High-performance triboelectric nanogenerator with double-surface

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High-performance triboelectric nanogenerator with double-surface shape-complementary microstructures prepared by using simple sandpaper templates Xu-wu Zhang, Gui-zhong Li, Gui-Gen Wang, Ji-li Tian, Yilin Liu, Da-ming Ye, Zheng Liu, Hua-yu Zhang, and Jiecai Han ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.7b03745 • Publication Date (Web): 29 Dec 2017 Downloaded from http://pubs.acs.org on December 31, 2017

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ACS Sustainable Chemistry & Engineering

High-performance triboelectric nanogenerator with double-surface shape-complementary microstructures prepared by using simple sandpaper templates Xu-Wu Zhang†,#, Gui-Zhong Li†,#, Gui-Gen Wang*,†,‡, Ji-Li Tian†, Yi-Lin Liu†, Da-Ming Ye†, Zheng Liu‡, Hua-Yu Zhang†, Jie-Cai Han†,⊥ †

Shenzhen Key Laboratory for Advanced Materials, Shenzhen Graduate School, Harbin

Institute of Technology, Building D, HIT Campus, University Town of Shenzhen, Nanshan District, Shenzhen 518055, China ‡

Centre for Programmable Materials, School of Materials Science and Engineering,

Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore ⊥

Center for Composite Materials, Harbin Institute of Technology, No.2 YiKuang Street,

Nangang District, Harbin 150080, China

AUTHOR INFORMATION Corresponding Author *

E-mail: [email protected] (Gui-Gen Wang)

#

Xu-Wu Zhang and Gui-Zhong Li contributed equally to this work.

KEYWORDS: triboelectric nanogenerator, polydimethylsiloxane, copper electrode, sandpaper template, double-sided complementary-like morphologies.

1

ACS Paragon Plus Environment

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ABSTRACT Triboelectric nanogenerator (TENG), based on triboelectrification and electrostatic induction, has been proven to be an ideal power supply device which converts all kinds of mechanical energy into electrical energy. However, high cost of fabrication and modification prevents wide application. In this work, we demonstrated a simple, cost-effective but efficient method, in which the friction pair materials, i.e., copper electrode and polydimethylsiloxane (PDMS), were both patterned by using sandpaper templates. The copper electrode and PDMS were patterned with sandpaper-like morphology and sandpaper-complementary-like morphology, respectively. Compared with TENG devices with non-patterned or single-sided patterned friction layer, TENG devices with two-sided patterned friction layers have better output properties when the sandpaper templates used for PDMS and copper electrode have the same large grit sizes (above #2000) due to closer contact and more sufficient friction. When the sandpaper

templates used for PDMS and copper electrode have the same grit size of 10000, the maximum output short-circuit current density, open-circuit voltage, transfer charge quantity and power density of as-prepared TENG devices are 3.89 mA/m2, 200 V, 76 nC and 4.36 W/m2, respectively. Overall, patterning microstructure morphology and corresponding complementary morphology on the respective two sides of friction pair shows efficient improvement for the performance of TENG device, providing a good guidance for its modification.

INTRODUCTION The operating principle of TENGs can be described by the coupling of 2


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triboelectrification and electrostatic induction, that is to say, the electrons move from one electrode to the other to balance the changing electric field through the external load while the friction pair contact and separate in turn. In theory, the outputs of TENGs only depend on the real contact area and surface-transferred charge density.1 In order to increase the real contact area, surface micro-nanostructures are often proposed to roughen the surface, including V-shape groove, strip, pyramid, forest and even hierarchical structure.2-7 On the other hand, the surface transferred charge density can be enhanced by using more suitable triboelectric materials,8 chemical treatment,9 injecting ionized air and grafting functional reagent.10,11 In addition, there are much more factors that can improve the properties of TENGs. For example, the grating structure,12 rotary-sliding structure,13 cylindrical rotating structure have been demonstrated to maximize the outputs of the TENGs due to the effective transfer of charges contributed by unique device structures.14 The optimization of the capacitance has proven to be also a good choice to enhance the output characteristics of TENGs, which can be achieved by filling high dielectric materials,15 introducing micro-capacitance and creating holes.16,17 Certainly, several layers or several devices integrated in series or parallel can also increase the outputs per unit area or volume.18-20 Although there are so many measures can be taken to enhance the performance of TENGs, most methods are only suitable for certain kinds of materials or structures except that roughing surface can be applied to every situation. To date, many methods have been developed to roughen surface, such as nanoimprint,21 lithograph,22 laser ablation.23 However, complex preparation of template and ultrahigh vacuum needed in etching

