Special Issue "Nanogenerators in Korea"

A special issue of Micromachines (ISSN 2072-666X). This special issue belongs to the section "A:Physics".

Deadline for manuscript submissions: closed (30 October 2018)

Special Issue Editors

Guest Editor
Dr. Dukhyun Choi

Department of Mechanical Engineering, College of Engineering, Kyung Hee University, 1732 Deogyeong-daero, Yongin-si, Gyeonggi-do, 17104, Korea
Website | E-Mail
Phone: +82-31-201-3320
Interests: mechanical energy harvesters; controlled energy transfer; surface treatments; self-powered sensors
Guest Editor
Dr. Yong Tae Park

Department of Mechanical Engineering, Myongji University, 116 Myongji-ro, Cheoin-gu, Yongin, Gyeonggi-do, 17058, Korea
Website | E-Mail
Phone: +82-31-330-6343
Interests: layer-by-layer assembly; graphene multilayer; wearable electronics; thermoelectric and triboelectric nanogerators

Special Issue Information

Dear Colleagues,

Fossil fuels leaded the 21st century industrial revolution but caused some critical problems such as exhaustion of resources and global warming. Also, current power plants require too much high cost and long time for establishment and facilities to provide electricity. Thus, developing new power production systems with environmental friendliness and low-cost is critical global needs. There are some emerging energy harvesting technologies such as thermoelectric, piezoelectric, and triboelectric nanogenerators, which have great advantages on eco-friendly low-cost materials, simple fabrication, and various operating sources. Since the introduction of various energy harvesting technologies, many novel designs and applications as power suppliers and physical sensors in the world have been demonstrated based on their unique advantages. In this Special Issue, we would like to address and share basic approaches, new designs, and industrial applications related to thermoelectric, piezoelectric, and triboelectric devices which are on-going in Korea. With this Special Issue, we aim to promote fundamental understanding and to find novel ways to achieve industrial product manufacturing for energy harvesters.

Dr. Dukhyun Choi
Dr. Yong Tae Park
Guest Editors

Manuscript Submission Information

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Keywords

  • Mechanical energy harvesters
  • Piezoelectric and triboelectric nanogenerators
  • Thermoelectricity
  • hybrid energy scavengers
  • Energy transfer
  • Self-powered sensors
  • Self-powered wearable electronics

Published Papers (10 papers)

