Ag Nanoparticle-Based Triboelectric Nanogenerator To Scavenge


Nov 28, 2017 - Here, we designed a Ag nanoparticle-based TENG for scavenging wind energy. After including a transformer and a power management circuit...
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Ag Nanoparticles-Based Triboelectric Nanogenerator to Scavenge Wind Energy for a Self-Charging Power Unit Qiang Jiang, Bo Chen, Kewei Zhang, and Ya Yang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b14618 • Publication Date (Web): 28 Nov 2017 Downloaded from http://pubs.acs.org on December 3, 2017

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Ag Nanoparticles-Based Triboelectric Nanogenerator to Scavenge Wind Energy for a Self-Charging Power Unit Qiang Jiang †,‡ , Bo Chen †,‡, Kewei Zhang †,‡, and Ya Yang †,‡* †

Beijing Institute of Nanoenergy and Nanosystems, Chinese Academy of Sciences, Beijing 100083,

China ‡

CAS Center for Excellence in Nanoscience, National Center for Nanoscience and Technology

(NCNST), Beijing 100190, P. R. China *To whom correspondence should be addressed: Email: [email protected] ABSTRACT: Li-ion battery is a green energy storage technology with advantages of high energy density, long lifetime, and sustainability, but it cannot generate electric energy by itself. As a novel energy-harvesting technology, triboelectric nanogenerator (TENG) is a promising power source for supplying electronic devices, however it is difficult to directly use its high output voltage and low output current. Here we designed a Ag nanoparticles-based TENG for scavenging wind energy. After using a transformer and a power management circuit into the system, constant output voltages such as 3.6 V and a pulsed current of about 100 mA can be obtained, which can be used to directly light up a light emitting diode. Furthermore, the produced electric energy can be effectively stored in a WO3/LiMn2O4 electrodes based Li-ion battery. Our present work provides a new approach to effectively scavenge wind energy and store the obtained electric energy, which is significant to explore a selfcharging power unit (SCPU). KEYWORDS: Ag nanoparticles, triboelectric nanogenerator, wind energy, self-charging, energy cells

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INTRODUCTION In the past decades, triboelectric nanogenerators (TENGs) have attracted considerable attention after first reported.1 As a novel energy-harvesting technology, TENG can convert mechanical energy from the natural world,2-5 such as wind energy,6,7 into electric energy on the basis of triboelectric effect and electrostatic induction.8-11 TENG takes the advantages of small size, light weight, low-cost, high output power, high efficiency, environmental friendliness, and universal availability.12,13 According to the previous work,14,15 the electrode materials have an important influence on the output power of TENG, and Cu or Al are the common choice. However, these materials often suffer serious drawbacks. For example, they are easily oxidized, even corroded in some harsh environments.16 To solve this problem, other micro/nano materials, such as nanoporous structured RHSiO2 and tellurium dioxide triangular microwires, were adopted to replace Cu or Al as electrode materials.17,18 Ag nanoparticles, serving as a positive triboelectric material, may offer a rapidly charging and discharging process, leading to a highoutput performance of TENG. As a green energy storage technology, the lithium ion battery (LIB) has been one of the most promising and most effective energy storage device due to its advantages of high energy density, long lifetime, and sustainability.19 In a Li-ion battery, electric energy can be effectively stored and recycled converting from chemical energy via the intercalation/deintercalation of Li ions on the electrode materials. LIBs are widely used in numerous fields, especially in electronic devices which are relevant to our daily life. However, LIB can only store energy, but it cannot generate electric energy by itself. And LIBs with high energy and stable performance can no longer meet human’s requirement, that is self-charging energy cells and fast charging speed are the demand of the new age. Therefore, researchers are trying to combine electricity generation with energy storage though they are two entirely different processes.20-23 For example, Xue et al.24 directly hybridizes electricity generation and energy storage by a mechanism that can directly convert mechanical energy into chemical energy, and this make it possible for the Li battery to be a self-charging unit (SCPU).

