Flexible and Stretchable Triboelectric Nanogenerator Devices E-Book
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- Herausgeber: Wiley-VCH Verlag GmbH & Co. KGaA
- Kategorie: Fachliteratur
- Sprache: Englisch
The book starts with the fundamentals of triboelectric nanogenerators (TENGs), and continues through to fabrication technologies to achieve flexible and stretchable. Then self-powered flexible microsystems are introduced and application examples are presented, including TENG-based active sensors, TENG-powered actuators, artificial intelligence and integrated systems.
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Veröffentlichungsjahr: 2019
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Table of Contents
Cover
Preface
Part I: Fundamentals of Triboelectric Nanogenerator
1 Overview of Triboelectric Nanogenerators
1.1 Energy Crisis of Microsystems
1.2 Microenergy Technologies
1.3 Triboelectric Nanogenerators
1.4 Summary
Abbreviations
References
2 Structures of Triboelectric Nanogenerators
2.1 Operation Mechanisms of TENGs
2.2 Typical Structures of TENGs
2.3 Summary
Abbreviations
References
3 Fabrication of Triboelectric Nanogenerators
3.1 Mass Fabrication Technologies for Triboelectric Nanogenerators
3.2 Performance Enhancement for Triboelectric Nanogenerators
3.3 Summary
Abbreviations
References
4 Characterization of Triboelectric Nanogenerators
4.1 Electrical Operating Cycles of Triboelectric Nanogenerators
4.2 Standard and Figure of Merits for Quantifying Triboelectric Nanogenerators
4.3 Summary
Abbreviations
References
5 Power Management of Triboelectric Nanogenerators
5.1 Theoretical Analysis of Power Transmittance of TENGs
5.2 The Progress in TENG Power Management
5.3 Summary
Abbreviations
References
Part II: Approaches to Flexible and Stretchable Device
6 Overview of Flexible and Stretchable Approaches
6.1 Intrinsically Flexible or Stretchable Materials
6.2 Structural Designs for Flexible and Stretchable Electronics
6.3 Summary
Abbreviations
References
7 Flexible and Stretchable Devices from 0D Nanomaterials
7.1 0D Nanomaterials
7.2 Thin Films Using 0D Nanomaterials
7.3 Patterning Methods and Applications
7.4 Applications of 0D Nanomaterials
7.5 Summary
Abbreviations
References
8 Flexible and Stretchable Devices from 1D Nanomaterials
8.1 Carbon Nanotubes
8.2 ZnO Nanowires
8.3 Ag Nanowires
8.4 Summary
Abbreviations
References
9 Flexible and Stretchable Devices from 2D Nanomaterials
9.1 2D Nanomaterials
9.2 Synthesis of Graphene
9.3 Graphene Transfer
9.4 Applications of Graphene
9.5 Summary
Abbreviations
References
10 Flexible and Stretchable Devices from Unconventional 3D Structural Design
10.1 Stretchable 3D Ribbon and Membrane Structures Formed by Basic Buckling
10.2 Deterministic 3D Assembly
10.3 Flexible and Stretchable Devices from 3D Assembly
10.4 Summary
Abbreviations
References
11 Flexible and Stretchable Devices from Other Materials
11.1 Polymer‐Based Conductive Materials
11.2 Composite‐Based Conductive Materials
11.3 Textile‐Based Conductive Materials
11.4 Summary
Abbreviations
References
Part III: Self-Powered Smart System
12 Active Sensors
12.1 Active Touch Sensors
12.2 Active Vibration Sensors
12.3 Active Motion Sensors
12.4 Active Chemical/Environmental Sensors
12.5 Summary
Abbreviations
References
13 Hybrid Sensing Technology
13.1 Dual Hybrid Power Technology
13.2 Multiple Hybrid Power Technology
13.3 Hybrid Sensors and Applications
13.4 Summary
Abbreviations
References
14 Smart Actuators
14.1 Actuators in Optics
14.2 Actuators in Biomedicine
14.3 Actuators in Industrial Application
14.4 Actuators in Microfluidic Manipulation
14.5 Summary
Abbreviations
References
15 Flexible and Stretchable Electronic Skin
15.1 Design of Electronic Skin
15.2 Electronic Skin for Mechanical Sensing
15.3 Electronic Skin for Physiological Sensing
15.4 Summary
Abbreviations
References
Part IV: Applications of Flexible and Stretchable Self-Powered Smart System
16 All‐in‐One Self‐Powered Microsystems
16.1 All‐in‐One Energy Harvester
16.2 All‐in‐One Power Unit
16.3 All‐in‐One Self‐Powered Microsystems
16.4 Summary
Abbreviations
References
17 Applications in Biomedical Systems
17.1 Power Sources of Implantable Medical Devices
17.2 Active Monitoring
17.3 Self‐Powered System for Electric Stimulation in Tissue Engineering
17.4 Summary
Abbreviations
References
18 Applications in Internet of Things and Artificial Intelligence
18.1 Applications in Internet of Things
18.2 Applications in Artificial Intelligence
18.3 Summary
Abbreviations
References
19 Applications in Environmental Monitoring/Protection
19.1 Self‐powered Environmental Monitoring System
19.2 Self‐powered Environmental Protection
19.3 Self‐powered Electrochemistry System
19.4 Self‐powered Anticorrosion
19.5 Summary
Abbreviations
References
Index
End User License Agreement
List of Tables
Chapter 1
Table 1.1 Comparison of five technologies for ambient energy harvesting...
