ultrahigh power output from triboelectric nanogenerator based on serrated electrode...

www.advenergymat.de

2002312 (1 of 7) © 2020 Wiley-VCH GmbH

Full PaPer

Ultrahigh Power Output from Triboelectric Nanogenerator Based on Serrated Electrode via Spark Discharge

Jihye Kim, Hanchul Cho, Maeum Han, Young Jung, Sung Soo Kwak, Hong-Joon Yoon, Byunggeon Park, Hyeok Kim, Hyoungjae Kim, Jinhyoung Park,* and Sang-Woo Kim*

DOI: 10.1002/aenm.202002312

purposes.[1–3] In addition, plasma plays an important role in many fields including space propulsion and biomedical tech-nology.[4–6] Cathode tubes and plasma gen-eration require an external power supply equipment, however unfortunately this equipment is not portable because of its heavy weight and large volume. There-fore, high voltage applications have severe limitations in harsh environments such as space, battlegrounds, and backcountry, where there is no electricity supply.

Triboelectric nanogenerators (TENGs)[7–11] based on a working mechanism of both triboelectrification and electrostatic induction can generate electricity from mechanical movements in our sur-roundings or human motion without the need for an external power supply.[12–16] Until now, the power generated by TENG has been applied as an energy source for body-implantable medical devices, light-emitting diodes, liquid crystal displays, sensors, and low power-

consuming electronic devices.[11,17–20] Considering self-powered high voltage and portability, TENG can be regarded as an ideal driving source for high voltage applications.

In this work, we propose a serrated electrode-based TENG (SE-TENG) that generates ultrahigh power output based on the spark discharge to drive high voltage-operating devices directly. When two different friction materials are in contact and then

An ultrahigh power output from a triboelectric nanogenerator (TENG) with a serrated electrode in a low-frequency contact-separation mode which is able to directly drive high voltage-operating devices without the need for an external power supply is demonstrated. When a serrated electrode-based TENG (SE-TENG) is driven, the microstructurally serrated electrode cre-ates a spark discharge in the gap between the serrated electrode and a wire, resulting in tremendously boosted triboelectric power output. Based on the spark discharge phenomenon, a boost adaptor is designed to secondarily boost the triboelectric power output performance, and consequently an ultrahigh triboelectric output voltage of 5 kV and current density of 2 A m−2 are achieved. The boost adaptor concept can be applied to any typical TENG for achieving higher power-generating performance. Finally, two high voltage applications, a Crookes tube and plasma generation, are demonstrated using the SE-TENG and boost adaptor without any external power supply equip-ment. The ultrahigh power-generating SE-TENG based on the spark discharge phenomenon occurring in the unique electrode structure has considerable potential to operate high voltage applications directly in harsh environments where electricity cannot be supplied.

1. Introduction

Over the centuries, high voltage applications such as cathode ray tubes and plasma generation have seen great progress. Cathode ray tubes are widely used in a number of elec-trical devices such as computer screens, television sets, radar screens, and oscilloscopes for both scientific and medical

The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/aenm.202002312.

Dr. J. Kim, Dr. S. S. Kwak, Dr. H.-J. Yoon, Prof. S.-W. KimSchool of Advanced Materials Science and EngineeringSungkyunkwan University (SKKU)Suwon 16419, Republic of KoreaE-mail: [email protected]. H. Cho, Y. Jung, B. Park, Dr. H. KimPrecision Mechanical Process and Control R&D GroupKorea Institute of Industrial Technology (KITECH)Busan 46938, Republic of KoreaM. HanSchool of Electronics EngineeringCollege of IT EngineeringKyungpook National UniversityDaegu 41566, Republic of Korea

Y. Jung, B. ParkGraduate School of Mechanical EngineeringPusan National UniversityBusan 46241, Republic of KoreaProf. H. KimDepartment of Electrical and Computer EngineeringUniversity of SeoulSeoul 02504, Republic of KoreaProf. J. ParkSchool of Mechatronics EngineeringKorea University of Technology & EducationCheonan 31253, Republic of KoreaE-mail: [email protected]. S.-W. KimSKKU Advanced Institute of Nanotechnology (SAINT)Samsung Advanced Institute for Health Sciences & Technology (SAIHST)Sungkyunkwan University (SKKU)Suwon 16419, Republic of Korea

