Arc‐Shaped Triboelectric Nanogenerator Based on Rolling Structure for Harvesting Low‐Frequency Water Wave Energy.pdf

2100359 (1 of 8) 2021 Wiley-VCH GmbHwww.advmattechnol.deReseaRch aRticleArc-Shaped Triboelectric Nanogenerator Based on Rolling Structure for Harvesting Low-Frequency Water Wave EnergyJie Ren, Cunjin Gao, Jie An, Quanxiao Liu, Jigang Wang,* Tao Jiang,* and Zhong Lin Wang*DOI: 10.1002/admt.2021003591. IntroductionWith the increasing demand for ecological and environmental protection, renew-able energy has become an important solution for relieving energy crisis and environmental problems.1,2 And renew-able energy can meet the demand of two-thirds of the global energy, and help achieve most of the greenhouse gas reduc-tion required from now to 2050. Ocean occupying 71% of the worlds surface area contains abundant renewable energy that can be applied in a wide range.35 How-ever, the ocean energy is usually intermit-tent and low-frequency energy requiring large-scale conversion and storage for opti-mizing the utilization.6,7 Nowadays, the main converter of ocean energy is relying on electromagnetic generator (EMG), but it is facing great challenges due to the high cost, seawater corrosion, and limited conversion efficiency.810 Therefore, it is desirable to seek new efficient energy con-version approaches for ocean energy.Triboelectric nanogenerator (TENG) invented by Wang and co-workers in 2012 is a new kind of energy technology that efficiently converts surrounding mechanical energy into electricity.1113 Compared to traditional EMG, the TENG has low fabrication cost, high efficiency, high output power, light weight, and other excellent charac-teristics.1417 The working principle of TENGs is based on the coupling effect of triboelectrification and electrostatic induction.6,18,19 The fundamental mechanism of Maxwells displacement current makes the TENG find potential “killer” applications in harvesting low-frequency mechanical energy, especially the water wave energy.2022 So far, a variety of TENG structures have been designed for water wave energy harvesting, and their output performance has been gradually improved.2329 In recent works, a spring-assisted structure and an internal swing structure were respectively introduced into the TENG systems to convert low frequency wave motion into high frequency vibration, bringing a large enhancement of energy conversion efficiency.7,3033 The two structures were also arrayed to elevate the output power density. The integrating and networking of multiple TENG units are of important practical value in large-scale wave energy harvesting. Therefore, it is nec-essary to further explore appropriate TENG structures which are very suitable for high-density integrating and packaging toward practical applications of ocean energy development.Ocean occupies about 71% of the global surface area and contains 97% of the total water on the earth. Ocean waves are regarded as one of the most promising renewable energy sources, but it is quite difficult to harvest such low-quality and low-frequency energy due to the technology limitations of traditional electromagnetic generators. In this work, a type of arc-shaped triboelectric nanogenerator (AS-TENG) with internal rolling structure is designed to harvest low-frequency water wave energy. The freestanding roller with flexible surfaces can scroll freely with low friction along the arched track under external triggering, generating induced current between the com-plementary electrodes. The arc-shaped design facilitates the high-density integrating of multiple TENG units and effective packaging for potential large-scope applications. One AS-TENG can deliver an output power density of 5.47 W m3 under regular triggering, while a power density of 2.34 W m3 is achieved for an AS-TENG array under real water wave triggering of 1.2Hz. Moreover, through harvesting water wave energy by the AS-TENG array, self-powered temperature sensing and wireless transmission systems have been successfully constructed. This work demonstrates huge application prospects of the AS-TENGs toward large-scale ocean blue energy harvesting and envi-ronmental monitoring.J. Ren, C. Gao, Q. Liu, Dr. J. WangBeijing Key Laboratory of Printing and Packaging Materials and TechnologyBeijing Institute of Graphic CommunicationBeijing 102600, P. R. ChinaE-mail: J. Ren, J. An, Dr. T. Jiang, Prof. Z. L. WangCAS Center for Excellence in NanoscienceBeijing Key Laboratory of Micro-nano Energy and SensorBeijing Institute of Nanoenergy and NanosystemsChinese Academy of SciencesBeijing 101400, P. R. ChinaE-mail: ; zlwanggatech.eduJ. An, Dr. T. Jiang, Prof. Z. L. WangSchool of Nanoscience and TechnologyUniversity of Chinese Academy of SciencesBeijing 100049, P. R. ChinaDr. T. Jiang, Prof. Z. L. WangCUSPEA Institute of TechnologyWenzhou, Zhejiang 325024, P. R. ChinaProf. Z. L. WangSchool of Materials Science and EngineeringGeorgia Institute of TechnologyAtlanta, GA 30332-0245, USAThe ORCID identification number(s) for the author(s) of this article can be found under https:/doi.org/10.1002/admt.202100359.Adv. Mater. Technol. 