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process result in high cost and time consumption, limiting the TENGs for wide applications. In addition, the surface patterns are usually just on one side of friction pair, or the patterns on the two sides of friction pair have not correlation and so do not match with each other. Herein, we proposed a simple surface-roughening method, in which copper electrode and PDMS were patterned with matched morphologies. In detail, the PDMS film was deposited by simple spin-coating on the sandpapers and then peeled off to obtain sandpaper-complementary-like morphology. On the other hand, the copper electrode was prepared directly by heat evaporation onto the sandpapers to obtain sandpaper-like morphology. As to as-fabricated TENG based on the patterned PDMS and copper electrode, its electric parameters were investigated, including maximum output short-circuit current, open-circuit voltage, transfer charge quantity and power density.

EXPERIMENTAL SECTION Preparation of Friction and Electrode Materials Fabrication of PDMS film and copper electrode: The PDMS solution was prepared by mixing the pre-polymer and curing agent (Sylgard 184, Dow Corning) at a ratio of 10:1. For further homogeneous mixing, 0.5 ml n-hexane was added to reduce the viscosity and then the solution was stirred in a magnetic stirrer for 1h to volatilize the n-hexane completely. After mixing well, the solution was firstly centrifuged to remove air bubbles in solution. Secondly, the obtained mixture was spin-coating onto the sandpapers with different roughness values (grit: #400, #800, #1200, #2000, #5000, #7000, #10000), respectively, and was then cured at 150℃ for 15 min. Finally, the

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PDMS film was peeled off from the sandpaper template. Meanwhile, the copper films (thickness: 500 nm) were evaporated onto the different sandpapers (grit: #800, #1200, #2000, #5000, #7000, #10000) directly by thermal evaporation method. Fabrication of the Nanogenerator As shown in Figure 1, two transparent glasses were chosen as the supporting skeleton, four springs were fixed on the four corners of the supporting glass by strong glue, and a sponge was used as a buffer layer between the glass and sandpaper to guarantee sufficient contact. The ITO glass, PDMS film and copper electrode evaporated on the sandpaper were all cut to the size of 30 mm×30 mm. On one supporting glass, the ITO was stuck through double-sided adhesive sticky tape and the PDMS film was then attached directly onto the ITO. On the other supporting glass, the copper electrode evaporated on sandpaper was also stuck to it through double-sided adhesive sticky tape. Lastly, two copper wires were stuck to the two electrode materials to extract and conduct the electrons. Table 1 lists different types of the TENG devices in each group. Section A: In this part, three large groups of TENGs, named untreated group, group A and group B, were prepared to analyze the relationship between the outputs of the TENGs with which one friction layer was patterned and the grit sizes of the sandpapers. The PDMS and copper of Untreated Group were prepared with smooth glass template. The TENGs of Group A were fabricated with non-patterned PDMS, and copper electrodes evaporated on the sandpapers with different grit sizes (#800, #1200, #2000, #5000, #7000, #10000). Meanwhile, the TENGs of Group B were fabricated with non-patterned copper electrodes evaporated on smooth glass and PDMS spin-coated on

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the sandpapers with different grit sizes (#400, #800, #1200, #2000, #5000, #7000, #10000). Section B: Five other large groups of TENGs, named C, D, E, F, G, were fabricated to study the relationship between the outputs of the TENGs with which two friction layers (PDMS and copper) were also both patterned and the grit sizes of sandpapers,. Each group contains seven TENGs made up of the copper electrodes patterned with a same grit size and a series of PDMS patterned with different grit sizes, respectively. The grit sizes of copper electrodes for group C, D, E, F, G, H were #1200, #2000, #5000, #7000, #10000, respectively. The detail types of the TENG devices for each group were listed in Table 1. Characterization Methods The morphologies of PMDS films and copper electrodes before and after patterning were characterized by field emission scanning electron microscopy (HITACHI S-4700 FE-SEM). Atomic force microscopy (AFM) images were also recorded with tapping mode using Veeco RTESP-type silicon tips (Bruker Dimension Icon). As to the TENGs, their output characteristics such as open-circuit voltage and transferred charge quantity, were measured by an electrometer with ultra-high resistance (Keithley, 6514A), and the short-circuit current was also measured by a low-noise current pre-amplifier (Stanford Research System, SR570). The thickness of PDMS films were characterized by Surface Profilometer (Veeco Dektak 150). In addition, a self-made mechanical motor was adopted to control the applied force and separation distance.