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In this work, we design a Ag nanoparticles-based TENG that could be used for scavenging wind energy. The fabricated TENG presents a stable output performance by using Ag nanoparticles based electrodes and fluorinated ethylene propylene (FEP) film as a negative triboelectric material, and can deliver an output voltage of about 200 V and an output current of about 20 µA at a wind speed of 20 m/s. The Li-ion battery with WO3 film based anode electrode and LiMn2O4 (LMO) based cathode electrode exhibits stable electrochemical properties. In order to charge the Li-ion battery, we choose a rectifier, a transformer together with a rectifier, as well as a transformer together with a power management circuit (PMC) to control the output voltage and current signals, respectively, among which using the transformer and a PMC is the most suitable approach. The results show that constant output voltage (1.8, 2.5, 3.3, and 3.6 V) and a pulsed current of about 100 mA can be obtained after transformed by a transformer and a PMC, which can directly light up a light emitting diode (LED). Furthermore, the produced electric energy can be rapidly stored in a Li-ion battery, and the charged cell can also light up a LED. Our research work provides a new approach to effectively harvesting wind energy, and also, it is significant to explore a SCPU.

RESULTS AND DISCUSSION Figure 1a shows the schematic diagram of the fabricated TENG, where the photographic paper coated with Ag nanoparticles was deposited on an acrylic bar, and a FEP film was placed between two Ag electrodes. Figure 1b is the photograph of the fabricated TENG, in which we can see the TENG has a dimension of 120 mm ×10mm × 5 mm, and each of the air gap between FEP film and top/bottom Ag electrode is 2 mm. Figure 1c displays the working mechanism of the TENG based on wind-driven vibration. The whole cyclic process can be described as follows: Firstly, due to the wind-induced vibration, rubbing between FEP film and Ag electrodes will result in positive charges on the Ag electrode surface and negative charges on the FEP film surface. There is no output voltage and current in external circuit because there exists no electric potential difference (EPD) between the two Ag electrodes (Process i).9 When the FEP film moves down, EPD across the two Ag electrodes is produced, ACS Paragon Plus Environment

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thus, the electrons move from the top Ag electrode to the bottom Ag electrode through the external circuit, and subsequent output current flow and voltage between two Ag electrodes are produced (Process ii). After that, the FEP film continuously moves down and contacts the bottom Ag electrode (Process iii). When the FEP film is separated from the bottom electrode, the electrons move back from the top Ag electrode to the bottom Ag electrode (Process iv), and the FEP film continuously moves up until back to the middle place of the device (Process v). Then the FEP film is continuously moving upward, and the electrons move from the top Ag electrode to the bottom Ag electrode (Process vi). Until contacting the top Ag electrode (Process vii). Next, the FEP film in turn moves down again, where the electrons move from bottom to up through external circuit (Process viii). Finally, the TENG returns to the original state again (Process i).25 Figure 1d and 1e are the SEM images of the Ag nanoparticles and Ag nanoparticles on the photographic paper, respectively. As shown in Figure 1d, the Ag nanoparticles present a uniform morphology, and the diameter of each Ag nanoparticle is about 50 nm. As depicted in Figure 1e, a dense membrane is formed and evenly covered on the photographic paper, where Ag nanoparticles are evenly distributed with less aggregation. The output current and voltage of the TENGs are measured and displayed in Figure 2. The measured output current of the TENG (FEP film as a negative triboelectric material) and corresponding enlarged curves are shown in Figure 2a and 2b, indicating the output current of the TENG is stable with a high value of around 20 µA. From Figure 2c, we can see the output voltage of the device can be as high as 200 V. Figure 2d shows the output current and power of the TENG with various resistances loads (1 MΩ ~100 MΩ), from which we can see as the resistance increases, the output current decreases and the power follows a trend of first increasing and then decreasing. When the resistance reaches 7.20 MΩ, the power can achieve a largest value of about 1.37 mW. We also choose Ag films as the electrodes obtained from magnetron sputtering. Though there is no obvious change between Ag nanoparticles-based and Ag films-based TENGs, the Ag film can easily fall off from the photographic paper after rubbing with the FEP film in a short time. Instead, the Ag nanoparticles electrode can hardly

