechanism of TENG units.
device to respond effectively to external low-frequency mechanical agitations, such as water waves, and the structure is more compact without a suspending string. The period of a pendulum with small amplitudes can be estimated by T = 2π L/g , where L represents the length of the pendulum and is equal to R-r here. Such a period is affected by friction force and other factors in real devices. However, as a rough estimation, the equation can still be used to guide the design of the guide track for a better response to water waves with certain periods. The fundamental working mechanism of the TENG is based on the conjugation of tribo-electrification and electrostatic induction in a freestanding-triboelectric-layer mode, as demonstrated in Fig. 1d [31,32]. The electrodes of different electrode layers at the left or right side are interconnected, respectively. While rolling on the guide track, the metal disk will rub with the PTFE films on the electrode panels, and electrons will transfer from the disk to the surfaces of the PTFE films due to their higher affinity to electrons [33]. Thus the disk will be positively charged. The positive charges in the disk will induce a higher potential on adjacent electrodes, and electrons will transfer between the electrodes through an external circuit to compensate the potential difference, forming current in the circuit. More specifically, when the disk rolls to the right side, the current will flow from the right electrodes to the left electrodes, and a reverse current will appear when the disk returns to the left side. With the disk swinging back and forth, alternating current will be generated in the load and mechanical energy of the disk can be converted into electricity. Compared to typical ball-shell structured device, the design uses area contact instead of point contact, thus the tribo-electrification can be greatly enhanced [21,23,25]. However, the side effect is that the friction force can also rise dramatically which can even prohibit the disk from rolling with the attraction of static charges. So the wrinkle structure of aluminum foil is adopted to adjust the contact area and lower the friction force, which is facile to be applied. To characterize the basic output performance of the PS-TENG, we tested the device on a linear motor that can simulate the agitation of
Here, we proposed a stacked pendulum-structured triboelectric nanogenerator (PS-TENG) for effectively harvesting low-frequency water wave energy. The device works based on a pendulum-like principle through a compact disk-track structure which enables area contact instead of point contact while maintaining the susceptible rolling motion. Thus, the tribo-electrification and the output are greatly enhanced in slow water waves. While only considering the volume of the TENG units, charge output density of 4622 μC m−3 can be achieved, and a peak power density of 14.71 W m−3 and an average power density of 1.05 W m−3 are obtained in low-frequency water waves below 0.5 Hz. The device shows great potential of the rolling area-contact design in improving the output of TENGs for wave energy harvesting.
2. Results and discussion The structure of the PS-TENG is schematically shown in Fig. 1a. There are three major parts in the device, namely electrode panels, guide spacers and rolling disks. The electrode panel is composed by an epoxy glass fiber plate, two metal (Au + Cu) electrode layers and two polytetrafluoroethylene (PTFE) films, and each electrode layer is separated into two electrodes. The guide spacer is made of acrylic with specific guide track inside, which can form a chamber with the electrode panel. The disk is fabricated by covering half of a circular copper plate with wrinkled aluminum foil at both sides (Fig. 1b), and the wrinkle structure is demonstrated in the inset of Fig. 1b. The design of wrinkled aluminum foil is used to adjust the contact area of the disk and the electrode panel, which will be discussed in details afterwards. A simplest TENG unit can be assembled by placing one rolling disk in the chamber formed by one electrode panel and one guide spacer. The PSTENG can be consistent by several such TENG units. Details of the fabrication process are provided in the Experimental Section. The device operates on a pendulum-like principle, as shown in Fig. 1c. The inside track of the guide spacer has a shape of circular arc with a radius of R. The rolling disk, with a radius of r, can swing on the track, just like a pendulum with a length of R-r. The pendulum design enables the 2
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Fig. 2. Basic characterization of the PS-TENG in air. (a) Schematic illustration of the experimental setup. (b–d) Transferred charges (b), short-circuit current (c) and open-circuit voltage (d) of the PS-TENG. (e) Peak power and average power of the PS-TENG with resistive loads. The agitation frequency is 1 Hz and the amplitude is 11.3°.
where the resonance of the PS-TENG is achieved. Outputs of 0.57 μC and 4.4 μA can be delivered at the resonance state. With higher frequencies, the output will decrease, as shown in Fig. 3c and d. The performance of the PS-TENG consisting of different quantities of TENG units was also studied, as demonstrated in Fig. 3e and f. The charge and current outputs increase almost linearly with the quantity of the TENG unit, which implies that the device should have good scale-up performance. The detailed output of each unit is presented in Fig. 3g. The output of each unit in the PS-TENG shows some fluctuations. The transferred charges are approximately between 0.03 μC and 0.06 μC, and the peak short-circuit currents are between 0.3 μA and 0.68 μA. The non-uniformity should originate from the contact state of the disk with the electrode panel in each unit, and a stable output can be obtained when the output of a few TENG units are superposed as in the PS-TENG. For the application of harvesting wave energy, it is critical to store the instantaneously generated electrical energy for driving external electrical devices which usually have larger energy consumption. Fig. 3h shows the circuit diagram for the PS-TENG to charge a capacitor for storing the harvested energy. The charging performance to different capacitors is shown in Fig. 3i. A capacitor of 22 μF could be charged to 2.35 V in 70 s, and charges of 51.7 μC were stored. For lowering the expense of packaging, the PS-TENG is designed as a stackable device and several such devices can be accommodated in one package. Here, the output of three stacked devices was studied, as shown in Fig. 4a. The experimental setup is similar to single PS-TENG tests and the agitation frequency and amplitude were fixed at 1 Hz and 11.3°, respectively. The three PS-TENGs are noted as the 1st, 2nd and 3rd PS-TENG from the bottom to the top. Fig. 4b and c shows the transferred charges and short-circuit current of each PS-TENG. The output increases gradually from the bottom PS-TENG to the top one, where 0.43 μC and 2.77 μA for the 1st PS-TENG, 0.74 μC and 3.85 μA for the 2nd one and 0.83 μC and 4.63 μA for the 3rd one are achieved. The enhancement for the output could be attributed to stronger swing at the top. The peak power of each PS-TENG was also tested. The