Adv. Energy Mater. 2020, 2002312

http://crossmark.crossref.org/dialog/?doi=10.1002%2Faenm.202002312&domain=pdf&date_stamp=2020-10-07

www.advenergymat.dewww.advancedsciencenews.com

© 2020 Wiley-VCH GmbH2002312 (2 of 7)

separated, spark discharge can occur in the gap between the serrated electrode and metal (copper) wire due to triboelectrifi-cation and electrostatic induction. To investigate this spark dis-charge phenomenon between the serrated electrode and metal wire, we studied the electric field distribution depends on elec-trode shape using a finite element method (FEM) simulation with COMSOL multiphysics. This spark discharge allows large amounts of electrons to move from the serrated electrode to the metal wire at a rapid speed, thereby boosting the triboelectric power output performance. Based on this spark discharge phe-nomenon, we design a boost adaptor for secondary boosting of triboelectric output performance. Using the SE-TENG and boost adaptor, we could directly drive a Crookes tube and gen-erate plasma in vacuum conditions with no external power supply equipment. With the development of SE-TENG that produces self-powered high voltage, we theoretically reveal the mechanism of output amplification in a unique serrated elec-trode and consequently realize the possibility of driving high voltage applications directly in extreme environments.

2. Results and Discussion

Figure 1a shows a schematic image of the SE-TENG structure. Al wool used as serrated electrode of SE-TENG is embedded in a silicone rubber matrix which has a negative triboelectric property. Figure S1 (Supporting Information) shows a fabri-cation process of the serrated electrode-embedded silicone rubber. Opposite friction material is a nitrile rubber with a posi-tive triboelectric property. Video S1 (Supporting Information) shows a fabrication process of the serrated electrode. The cir-cular Al plate is fixed to the diamond turning machine chuck and rotated. The 10 R diamond tool cuts the edge of circular Al plate to a depth of 10 µm, and then moves toward the center of the circular Al plate, resulting in a serrated electrode like wool. The sharpness of the serrated electrode can be adjusted by controlling the speed at which the diamond tool moves toward

the center of the circular Al plate. Figure 1b shows the shape of serrated electrode. Figure 1c shows a field emission scan-ning electron microscope (FE-SEM) image of the serrated elec-trode, which has a fine tip structure on the micrometer scale. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FT-IR) spectroscopy analysis were performed to con-firm the chemical structure of the silicone rubber and nitrile rubber. In Figure S2 (Supporting Information), the XPS results of silicone rubber show that the silicone rubber consists of C, O, and Si atoms. FT-IR results show chemical bonding of the silicone rubber, as shown in Figure S3 (Supporting Informa-tion).[21–24] In Figure S4 (Supporting Information), the XPS results of nitrile rubber appear that it consists of C, O, N, and S atoms. Based on FT-IR results, we investigated the chemical bonding of nitrile rubber, as shown in Figure S5 (Supporting Information).[25] In order to obtain surface potential informa-tion of two friction materials, contact potential difference (CPD) values of the silicone rubber and nitrile rubber were meas-ured by Kelvin probe force microscopy (KPFM), as shown in Figure 1d,e, respectively. Silicone rubber and nitrile rubber have CPD values of – 817 and 805 mV, which mean highly negative and positive triboelectric properties, respectively. As a result, silicone rubber and nitrile rubber can generate the high output power of TENG.

When a conducting material with infinite permittivity is embedded in a polymer matrix, the relative permittivity and capacitance of the composite material increase,[26–28] thereby the transferred charge density in the electrode of TENG increases according to Equation (1)[29,30]

x

x d r/0σ σ

ε′ =

+ (1)

where σ′ is the transferred charge density, σ0 is the triboelectric charge density at the equilibrium state, x is the gap distance, d is the thickness, and εr is the relative permittivity. Since the ser-rated electrode is embedded in the silicone rubber, SE-TENG

Figure 1. A schematic illustration of a) SE-TENG and b) serrated electrode. c) FE-SEM image of serrated electrode. CPD results of d) silicone rubber and e) nitrile rubber measured by KPFM. f) Capacitance of the flat electrode and serrated electrode-based silicone rubber depending on force.