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be damaged after working for a long time (as shown in Figure S1). This is mainly because ethylene glycol (EG) can play an important role in strengthening the adhesive force between Ag nanoparticles and the photographic paper. Moreover, in order to demonstrate the stability of Ag nanoparticles-based TENG by using FEP film as a triboelectric material, the output voltage and current stability of the TENG are illustrated in Figure S1c. There was no obvious decrease of the output voltage and current after the TENG was continuously working for 3 h, indicating the good stability of the TENG. In addition, we also choose Nylon film and FEP-Nylon film as the negative triboelectric materials. The detailed output current/voltage are presented in Figure S2 and S3, indicating the FEP film is the most suitable which can obtain the largest output current and voltage in a same condition. As illustrated in Figure 2e and 2f, a statistics analysis of output voltage/current signals of different devices are carried out to reveal the Ag nanoparticles-based TENGs by using FEP film as a negative triboelectric material exhibiting a high and stable output performance. Therefore, here we choose Ag nanoparticles as electrode, and FEP film as the final negative triboelectric material in the following study. Figure 3a and 3b are the SEM images of WO3 film and LMO. The as-synthesizedWO3 film presents a nanoporous layer thickness of 100 nm. The WO3 film with the special nanoporous structure is directly used as the anode electrode in the Li-ion battery. The crystallographic structure of the assynthesized WO3 film is confirmed by X-ray diffraction (XRD), as shown in Figure S4a. The diffraction peaks mainly appear at 2θ=23.109°, 23.579°, 24.349°, 26.585°, 28.914°, 33.252° and 34.151° in the XRD pattern of WO3, which can be ascribed to (0 0 2), (0 2 0), (2 0 0), (1 2 0), (1 1 2), (0 2 2) and (2 0 2) lattice planes of the monoclinic structure (WO3, JCPDS card No. 72-0677), respectively.26 Moreover, there is no other impurity diffraction peaks, revealing pure phased WO3 film is successfully obtained. As for the cathode electrode (LMO), the SEM image shows that it also possesses a nanoscale structures, and the diameter of each nanoparticle is smaller than 500 nm (Figure 3b). Figure 3c presents the charging-discharging current and voltage of the LIB by using LMO as cathode electrode and WO3 film as anode electrode with the voltage range of 1.5 ~ 3.6 V (vs. Li+/Li) at

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a current of 0.1 mA. As can be seen from the initial charging/discharging curves in Figure S4b, the charge and discharge capacity for the first cycle are 194.5 and 94.5 µAh, respectively. And in the following 2nd, 10th, 50th and 100th cycle, the charge and discharge capacities are 90.7/79.9, 74.8/72.2, 58/56.8, and 43.1/41.8 µAh, respectively. In addition, compared with the first cycle, a capacity loss of about 14.6 µAh can be found in the second cycle, which can be ascribed to the loss of some irreversible capacities, such as the dissolution of the solid electrolyte interphase (SEI) film.17 As we know, both excellent cycling performance and high rate capability of electrode materials are important measures for battery stability. Figure 3e and 3f display the cycling behavior and rate capability of the LMO/WO3 LIB. As can be observed from Figure 3e, the LIB presents a remarkable cycling stability with a desirable reversible capacity of about 79.9 µAh, which can be maintained as 41.8 µAh after 100 cycles. Moreover, the fabricated Li-ion battery shows a high coulombic efficiency above 95% after the first few cycles. Besides, Figure 3f displays the rate properties of the Li-ion battery. We collect the charge and discharge capacities at various currents (0.1, 0.3 and 0.5 mA) with the same voltage range (1.5 ~ 3.6 V). Here, the discharge capacities of the cell at the current of 0.1, 0.3, and 0.5 mA are 50, 20, and 4 µAh, respectively. And it is worth mentioning that when the current is restored from 0.5 to 0.1 mA, the capacity can return back to 50 µAh again, further demonstrating the excellent cycling stability of the fabricated Li-ion battery, and this result is also consistent with the above cycling performances. According to all above studies, we believe the fabricated TENGs possess a high output voltage of 200 V, and a low output current of 20 µA, which can be hardly directly used as a power supply system for our self-charging device. Also, in order to charge the Li-ion battery, the produced alternating current (AC) signals should be transformed into direct current (DC) signals. Herein, we choose three ways to control the output current and voltage: (1) using a rectifier; (2) using a transformer together with a rectifier; (3) using a transformer together with a PMC. Figure S5a and S5b show the output current and voltage of the TENG after using a rectifier, in which we can see the AC signals are successfully transformed into DC signals, and the output current/voltage are 20 µA /150 V with no obvious change