water waves. As shown in Fig. 2a, the PS-TENG was placed on a plate that can have angular displacement by the pull of the linear motor through a string, simulating the wave motion. Initially, the plate is parallel to the horizontal plane (State I). When the linear motor pulls the string, the device and the plate will tilt to the left with an angle of α relative to the horizontal plane and the disk will roll to the left (State II). When the linear motor releases the rope, the device will tilt to the right and the disk will roll to the right (State III). Here, we integrated nine TENG units in the PS-TENG, which has a volume of 1.94 × 10−4 m3, equal to a ball with a diameter of 72 mm. For an agitation frequency of 1 Hz and amplitude of 11.3°, the transferred charges of the PS-TENG can achieve 0.43 μC (Fig. 2b), which is about 5.9 times of recently reported ball-shell structured device with a similar volume [23]. It is evident that the improved contact area has greatly enhanced the charge output, which is crucial for the performance of the device. The short-circuit current and open-circuit voltage are shown in Fig. 2c and d, respectively. The short-circuit current is 2.77 μA, and the peak-to-peak open-circuit voltage is 3072 V. The power output of the device is demonstrated in Fig. 2e. The highest peak power of the PSTENG is 2.03 mW with a resistive load of 1 GΩ. The average power is calculated according to the following equation with the highest value 0.4 mW:
Pave =
T ∫0 I 2Rdt
T
(1)
where T is the period of the output; I is the output current and R is the load resistance. We further investigated the response of the device to different agitation amplitudes and frequencies. As shown in Fig. 3a and b, when fixing the frequency at 1 Hz, with increasing amplitudes, the transferred charges and peak short-circuit current also rise dramatically, reaching 0.6 μC and 3.2 μA with an amplitude of 15.9°. For testing the frequency response, the amplitude is fixed at 11.3°. The transferred charges and peak short-circuit current increase with the frequency until 1.4 Hz, 3
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Fig. 3. Output performance of the PS-TENG. (a, b) Transferred charges (a) and short-circuit current (b) with different agitation amplitudes. (c, d) Transferred charges (d) and short-circuit current (d) with different agitation frequencies. (e, f) Superimposed output of the transferred charges (e) and short-circuit current (f) with different quantities of TENG units. (g) The transferred charges and short-circuit current of each TENG unit. (h) Rectification circuit diagram of the PS-TENG connected to a capacitor. (i) Charging performance of the PS-TENG to different capacitors. The agitation frequency is 1 Hz and the amplitude is 11.3° unless otherwise specified.
calculated, and the maximum average power can achieve 1.51 mW under the load resistance of 200 MΩ, as shown in Fig. 5d. Considering the volume of each PS-TENG is 1.94 × 10−4 m3, the corresponding peak and average power density are 15.15 W m−3 and 2.59 W m−3, respectively. Fig. 5e and f demonstrate the circuit diagram for charging capacitors and the charging performance of three stacked PS-TENGs. Typically, a capacitor of 100 μF can be charged to 3.58 V for only 120 s, and the amount of stored charges is 358 μC. To test the device in real water wave environment, wave tank experiments were carried out to characterize the performance of packaged devices, as shown in Fig. 6a. Here, three stacked PS-TENGs were packaged by silicone rubber and acrylic plates (the inset in Fig. 6a). The agitation mechanism of the packed device in water is shown in Fig. 6b. The device was anchored to a pole in water and can rotate around the pole. A piece of foam was attached to the outer shell of the device to provide extra buoyant force Ff. In Stage I and II, with the thrust of water waves, the device will swing to the right, and the inertia effect will make the device immersed in water, resulting in large restoring buoyant force Ff (Stage III), which will drive the device to move back, returning to Stage I through the transition of Stage IV. In this way, the device can operate continuously in water waves and provide effective agitations to
highest peak power also rises from the bottom to the top. More specifically, the highest peak power is 2.03 mW for the 1st PS-TENG under a load resistance of 1 GΩ, 3.06 mW for the 2nd one under a load resistance of 812 MΩ and 3.56 mW for the 3rd one under a load resistance of 712 MΩ, as shown in Fig. 4d. The variation of the optimum resistance should reflect the influence of the motion status on the impedance matching of the device [11]. Fig. 4e presents the current of each PSTENG under the optimum resistance, where 1.42 μA, 1.94 μA and 2.24 μA are obtained for the 1st to the 3rd PS-TENG, respectively. The superimposed output of different amounts of stacked PS-TENGs was also investigated. As shown in Fig. 5a and b, the total transferred charges and short-circuit current rise with the amount of PS-TENGs based on parallel connection, achieving 1.95 μC and 10.73 μA for three stacked PS-TENGs (1st + 2nd + 3rd). The peak power of stacked PSTENGs has similar trend (Fig. 5c). The highest peak power of 2.03 mW for one PS-TENG under the load resistance of 1 GΩ increases to 5.46 mW for two PS-TENGs under a load resistance of 512 MΩ, and 8.82 mW for three PS-TENGs under a load resistance of 200 MΩ. The results show evidently that the optimum resistance will decrease with more stacked devices due to lower internal impedance by parallel connection [11]. The average power of three stacked PS-TENGs is also 4
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Fig. 4. Basic characterization of PS-TENGs in stacking. (a) Schematic illustration of the experimental setup. (b) Transferred charges for each stacked device. (c) Shortcircuit current for each stacked device. (d) Peak power of each stacked device with different resistive loads. (e) Current of each stacked device with their optimum resistance. The agitation frequency is 1 Hz and the amplitude is 11.3°.
function generator. The transferred charges and short-circuit current under agitations of different frequencies are shown in Fig. 6c and d. The output peaks at around 0.3 Hz with values of 2.69 μC and 13.35 μA, which are even larger than the output agitated by the linear motor,
the TENG units inside. In our experiments, the water waves were generated by nine wave makers, which were controlled by a function generator. The wave frequency and amplitude can be tuned by changing the frequency and amplitude of the output sinusoidal signal of the
Fig. 5. Output performance of the stacked PS-TENGs. (a–b) Transferred charges (a) and short-circuit current (b) for different amounts of stacked devices. (c) Peak power of stacked PS-TENGs with different resistive loads. (d) Average power of three stacked PS-TENGs. (e) Rectification circuit diagram of stacked PS-TENGs connected to a capacitor. (f) Charging performance of three stacked PS-TENGs to different capacitors. The agitation frequency is 1 Hz and the amplitude is 11.3°. 5
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Fig. 6. Output performance of the PS-TENGs in water. (a) Photograph of the PS-TENGs working in water. Inset shows the packaged device (Scale bar: 5 cm). (b) Schematic illustration of the working principle of the device in water. (c, d) Transferred charges (c) and short-circuit current (d) of the PS-TENGs with different wave frequencies. (e, f) Transferred charges (e) and short-circuit current (f) of the PS-TENGs with different wave amplitudes. The agitation frequency is 0.4 Hz. (g) Charging performance of the PS-TENGs to different capacitors. (h) Peak power of the PS-TENGs with different wave frequencies. (i) Average power of the PS-TENGs with water waves of 0.4 Hz. The amplitude of the drive signal is 2.5 V unless otherwise specified.