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Research

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Open AccessArticle Mesoporous Highly-Deformable Composite Polymer for a Gapless Triboelectric Nanogenerator via a One-Step Metal Oxidation Process
Micromachines 2018, 9(12), 656; https://doi.org/10.3390/mi9120656 (registering DOI)
Received: 16 November 2018 / Revised: 3 December 2018 / Accepted: 8 December 2018 / Published: 11 December 2018
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Abstract
The oxidation of metal microparticles (MPs) in a polymer film yields a mesoporous highly-deformable composite polymer for enhancing performance and creating a gapless structure of triboelectric nanogenerators (TENGs). This is a one-step scalable synthesis for developing large-scale, cost-effective, and light-weight mesoporous polymer composites.
[...] Read more.
The oxidation of metal microparticles (MPs) in a polymer film yields a mesoporous highly-deformable composite polymer for enhancing performance and creating a gapless structure of triboelectric nanogenerators (TENGs). This is a one-step scalable synthesis for developing large-scale, cost-effective, and light-weight mesoporous polymer composites. We demonstrate mesoporous aluminum oxide (Al2O3) polydimethylsiloxane (PDMS) composites with a nano-flake structure on the surface of Al2O3 MPs in pores. The porosity of mesoporous Al2O3-PDMS films reaches 71.35% as the concentration of Al MPs increases to 15%. As a result, the film capacitance is enhanced 1.8 times, and TENG output performance is 6.67-times greater at 33.3 kPa and 4 Hz. The pressure sensitivity of 6.71 V/kPa and 0.18 μA/kPa is determined under the pressure range of 5.5–33.3 kPa. Based on these structures, we apply mesoporous Al2O3-PDMS film to a gapless TENG structure and obtain a linear pressure sensitivity of 1.00 V/kPa and 0.02 μA/kPa, respectively. Finally, we demonstrate self-powered safety cushion sensors for monitoring human sitting position by using gapless TENGs, which are developed with a large-scale and highly-deformable mesoporous Al2O3-PDMS film with dimensions of 6 × 5 pixels (33 × 27 cm2). Full article
(This article belongs to the Special Issue Nanogenerators in Korea)
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Open AccessArticle Manipulation of p-/n-Type Thermoelectric Thin Films through a Layer-by-Layer Assembled Carbonaceous Multilayer Structure
Micromachines 2018, 9(12), 628; https://doi.org/10.3390/mi9120628
Received: 30 October 2018 / Revised: 23 November 2018 / Accepted: 25 November 2018 / Published: 28 November 2018
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Abstract
Recently, with the miniaturization of electronic devices, problems with regard to the size and capacity of batteries have arisen. Energy harvesting is receiving significant attention to solve these problems. In particular, the thermoelectric generator (TEG) is being studied for its ability to harvest
[...] Read more.
Recently, with the miniaturization of electronic devices, problems with regard to the size and capacity of batteries have arisen. Energy harvesting is receiving significant attention to solve these problems. In particular, the thermoelectric generator (TEG) is being studied for its ability to harvest waste heat energy. However, studies on organic TEGs conducted thus far have mostly used conductive polymers, making the application range of TEGs relatively narrow. In this study, we fabricated organic TEGs using carbonaceous nanomaterials (i.e., graphene nanoplatelet (GNP) and single-walled carbon nanotube (SWNT)) with polyelectrolytes (i.e., poly(vinyl alcohol) (PVA) and poly (diallyldimethyl ammonium chloride) (PDDA)) via layer-by-layer (LbL) coating on polymeric substrates. The thermoelectric performance of the carbonaceous multilayer structure was measured, and it was confirmed that the thermoelectric performance of the TEG in this study was not significantly different from that of the existing organic TEG fabricated using the conductive polymers. The 10 bilayer SWNT thin films with polyelectrolyte exhibited a thermopower of −14 μV·K−1 and a power factor of 25 μW·m−1K−2. Moreover, by simply changing the electrolyte, p- or n-type TEGs could be easily fabricated with carbonaceous nanomaterials via the LbL process. Also, by just changing the electrolyte, p- or n-type of TEGs could be easily fabricated with carbonaceous nanomaterials with a layer-by-layer process. Full article
(This article belongs to the Special Issue Nanogenerators in Korea)
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Open AccessArticle A Spherical Hybrid Triboelectric Nanogenerator for Enhanced Water Wave Energy Harvesting
Micromachines 2018, 9(11), 598; https://doi.org/10.3390/mi9110598
Received: 22 October 2018 / Revised: 10 November 2018 / Accepted: 12 November 2018 / Published: 15 November 2018
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Abstract
Water waves are a continuously generated renewable source of energy. However, their random motion and low frequency pose significant challenges for harvesting their energy. Herein, we propose a spherical hybrid triboelectric nanogenerator (SH-TENG) that efficiently harvests the energy of low frequency, random water
[...] Read more.