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compared with the previously unrectified value. Figure S5c displays self-charging and discharging curves of the Li-ion battery charged by the TENG after transformed by a rectifier in a voltage range of 0.5 - 2.5 V. It is clear that the voltage of the cell can be only charged to about 2 V after a long time (7 h), indicating the obtained current by this means is too small to charge the cell. As can be observed from Figure S6a-d, the output current and voltage of the TENG after transformed by a transformer are about 0.3 mA and 10 V, respectively. After connected with a rectifier, the above AC signals are transformed into DC signals, meanwhile the output current and voltage of the TENG are changed to 0.4 mA and 15 V, respectively. Figure S6 e presents self-charging and discharging curves of the Li-ion battery via the TENG after transformed by a transformer together with a rectifier in a voltage range of 0.5 - 2.5 V, from which we can see the voltage of the self-charging Li-ion battery can be charged to 2.5 V within 15 min. Moreover, as show in Figure S7, the TENG presents a pulsed current as high as 100 mA after transformed by a transformer and a PMC, and constant output voltage of 1.8, 2.5, 3.3 V, and 3.6 V can be obtained within 0.8, 2.0, 3.2 and 3.7 s, respectively. And from self-charging and discharging curves of the Li-ion battery charged by the TENG after transformed by a transformer together with a PMC in a voltage range of 0.5 - 2.5 V in Figure S7h. We can also find the cell can be rapidly charged to 2.5 V within 10 min. Figure S8 illustrates the self-charging and discharging curves of the Li-ion battery charged by the TENG after transformed by a rectifier, a transformer together with a PMC in a voltage range of 0.5 - 1.5 V with the corresponding enlarged first cycle, respectively. As displayed in Figure S8 b, the cell need a long charging time (55 min) to reach 1.5 V by the TENG directly using a rectifier, and the discharging time at a current of 0.1 mA is 3 min. While the cell can be charged to 1.5 V in a quite short time (1.3 min) charged by the TENG transformed by a transformer together with a PMC, with a discharging time of 2.4 min at the same current (0.1 mA) (Figure S8d). These results show that the TENGs can deliver a large output current after involving a transformer and a PMC into the system, which is beneficial for rapidly charging our self-charging energy cells. This is because the PMC possesses a low-loss full-wave bridge with a high efficiency buck converter and an ultralow quiescent