low-frequency water waves of 0.4 Hz, a capacitor of 100 μF can be charged to 1.63 V for only 100 s. The stored energy in capacitors can be applied widely to power electronic devices for self-powered systems. We also investigated the power output of the device in different lowfrequency water waves. The peak power in water waves of 0.2, 0.3, 0.4 and 0.5 Hz is presented in Fig. 6h. The highest peak power of 8.56 mW is achieved at the frequency of 0.3 Hz under a load resistance of 191 MΩ, corresponding to a peak power density of 14.71 W m−3 while only considering the volume of the TENG units and 2.53 W m−3 while the volume of the whole packaged device is calculated. The much lower density of the whole packaged device can be attributed to that the packaged space is not fully occupied by TENG units. Through
demonstrating good adaptability and performance in low-frequency water waves. The corresponding output charge density of the device in water is 4622 μC m−3 without the package (5.82 × 10−4 m3) and 793.51 μC m−3 with the package (3.39 × 10−3 m3), which are about 13.2 times and 2.27 times comparing with typical ball-shell structured device [23], indicating great potential of the structure design to improve the charge output of wave energy harvesting devices. The effect of wave amplitude on the output of the device was also tested, as shown in Fig. 6e and f. As the amplitude of the signal increases from 1.7 V to 2.5 V, the transferred charges and short-circuit current of the device also rise gradually. Fig. 6g demonstrates the charging performance of the packaged device to different capacitors agitated by water waves. In 6
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4.3. Device characterization
integrating more TENG units in the packaged space, the power density of the whole device can be greatly improved and approach the density of bare TENG units. Fig. 6i shows the calculated average power at the frequency of 0.4 Hz. A maximum value of 0.61 mW is obtained, corresponding to an average power density of 1.05 W m−3 considering the volume of the TENG units. As an effective low-frequency wave energy harvester, the PS-TENG is promising for the application of powering sensory platforms in ocean. It can also be applied in the form of networks to harvest large-area water wave energy to generate electricity for the power grid or other high-power applications [9,15].
The output charge and current of the TENG and the voltage of the capacitor were measured by an electrometer (Keithley 6514). The opencircuit voltage of the TENG was measured by an electrostatic voltmeter (Trek 344). A linear motor (LinMot E1100) was adopted to agitate the device for experiments in air. A function generator (Tektronix AFG3011C) was used to control the wave makers for experiments in water. Conflict of interest
3. Conclusions
The authors declared that they have no conflicts of interest to this work.
In summary, a pendulum-structured triboelectric nanogenerator for effectively harvesting low-frequency water wave energy is proposed. The device works based on a pendulum-like principle through a compact disk-track structure without a suspending string. Compared to typical ball-shell structured device, the PS-TENG adopts area contact instead of point contact, thus the tribo-electrification and the output can be greatly enhanced. A wrinkle structure of aluminum foil is used to tune the contact area and lower the friction force, enabling effective agitation by slow water waves. Moreover, the PS-TENG is designed as a stackable device and large amount of such devices can be accommodated in one package which can reduce the expense of packaging. While only considering the volume of the TENG units, the charge output density can achieve 4622 μC m−3 and a peak power density of 14.71 W m−3 and an average power density of 1.05 W m−3 can be obtained in low-frequency water waves below 0.5 Hz. The device provides an effective design to enhance the output of TENG-based wave energy harvester with excellent low-frequency performance, which is crucial to the development of TENGs for effectively exploiting abundant water wave energy.
Acknowledgements The research was supported by the National Key R & D Project from Minister of Science and Technology, China (2016YFA0202704), National Natural Science Foundation of China (Grant No. 51605033, 51432005, 5151101243, and 51561145021), Youth Innovation Promotion Association, CAS, China Postdoctoral Science Foundation (Grant No. 2015M581041), and Beijing Municipal Science and Technology Commission (Grant No. Z171100002017017, and Y3993113DF). References [1] [2] [3] [4] [5] [6]
4. Experimental section
[7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18]
4.1. Fabrication of the PS-TENG First, acrylic plates (2.5 mm in thickness) were cut into the shape of the guide spacer shown in Fig. 1. The inner lower track has a radius of 180 mm, and the two ends of the track are tangent to two arcs with a radius of 25 mm. The border of the guide spacer has a width of 5 mm. The electrode panels were mainly fabricated by the printed circuit board fabrication techniques with the same outer shape of the guide spacer. Specifically, the substrate is epoxy glass fiber plate with a thickness of 1 mm, and a layer of copper (35 μm) was plated on the two sides of the resin as electrodes which was then covered with a thin layer of gold to prohibit oxidation. PTFE films (80 μm) were attached to the two sides as triboelectric layers. For the rolling disks, copper plates with a diameter of 50 mm and a thickness of 2 mm were first prepared. Aluminum foil with a thickness of 20 μm was crumpled and attached to the copper plates, covering half of the circular plates on the two sides. The prepared electrode panels and guide spacers were alternately assembled by screws, and one rolling disk was placed in each guide spacer.
[19] [20] [21] [22] [23] [24] [25] [26] [27]
4.2. Packaging of stacked PS-TENGs
[28]
Three PS-TENGs were stacked together and fixed with an elliptical acrylic plate. Then the stacked PS-TENGs were encapsulated by a silicone rubber sleeve with an inner circumference of 631.36 mm and a length of 101 mm. Two acrylic sheets with the same circumference were used to block the two ends of the sleeve and sealed with waterproof glue. A piece of foam with a size of 80 mm × 170 mm × 100 mm was attached to the upper corner of the rubber sleeve.