Water waves are a continuously generated renewable source of energy. However, their random motion and low frequency pose significant challenges for harvesting their energy. Herein, we propose a spherical hybrid triboelectric nanogenerator (SH-TENG) that efficiently harvests the energy of low frequency, random water waves. The SH-TENG converts the kinetic energy of the water wave into solid–solid and solid–liquid triboelectric energy simultaneously using a single electrode. The electrical output of the SH-TENG for six degrees of freedom of motion in water was investigated. Further, in order to demonstrate hybrid energy harvesting from multiple energy sources using a single electrode on the SH-TENG, the charging performance of a capacitor was evaluated. The experimental results indicate that SH-TENGs have great potential for use in self-powered environmental monitoring systems that monitor factors such as water temperature, water wave height, and pollution levels in oceans. Full article
(This article belongs to the Special Issue Nanogenerators in Korea)
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Open AccessFeature PaperArticle Superhydrophobic Water-Solid Contact Triboelectric Generator by Simple Spray-On Fabrication Method
Micromachines 2018, 9(11), 593; https://doi.org/10.3390/mi9110593
Received: 26 October 2018 / Revised: 8 November 2018 / Accepted: 10 November 2018 / Published: 13 November 2018
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Abstract
Energy harvesting is a method of converting energy from ambient environment into useful electrical energy. Due to the increasing number of sensors and personal electronics, energy harvesting technologies from various sources are gaining attention. Among energy-harvesting technologies, triboelectric nanogenerator (TENG) was introduced as
[...] Read more.
Energy harvesting is a method of converting energy from ambient environment into useful electrical energy. Due to the increasing number of sensors and personal electronics, energy harvesting technologies from various sources are gaining attention. Among energy-harvesting technologies, triboelectric nanogenerator (TENG) was introduced as a device that can effectively generate electricity from mechanical motions by contact-electrification. Particularly, liquid-solid contact TENGs, which use the liquid itself as a triboelectric material, can overcome the inevitable friction wear between two solid materials. Using a commercial aerosol hydrophobic spray, liquid-solid contact TENGs, with a superhydrophobic surface (contact angle over 160°) can be easily fabricated with only a few coating processes. To optimize the fabrication process, the open-circuit voltage of sprayed superhydrophobic surfaces was measured depending on the number of coating processes. To demonstrate the simple fabrication and applicability of this technique on random 3D surfaces, a liquid-solid contact TENG was fabricated on the brim of a cap (its complicated surface structure is due to the knitted strings). This simple sprayed-on superhydrophobic surface can be a possible solution for liquid-solid contact TENGs to be mass produced and commercialized in the future. Full article
(This article belongs to the Special Issue Nanogenerators in Korea)
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Open AccessArticle Development of the Triboelectric Nanogenerator Using a Metal-to-Metal Imprinting Process for Improved Electrical Output
Micromachines 2018, 9(11), 551; https://doi.org/10.3390/mi9110551
Received: 1 October 2018 / Revised: 18 October 2018 / Accepted: 23 October 2018 / Published: 27 October 2018
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Abstract
Triboelectric nanogenerators (TENG), which utilize contact electrification of two different material surfaces accompanied by electrical induction has been proposed and is considered as a promising energy harvester. Researchers have attempted to form desired structures on TENG surfaces and successfully demonstrated the advantageous effect
[...] Read more.
Triboelectric nanogenerators (TENG), which utilize contact electrification of two different material surfaces accompanied by electrical induction has been proposed and is considered as a promising energy harvester. Researchers have attempted to form desired structures on TENG surfaces and successfully demonstrated the advantageous effect of surface topography on its electrical output performance. In this study, we first propose the structured Al (SA)-assisted TENG (SA-TENG), where one of the contact layers of the TENG is composed of a structured metal surface formed by a metal-to-metal (M2M) imprinting process. The fabricated SA-TENG generates more than 200 V of open-circuit voltage and 60 µA of short-circuit current through a simple finger tapping motion. Given that the utilization of the M2M imprinting process allows for the rapid, versatile and easily accessible structuring of various metal surfaces, which can be directly used as a contact layer of the TENG to substantially enhance its electrical output performance, the present study may considerably broaden the applicability of the TENG in terms of its fabrication standpoint. Full article
(This article belongs to the Special Issue Nanogenerators in Korea)
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Open AccessCommunication Mechanical Fatigue Resistance of Piezoelectric PVDF Polymers
Micromachines 2018, 9(10), 503; https://doi.org/10.3390/mi9100503
Received: 18 September 2018 / Revised: 28 September 2018 / Accepted: 3 October 2018 / Published: 4 October 2018
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Abstract