Table 1.2 Triboelectric series of different materials.
Table 1.3 The configuration of triboelectric pairs (up to October 2017)...
Chapter 4
Table 4.1 Output energy per cycle for three cycles operated in RS‐mode ...
Table 4.2 Parameters utilized in the simulation for different structure...
Table 4.3
σ
N
and FOM
DM
of different materials.
Chapter 6
Table 6.1 Comparison of nanomaterials in different dimensions.
Table 6.2 Organic materials for flexible and stretchable electronics.
Chapter 14
Table 14.1 Performance of TENGs when applied in different actuators.
Table 14.2 Output function of concentration of HA.
List of Illustrations
Chapter 1
Figure 1.1 Schematic view of the Internet of things (IoT) and its power su...
Figure 1.2 Summary of technical progress of five promising methods for har...
Figure 1.3 The working principle of contact‐separation‐mode triboelectric ...
Chapter 2
Figure 2.1 Four operation mechanisms of triboelectric nanogenerators (TENG...
Figure 2.2 Mechanism of CS‐mode triboelectric nanogenerators.
Figure 2.3 Mechanism of RS‐mode triboelectric nanogenerators.
Figure 2.4 Mechanism of SE‐mode triboelectric nanogenerators.
Figure 2.5 Mechanism of FS‐mode triboelectric nanogenerators.
Figure 2.6 3D plane‐shaped TENG structures. (a) Diagram of a TENG with spa...
Figure 2.7 2D plane‐shaped TENG structures. (a) Diagram of a super‐flexibl...
Figure 2.8 Arch‐shaped high‐performance TENG.
Figure 2.9 Counterarch‐shaped triboelectric nanogenerators.
Figure 2.10 Stacked arch‐shaped TENG. (a) Diagram of the stacked arch‐shap...
Figure 2.11 Sandwich arch‐shaped TENG. (a) Schematic and (b) its working m...
Figure 2.12 Zig‐zag‐shaped triboelectric nanogenerators. (a) The diagram o...
Figure 2.13 Wavy‐shaped TENG structures. (a) Diagram of the wavy‐shaped hy...
Figure 2.14 Tank‐shaped TENG. (a) Diagram of the tank‐shaped TENG with enc...
Figure 2.15 Rotor‐shaped TENG. (a) A coaxial cylindrical‐structured rotati...
Figure 2.16 Disk‐shaped TENG. (a, b) Photograph of the disk‐shaped TENG. (...
Chapter 3
Figure 3.1 Structure and fabrication process of a TENG fabricated using so...
Figure 3.2 Photographs and SEM images of the films fabricated using the so...
Figure 3.3 Schematics of the fabrication process of a TENG through thermal...
Figure 3.4 Schematic and fabrication process of an FPC‐based TENG. (a) Sch...
Figure 3.5 Fabrication process of a roll‐to‐roll UV embossing manufactured...
Figure 3.6 Structure of the ultraflexible 3D‐TENG and its fabrication proc...
Figure 3.7 Structure and fabrication process of a textile TENG. (a) Schema...
Figure 3.8 Analysis and measurement of TENG enhanced by fluorocarbon plasm...