[29] [30] [31] [32] [33]
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J. Tollefson, Nature 508 (2014) 302–304. E. Callaway, Nature 450 (2007) 156–159. J. Scruggs, P. Jacob, Science 323 (2009) 1176–1178. Q. Schiermeier, J. Tollefson, T. Scully, A. Witze, O. Morton, Nature 454 (2008) 816–823. S.H. Salter, Nature 249 (1974) 720–724. B. Drew, A.R. Plummer, M.N. Sahinkaya, Proc. Inst. Mech., Part A 223 (2009) 887–902. A.F.D. Falcao, Renew. Sustain. Energy Rev. 14 (2010) 899–918. F.R. Fan, Z.Q. Tian, Z.L. Wang, Nano Energy 1 (2012) 328–334. Z.L. Wang, Nature 542 (2017) 159–160. Z.L. Wang, Faraday Discuss 176 (2014) 447–458. S.M. Niu, Z.L. Wang, Nano Energy 14 (2015) 161–192. Z.L. Wang, Mater. Today 20 (2017) 74–82. Z.L. Wang, J. Chen, L. Lin, Energy Environ. Sci. 8 (2015) 2250–2282. B. Chen, Y. Yang, Z.L. Wang, Adv. Energy Mater. 8 (2018) 1702649. Z.L. Wang, T. Jiang, L. Xu, Nano Energy 39 (2017) 9–23. L. Xu, T.Z. Bu, X.D. Yang, C. Zhang, Z.L. Wang, Nano Energy 49 (2018) 625–633. Y. Zi, H. Guo, Z. Wen, M.H. Yeh, C. Hu, Z.L. Wang, ACS Nano 10 (2016) 4797–4805. C.S. Wu, A.C. Wang, W.B. Ding, H.Y. Guo, Z.L. Wang, Adv. Energy Mater. 9 (2019) 1802906. G. Liu, J. Chen, Q. Tang, L. Feng, H. Yang, J. Li, Y. Xi, X. Wang, C. Hu, Adv. Energy Mater. 8 (2018) 1703086. J. Chen, J. Yang, Z.L. Li, X. Fan, Y.L. Zi, Q.S. Jing, H.Y. Guo, Z. Wen, K.C. Pradel, S.M. Niu, Z.L. Wang, ACS Nano 9 (2015) 3324–3331. X.F. Wang, S.M. Niu, Y.J. Yin, F. Yi, Z. You, Z.L. Wang, Adv. Energy Mater. 5 (2015) 1501467. L. Xu, Y.K. Pang, C. Zhang, T. Jiang, X.Y. Chen, J.J. Luo, W. Tang, X. Cao, Z.L. Wang, Nano Energy 31 (2017) 351–358. L. Xu, T. Jiang, P. Lin, J.J. Shao, C. He, W. Zhong, X.Y. Chen, Z.L. Wang, ACS Nano 12 (2018) 1849–1858. X.J. Zhao, S.Y. Kuang, Z.L. Wang, G. Zhu, ACS Nano 12 (2018) 4280–4285. P. Cheng, H.Y. Guo, Z. Wen, C.L. Zhang, X. Yin, X.Y. Li, D. Liu, W.X. Song, X.H. Sun, J. Wang, Z.L. Wang, Nano Energy 57 (2019) 432–439. G. Liu, H. Guo, S. Xu, C. Hu, Z.L. Wang, Adv. Energy Mater. (2019) 1900801. J. Wang, L. Pan, H. Guo, B. Zhang, R. Zhang, Z. Wu, C. Wu, L. Yang, R. Liao, Z.L. Wang, Adv. Energy Mater. (2019) 1802892. A. Ahmed, Z. Saadatnia, I. Hassan, Y. Zi, Y. Xi, X. He, J. Zu, Z.L. Wang, Adv. Energy Mater. 7 (2017) 1601705. S.H. Wang, Y.N. Xie, S.M. Niu, L. Lin, C. Liu, Y.S. Zhou, Z.L. Wang, Adv. Mater. 26 (2014) 6720–6728. Y.L. Zi, S.M. Niu, J. Wang, Z. Wen, W. Tang, Z.L. Wang, Nat. Commun. 6 (2015) 8376. S.H. Wang, Y.N. Xie, S.M. Niu, L. Lin, Z.L. Wang, Adv. Mater. 26 (2014) 2818–2824. S.M. Niu, Y. Liu, X.Y. Chen, S.H. Wang, Y.S. Zhou, L. Lin, Y.N. Xie, Z.L. Wang, Nano Energy 12 (2015) 760–774. C. Zhang, W. Tang, C.B. Han, F.R. Fan, Z.L. Wang, Adv. Mater. 26 (2014) 3580–3591.
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Full paper
Stacked pendulum-structured triboelectric nanogenerators for effectively harvesting low-frequency water wave energy
T
Wei Zhonga,b,1, Liang Xua,b,1, Haiming Wanga,b,1, Ding Lia,b, Zhong Lin Wanga,b,c,∗ a
CAS Center for Excellence in Nanoscience, Beijing Key Laboratory of Micro-nano Energy and Sensor, Beijing Institute of Nanoenergy and Nanosystems, Chinese Academy of Sciences, Beijing, 100083, PR China b School of Nanoscience and Technology, University of Chinese Academy of Sciences, Beijing, 100049, PR China c School of Material Science and Engineering, Georgia Institute of Technology, Atlanta, GA, 30332, USA
A R T I C LE I N FO
A B S T R A C T
Keywords: Triboelectric nanogenerator Water wave energy Pendulum structure Disk-track structure Blue energy
The invention of triboelectric nanogenerators (TENGs) provides an effective approach for harvesting water wave energy that is clean and renewable. Here, stacked pendulum-structured triboelectric nanogenerators for harvesting low-frequency water wave energy is proposed. The device works based on a pendulum-like principle through a compact disk-track structure that enables area contact instead of point contact while maintaining the susceptible rolling motion. Thus the tribo-electrification and the output are greatly enhanced in slow water waves. While only considering the volume of the TENG units, charge output density of 4622 μC m−3 can be achieved, which is more than 13.2 times of a typical ball-shell structured device. A peak power density of 14.71 W m−3 and an average power density of 1.05 W m−3 are obtained in low-frequency water waves below 0.5 Hz. The device shows great potential of the rolling area-contact design to enhance the output of TENG-based wave energy harvester with excellent low-frequency performance, which is crucial to the development of TENGs for effectively exploiting abundant water wave energy.