The fatigue resistance of piezoelectric PVDF has been under question in recent years. While some report that a significant degradation occurs after 106 cycles of repeated voltage input, others report that the reported degradation originates from the degraded metal electrodes instead of
[...] Read more.
The fatigue resistance of piezoelectric PVDF has been under question in recent years. While some report that a significant degradation occurs after 106 cycles of repeated voltage input, others report that the reported degradation originates from the degraded metal electrodes instead of the piezoelectric PVDF itself. Here, we report the piezoelectric response and remnant polarization of PVDF during 107 cycles of repeated compression and tension, with silver paste-based electrodes to eliminate any electrode effect. After applying repeated tension and compression of 1.8% for 107 times, we do not observe any notable decrease in the output voltage generated by PVDF layers. The results from tension experiments show stable remnant polarization of 5.5 μC/cm2, however, the remnant polarization measured after repeated compression exhibits a 7% decrease as opposed to the tensed PVDF. These results suggest a possible anisotropic response to stress direction. The phase analyses by Raman spectroscopy reveals no significant change in the phase content, demonstrating the fatigue resistance of PVDF. Full article
(This article belongs to the Special Issue Nanogenerators in Korea)
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Open AccessArticle Effects of Embedded TiO2−x Nanoparticles on Triboelectric Nanogenerator Performance
Micromachines 2018, 9(8), 407; https://doi.org/10.3390/mi9080407
Received: 23 July 2018 / Revised: 10 August 2018 / Accepted: 14 August 2018 / Published: 17 August 2018
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Abstract
Triboelectric nanogenerators (TENGs) are used as self-power sources for various types of devices by converting external waves, wind, or other mechanical energies into electric power. However, obtaining a high-output performance is still of major concern for many applications. In this study, to enhance
[...] Read more.
Triboelectric nanogenerators (TENGs) are used as self-power sources for various types of devices by converting external waves, wind, or other mechanical energies into electric power. However, obtaining a high-output performance is still of major concern for many applications. In this study, to enhance the output performance of polydimethylsiloxane (PDMS)-based TENGs, highly dielectric TiO2−x nanoparticles (NPs) were embedded as a function of weight ratio. TiO2−x NPs embedded in PDMS at 5% showed the highest output voltage and current. The improved output performance at 5% is strongly related to the change of oxygen vacancies on the PDMS surface, as well as the increased dielectric constant. Specifically, oxygen vacancies in the oxide nanoparticles are electrically positive charges, which is an important factor that can contribute to the exchange and trapping of electrons when driving a TENG. However, in TiO2−x NPs containing over 5%, the output performance was significantly degraded because of the increased leakage characteristics of the PDMS layer due to TiO2−x NPs aggregation, which formed an electron path. Full article
(This article belongs to the Special Issue Nanogenerators in Korea)
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Open AccessArticle Performance Evaluation of Thermoelectric Energy Harvesting System on Operating Rolling Stock
Micromachines 2018, 9(7), 359; https://doi.org/10.3390/mi9070359
Received: 6 July 2018 / Revised: 16 July 2018 / Accepted: 18 July 2018 / Published: 20 July 2018
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Abstract
During rolling stock operation, various kinds of energy such as vibration, heat, and train-induced wind are dissipated. The amount of energy dissipation cannot be overlooked when a heavy railroad vehicle operates at high speed. Therefore, if the wasted energy is effectively harvested, it
[...] Read more.
During rolling stock operation, various kinds of energy such as vibration, heat, and train-induced wind are dissipated. The amount of energy dissipation cannot be overlooked when a heavy railroad vehicle operates at high speed. Therefore, if the wasted energy is effectively harvested, it can be used to power components like low power sensor nodes. This study aims to review a method of collecting waste heat, caused by the axle bearing of bogie in a rolling stock. A thermoelectric module (TEM) was used to convert the temperature gradient between the surface of the axle bearing housing and the outdoor air into electric energy. In this study, the output performance by temperature difference in the TEM was lab-tested and maximized by computational fluid analysis of the cooling fins. The optimized thermoelectric energy harvesting system (TEHS) was designed and applied on a rolling stock to analyze the power-generating performance under operation. When the rolling stock was operated for approximately 57 min including an interval of maximum speed of 300 km/h, the maximum open circuit voltage was measured at approximately 0.4 V. Based on this study, the system is expected to be utilized as a self-powered independent monitoring system if applied to a low-power sensor node in the future. Full article
(This article belongs to the Special Issue Nanogenerators in Korea)
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Review