Figure 3.9 Theoretical calculation and FTIR spectra analysis of the plasma...
Figure 3.10 Fabrication process of a wrinkle‐structure‐patterned TENG. (a)...
Figure 3.11 Schematic depiction of the fabrication process of PP nanowires...
Chapter 4
Figure 4.1 Electrical operation cycles of TENG. (a) Schematic diagram of t...
Figure 4.2 CMEO of TENG. (a) The CMEO with load resistance
R
= 100 MΩ, whe...
Figure 4.3 Experimental results of the
V–Q
plot. (a) The CEO with ex...
Figure 4.4 Illustration of symbols in five structures of TENGs. (a) CS‐mod...
Figure 4.5 The structural figure of merits under optimum resistance (FOM
RS
Figure 4.6 The methods of triboelectric surface charge measurement. (a) Sc...
Figure 4.7 The standard
σ
measured by liquid metal as one electrode. ...
Chapter 5
Figure 5.1 Theoretical model of any mode of TENGs.
Figure 5.2 Resistive load characteristics of a TENG. (a) The equivalent ci...
Figure 5.3 Capacitive load characteristics of a TENG. (a) The equivalent c...
Figure 5.4 Using a TENG to charge a cellphone via a transformer. (a) Circu...
Figure 5.5 The factor of coil turn ratio of a transformer. (a) Circuit dia...
Figure 5.6 Capacitive transformer for a TENG. (a) A 3D structure of the PT...
Figure 5.7 Capacitive transformer for a lateral sliding TENG. (a) The 3D i...
Figure 5.8 A temporary capacitor and LC oscillation circuit. (a) Circuit d...
Figure 5.9 Power management of a TENG using an LC oscillation circuit. (a)...
Figure 5.10 Power management module on flexible and silicon wafer substrat...
Figure 5.11 LC oscillation with a passive switch for a TENG. (a) Electrost...
Chapter 6
Figure 6.1 Flexible and stretchable electronics from 0D, 1D, and 2D nanoma...
Figure 6.2 Flexible and stretchable electronics from organic materials. (a...
Figure 6.3 NMs and their application in flexible electronics. (a) SEM imag...
Figure 6.4 Stretchable electronics based on 2D serpentine design. (a) Repr...
Figure 6.5 Flexible and stretchable electronics based on 3D structures. (a...
Chapter 7
Figure 7.1 Size‐tunable fluorescence properties and spectral range of QDs....
Figure 7.2 Representative QD core with emission wavelength superimposed ov...
Figure 7.3 Excitation‐dependent luminescence of CQDs. Photographs of polye...
Figure 7.4 The casting process. (a) A photograph showing the drop‐casting ...
Figure 7.5 The dip coating process. (a) A schematic of the dip‐coating pro...
Figure 7.6 The LB deposition process. (a) A schematic showing the LB depos...
Figure 7.7 The screen‐printing process. (a) A schematic illustrating the s...
Figure 7.8 The inkjet‐printing process. (a) A schematic depicting the inkj...
Figure 7.9 The microcontact‐printing process. (a) Schematic showing the ad...
Figure 7.10 The 3D printing method. (a) Optical image of 3D‐printed LiFePO
Figure 7.11 Light‐emitting diodes using colloidal NCs. (a) A schematic sho...
Figure 7.12 Transistors using NP layers. (a) A schematic of the device str...
Chapter 8
Figure 8.1 Fabrication methods for bulk CNTs. (a) Cross‐sectional scanning...
Figure 8.2 Fabrication methods for surface CNTs. (a) Schematics and corres...
Figure 8.3 Application of CNTs. (a) Key steps in fabricating the SWCNT str...
Figure 8.4 Basic mechanism of piezoelectric potential. (a) Atomic model of...
Figure 8.5 Morphology of various types of ZnO nanowires. (a) Field‐emissio...
Figure 8.6 Applications of ZnO nanowires. (a) Illustration of readily comp...
Figure 8.7 Methods for Ag nanowires in composite flexible and stretchable ...
Figure 8.8 Applications of Ag nanowires. (a) Force mapping properties of t...
Chapter 9
Figure 9.1 Illustration of different 2D nanomaterials, including graphene,...
Figure 9.2 Graphene films grown by different methods. (a) AFM image of the...
Figure 9.3 Schematics of different graphene transfer methods. (a) Mechanic...