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current under-voltage lockout mode.12 Therefore, we choose PMC to control the output current and voltage of the TENGs, and use the transformed TENGs with a constant low output voltage and a high pulsed output current to charge self-charging Li-ion battery. Figure 4a displays self-charging and discharging curves of the Li-ion battery charged by the TENG after transformed by a transformer together with PMC under different voltages (1.8, 2.5, 3.3 and 3.6 V), in which we can observe that it takes 5 s, 3 min, 24 min, and 40 min to charge the cell up to 1.8, 2.5, 3.3, and 3.6 V, respectively. And the discharging times at 1.8, 2.5, 3.3, and 3.6 V are 48 s, 5 min, 19 min, and 25 min, respectively. In addition, there are some peaks in the charged curve, which is mainly because after employing a PMC, the output current of the TENG was transformed into pulsed current, as can be seen from Figure 4c. Hence, the charging process was discontinuous, presenting a peaky charged curve. In the charging process, when a pulsed current signal appeared, the self-charging Li ion battery was charged and its voltage increased. However, when the pulsed current signal disappeared, the battery would trend to return to a stable state, thus the voltage of the battery would decrease till another pulsed current signal applied. Moreover, it can be clearly seen from Figure 3a, when the battery was charged by a constant current of 0.1 mA, there existed no peak in the charged curve. Figure 4b shows a photograph of the fabricated self-charging device including a TENG, a Li-ion battery and a LED, where the TENG is used as a power supply system by harvesting wind energy. After the output current and voltage being transformed via a transformer together with a PMC, the pulsed voltage and current can directly charge the Li-ion battery or light up a LED. Moreover, the charged Li-ion battery can also be applied to light up a LED. Figure 4c displays the output pulsed current can reach as high as 90 mA by use of the TENG after transformed by a transformer together with a PMC. The corresponding enlarged pulsed current curve is shown in Figure S9. We can clearly see the peak width and half peak width of the pulsed current signals are 7 ms and 1 ms, respectively. As demonstrated in Figure 4d and 4e (movie S1 and movie S2, Supporting Information), a green LED can be easily lighted up by the TENG after using a transformer together with PMC as well as the charged Li-ion battery, respectively, revealing that the

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self-charging Li-ion battery is successfully fabricated and can be stably applied.

CONCLUSION In summary, we successfully fabricated a Ag nanoparticles-based TENG by using FEP film as a triboelectric material based on wind-driven vibration, presenting a high output voltage of 200 V and a low output current of 20 µA at a wind speed of 20 m/s. Constituted by WO3 film as anode and LMO as cathode, the Li-ion battery exhibits an excellent and stable electrochemical properties. It is demonstrated that the PMC is an effective approach to transform the output current and voltage signals of the TENG. After using a transformer together with a PMC into the system, a constant output voltage (1.8, 2.5, 3.3, and 3.6 V) and a pulsed current of about 100 mA can be obtained. The produced electric energy can directly light up a LED or stored in the Li-ion battery, and the charging speed is quite fast. Moreover, the charged Li-ion battery can also light up a LED. More importantly, our research work demonstrates the feasibility of hybridizing electricity generation unit with energy storage unit, that is to use TENGs for harvesting wind energy as an effective approach to powering self-charging energy power units.

EXPERIMENTAL SECTION Synthesis of Ag Nanoparticles. Ag nanoparticles were synthesized through an ice-water bath method by using silver nitrate (99.8%, Coolaber Science & Technology), poly (vinyl pyrrolidone) (PVP, MW = 1,300,000) and hydrazine hydrate (80%, Aladdin Industrial Corporation) as raw materials. Typically, 5 g AgNO3 were sufficiently dissolved in 5 g deionized water to obtain homogeneous solution A. 2.22 g N2H4·H2O were dissolved in 3.89 g deionized water to obtain homogeneous solution B. 0.978 g PVP were dissolved in 30 g deionized water to obtain homogeneous solution C, and the pH of solution C was adjusted to 10.3 by sodium hydroxide solution (NaOH, 1mol·L-1). After adding moderate n-caprylic alcohol to solution C, solution A and solution B were slowly added into solution C simultaneously under continuous mechanical stirring in an ice-water bath for 1 h. Then the as-obtained precursor Ag solution was washed and precipitated by acetone to get Ag nanoparticles.