1. Introduction The ocean, which covers more than 70% of the surface of the earth, contains huge amounts of clean and renewable energy in the form of wave energy, tidal energy and thermal energy etc. [1–3]. Under the concern for environment protection and clean energy, to exploit the ocean energy has drawn worldwide attention [1,4]. Among different forms of ocean energy, the wave energy is one of the most focused due to its large reserves and vast distribution [2,3]. However, although efforts have been made for several decades on the research of wave energy, there are still many obstacles for its commercialization [2,5–7]. The current technologies are mainly based on electromagnetic generators (EMGs) which usually lead to cumbersome and expensive machines [6,7]. Very recently, another approach based on triboelectric nanogenerators (TENGs) has emerged, bringing new opportunities for this field [8–10]. The TENG works based on the effects of tribo-electrification and electrostatic induction [11]. It has merits of lightweight, low cost, versatile choices of structures and materials etc. [12]. Since its invention in 2012, the TENG has demonstrated its great potential in
harvesting various low-frequency mechanical energies for self-powered systems, such as wind, water flow, human motion and vibration [8,12–19]. The idea of using TENG to harvest wave energy was brought out in 2014 [10], and several prototypes have proved the feasibility of this approach [15,18,20–28]. Among all the wave energy harvesting devices, the ball-shell structure is one of the most common types, where a solid ball is adopted to roll in a spherical shell [21,23,25]. Several designs have improved the output, especially the transferred charges, which are the basis for the performance of the device [29,30]. A fully enclosed TENG that encapsulated a hard rolling ball inside a spherical shell was proposed in 2015 with a transferred charge density of 212.39 μC m−3 in water [21]. The work using soft silicone rubber ball improved the value to about 350 μC m−3 in 2018 [23]. Another design adopted highly soft silicone rubber ball and produced a charge density of 361.11 μC m−3 in water in 2019 [25]. For the ball-shell structure, the contact is essentially point contact with small contact area which limits the tribo-electrification. For further improving the output performance, designs that enable area contact with easy rolling abilities are highly desired.
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Corresponding author. CAS Center for Excellence in Nanoscience, Beijing Key Laboratory of Micro-nano Energy and Sensor, Beijing Institute of Nanoenergy and Nanosystems, Chinese Academy of Sciences, Beijing, 100083, PR China. E-mail address: [email protected] (Z.L. Wang). 1 These authors contributed equally to this work. https://doi.org/10.1016/j.nanoen.2019.104108 Received 14 August 2019; Received in revised form 2 September 2019; Accepted 7 September 2019 Available online 09 September 2019 2211-2855/ © 2019 Elsevier Ltd. All rights reserved.
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Fig. 1. Structure and working principle of the PS-TENG device. (a) Schematic explosive view of the device. (b) Photograph of the rolling disk (Scale bar: 3 cm). Inset: Photograph of the surface of wrinkled aluminum foil (Scale bar: 1 mm). (c) The operation principle of the TENG like a pendulum. (d) Basic working mechanism of TENG units.
device to respond effectively to external low-frequency mechanical agitations, such as water waves, and the structure is more compact without a suspending string. The period of a pendulum with small amplitudes can be estimated by T = 2π L/g , where L represents the length of the pendulum and is equal to R-r here. Such a period is affected by friction force and other factors in real devices. However, as a rough estimation, the equation can still be used to guide the design of the guide track for a better response to water waves with certain periods. The fundamental working mechanism of the TENG is based on the conjugation of tribo-electrification and electrostatic induction in a freestanding-triboelectric-layer mode, as demonstrated in Fig. 1d [31,32]. The electrodes of different electrode layers at the left or right side are interconnected, respectively. While rolling on the guide track, the metal disk will rub with the PTFE films on the electrode panels, and electrons will transfer from the disk to the surfaces of the PTFE films due to their higher affinity to electrons [33]. Thus the disk will be positively charged. The positive charges in the disk will induce a higher potential on adjacent electrodes, and electrons will transfer between the electrodes through an external circuit to compensate the potential difference, forming current in the circuit. More specifically, when the disk rolls to the right side, the current will flow from the right electrodes to the left electrodes, and a reverse current will appear when the disk returns to the left side. With the disk swinging back and forth, alternating current will be generated in the load and mechanical energy of the disk can be converted into electricity. Compared to typical ball-shell structured device, the design uses area contact instead of point contact, thus the tribo-electrification can be greatly enhanced [21,23,25]. However, the side effect is that the friction force can also rise dramatically which can even prohibit the disk from rolling with the attraction of static charges. So the wrinkle structure of aluminum foil is adopted to adjust the contact area and lower the friction force, which is facile to be applied. To characterize the basic output performance of the PS-TENG, we tested the device on a linear motor that can simulate the agitation of
Here, we proposed a stacked pendulum-structured triboelectric nanogenerator (PS-TENG) for effectively harvesting low-frequency water wave energy. The device works based on a pendulum-like principle through a compact disk-track structure which enables area contact instead of point contact while maintaining the susceptible rolling motion. Thus, the tribo-electrification and the output are greatly enhanced in slow water waves. While only considering the volume of the TENG units, charge output density of 4622 μC m−3 can be achieved, and a peak power density of 14.71 W m−3 and an average power density of 1.05 W m−3 are obtained in low-frequency water waves below 0.5 Hz. The device shows great potential of the rolling area-contact design in improving the output of TENGs for wave energy harvesting.
2. Results and discussion The structure of the PS-TENG is schematically shown in Fig. 1a. There are three major parts in the device, namely electrode panels, guide spacers and rolling disks. The electrode panel is composed by an epoxy glass fiber plate, two metal (Au + Cu) electrode layers and two polytetrafluoroethylene (PTFE) films, and each electrode layer is separated into two electrodes. The guide spacer is made of acrylic with specific guide track inside, which can form a chamber with the electrode panel. The disk is fabricated by covering half of a circular copper plate with wrinkled aluminum foil at both sides (Fig. 1b), and the wrinkle structure is demonstrated in the inset of Fig. 1b. The design of wrinkled aluminum foil is used to adjust the contact area of the disk and the electrode panel, which will be discussed in details afterwards. A simplest TENG unit can be assembled by placing one rolling disk in the chamber formed by one electrode panel and one guide spacer. The PSTENG can be consistent by several such TENG units. Details of the fabrication process are provided in the Experimental Section. The device operates on a pendulum-like principle, as shown in Fig. 1c. The inside track of the guide spacer has a shape of circular arc with a radius of R. The rolling disk, with a radius of r, can swing on the track, just like a pendulum with a length of R-r. The pendulum design enables the 2
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Fig. 2. Basic characterization of the PS-TENG in air. (a) Schematic illustration of the experimental setup. (b–d) Transferred charges (b), short-circuit current (c) and open-circuit voltage (d) of the PS-TENG. (e) Peak power and average power of the PS-TENG with resistive loads. The agitation frequency is 1 Hz and the amplitude is 11.3°.