Figure 9.4 Stretchable and transparent graphene‐based electrodes. (a) Phot...
Figure 9.5 Graphene‐based nanogenerators. (a) Piezoelectric nanogenerator ...
Chapter 10
Figure 10.1 Buckling of semiconductor nanoribbons for stretchable electron...
Figure 10.2 Biaxially stretchable “wavy” nanomembranes. (a) Schematic illu...
Figure 10.3 Stretchable, noncoplanar electronics. (a) Schematic illustrati...
Figure 10.4 Schematic illustration of the assembly approach for forming 3D...
Figure 10.5 3D structures fabricated using the deterministic 3D assembly a...
Figure 10.6 Examples of mechanically driven kirigami for deterministic 3D ...
Figure 10.7 Buckling control assisted by stress and strain engineering. (a...
Figure 10.8 Deterministic assembly of 3D mesostructures from multilayer 2D...
Figure 10.9 Freestanding 3D structures. (a) Interfacial photopolymerizatio...
Figure 10.10 Morphable 3D structures by loading‐path‐controlled mechanical...
Figure 10.11 Exemplary flexible electronic devices fabricated using determ...
Figure 10.12 An exemplary flexible 3D‐structure‐based device for optical a...
Figure 10.13 3D electronic scaffolds for engineering neural network. (a) S...
Chapter 11
Figure 11.1 All‐solid‐state stretchable supercapacitor using PANI as elect...
Figure 11.2 Stretchable strain sensor using PPy/PU as stretchable conducto...
Figure 11.3 Electronic properties of transparent conductive films of PEDOT...
Figure 11.4 (a) Schematic illustration of organic semiconducting NW FET. C...
Figure 11.5 (a) The fabrication process of CNT–PDMS. (b) The pattern metho...
Figure 11.6 (a) Picture showing the stencil printing of Ag‐PDMS composites...
Figure 11.7 (a) Schematic of the PEDOT/PU/PEDOT film sandwich with crossin...
Figure 11.8 (a) Fabrication process of the strain sensors. (b) Photographs...
Figure 11.9 (a) Fabrication procedure for the AgNW/PDMS flexible patch ant...
Figure 11.10 Ag‐based conductive fiber.
Figure 11.11 (a) Schematic diagram of the side view and top view of each y...
Figure 11.12 (a) Schematic structure of the all‐fiber electric power nanog...
Figure 11.13 (a) Schematic of the all‐fabric‐based self‐charging power clo...
Chapter 12
Figure 12.1 Self‐powered pressure sensor based on CS‐mode TENG. (a) Schema...
Figure 12.2 Self‐powered pressure mapping based on the TEAS array. (a) A s...
Figure 12.3 Self‐powered touch sensor. (a) Schematic of the device using a...
Figure 12.4 Self‐powered vibration sensor. (a) Schematic diagram showing t...
Figure 12.5 Self‐powered triboelectric accelerometer. (a) Schematic diagra...
Figure 12.6 Self‐powered vibration direction sensor. (a) Schematic diagram...
Figure 12.7 Self‐powered acoustic sensor. (a) Schematic diagram of the act...
Figure 12.8 Self‐powered linear displacement sensor. (a) Schematic structu...
Figure 12.9 Self‐powered angle sensor. (a) Schematic illustration of the s...
Figure 12.10 Self‐powered tilt sensor. (a) Schematic diagram and (b) photo...
Figure 12.11 Self‐powered mercury ion sensor. (a) Fabrication process of t...
Figure 12.12 Self‐powered UV sensor. (a) Fabrication process of the self‐p...
Chapter 13
Figure 13.1 The illustration of hybrid sensors.
Figure 13.2 The schematic diagrams and outputs of TPNGs. (a–c) The schemat...
Figure 13.3 Schematic illustration of triboelectric–photovoltaic nanogener...
Figure 13.4 Electrical outputs of (a) the textile‐based triboelectric–phot...
Figure 13.5 Output performance of the hybrid triboelectric–electromagnetic...
Figure 13.6 The photograph of the hybrid nanogenerator. (a) Photograph of ...
Figure 13.7 The structure and photograph of the device. (a, b) Schematic d...
Figure 13.8 Schematic diagram and photograph of the multiple hybridized na...
Figure 13.9 The output performance of four nanogenerators. (a) Rectified o...
Figure 13.10 Hybrid sensors based on piezoelectric–triboelectric hybrid na...