RESULTS AND DISCUSSION 6


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The operating principle of TENGs can be described by the coupling of triboelectrification and electrostatic induction, in which friction materials and electrode materials play important roles. Usually, triboelectric difference between two friction layers, the conductivity and cost for electrode materials should be taken into consideration. In this study, PDMS attached on ITO was chosen as negative triboelectric material, and copper served as both positive triboelectric material and electrode. The schematic fabrication process of TENGs was shown in Figure 1(a)~(d). Firstly, the PDMS solution was spin-coated on the sandpaper for curing and was then peeled off to obtain sandpaper-complementary-like morphology. Secondly, the copper film was directly evaporated onto the sandpaper to obtain sandpaper-like morphology. Finally, as shown in Figure 1(e), the TENG device was assembled (the photographs of TENG were shown in Figure S1), in which the ITO was attached with PDMS, the springs separated the friction pair, and two glasses were used for the supporting. For the as-assembled TENG, as shown in Figure 1(f), the periodic contact and separation between PDMS and copper cause charge transfer and redistribution on the contact surface. The charge transfer brings a changing electric field which drives the electron flowing through the external load to balance the changing electric field. During the process, a pulsed alternating-current signal is created and two sign peaks occur in a whole period. While operating the TENG devices, it will take several seconds to activate the functional groups on the friction surface, named saturation time, shown in Figure S2. In order to obtain the precise data, all of the electric properties were measured after the saturation time, which is related to the dielectric performance of PDMS, shown in Figure

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S3 and Figure S4. Specifically, the characteristics of capacity and dielectric loss tangent determine the saturation time.11 To analyze the relationship between the output performance of the TENGs and the size of the microstructure, the sandpapers with different grit sizes were chosen as templates. The morphologies of PDMS and copper were characterized by optical microscopy shown in supporting information (Figure S5 and Figure S6) and SEM shown in Figure 2. All of the samples show rough surface with the same shape but different sizes, in which the larger the grit size of sandpaper is, the smaller the size of the microstructure is patterned on the surface. In detail, there are convex and concave microstructures for the surface of copper and PDMS, respectively. And the size of microstructure decreases from about 30.0 µm to about 2.0 µm while the grit of sandpaper increases from 800 to 10000. At the first stage, we prepared two groups of TENGs with one-sided patterned friction materials (PDMS or copper electrode). The TENGs with patterned copper electrodes and non-patterned PDMS are set as group A, and the TENGs with patterned PDMS and non-patterned copper electrodes are set as group B. The open-circuit voltage and transferred charge quantity of the untreated group were about 35 V and 15 nC, respectively (Figure 3(a) and 3(b)), which was comparable with the similar PDMS-based TENG device with non-patterned PDMS and copper ( the transferred charge quantity was about 14 nC).17 The open-circuit voltage and transferred charge of group A and B (grit size: above #2000) are larger than the untreated group, which are increased with the grit size of sandpaper shown in Figure 3(c) to 3(f). The improvement can be explained as

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follows: on the one hand, the larger the grit size of sandpaper template is, the higher density of concave or convex microstructure and the larger contact area for the TENGs have during friction. On the other hand, the larger the grit size of sandpaper template is, the shorter the size of the concave or convex microstructure in the vertical direction, which contributes to closer contact and more sufficient friction. The detail contact situation for copper electrode and PDMS can be described schematically by Figure 3(g) and Figure 3(h). It is worth noting that the there is no obvious inflexion point with increasing the grit size. That is to say, it is possible to further enhance the performance of TENGs by using the template with smaller micro-nanostructure. It deserves further study for the influences of much smaller micro-nanostructure without the limitation of sandpaper template. In the case that one-sided patterned friction material using the sandpaper with large grit size (above #2000) can dramatically enhance the performance of TENGs, what