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Preparation of WO3 Films and LMO Electrode. Nanostructed WO3 films were obtained via an anodization method by using tungsten foils (>99% purity, 12 cm × 3 cm × 0.1 mm) as both W source and counter electrode. In a typical procedure, the W foil was firstly washed ultrasonically with deionized water, ethanol, and acetone for 15 min, respectively, and then dried in air. In the anodization process, two pieces of W foils were placed vertically with each other in a mixed electrolyte of 1 mol·L-1 sodium sulfate (Na2SO4) and 7 wt% ammonium fluoride (NH4F), and the pH of electrolyte was adjusted to 3 by concentrated sulfuric acid (H2SO4).26 After anodizing at 40 V for 15 min, the obtained foil (anode) was then washed by deionized water and ethanol, and finally annealed at 450 °C in air for 3 h. To prepare LMO electrode, the purchased LMO powder, PVP, and acetylene black (with the mass radio of 8:1:1) were firstly mixed into homogeneous slurry in deionized water under continuous stirring. The well-mixed slurry was then pasted onto the aluminum foil and dried in vacuum at 100 °C for 24 h. Fabrication of TENGs and LIBs. According to our previous research, the fabricated TENG is based on wind-driven vibration. The as-prepared Ag nanoparticles were mixed with isopropanol and EG to form Ag slurry under continuous stirring. The well-mixed slurry was then pasted onto the photographic paper, and then dried at 80 °C in air for 1 h. The photographic paper coated with Ag nanoparticles was deposited on an acrylic bar (120 mm × 10 mm × 5 mm). The vibrating membrane (a FEP film with the thickness of 25 µm) was placed between two Ag electrodes, where the air gap between FEP film and top/bottom Ag electrode is 2 mm. CR2032 type coin cells were assembled in an argon-filled glove box, and LMO electrode, WO3 film were used as the cathode and anode electrode, respectively. A Celgard 2500 membrane was used as a separator, and the electrolyte was LiPF6 (1 M) in a mixture of dimethyl carbonate (DEC) and ethylene carbonate (EC) (1:1, by volume). Characterization and Measurement. The structure and crystalline of WO3 film were characterized by using x-ray diffraction (XRD, X’ Pert Powder, Panalytical) with Cu Kα radiation. The morphology of Ag nanoparticles, WO3 film and LMO were characterized by using a field-emission

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scanning electron microscope (SEM, SU8020, Japan). Charge-discharge tests of the LIBs were performed using an MTI 8 channels battery analyzer (CTS8-5 V 1 mA, Neware) at a constant current of 0.1 mA over a voltage range of 1.5 - 3.6 V (vs. Li+/Li) at room temperature. The output voltage signals of the TENGs were measured on the mixed domain oscilloscope (Tektronix MDO3024) and 6514 System Electrometer (Keithley), and the output current signals of the TENGs were tested on low-noise current preamplifier (Stanford Research SR570) and 2611B System Sourcemeter (Keithley) at a wind speed of 20 m/s. The designed PMC includes a low-loss full-wave bridge with a high efficiency buck converter, where an input capacitor can efficiently transfer the stored charges to the output.

ASSOCIATED CONTENT Supporting Information Supporting information includes additional characterization and electrical test results. This material is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION Corresponding Author *Tel: 0086-010-82854696; E-mail: [email protected] Notes The authors declare no competing financial interest.

ACKNOWLEDGEMENTS This work was supported by the National Key R & D Program of China (Grant No. 2016YFA0202701), the National Natural Science Foundation of China (Grant No. 51472055, Grant No. 61404034), External Cooperation Program of BIC, Chinese Academy of Sciences (Grant No. 121411KYS820150028),

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Qingdao National Laboratory for Marine Science and Technology (Grant No. 2015ASKJ01), the 2015 Annual Beijing Talents Fund (Grant No. 2015000021223ZK32), and the "thousands talents" program for the pioneer researcher and his innovation team, China.