2021, 2021 Wiley-VCH GmbH2100359 (2 of 8)www.advmattechnol.deIn this work, we designed an arc-shaped TENG (AS-TENG) based on an internal rolling structure that can scroll forward and backward to collect low-frequency water wave energy. The AS-TENG can fully improve the space utilization of the device and achieve stable power output. Due to the weight of the roller itself, through inertia, the two tribo-surfaces with a flexible con-tact can be easily rubbed with each other. Under the water wave triggering of 1.2Hz, the peak power and average power densi-ties of the AS-TENG array with four parallel units can reach 2.34 and 0.21 W m3, respectively. In addition, the TENG array has successfully realized self-powered temperature sensing and wireless transmission based on the translated electrical energy from the water waves. The unique movement mode and struc-ture make such TENG a promising candidate for effective water wave energy harvesting toward large-scale blue energy.2. Results and DiscussionAn arc-shaped TENG with an internal freestanding roller was designed, as schematically shown in Figure1a. The arc-shaped design was proposed to facilitate the high-density integrating of multiple TENG units and the effective packaging, which is very important for large-scale harvesting of water wave energy. The AS-TENG is composed of two parts: one is made of two customized printed circuit boards (PCB) on which complemen-tary copper electrodes are adhered, and the other is a freely-movable roller containing acrylic blocks and two commercial bearings. The electrode side of each PCB board is attached by a polytetrafluoroethylene (PTFE) film. To enhance the surface charge density, electrons were preinjected onto the PTFE sur-faces. The two PCB boards serving as the outer walls are fixed by two acrylic semicircular pipes. The lower semicircular pipe is used as the track for the roller to scroll back and forth by means of the inertia under external triggering. Figure1b shows the front view structure of the TENG and the roller surface. The aluminum film on the roller surface has a corresponding grating structure to the grating electrodes (the case of 24 grating units is shown for example). A layer of polyvinyl chloride (PVC) film is sandwiched between the acrylic surface of roller and the Al film, which serves as a buffer layer to improve the contact intimacy for generating higher surface charge density. The enlarged view of the internal structure of the TENG can be seen in Figure1c, and the fabrication details can be found in the Experimental Section. The photograph of as-fabricated AS-TENG device with an encapsulated structure is shown in Figure S1 in the Supporting Information.The AS-TENG is based on the triboelectrification between the Al film on the roller surface and the PTFE film onto the electrodes. Due to the difference in the electronegativity, negative electrostatic charges are generated on the PTFE sur-face, while positive charges are produced on the Al film. The working principle of the AS-TENG is schematically shown in Figure1d. At the initial state (state i), the PTFE surface at the non-overlapped region has negative charges of certain charge density, and the positive net charges with the same density exists on the Al film. The neutralized charges at the overlapped region between the Al and PTFE are not shown. Induced charges with opposite signs on the two electrodes are gener-ated to equilibrate the electrical potential difference resulting from the net opposite charges on two triboelectric materials. At the stable state, there is no electron flow and current through the external circuit. When an external excitation is applied on the TENG device, the roller will naturally scroll from the right to the left side. As shown in state ii, the positively-charged Al film moves leftward, inducing the electrons to flow from the right electrode to the left electrode, and a current from the left to the right electrode is generated. When the roller continues to move until the left electrode (state iii), the maximum charge transfer is achieved, and the current becomes zero. After that, a further scrolling of the roller or the scrolling to the right will cause reverse flow of electrons and generate reverse current Figure 1. a) Schematic diagram of the arc-shaped TENG with internal rolling structure. b) Schematic illustration for the structures of the complemen-tary electrodes adhered onto the internal wall of the AS-TENG and the Al electrodes on the roller surface. c) Enlarged view of the internal structure of the AS-TENG. d) Schematic working principle for the AS-TENG based on the freestanding mode.Adv. Mater. Technol. 