© 2020 Wiley-VCH GmbH2002312 (3 of 7)

has higher relative permittivity and capacitance than typical flat electrode-based TENG (FE-TENG). Therefore, SE-TENG can generate high triboelectric power output due to the large charge density transferred in the electrode of TENG. To verify this mechanism, we measured the capacitance of the flat elec-trode and serrated electrode-based silicone rubber depending on a force. The Al plate with thickness of 16 µm was used as the flat electrode. In Figure 1f, serrated electrode-based silicone rubber has a higher capacitance than flat electrode-based silicone rubber, thereby generating a higher triboelectric power output. In addition, as a force increases, the capacitance of the two samples increases. Because the thickness of the dielectric layer decreases when force is applied to the dielectric layer (Figure S6, Supporting Information), the capacitance of the dielectric layer increases according to Equation (2)[31]

C A dr /0ε ε= (2)

where C is the capacitance, ε0 is the permittivity of free space, εr is the relative permittivity, A is active area, and d is the thick-ness. Also, the serrated electrode-based silicone rubber has higher mechanical durability than the flat electrode-based silicone rubber. Figure S7 (Supporting Information) shows the resistance change of flat electrode and serrated electrode-based silicone rubber depends on the bending cycles. The flat electrode had an exponential increase in resistance at 200 bending cycles due to the crack of electrode. On the other

hand, the serrated electrode had little resistance change even in 400 bending cycles. These results show that the serrated elec-trode has a higher bending durability than the flat electrode.

The most important feature of the unique electrode structure in SE-TENG is the spark discharge for boosting the triboelec-tric output performance. When the silicone rubber and nitrile rubber rub against each other, spark discharge occurs in the gap between the serrated electrode and metal wire connected to the oscilloscope. When the silicone rubber and nitrile rubber are in contact, negative charges are formed on the surface of the silicone rubber and positive charges are formed on the surface of the nitrile rubber based on the triboelectrification effect, as shown in Figure 2a. When the silicone rubber and nitrile rubber are separated, to neutralize the negative charges on the surface of the silicone rubber, positive charges move from the metal wire to the serrated electrode. This means that electrons move from the serrated electrode to the metal wire. Since there is a gap between the serrated electrode and the metal wire, an electric field is strongly formed in the gap so spark discharge occurs in the gap. In here, large amounts of electrons move at a rapid speed. At the instantaneous short cir-cuit condition, the total cycling charge is maximized up to the maximum transferred charges value, resulting in the enhanced output power.[32] According to this mechanism, the key to boosting the output of SE-TENG based on spark discharge is to formation of the instantaneous short circuit condition by spark discharge. Figure 2b shows a photograph of the spark discharge

Figure 2. a) A schematic illustration of mechanism in which spark discharge occurs in a gap between the serrated electrode and metal wire. b) A photograph of spark discharge when silicone rubber and nitrile rubber are separated (taken by a commercial cell phone camera with no use of high speed image-capturing function). FEM simulation results for electric field distribution between the metal wire and serrated electrode with c) round shape and d) sharp shape.



© 2020 Wiley-VCH GmbH2002312 (4 of 7)

generated by electrons moving from the serrated electrode to the metal wire taken by a commercial cell phone camera. Figure S8a (Supporting Information) shows a schematic image of the mechanism by which spark discharge occurs when the silicone rubber and nitrile rubber are in contact. Figure S8b (Supporting Information) is a photograph of the spark dis-charge generated by electrons moving from the metal wire to the serrated electrode. Video S2 (Supporting Information) shows a spark discharge in a gap between the serrated electrode and the metal wire when the silicone rubber and nitrile rubber are in contact and separated.