where the resonance of the PS-TENG is achieved. Outputs of 0.57 μC and 4.4 μA can be delivered at the resonance state. With higher frequencies, the output will decrease, as shown in Fig. 3c and d. The performance of the PS-TENG consisting of different quantities of TENG units was also studied, as demonstrated in Fig. 3e and f. The charge and current outputs increase almost linearly with the quantity of the TENG unit, which implies that the device should have good scale-up performance. The detailed output of each unit is presented in Fig. 3g. The output of each unit in the PS-TENG shows some fluctuations. The transferred charges are approximately between 0.03 μC and 0.06 μC, and the peak short-circuit currents are between 0.3 μA and 0.68 μA. The non-uniformity should originate from the contact state of the disk with the electrode panel in each unit, and a stable output can be obtained when the output of a few TENG units are superposed as in the PS-TENG. For the application of harvesting wave energy, it is critical to store the instantaneously generated electrical energy for driving external electrical devices which usually have larger energy consumption. Fig. 3h shows the circuit diagram for the PS-TENG to charge a capacitor for storing the harvested energy. The charging performance to different capacitors is shown in Fig. 3i. A capacitor of 22 μF could be charged to 2.35 V in 70 s, and charges of 51.7 μC were stored. For lowering the expense of packaging, the PS-TENG is designed as a stackable device and several such devices can be accommodated in one package. Here, the output of three stacked devices was studied, as shown in Fig. 4a. The experimental setup is similar to single PS-TENG tests and the agitation frequency and amplitude were fixed at 1 Hz and 11.3°, respectively. The three PS-TENGs are noted as the 1st, 2nd and 3rd PS-TENG from the bottom to the top. Fig. 4b and c shows the transferred charges and short-circuit current of each PS-TENG. The output increases gradually from the bottom PS-TENG to the top one, where 0.43 μC and 2.77 μA for the 1st PS-TENG, 0.74 μC and 3.85 μA for the 2nd one and 0.83 μC and 4.63 μA for the 3rd one are achieved. The enhancement for the output could be attributed to stronger swing at the top. The peak power of each PS-TENG was also tested. The
water waves. As shown in Fig. 2a, the PS-TENG was placed on a plate that can have angular displacement by the pull of the linear motor through a string, simulating the wave motion. Initially, the plate is parallel to the horizontal plane (State I). When the linear motor pulls the string, the device and the plate will tilt to the left with an angle of α relative to the horizontal plane and the disk will roll to the left (State II). When the linear motor releases the rope, the device will tilt to the right and the disk will roll to the right (State III). Here, we integrated nine TENG units in the PS-TENG, which has a volume of 1.94 × 10−4 m3, equal to a ball with a diameter of 72 mm. For an agitation frequency of 1 Hz and amplitude of 11.3°, the transferred charges of the PS-TENG can achieve 0.43 μC (Fig. 2b), which is about 5.9 times of recently reported ball-shell structured device with a similar volume [23]. It is evident that the improved contact area has greatly enhanced the charge output, which is crucial for the performance of the device. The short-circuit current and open-circuit voltage are shown in Fig. 2c and d, respectively. The short-circuit current is 2.77 μA, and the peak-to-peak open-circuit voltage is 3072 V. The power output of the device is demonstrated in Fig. 2e. The highest peak power of the PSTENG is 2.03 mW with a resistive load of 1 GΩ. The average power is calculated according to the following equation with the highest value 0.4 mW:
Pave =
T ∫0 I 2Rdt
T
(1)
where T is the period of the output; I is the output current and R is the load resistance. We further investigated the response of the device to different agitation amplitudes and frequencies. As shown in Fig. 3a and b, when fixing the frequency at 1 Hz, with increasing amplitudes, the transferred charges and peak short-circuit current also rise dramatically, reaching 0.6 μC and 3.2 μA with an amplitude of 15.9°. For testing the frequency response, the amplitude is fixed at 11.3°. The transferred charges and peak short-circuit current increase with the frequency until 1.4 Hz, 3
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Fig. 3. Output performance of the PS-TENG. (a, b) Transferred charges (a) and short-circuit current (b) with different agitation amplitudes. (c, d) Transferred charges (d) and short-circuit current (d) with different agitation frequencies. (e, f) Superimposed output of the transferred charges (e) and short-circuit current (f) with different quantities of TENG units. (g) The transferred charges and short-circuit current of each TENG unit. (h) Rectification circuit diagram of the PS-TENG connected to a capacitor. (i) Charging performance of the PS-TENG to different capacitors. The agitation frequency is 1 Hz and the amplitude is 11.3° unless otherwise specified.
calculated, and the maximum average power can achieve 1.51 mW under the load resistance of 200 MΩ, as shown in Fig. 5d. Considering the volume of each PS-TENG is 1.94 × 10−4 m3, the corresponding peak and average power density are 15.15 W m−3 and 2.59 W m−3, respectively. Fig. 5e and f demonstrate the circuit diagram for charging capacitors and the charging performance of three stacked PS-TENGs. Typically, a capacitor of 100 μF can be charged to 3.58 V for only 120 s, and the amount of stored charges is 358 μC. To test the device in real water wave environment, wave tank experiments were carried out to characterize the performance of packaged devices, as shown in Fig. 6a. Here, three stacked PS-TENGs were packaged by silicone rubber and acrylic plates (the inset in Fig. 6a). The agitation mechanism of the packed device in water is shown in Fig. 6b. The device was anchored to a pole in water and can rotate around the pole. A piece of foam was attached to the outer shell of the device to provide extra buoyant force Ff. In Stage I and II, with the thrust of water waves, the device will swing to the right, and the inertia effect will make the device immersed in water, resulting in large restoring buoyant force Ff (Stage III), which will drive the device to move back, returning to Stage I through the transition of Stage IV. In this way, the device can operate continuously in water waves and provide effective agitations to
highest peak power also rises from the bottom to the top. More specifically, the highest peak power is 2.03 mW for the 1st PS-TENG under a load resistance of 1 GΩ, 3.06 mW for the 2nd one under a load resistance of 812 MΩ and 3.56 mW for the 3rd one under a load resistance of 712 MΩ, as shown in Fig. 4d. The variation of the optimum resistance should reflect the influence of the motion status on the impedance matching of the device [11]. Fig. 4e presents the current of each PSTENG under the optimum resistance, where 1.42 μA, 1.94 μA and 2.24 μA are obtained for the 1st to the 3rd PS-TENG, respectively. The superimposed output of different amounts of stacked PS-TENGs was also investigated. As shown in Fig. 5a and b, the total transferred charges and short-circuit current rise with the amount of PS-TENGs based on parallel connection, achieving 1.95 μC and 10.73 μA for three stacked PS-TENGs (1st + 2nd + 3rd). The peak power of stacked PSTENGs has similar trend (Fig. 5c). The highest peak power of 2.03 mW for one PS-TENG under the load resistance of 1 GΩ increases to 5.46 mW for two PS-TENGs under a load resistance of 512 MΩ, and 8.82 mW for three PS-TENGs under a load resistance of 200 MΩ. The results show evidently that the optimum resistance will decrease with more stacked devices due to lower internal impedance by parallel connection [11]. The average power of three stacked PS-TENGs is also 4
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Fig. 4. Basic characterization of PS-TENGs in stacking. (a) Schematic illustration of the experimental setup. (b) Transferred charges for each stacked device. (c) Shortcircuit current for each stacked device. (d) Peak power of each stacked device with different resistive loads. (e) Current of each stacked device with their optimum resistance. The agitation frequency is 1 Hz and the amplitude is 11.3°.