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(8) Xi, Y.; Guo, H. Y.; Zi, Y. L.; Li, X. G.; Wang, J.; Deng, J. N.; Li, S. M.; Hu, C. G.; Cao, X.; Wang, Z. L. Multifunctional TENG for Blue Energy Scavenging and Self-Powered Wind-Speed Sensor. Adv. Energy Mater. 2017, 7, 1602397. (9) Chung, J.; Lee, S.; Yong, H.; Moon, H.; Choi, D.; Lee, S. Self-Packaging Elastic Bellows-Type Triboelectric Nanogenerator. Nano Energy 2016, 20, 84-93. (10) Ryu, H.; Lee, J.-H.; Kim, T.-Y.; Khan, U.; Lee, J. H.; Kwak, S. S.; Yoon, H.-J.; Kim, S.-W. HighPerformance Triboelectric Nanogenerators Based on Solid Polymer Electrolytes with Asymmetric Pairing of Ions. Adv. Energy Mater. 2017, 7, 1700289. (11) Khan, U.; Kim, T.-H.; Ryu, H.; Seung, W.; Kim, S.-W. Graphene Tribotronics for Electronic Skin and Touch Screen Applications. Adv. Mater. 2017, 29, 1603544. (12) Zhao, K.; Wang, X.; Yang, Y. Ultra-Stable Electret Nanogenerator to Scavenge High-Speed Rotational Energy for Self-Powered Electronics. Adv. Mater. Technol. 2017, 2, 1600233. (13) Zhao, K.; Qin, Q.; Wang, H.; Yang, Y.; Yan, J.; Jiang, X. Antibacterial Triboelectric MembraneBased Highly-Efficient Self-Charging Supercapacitors. Nano Energy 2017, 36, 30-37. (14) Li, S.; Wang, S.; Zi, Y.; Wen, Z.; Lin, L.; Zhang, G.; Wang, Z. L. Largely Improving the Robustness and Lifetime of Triboelectric Nanogenerators through Automatic Transition between Contact and Noncontact Working States. ACS Nano 2015, 9, 7479-7487. (15) Li, Z.; Chen, J.; Yang, J.; Su, Y.; Fan, X.; Wu, Y.; Yu, C.; Wang, Z. L. β-Cyclodextrin Enhanced Triboelectrification for Self-Powered Phenol Detection and Electrochemical Degradation. Energy Environ. Sci. 2015, 8, 887-896. (16) Wang, J.; Xu, Y.; Sun, X.; Mao, C.; Xiao, F. Polypyrrole Films Electrochemically Doped with Dodecylbenzenesulfonate for Copper Protection. J. Electrochem. Soc. 2007, 154, C445-C450. (17) Wu, J. M.; Chang, C. K.;Chang, Y. T. High-output current density of the triboelectric nanogenerator made from recycling rice husks. Nano Energy 2016, 19, 39-47. (18) Wu, J. M.; Lee, C. C.; Lin, Y. H. High sensitivity wrist-worn pulse active sensor made from