In the case of a conductor, a sharp point has a high charge density which creates a high electric field. This high electric field formed at a sharp point makes air breakdown easier. In order to investigate the electric field distribution between the serrated electrode and the metal wire with a 250 µm diameter depends on electrode shape, we used a FEM simulation with COMSOL multiphysics. A triboelectric voltage of 492 V is applied to the serrated electrode, and the gap between the ser-rated electrode and the wire is 1000 µm. Figure 2c,d shows the serrated electrodes with round and sharp shape, respectively. In FEM simulation results, the serrated electrode with sharp shape forms a higher electric field than that with round shape. Interestingly, the serrated electrode with sharp shape forms an

electric field of 3.23 × 106 V m−1, which is higher than the theo-retical air breakdown voltage of 3 × 106 V m−1, thereby spark discharge can occur.Figure 3a,b shows the open circuit voltage and short circuit

current density for three types of TENG; the FE-TENG, the SE-TENG that electrode is fully connected with a metal wire, and the SE-TENG with a gap between the serrated electrode and metal wire. Figure S9 (Supporting Information) shows the measurement method of the contact-mode TENG using a pushing tester. We measured the triboelectric output peak and then calculate a root-mean-square (RMS) value. By comparing the output performance of FE-TENG and the fully connected SE-TENG, the fully connected SE-TENG has higher output peak and RMS value than the FE-TENG. There are two reasons for these results; the increased capacitance due to the serrated electrode impregnation and the increased amount of trans-ferred charge in the bottom electrode due to the larger surface area of the serrated electrode. Figure S10 (Supporting Informa-tion) shows the amount of transferred charge on the bottom electrode for FE-TENG, the fully connected SE-TENG, and the spark discharge SE-TENG. The fully connected SE-TENG has a larger amount of transferred charge than the FE-TENG. Next, we compared the fully connected SE-TENG and the spark discharge SE-TENG with a gap between the serrated electrode

Figure 3. Triboelectric output a) voltage and b) current density of the FE-TENG, the SE-TENG which electrode is fully connected with a metal wire, and the spark discharge SE-TENG with a gap between the serrated electrode and metal wire.



© 2020 Wiley-VCH GmbH2002312 (5 of 7)

and the metal wire. The spark discharge SE-TENG produced a higher triboelectric output peak and RMS value than the fully connected SE-TENG. Because the spark discharge in the gap causes large amounts of electrons to move rapidly from the ser-rated electrode to the wire, thereby amplifying the triboelectric output peak and RMS values.

Based on the mechanism of boosting triboelectric power output via the spark discharge at the sharp tip, we designed a triboelectric output boost adaptor which is able to produce ultrahigh triboelectric output performance to drive high voltage-operating devices directly. Figure 4a shows a schematic illus-tration of SE-TENG and boost adaptor. First spark discharge occurs between the serrated electrode and the metal wire, and

second spark discharge occurs through an instantaneous metal-metal contact inside the boost adaptor. A photograph of the boost adaptor is shown in Figure S11 (Supporting Information). A detailed triboelectric output amplification mechanism of the boost adaptor is shown in Figure 4b,c. The boost adaptor con-sists of a fixed metal ring (in black) connected to the wire and a metal cantilever (in yellow) with a spherical weight that causes vibration by mechanical movements. Since the TENGs are driven by mechanical movements, vibration is always applied to the boost adaptor. When the metal cantilever is vibrated by mechanical movements, the instantaneous contact between the fixed metal ring and the end of metal cantilever occurs. In here, electrons transferred from the serrated electrode to the

Figure 4. a) A schematic illustration of SE-TENG and boost adaptor. b,c) Triboelectric power output amplification mechanism in the boost adaptor. d) First boosted triboelectric output voltage of SE-TENG and second boosted triboelectric output voltage of SE-TENG with boost adaptor. Photographs of f) Crookes tube and g) plasma generation driven by SE-TENG with boost adaptor (Nikon D750, 0.1 s exposure).



© 2020 Wiley-VCH GmbH2002312 (6 of 7)

metal wire are stored in the metal wire connected to the fixed metal ring of the boost adaptor. When the metal cantilever of the boost adaptor instantaneously contacts the fixed metal ring of the boost adaptor, the stored electrons move from the fixed metal ring to the metal cantilever, resulting in second spark dis-charge. The second spark discharge gives secondary amplifica-tion of the triboelectric power output. Figure 4d shows the first and second boosted triboelectric output voltage of SE-TENG and boost adaptor, which values are 1.32 and 5 kV, respec-tively. Figure S12 (Supporting Information) shows the second boosted triboelectric output current density of about 2 A m−2. In order to confirm the peak power of the SE-TENG with the boost adaptor, we measured the peak current depends on the resistance and then calculated the peak voltage and peak power according to Equations (3) and (4)