happens if two-sided friction materials are both patterned? Here there are five groups of TENGs, in which each group consists of the copper electrode with a fixed grit size and PDMS film with different grit size, as shown in Figure 4. For example, in group C, the copper electrode was patterned by the sandpaper with grit size of #1200. It can be observed that the open-circuit voltage and transferred charge are changed synchronously. Specifically, with increasing the grit size of sandpaper for PDMS, the open-circuit voltage and transferred charge increase firstly and then decrease. When the sandpaper templates used for PDMS and copper electrode have the same grit size of 1200, there are maximum open-circuit voltage and transferred charge, i.e., 32 V and 14 nC, respectively.

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The same trend can be observed for group D, E, F, and G , in which the open-circuit voltage and transferred charge for these groups reach maximum only when the sandpaper templates used for PDMS and copper electrode have the same grit size, as shown in Figure 5(b) and 5(c). The contact situation for copper electrode and PDMS can be described schematically by Figure 5(a). As to a copper electrode with a fixed grit size, only when the sandpaper templates used for PDMS and copper electrode have the same grit size, the morphology on PDMS can fit with that of copper electrode perfectly and the contact area reaches maximum and the TENG has the optimal output performance. In addition, the larger the difference between the sandpaper templates used for PDMS and copper electrode is, the higher the degree of mismatch is, resulting in higher degradation of the output characteristics. As shown in Figure 5(d) and Figure 5(e), the largest voltage and transferred charge quantity sharply increase with increasing the grit size of copper electrode, ie, from group C to D, E, F, G. Overall, the maximum voltage and charge reach 200 V and 76 nC when both the sandpaper templates used for copper electrode and PDMS have the same maximum grit size of 10000 (group G), which are almost six times and five times as high as that of the untreated group. The remarkable improvement for the electric properties of TENG devices are supposed to the increase of contact area. It can be verified by Figure S7 and S8, which show surface AFM images of patterned copper electrode and PDMS prepared using the sandpapers of 10000# grit. Although just using simple sandpapers instead of complicated micro-nanofabrication technologies, there are acceptable

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homogeneous and shape-complementary patterns distributed on the surface of the copper electrode and PDMS film, respectively. The convex height for patterned copper electrode and concave depth for patterned PDMS film are both about 2.0 um, so it is more possible to

prepare

high-performance

triboelectric

nanogenerator

with

double-surface

shape-complementary microstructures. However, it should be also noted that some surface roughening by the sandpapers with small grit sizes (below #1200) decrease the performance of the TENG device on the contrary. As shown in Fig. 3c-f, the output performance of the TENG for group A with patterned copper electrode prepared using the sandpaper with small grit size below 1200 are smaller than that of untreated group, and the same phenomenon can also be observed for the group B with patterned PDMS. As to the sandpaper of small grit sizes (400, 800, 1200), the superficial areas of patterned copper and PDMS are obviously increased through patterning, but the virtual heights of the convex and concave microstructures on these surface are too large to be contacted while applied a not large force, so that the output performances of some device in group A are smaller than that of untreated group. Furthermore, the poor alignment of the triboelectric pair prepared using the sandpaper with small grit size also results in the degradation of TENG device. In the case of grit sizes for 1200 and 2000, the open-circuit voltages of single-sided patterned copper group A (~ 35 V, ~ 50 V) and single-sided PDMS patterned group B (~ 37 V and ~ 37 V) are higher than the open-circuit voltages of double-sided patterned group C and group D (~ 32 V, ~ 35 V), respectively. It is because that the smaller the grit size of the sandpaper, less uniform and homogeneous sand particles distributed on the surface of the sandpaper.