function generator. The transferred charges and short-circuit current under agitations of different frequencies are shown in Fig. 6c and d. The output peaks at around 0.3 Hz with values of 2.69 μC and 13.35 μA, which are even larger than the output agitated by the linear motor,
the TENG units inside. In our experiments, the water waves were generated by nine wave makers, which were controlled by a function generator. The wave frequency and amplitude can be tuned by changing the frequency and amplitude of the output sinusoidal signal of the
Fig. 5. Output performance of the stacked PS-TENGs. (a–b) Transferred charges (a) and short-circuit current (b) for different amounts of stacked devices. (c) Peak power of stacked PS-TENGs with different resistive loads. (d) Average power of three stacked PS-TENGs. (e) Rectification circuit diagram of stacked PS-TENGs connected to a capacitor. (f) Charging performance of three stacked PS-TENGs to different capacitors. The agitation frequency is 1 Hz and the amplitude is 11.3°. 5
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Fig. 6. Output performance of the PS-TENGs in water. (a) Photograph of the PS-TENGs working in water. Inset shows the packaged device (Scale bar: 5 cm). (b) Schematic illustration of the working principle of the device in water. (c, d) Transferred charges (c) and short-circuit current (d) of the PS-TENGs with different wave frequencies. (e, f) Transferred charges (e) and short-circuit current (f) of the PS-TENGs with different wave amplitudes. The agitation frequency is 0.4 Hz. (g) Charging performance of the PS-TENGs to different capacitors. (h) Peak power of the PS-TENGs with different wave frequencies. (i) Average power of the PS-TENGs with water waves of 0.4 Hz. The amplitude of the drive signal is 2.5 V unless otherwise specified.
low-frequency water waves of 0.4 Hz, a capacitor of 100 μF can be charged to 1.63 V for only 100 s. The stored energy in capacitors can be applied widely to power electronic devices for self-powered systems. We also investigated the power output of the device in different lowfrequency water waves. The peak power in water waves of 0.2, 0.3, 0.4 and 0.5 Hz is presented in Fig. 6h. The highest peak power of 8.56 mW is achieved at the frequency of 0.3 Hz under a load resistance of 191 MΩ, corresponding to a peak power density of 14.71 W m−3 while only considering the volume of the TENG units and 2.53 W m−3 while the volume of the whole packaged device is calculated. The much lower density of the whole packaged device can be attributed to that the packaged space is not fully occupied by TENG units. Through
demonstrating good adaptability and performance in low-frequency water waves. The corresponding output charge density of the device in water is 4622 μC m−3 without the package (5.82 × 10−4 m3) and 793.51 μC m−3 with the package (3.39 × 10−3 m3), which are about 13.2 times and 2.27 times comparing with typical ball-shell structured device [23], indicating great potential of the structure design to improve the charge output of wave energy harvesting devices. The effect of wave amplitude on the output of the device was also tested, as shown in Fig. 6e and f. As the amplitude of the signal increases from 1.7 V to 2.5 V, the transferred charges and short-circuit current of the device also rise gradually. Fig. 6g demonstrates the charging performance of the packaged device to different capacitors agitated by water waves. In 6
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4.3. Device characterization
integrating more TENG units in the packaged space, the power density of the whole device can be greatly improved and approach the density of bare TENG units. Fig. 6i shows the calculated average power at the frequency of 0.4 Hz. A maximum value of 0.61 mW is obtained, corresponding to an average power density of 1.05 W m−3 considering the volume of the TENG units. As an effective low-frequency wave energy harvester, the PS-TENG is promising for the application of powering sensory platforms in ocean. It can also be applied in the form of networks to harvest large-area water wave energy to generate electricity for the power grid or other high-power applications [9,15].
The output charge and current of the TENG and the voltage of the capacitor were measured by an electrometer (Keithley 6514). The opencircuit voltage of the TENG was measured by an electrostatic voltmeter (Trek 344). A linear motor (LinMot E1100) was adopted to agitate the device for experiments in air. A function generator (Tektronix AFG3011C) was used to control the wave makers for experiments in water. Conflict of interest
3. Conclusions
The authors declared that they have no conflicts of interest to this work.
In summary, a pendulum-structured triboelectric nanogenerator for effectively harvesting low-frequency water wave energy is proposed. The device works based on a pendulum-like principle through a compact disk-track structure without a suspending string. Compared to typical ball-shell structured device, the PS-TENG adopts area contact instead of point contact, thus the tribo-electrification and the output can be greatly enhanced. A wrinkle structure of aluminum foil is used to tune the contact area and lower the friction force, enabling effective agitation by slow water waves. Moreover, the PS-TENG is designed as a stackable device and large amount of such devices can be accommodated in one package which can reduce the expense of packaging. While only considering the volume of the TENG units, the charge output density can achieve 4622 μC m−3 and a peak power density of 14.71 W m−3 and an average power density of 1.05 W m−3 can be obtained in low-frequency water waves below 0.5 Hz. The device provides an effective design to enhance the output of TENG-based wave energy harvester with excellent low-frequency performance, which is crucial to the development of TENGs for effectively exploiting abundant water wave energy.