V IR= (3)

P I R2= (4)

where V is the voltage, P is the power, I is the current, and R is the resistance. As shown in Figure S13 (Supporting Informa-tion), the maximum peak power of the SE-TENG with boost adaptor was calculated as 9.7 W at the resistance of 1 MOhm. Our boost adaptor has the significant advantage that it can be universally applied to any typical TENG to boost their output performance. Figure S14 (Supporting Information) shows the boosted triboelectric output voltage and current density of FE-TENG amplified by the boost adaptor. These results indicate that the boost adaptor can also amplify the power-generating performance of a typical TENG.

To directly operate high voltage applications such as cathode ray tubes and plasma generation without an external power supply, we used our SE-TENG with boost adaptor. Crookes tube consists of a glass bulb with two metal electrodes; a cathode and an anode. When a high voltage is applied between two elec-trodes, electrons are emitted from the cathode and hit the inner surface of the glass bulb coated with a fluorescent material, and thereby the interacted spot is illuminated in green. We applied a high voltage of the SE-TENG with boost adaptor to the two electrodes of Crookes tube, thereby directly driving the Crookes tube without any external power supply equipment, as shown in Figure 4f and Video S3 (Supporting Information). The set-tings for driving the Crookes tube are shown in Figure S15 (Supporting Information). Furthermore, for the plasma genera-tion, we prepared SE-TENG in a 10 × 10 cm2 area with boost adaptor, rectifier, and desiccator, as shown in Figure S16 (Sup-porting Information). We directly generated plasma using SE-TENG with boost adaptor without any external power supply. Videos S4 and S5 (Supporting Information) show the plasma generation under a vacuum using SE-TENG with boost adaptor. Figure 4g shows the photograph of plasma generation, which was taken for a very short exposure time of 0.1 s. Our SE-TENG and boost adaptor have significant importance in that it is easy and simple to directly drive high voltage applications such as Crookes tubes and plasma generation. The proposed SE-TENG is lightweight and compact, making it portable and easy to operate. For this reason, it can be suggested that SE-TENG is ideal as a powering source in a low frequency operation for

self-powered high voltage applications in harsh environments which cannot use an external power supply.

3. Conclusion

In summary, we developed an ultrahigh performance TENG with a unique microstructure serrated electrode based on spark discharge to directly drive high voltage applications without any external power supply. When two friction materials are in contact and separated, the serrated electrode creates spark discharge in the gap between the serrated electrode and wire, resulting in boosted triboelectric output performance. We designed a boost adaptor based on the spark discharge for ultra-high output voltage of 5 kV and current density of 2 A m−2. We directly drove a Crookes tube and generated plasma under a vacuum using our SE-TENG with boost adaptor. Finally, it was demonstrated that our SE-TENG based on the spark discharge could directly and easily drive high voltage applications in harsh environments without the need for external power supply equipment.

4. Experimental SectionFabrication of SE-TENG: The serrated electrode was produced by

cutting an Al plate with the diamond tool from a diamond turning machine (Precitec). Silicone rubber base and a hardener (Smooth-On, Inc., Dragon Skin 10 NV) were placed in a beaker in a 1:1 ratio and then stirred for 5 min using a magnetic bar. After the silicone rubber solution was completely mixed, silicone rubber of 16 g was poured into a petri dish containing the serrated electrode of 0.2 g and dried at room temperature for 2 h. The concentration of the serrated electrode on the silicone rubber was 1.25 wt%. The nitrile rubber was purchased from ANSELL LTD (Microflex Supreno 93–743).