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As to the sandpapers with small grit sizes (below #2000), the sand particles are not very homogeneousness compared to the sandpapers with large grit sizes, the convex microstructures on the surface of copper and concave microstructures on the surface of PDMS can not be matched completely with each other even using the sandpaper templates obtained from a same sandpaper. Although there are poor alignments occurred in the case of sandpapers with smaller grit sizes (below #2000), the enhancements for TENG devices are efficient and obvious for the sandpapers with large grit sizes (above #2000), in which the optimized devices have good prospects to supply electric energy. Certainly, combined some more advanced micro/nano templates and external alignment design, more experiments deserve further investigation in the future. Moreover, TENG can be served as not only power source but also charge storage device, in which the thickness of dielectric material (PDMS) plays an important role. The PDMS films with different thicknesses can be obtained by repeated spin-coating, curing and stripping off. The relationship between the thickness and the number of layers is given in Figure 6(a). With increasing the thickness, the output voltage increases firstly and then decreases, reaching maximum value (200 V) when the thickness of PDMS film is about 110 µm. The influences of the thickness on TENG properties can be explained as followings: with increasing the thickness of PDMS film, there are more transferred electrons accumulated during the friction process.24 However, with further increase of the PDMS thickness, due to thicker PDMS dielectric layer, the electrostatic induction is more seriously weaken and results in sharp degradation instead. The contact area is an important influencing item for TENGs, and enough large

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force can ensure good contact. As shown in Figure 6(b), the increase of contact pressure contributes to larger contact area until the pressure reaches 80 kPa. With increasing the contact pressure, the contact area reaches maximum and then remains constant, so the voltage increases firstly and keeps constant while reaching maximum value. In order to evaluate the device application, the group G is chosen for its outstanding output performance. As a power source, the short-circuit current density of TENG can reach 3.89 mA/m2, which is shown in Figure 6(c). The output characteristics of TENGs with various load resistances ranging from 100 KΩ to 1 GΩ are shown in Figure 6(d).When the external load resistance is 500 MΩ, the voltage and current reaches 185 V and 2.8 µA, respectively, in which the output power density reaches maximum value of 4.36

W/m2.25,26

The

power

density

of

our

TENG

with

double-surface

shape-complementary microstructures can be even comparable with that of TENG using copper electrode and modified PDMS (aligned graphene sheets (AGS) embedded in PDMS (AGS@PDMS)) friction layer.16 The optimized TENG can directly light up 161 blue LEDs at the same time (Figure 6(e)),27,28 proving the possibility of the devices as direct power supply. As to device stability, the open-circuit voltage of the device does not have sharp degradation and just decreases from 200 V to 180 V by only 10% after 30 days (Figure 6(f)). It can be verified from the SEM images and EDS of the copper electrode before and after the stability test in Figure S9, in which there are no apparent changes of morphologies and chemical compositions. The preparation of double-sided surface complementary patterns on friction layers by using simple sandpaper template is a feasible, economical and convenient approach and has good application prospective for

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triboelectric nanogenerators.

CONCLUSIONS In summary, we have demonstrated a novel methodology to roughen the surface of the friction pair of TENG and enhance the output performance effectively. The simple sandpaper

templates

were

adopted

to

create

sandpaper-morphology

and

sandpaper-complementary-morphology on the friction layers. Compared with TENG devices with non-patterned or single-sided patterned friction layer, TENG devices with two-sided patterned friction layers have better output properties when the sandpaper templates used for PDMS and copper electrode have the same large grit sizes (above #2000) due to closer contact and more sufficient friction. When the sandpaper templates used for

PDMS and copper electrode have the same grit size of 10000, the maximum output short-circuit current density, open-circuit voltage, transfer charge quantity and power density of as-prepared TENG devices are 3.89 mA/m2, 200 V, 76 nC and 4.36 W/m2, respectively. The modification method provides a feasible, economical and convenient approach to improve the performance of TENG.

ASSOCIATED CONTENT Supporting Information Additional characterization data includes the picture of as-fabricated TENG, the optical microscope images of PDMS films, copper electrodes evaporated on the sandpaper and TENG, the dielectric properties of the PDMS film, saturation time of the optimized TENG, the AFM images of the copper electrode and PDMS, surface SEM images and EDS spectra of the copper electrodes before and after the stability test.

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ACKNOWLEDGMENTS This work was supported by National Natural Science Foundation of China (Grant No.11672084), Natural Science Foundation of Guangdong Province (Grant No. 2016A030313663), Shenzhen Science and Technology Plan Supported Project (Grant Nos. JCYJ20170413105844696, JCYJ20160226201232552), and China Scholarship Council (Grant No. 201606125092).