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tellurium dioxide microwires. Nano Energy 2015, 14, 102-110. (19) Jiang, Q.; Chen, X.; Gao, H.; Feng, C.Q.; Guo, Z.P. Synthesis of Cu2ZnSnS4 as Novel Anode Material for Lithium-Ion Battery. Electrochim. Acta 2016, 190, 703-712. (20) Yang, Y.; Zhou, Y. S.; Wu, J. M.; Wang, Z. L. Human Skin Based Triboelectric Nanogenerators for Harvesting Biomechanical Energy and as Self-Powered Active Tactile Sensor System. ACS Nano 2013, 7, 9213-9222. (21) Yang, Y.; Zhang, H. L.; Zhong, X. D.; Yi, F.; Yu, R. M.; Zhang, Y.; Wang, Z. L. Electret FilmEnhanced Triboelectric Nanogenerator Matrix for Self-Powered Instantaneous Tactile Imaging. ACS Appl. Mater. Interfaces 2014, 6, 3680-3688. (22) Sun, N.; Wen, Z.; Zhao, F.; Yang, Y.; Shao, H.; Zhou, C.; Shen, Q.; Feng, K.; Peng, M.; Li, Y.; Sun, X. All Flexible Electrospun Papers Based Self-Charging Power System. Nano Energy 2017, 38, 210-217. (23) Wen, Z.; Yeh, M.-H.; Guo, H.; Wang, J.; Zi, Y.; Xu, W.; Deng, J.; Zhu, L.; Wang, X.; Hu, C.; Zhu, L.; Sun, X.; Wang, Z. L. Self-Powered Textile for Wearable Electronics by Hybridizing Fiber-Shaped Nanogenerators, Solar Cells, and Supercapacitors. Sci. Adv. 2016, 2, e1600097. (24) Xue, X.; Wang, S.; Guo, W.; Zhang, Y.; Wang, Z. L. Hybridizing Energy Conversion and Storage in a Mechanical-to-Electrochemical Process for Self-Charging Power Cell. Nano Lett. 2012, 12, 50485054. (25) Zhao, K.; Wang, Z. L.; Yang, Y. Self-Powered Wireless Smart Sensor Node Enabled by an Ultrastable, Highly Efficient, and Superhydrophobic-Surface-Based Triboelectric Nanogenerator. ACS Nano 2016, 10, 9044-9052. (26) Ng, C. Y.; Razak, K. A.; Lockman, Z. Effect of Annealing Temperature on Anodized Nanoporous WO3. J. Porous Mater. 2015, 22, 537-544.

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FIGURES

Figure 1. (a) The schematic illustration of the fabricated TENG. (b) A photograph of the fabricated TENG. (c) Schematic illustration of the electricity generation process under a wind-load of the Ag nanoparticles-based TENG: (i) Activated state with positive charges on the Ag electrode surface and negative charges on the FEP film surface, (ii-iii, viii) the FEP film moves down until it contacts the bottom Ag electrode due to the wind-induced vibration, (iv-vii) the FEP film moves up until it contacts the top Ag electrode due to the wind-induced vibration. (d,e) SEM images of as-synthesized Ag ACS Paragon Plus Environment

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nanoparticles (d) and Ag nanoparticles on photographic paper (e).

Figure 2. (a-c) Measured output current (a) with the corresponding enlarged curve in (b) and voltage (c) of the TENG by using FEP film as a triboelectric material with negative polarity at a wind speed of 20 m/s. (d) Measured output current and calculated output power of the TENG under different loading resistances. (e,f) Variance statistics of measured output voltage (e) and current (f) signals ( the vibrating membrane was prepared by adhering double layers of FEP (FEP-FEP) film, double layers of Nylon (Nylon-Nylon) film, a FEP and a Nylon (FEP-Nylon) film, respectively. ). ACS Paragon Plus Environment

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Figure 3. (a,b) SEM images of as-synthesized WO3 film (a) and LMO (b). (c) Measured chargingdischarging curves of the Li-ion battery with a voltage limit between 1.5 and 3.6 V at a current of 0.1 mA. (d) Measured galvanostatic charging-discharging curves of the Li-ion battery under different cycles. (e,f) Cycling performances and coulombic efficiencies (e) and rate capability (f) of the Li-ion battery under various current (0.1, 0.3 and 0.5 mA).

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Figure 4. (a) Self-charging and discharging curves of the Li-ion battery via the TENG after transformed by a transformer and power management circuit under the different voltages (1.8, 2.5, 3.3 and 3.6 V). (b) A photograph of the fabricated self-charging device including a TENG, a Li-ion battery and a LED. (c) Measured output current signals of the TENG after transformed by a transformer and power management circuit with the corresponding output voltage of 2.5 V. (d,e) Photographs of a green LED that can be lighted up by the charged Li-ion battery (d) and the TENG after transformed by a transformer and power management circuit with the corresponding output voltage of 2.5 V (e).

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Table of Contents

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