Characterization and Measurements: The structure of serrated electrode was confirmed by FE-SEM (Jeol Ltd., JSM-7500F) measurement. XPS (VG SCIENTA, ESCALAB250) and FT-IR (Bruker, IFS-66/S TENSOR27) measurements were carried out to confirm the chemical bonding of the silicone rubber and nitrile rubber. For KPFM measurements (Park Systems, XE-100), the silicone rubber and nitrile rubber were prepared on stainless steel holder and measured under a set point of 13 nm at a scan rate of 0.5 Hz (temperature = 21 °C, humidity = 17%). KPFM measurements were performed with a Pt/Cr-coated silicon tip; a lock-in amplifier (Stanford Research, SR830) and a 2 Vac signal at a frequency of 17 kHz. The thickness displacement depends on force was measured by a universal testing machine (JISC, JSV-H1000) with a load cell (JISC, HF-10); a maximum load of 100 N and a load resolution of 0.01 N. Capacitance and resistance were measured by LCR-meter (HIOKI, HIOKI-3536) with 1 V bias at frequencies of 200 kHz and 4 Hz, respectively. For the resistance change of the silicone rubber with the flat and serrated electrode depends on bending cycles; a bending tester was used including a linear axis encoder (Misumi, SRSH24YN-200) and linear actuator (Misumi, LX2001CP). The photographs of the spark discharge between the serrated electrode and metal wire were taken by an i-Phone 8. For the TENG characterizations, a pushing tester (Z-Tech, ZPS-100), a digital phosphor oscilloscope (Tektronix, DPO 3052 Digital Phosphor), and a low-noise current preamplifier (Stanford Research Systems Inc., SR570) were used.

Supporting InformationSupporting Information is available from the Wiley Online Library or from the author.



© 2020 Wiley-VCH GmbH2002312 (7 of 7)

AcknowledgementsJ.K. and H.C. contributed equally to this work. This work was financially supported by the Nano Material Technology Development Program (2020M3H4A1A03084600) and the Basic Science Research Program (2018R1D1A1B07040446 and 2019R1C1C1010730) through the National Research Foundation of Korea (NRF) funded by Ministry of Science and ICT.

Conflict of InterestThe authors declare no conflict of interest.

Keywordsself-powered high voltage applications, serrated electrodes, spark discharge, triboelectric nanogenerators, ultrahigh power output

Received: July 15, 2020Revised: September 19, 2020

Published online:

[1] Y. C. Kim, K. H. Kim, D.-Y. Son, D.-N. Jeong, J.-Y. Seo, Y. S. Choi, I. T. Han, S. Y. Lee, N.-G. Park, Nature 2017, 550, 87.

[2] Q. Chen, J. Wu, X. Ou, B. Huang, J. Almutlaq, A. A. Zhumekenov, X. Guan, S. Han, L. Liang, Z. Yi, J. Li, X. Xie, Y. Wang, Y. Li, D. Fan, D. B. L. Teh, A. H. All, O. F. Mohammed, O. M. Bakr, T. Wu, M. Bettinelli, H. Yang, W. Huang, X. Liu, Nature 2018, 561, 88.

[3] K. P. Heeg, A. Kaldun, C. Strohm, P. Reiser, C. Ott, R. Subramanian, D. Lentrodt, J. Haber, H.-C. Wille, S. Goerttler, R. Ruffer, C. H. Keitel, R. Rohlsberger, T. Pfeifer, J. Evers, Science 2017, 357, 375.

[4] X. Wang, R. Zgadzaj, N. Fazel, Z. Li, S. A. Yi, X. Zhang, W. Henderson, Y.-Y. Chang, R. Korzekwa, H.-E. Tsai, C.-H. Pai, H. Quevedo, G. Dyer, E. Gaul, M. Martinez, A. C. Bernstein, T. Borger, M. Spinks, M. Donovan, V. Khudik, G. Shvets, T. Ditmire, M. C. Downer, Nat. Commun. 2013, 4, 1988.

[5] D. B. Graves, Phys. Plasmas 2014, 21, 080901.[6] D. B. Graves, J. Phys. D: Appl. Phys. 2012, 45, 263001.[7] F.-R. Fan, Z.-Q. Tian, Z. L. Wang, Nano Energy 2012, 1, 328.[8] S. Niu, S. Wang, Y. Liu, Y. S. Zhou, L. Lin, Y. Hu, K. C. Pradel,

Z. L. Wang, Energy Environ. Sci. 2014, 7, 2339.

[9] Z. L. Wang, Nano Energy 2020, 68, 104272.[10] C. Zhang, T. Zhou, W. Tang, C. Han, L. Zhang, Z. L. Wang, Adv.