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Wave Energy. Nano Energy 2016, 22, 87-94. DOI: 10.1016/j.nanoen.2016.01.009. 19. Jiang, T.; Zhang, L. M.; Chen, X. Y.; Han, C. B.; Tang, W.; Zhang, C.; Xu, L.; Wang, Z. L. Structural Optimization of Triboelectric Nanogenerator for Harvesting Water Wave Energy. ACS Nano 2015, 9, 12562-12572. DOI: 10.1021/acsnano.5b06372. 20. Yang, W. Q.; Chen, J.; Zhu, G.; Yang, J.; Bai, P.; Su, Y. J.; Jing, Q. S.; Cao, X.; Wang, Z. L. Harvesting Energy from the Natural Vibration of Human Walking. ACS Nano 2013, 7, 11317-11324. DOI: 10.1021/nn405175z. 21. Deng, W.; Zhang, B.; Jin, L.; Chen, Y.; Chu, W.; Zhang, H.; Zhu, M.; Yang, W. Enhanced Performance of ZnO Microballoon Arrays for a Triboelectric Nanogenerator. Nanotechnology 2017, 28, 135401. DOI: 10.1088/1361-6528/aa5f34. 22. Mahmud, M. A. P.; Lee, J.; Kim, G.; Lim, H.; Choi, K. B. Improving the Surface Charge Density of a Contact-separation-based Triboelectric Nanogenerator by Modifying the

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10.1016/j.mee.2016.02.066. 23. Xiao, X. Z; Lu, C.; Wang, G.; Xu, Y.; Wang, J. P.; Yang, H. Flexible Triboelectric Nanogenerator from Micro-nano Structured Polydimethylsiloxane. Chem. Res. Chinese U. 2015, 31, 434-438. DOI: 10.1007/s40242-015-4432-8. 24. Cui, N. Y.; Gu, L.; Lei, Y. M.; Liu, J. M.; Qin, Y.; Ma, X. H.; Hao, Y.; Wang, Z. L. Dynamic Behavior of the Triboelectric Charges and Structural Optimization of the Friction Layer for a Triboelectric Nanogenerator. ACS Nano 2016, 10, 6131-6138. DOI: 10.1021/acsnano.6b02076. 25. Wang, Z. L. On Maxwell's Displacement Current for Energy and Sensors: The Origin

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of Nanogenerators. Mater. Today, 2017, 20, 74-82. DOI: 10.1016/j.mattod.2016.12.001. 26. Niu, S. M.; Wang, S. H.; Lin, L.; Liu, Y.; Zhou, Y. S.; Hu, Y. F.; Wang, Z. L. Theoretical Study of Contact-Mode Triboelectric Nanogenerators as an Effective Power Source. Energ Environ Sci, 2013, 6, 3576-3583. DOI: 10.1039/c3ee42571a. 27. Kwon, Y. H.; Shin, S. H.; Jung, J. Y.; Nah, J. Scalable and Enhanced Triboelectric Output

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Captions for Figures and Table Figure 1. Schematic diagram of the fabrication processes for friction materials and TENG. (a) Sandpaper template. (b) Sandpaper-morphology copper electrode. (c) Spin-coating and curing of PDMS film. (d) Sandpaper-complementary-morphology PDMS. (e) The schematic structure of TENG device. (f) Operating mechanism of TENG：(Ⅰ) The initial state. (Ⅱ) The pressed state. (Ⅲ) The releasing state. (Ⅳ) The released state. (Ⅴ) The pressing state. Figure 2. The SEM images of copper electrodes patterned with different sandpapers: (a) #800, (b) #1200, (c) #2000, (d) #5000, (e) #7000, (f) #10000. The SEM image of PDMS patterned with different sandpaper: (g) #400, (h) #800, (i) #1200, (j) #2000, (k) #5000, (l) #7000. (m) #10000. The AFM images of the electrodes patterned with the sandpaper of 10000# grit: (n) 2D image, (o) 3D image. Figure 3. The output open-circuit voltages of the TENGs for (a) Untreated group, (c) Group A, (e) Group B. The transferred charge quantities of TENGs for (b) Untreated group, (d) Group A, (f) Group B. The theorical contact model for (g) Group A, (h) Group B. Figure 4. The output open-circuit voltages of the TENGs consisting of a fixed grit copper and various PDMS for (a1) Group C with 1200 grit copper, (b1) Group D with 2000 grit copper, (c1) Group E with 5000 grit copper, (d1) Group F with 7000 grit copper, (e1) Group G with 10000 grit copper, and the transfer charge quantities of the TENGs for (a2) Group C, (b2) Group D, (c2) Group E, (d2) Group F, (e2) Group G. Figure 5. (a) The theorical contact model for Group C, D, E, F, G. The summary of (b)