2021, 2021 Wiley-VCH GmbH2100359 (3 of 8)www.advmattechnol.deacross the external load (state iv). The Al film slides back and forth on the two copper electrodes covered with PTFE film to form a complete electron flow loop. In order to better present the whole movement process of the AS-TENG, the detailed sit-uation is animated in Video S1 in the Supporting Information.In order to better adapt to the external environment, it is necessary to achieve the best motion state of the AS-TENG through appropriate triggering at certain acceleration and dis-placement. An AS-TENG device with the grating number of N = 24 for the complementary electrodes was first designed and fabricated. At the same time, the internal roller has four grating Al units with the corresponding size to the grating elec-trodes. The output performance of the AS-TENG device under the regular triggering of linear motor was measured, as shown in Figure2. The influences of the motor acceleration on the output voltage, output current, and transferred charge of the TENG are presented in Figure2ac. The maximum displace-ment of the TENG driven by the motor was fixed as 9cm, and the dwell time at two ends was set to be 200ms. As the accel-eration increases from 1.5 to 15 m s2, the peak values of output voltage and transferred charge of the TENG both increase slightly until saturation. The lower output voltage and trans-ferred charge at lower acceleration (1.5 m s2) may be contrib-uted to the smaller scrolling amplitude and insufficient contact between the roller Al surface and PTFE film due to the smaller triggering force. The peak value of output current, as shown in Figure2c, gradually increases with the acceleration without the saturating tendency, which is dependent on the moving velocity of the internal roller.The influence of the motor displacement on the basic output performance of the AS-TENG at a fixed motor acceleration of 15 m s2 was also investigated, as shown in Figure2df. It can be found that with increasing the maximum displacement of the motor from 2 to 9cm, the peak values of output voltage, output current, and transferred charge all increase. That is because the scrolling amplitude and velocity of the roller increase under the increased triggering force, similar to the increase in the motor acceleration. When the displacement dis-tance arrives at 9cm, the friction frequency between the Al and PTFE films is large enough to realize the highest outputs.Besides the basic output characteristics, the output power-resistance relationships of the AS-TENG with N = 24 were also studied under the triggering of s= 9cm and a= 15 m s2. The peak power and peak current with respect to the load resistance are shown in Figure 3a. The peak power was calculated by the maximum value of peak current square multiplied by the load resistance. It can be seen that the peak current decreases gradually with increasing the resistance, and the peak power can reach the maximum value of 0.7mW at the matched resistance of 30 M. The corresponding peak power density of the AS-TENG is 5.47 W m3, and the average power density is 0.49 W m3. Figure3b presents the effect of the motor displacement on the power-resistance relation-ship profiles. The motor acceleration was fixed as 15 m s2. As the maximum displacement increases, the peak power at the matched resistance also increases, while the matched resist-ance decreases slightly due to the increase in the scrolling velocity. In addition, the charging performance of the AS-TENG to various capacitors was also evaluated. The results in Figure3c indicate the good charging ability of the AS-TENG under the external triggering. The capacitor of 10 F can be charged to 4.79V within 60 s, while 0.27V for the 220 F capacitor, which corresponds to a stored charge amount of 59.4 C 2021 Wiley-VCH GmbH2100359 (4 of 8)www.advmattechnol.deThe grating number N of the complementary electrodes is an important parameter influencing the output and charging performance of the AS-TENG. Figure3d,e and Figure S2 (Sup-porting Information) shows the output voltage, output current, and transferred charge of the TENG with N= 12, 18, and 24. When the grating electrode number varies, the Al units with fixed number of 4 on the roller surface are changed corre-spondingly. The roller length changes with the grating number. The motor parameters are still the same as mentioned above. The increase in the grating number was found to increase the output current, but slightly affect the output voltage and trans-ferred charge. At N= 24, the peak current reaches about 6 A, where the frequency of charge transfer is the highest. At such situation, the decrease in roller length can increase the output current. However, if we fix the unit size, increasing the roller length, accompanied by the increase of Al unit number, the electric outputs increase, due to the increase in the triboelec-tric charge amount. The principle for increasing the outputs through increasing the radius size of the arc shape is similar. The comparison of the charging voltage on a capacitor of 22 F for the AS-TENG with various grating numbers under the regular triggering was made, as shown in Figure3f. It indicates the faster charging speed for the TENG with N= 24, beca