Energy Mater. 2014, 4, 1301798.[11] R. Hinchet, H.-J. Yoon, H. Ryu, M.-K. Kim, E.-K. Choi, D.-S. Kim,

S.-W. Kim, Science 2019, 365, 491.[12] X. Liang, T. Jiang, G. Liu, Y. Feng, C. Zhang, Z. L. Wang, Energy

Environ. Sci. 2020, 13, 277.[13] S. Wang, Y. Xie, S. Niu, L. Lin, Z. L. Wang, Adv. Mater. 2014, 26,

2818.[14] J. Kim, J. H. Lee, H. Ryu, J.-H. Lee, U. Khan, H. Kim, S. S. Kwak,

S.-W. Kim, Adv. Funct. Mater. 2017, 27, 1700702.[15] M. Seol, S. Kim, Y. Cho, K.-E. Byun, H. Kim, J. Kim, S. K. Kim,

S.-W. Kim, H.-J. Shin, S. Park, Adv. Mater. 2018, 30, 1801210.[16] S. S. Kwak, H. Kim, W. Seung, J. Kim, R. Hinchet, S.-W. Kim, ACS

Nano 2017, 11, 10733.[17] W. Liu, Z. Wang, G. Wang, G. Liu, J. Chen, X. Pu, Y. Xi, X. Wang,

H. Guo, C. Hu, Z. L. Wang, Nat. Commun. 2019, 10, 1426.[18] S. S. Kwak, S. M. Kim, H. Ryu, J. Kim, U. Khan, H.-J. Yoon,

Y. H. Jeong, S.-W. Kim, Energy Environ. Sci. 2019, 12, 3156.[19] W. Seung, H.-J. Yoon, T. Y. Kim, H. Ryu, J. Kim, J.-H. Lee, J. H. Lee,

S. Kim, Y. K. Park, Y. J. Park, S.-W. Kim, Adv. Energy Mater. 2017, 7, 1600988.

[20] J. Kim, H. Ryu, J. H. Lee, U. Khan, S. S. Kwak, H.-J. Yoon, S.-W. Kim, Adv. Energy Mater. 2020, 10, 1903524.

[21] D. Bodas, C. Khan-Malek, Microelectron. Eng. 2006, 83, 1277.[22] A. Karkhaneh, H. Mirzadeh, A. R. Ghaffariyeh, J. Appl. Polym. Sci.

2007, 105, 2208.[23] C. D. M. Atayde, I. Doi, Phys. Status Solidi C 2010, 7, 189.[24] C. Kapridaki, P. Maravelaki-Kalaitzaki, Prog. Org. Coat. 2013, 76,

400.[25] S. Samantarai, A. Nag, N. Singh, D. Dash, A. Basak, G. B. Nando,

N. C. Das, J. Elastomers Plast. 2019, 51, 99.[26] G. Bhimarasetti, M. K. Sunkara, U. M. Graham, B. H. Davis, C. Suh,

K. Rajan, Adv. Mater. 2003, 15, 1629.[27] L. Wang, Z.-M. Dang, Appl. Phys. Lett. 2005, 87, 042903.[28] P. Fan, L. Wang, J. Yang, F. Chen, M. Zhong, Nanotechnology 2012,

23, 365702.[29] Z.-H. Lin, G. Cheng, Y. Yang, Y. S. Zhou, S. Lee, Z. L. Wang, Adv.

Funct. Mater. 2014, 24, 2810.[30] J. W. Lee, H. J. Cho, J. Chun, K. N. Kim, S. Kim, C. W. Ahn, I. W. Kim,

J.-Y. Kim, S.-W. Kim, C. Yang, J. M. Baik, Sci. Adv. 2017, 3, e1602902.[31] S. K. Bhattacharya, J. Y. Park, R. R. Tummala, M. G. Allen, J. Mater.

Sci.: Mater. Electron. 2000, 11, 455.[32] Y. Zi, S. Niu, J. Wang, Z. Wen, W. Tang, Z. L. Wang, Nat. Commun.

2015, 6, 8376.


ultrahigh power output from triboelectric nanogenerator based on serrated electrode...

Documents