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open-circuit voltages and (c) transferred charge quantities with different grits of PDMS and different grits of PDMS. (d) Peak voltage and (e) Peak transferred charge quantity with different grits of microstructure from (b) and (c). Figure 6. (a) The open-circuit voltages of the TENGs with the PDMS films of different thicknesses. (b) The voltages of TENGs under different external pressures. (c) The short-circuit current of TENGs with optimized treatment. (d) The output voltages, current and power densities of TENGs loaded with different external resistances. (e) The digital photographs of blue LEDs arrays before (the above) and after lighting (the below) powered by the TENG. (f) The open-circuit voltages of TENGs after fabrication for 1 day and 30 days.

Table 1. The detail types of the TENG devices for each group.

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For Table of Contents Use Only

A Triboelectric Nanogenerator with Double-sided Patterned Surfaces Utilizing Mechanical Energy Achieved Remarkably Enhanced Output Properties.

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Table 1. The detail types of the TENG devices for each group. 529x366mm (96 x 96 DPI)



Figure 1. Schematic diagram of the fabrication processes for friction materials and TENG. (a) Sandpaper template. (b) Sandpaper-morphology copper electrode. (c) Spin-coating and curing of PDMS film. (d) Sandpaper-complementary-morphology PDMS. (e) The schematic structure of TENG device. (f) Operating mechanism of TENG：(Ⅰ) The initial state. (Ⅱ) The pressed state. (Ⅲ) The releasing state. (Ⅳ) The released state. (Ⅴ) The pressing state. 633x678mm (96 x 96 DPI)


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Figure 2. The SEM images of copper electrodes patterned with different sandpapers (a) #800. (b) #1200. (c) #2000. (d) #5000. (e) #7000. (f) #10000. The SEM image of PDMS patterned with different sandpaper (g) #400. (h) #800. (i) #1200. (j) #2000. (k) #5000. (l) #7000. (m) #10000. The AFM images of the electrodes patterned with the sandpaper of 10000# grit. (n) 2D image. (o) 3D image. 529x486mm (96 x 96 DPI)



Figure 3. The output open-circuit voltages of the TENGs for (a) Untreated group, (c) Group A, (e) Group B. The transferred charge quantities of TENGs for (b) Untreated group, (d) Group A, (f) Group B. The theorical contact model for (g) Group A, (h) Group B. 652x862mm (96 x 96 DPI)


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Figure 4. The output open-circuit voltages of the TENGs consisting of a fixed grit copper and various PDMS for (a1) Group C with 1200 grit copper, (b1) Group D with 2000 grit copper, (c1) Group E with 5000 grit copper, (d1) Group F with 7000 grit copper, (e1) Group G with 10000 grit copper, and the transfer charge quantities of the TENGs for (a2) Group C, (b2) Group D, (c2) Group E, (d2) Group F, (e2) Group G. 544x940mm (96 x 96 DPI)



Figure 5. (a) The theorical contact model for Group C, D, E, F, G. The summary of (b) open-circuit voltage and (c) transferred charge quantity with different grits of PDMS and different grits of PDMS. (d) Peak voltage and (e) Peak transferred charge quantity with different grits of microstructure from (b) and (c). 757x719mm (72 x 72 DPI)


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Figure 6. (a) The open-circuit voltages of the TENGs with the PDMS films of different thicknesses. (b) The voltages of TENGs under different external pressures. (c) The short-circuit current of TENGs with optimized treatment. (d) The output voltages, current and power densities of TENGs loaded with different external resistances. (e) The digital photographs of blue LEDs arrays before (the above) and after lighting (the below) powered by the TENG. (f) The open-circuit voltages of TENGs after fabrication for 1 day and 30 days. 614x685mm (96 x 96 DPI)


High-performance triboelectric nanogenerator with double-surface

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