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Open AccessReview Recent Progress in Flexible Organic Thermoelectrics
Micromachines 2018, 9(12), 638; https://doi.org/10.3390/mi9120638
Received: 29 October 2018 / Revised: 23 November 2018 / Accepted: 25 November 2018 / Published: 30 November 2018
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Abstract
Environmental energy issues caused by the burning of fossil fuel such as coal, and petroleum, and the limited resources along with the increasing world population pose a world-wide challenge. Alternative energy sources including solar energy, wind energy, and biomass energy, have been suggested
[...] Read more.
Environmental energy issues caused by the burning of fossil fuel such as coal, and petroleum, and the limited resources along with the increasing world population pose a world-wide challenge. Alternative energy sources including solar energy, wind energy, and biomass energy, have been suggested as practical and affordable solutions to future energy needs. Among energy conversion technologies, thermoelectric (TE) materials are considered one of the most potential candidates to play a crucial role in addressing today’s global energy issues. TE materials can convert waste heat such as the sun, automotive exhaust, and industrial processes to a useful electrical voltage with no moving parts, no hazardous working chemical-fluids, low maintenance costs, and high reliability. These advantages of TE conversion provide solutions to solve the energy crisis. Here, we provide a comprehensive review of the recent progress on organic TE materials, focused on polymers and their corresponding organic composites incorporated with carbon nanofillers (including graphene and carbon nanotubes). Various strategies to enhance the TE properties, such as electrical conductivity and the Seebeck coefficient, in polymers and polymer composites will be highlighted. Then, a discussion on polymer composite based TE devices is summarized. Finally, brief conclusions and outlooks for future research efforts are presented. Full article
(This article belongs to the Special Issue Nanogenerators in Korea)
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Open AccessReview The Progress of PVDF as a Functional Material for Triboelectric Nanogenerators and Self-Powered Sensors
Micromachines 2018, 9(10), 532; https://doi.org/10.3390/mi9100532
Received: 13 September 2018 / Revised: 12 October 2018 / Accepted: 16 October 2018 / Published: 20 October 2018
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Abstract
Ever since a new energy harvesting technology, known as a triboelectric nanogenerator (TENG), was reported in 2012, the rapid development of device fabrication techniques and mechanical system designs have considerably made the instantaneous output power increase up to several tens of mW/cm2
[...] Read more.
Ever since a new energy harvesting technology, known as a triboelectric nanogenerator (TENG), was reported in 2012, the rapid development of device fabrication techniques and mechanical system designs have considerably made the instantaneous output power increase up to several tens of mW/cm2. With this innovative technology, a lot of researchers experimentally demonstrated that various portable/wearable devices could be operated without any external power. This article provides a comprehensive review of polyvinylidene fluoride (PVDF)-based polymers as effective dielectrics in TENGs for further increase of the output power to speed up commercialization of the TENGs, as well as the fundamental issues regarding the materials. In the end, we will also review PVDF-based sensors based on the triboelectric and piezoelectric effects of the PVDF polymers. Full article
(This article belongs to the Special Issue Nanogenerators in Korea)
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