Acknowledgements The research was supported by the National Key R & D Project from Minister of Science and Technology, China (2016YFA0202704), National Natural Science Foundation of China (Grant No. 51605033, 51432005, 5151101243, and 51561145021), Youth Innovation Promotion Association, CAS, China Postdoctoral Science Foundation (Grant No. 2015M581041), and Beijing Municipal Science and Technology Commission (Grant No. Z171100002017017, and Y3993113DF). References [1] [2] [3] [4] [5] [6]
4. Experimental section
[7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18]
4.1. Fabrication of the PS-TENG First, acrylic plates (2.5 mm in thickness) were cut into the shape of the guide spacer shown in Fig. 1. The inner lower track has a radius of 180 mm, and the two ends of the track are tangent to two arcs with a radius of 25 mm. The border of the guide spacer has a width of 5 mm. The electrode panels were mainly fabricated by the printed circuit board fabrication techniques with the same outer shape of the guide spacer. Specifically, the substrate is epoxy glass fiber plate with a thickness of 1 mm, and a layer of copper (35 μm) was plated on the two sides of the resin as electrodes which was then covered with a thin layer of gold to prohibit oxidation. PTFE films (80 μm) were attached to the two sides as triboelectric layers. For the rolling disks, copper plates with a diameter of 50 mm and a thickness of 2 mm were first prepared. Aluminum foil with a thickness of 20 μm was crumpled and attached to the copper plates, covering half of the circular plates on the two sides. The prepared electrode panels and guide spacers were alternately assembled by screws, and one rolling disk was placed in each guide spacer.
[19] [20] [21] [22] [23] [24] [25] [26] [27]
4.2. Packaging of stacked PS-TENGs
[28]
Three PS-TENGs were stacked together and fixed with an elliptical acrylic plate. Then the stacked PS-TENGs were encapsulated by a silicone rubber sleeve with an inner circumference of 631.36 mm and a length of 101 mm. Two acrylic sheets with the same circumference were used to block the two ends of the sleeve and sealed with waterproof glue. A piece of foam with a size of 80 mm × 170 mm × 100 mm was attached to the upper corner of the rubber sleeve.
[29] [30] [31] [32] [33]
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J. Tollefson, Nature 508 (2014) 302–304. E. Callaway, Nature 450 (2007) 156–159. J. Scruggs, P. Jacob, Science 323 (2009) 1176–1178. Q. Schiermeier, J. Tollefson, T. Scully, A. Witze, O. Morton, Nature 454 (2008) 816–823. S.H. Salter, Nature 249 (1974) 720–724. B. Drew, A.R. Plummer, M.N. Sahinkaya, Proc. Inst. Mech., Part A 223 (2009) 887–902. A.F.D. Falcao, Renew. Sustain. Energy Rev. 14 (2010) 899–918. F.R. Fan, Z.Q. Tian, Z.L. Wang, Nano Energy 1 (2012) 328–334. Z.L. Wang, Nature 542 (2017) 159–160. Z.L. Wang, Faraday Discuss 176 (2014) 447–458. S.M. Niu, Z.L. Wang, Nano Energy 14 (2015) 161–192. Z.L. Wang, Mater. Today 20 (2017) 74–82. Z.L. Wang, J. Chen, L. Lin, Energy Environ. Sci. 8 (2015) 2250–2282. B. Chen, Y. Yang, Z.L. Wang, Adv. Energy Mater. 8 (2018) 1702649. Z.L. Wang, T. Jiang, L. Xu, Nano Energy 39 (2017) 9–23. L. Xu, T.Z. Bu, X.D. Yang, C. Zhang, Z.L. Wang, Nano Energy 49 (2018) 625–633. Y. Zi, H. Guo, Z. Wen, M.H. Yeh, C. Hu, Z.L. Wang, ACS Nano 10 (2016) 4797–4805. C.S. Wu, A.C. Wang, W.B. Ding, H.Y. Guo, Z.L. Wang, Adv. Energy Mater. 9 (2019) 1802906. G. Liu, J. Chen, Q. Tang, L. Feng, H. Yang, J. Li, Y. Xi, X. Wang, C. Hu, Adv. Energy Mater. 8 (2018) 1703086. J. Chen, J. Yang, Z.L. Li, X. Fan, Y.L. Zi, Q.S. Jing, H.Y. Guo, Z. Wen, K.C. Pradel, S.M. Niu, Z.L. Wang, ACS Nano 9 (2015) 3324–3331. X.F. Wang, S.M. Niu, Y.J. Yin, F. Yi, Z. You, Z.L. Wang, Adv. Energy Mater. 5 (2015) 1501467. L. Xu, Y.K. Pang, C. Zhang, T. Jiang, X.Y. Chen, J.J. Luo, W. Tang, X. Cao, Z.L. Wang, Nano Energy 31 (2017) 351–358. L. Xu, T. Jiang, P. Lin, J.J. Shao, C. He, W. Zhong, X.Y. Chen, Z.L. Wang, ACS Nano 12 (2018) 1849–1858. X.J. Zhao, S.Y. Kuang, Z.L. Wang, G. Zhu, ACS Nano 12 (2018) 4280–4285. P. Cheng, H.Y. Guo, Z. Wen, C.L. Zhang, X. Yin, X.Y. Li, D. Liu, W.X. Song, X.H. Sun, J. Wang, Z.L. Wang, Nano Energy 57 (2019) 432–439. G. Liu, H. Guo, S. Xu, C. Hu, Z.L. Wang, Adv. Energy Mater. (2019) 1900801. J. Wang, L. Pan, H. Guo, B. Zhang, R. Zhang, Z. Wu, C. Wu, L. Yang, R. Liao, Z.L. Wang, Adv. Energy Mater. (2019) 1802892. A. Ahmed, Z. Saadatnia, I. Hassan, Y. Zi, Y. Xi, X. He, J. Zu, Z.L. Wang, Adv. Energy Mater. 7 (2017) 1601705. S.H. Wang, Y.N. Xie, S.M. Niu, L. Lin, C. Liu, Y.S. Zhou, Z.L. Wang, Adv. Mater. 26 (2014) 6720–6728. Y.L. Zi, S.M. Niu, J. Wang, Z. Wen, W. Tang, Z.L. Wang, Nat. Commun. 6 (2015) 8376. S.H. Wang, Y.N. Xie, S.M. Niu, L. Lin, Z.L. Wang, Adv. Mater. 26 (2014) 2818–2824. S.M. Niu, Y. Liu, X.Y. Chen, S.H. Wang, Y.S. Zhou, L. Lin, Y.N. Xie, Z.L. Wang, Nano Energy 12 (2015) 760–774. C. Zhang, W. Tang, C.B. Han, F.R. Fan, Z.L. Wang, Adv. Mater. 26 (2014) 3580–3591.