Figure 13.11 The output performances of the hybrid sensor. (a, b) The outp...
Figure 13.12 The fabrication process step for FBHNG and SEM images for ZnO...
Figure 13.13 The output performances corresponding to different bending an...
Figure 13.14 Demonstration of the visualized tilt sensing system. (a) Meas...
Figure 13.15 Demonstration of the magnetic‐assisted TENG as a self‐powered...
Figure 13.16 The photograph and schematic illustration of the electromagne...
Figure 13.17 The schematic of hybridized nanogenerator and TENG unit worki...
Figure 13.18 The structure and working procession of the multiple hybrid n...
Figure 13.19 The output of the hybrid nanogenerator worked as temperature ...
Chapter 14
Figure 14.1 TENGs applied in optical modulation.
Figure 14.2 For the realization of two‐dimensional modulation of laser con...
Figure 14.3 Relationship between
V
oc
and displacement.
Figure 14.4 Characterization of load capacitance.
Figure 14.5 Toward an accurate control, a relationship between input displ...
Figure 14.6 Working mechanism of a dielectric elastomer. With an electric ...
Figure 14.7 Output performance of the TENG with or without an elastomer. A...
Figure 14.8 TENG is combined in the optical modulator system. (a) Structur...
Figure 14.9 Structure and mechanism of the proposed TENG–SMA actuator syst...
Figure 14.10 The whole system of bladder illness curation. (a) In vivo exp...
Figure 14.11 Output performance of the TENG. (a) Output voltage during the...
Figure 14.12 Transdermal drug delivery in porcine cadaver skin actuated by...
Figure 14.13 Effects of concentration of drug molecules in the output of t...
Figure 14.14 Processes of fabricating SDNA microneedles.
Figure 14.15 Electrospinning system employed rotating‐disk TENG. (a) Syste...
Figure 14.16 Performance of a self‐powered electrospinning system. (a) Pho...
Figure 14.17 Schematic view of a syringe printer. (a) The TENG is used to ...
Figure 14.18 Four structures for the manipulation of different drop motion...
Figure 14.19 Working principle of an electrostatic actuation system.
Figure 14.20 Working principle of a microfluidic transport system driven b...
Figure 14.21 Parameters of experiments for optimization of transport perfo...
Figure 14.22 The transportability was verified further by heavier load, sm...
Chapter 15
Figure 15.1 Structure of the human skin: the epidermis, the dermis, and th...
Figure 15.2 Triboelectric e‐skin for mechanical sensing and physiological ...
Figure 15.3 Mechanically durable and super‐stretchable nanogenerator for e...
Figure 15.4 Self‐powered artificial electronic skin for high‐resolution pr...
Figure 15.5 Graphene tribotronics for electronic skin and touch screen app...
Figure 15.6 Lateral sliding‐mode thin‐film motion vector sensor.
Figure 15.7 Triboelectrification‐based motion sensor for human–machine int...
Figure 15.8 Self‐powered analog smart skin.
Figure 15.9 Self‐powered noncontact electronic skin for motion sensing....
Figure 15.10 Graphene‐based strain sensors. (a) Schematic and atomic force...
Figure 15.11 Stretchable all‐graphene electronic skin. (a) Fabrication pro...
Figure 15.12 Hybrid nanogenerator used for healthcare monitoring.
Figure 15.13 Nanocomposite nanogenerator for self‐powered physiological mo...
Figure 15.14 Wireless self‐powered human–machine interaction.
Figure 15.15 E‐skin inspired by the skin of the electric eel.
Figure 15.16 Robust multilayered encapsulation for TENG.
Chapter 16
Figure 16.1 The diagram of the “all‐in‐one” self‐powered microsystem.
Figure 16.2 Schematic diagram and output performance of the triboelectric–...
Figure 16.3 One‐structure tribo–piezo–thermoelectric hybrid nanogenerator....
Figure 16.4 Some applications of the hybrid nanogenerator in healthcare mo...
Figure 16.5 Schematic diagram of the hybrid nanogenerator based on piezo‐t...
Figure 16.6 Structure and working mechanism of the piezo‐tribo‐pyro‐photoe...
Figure 16.7 Output performance of a designed device. (a, c, e) Short‐circu...
Figure 16.8 Work principle of PMM. (a) Schematic diagram of PMM. (b) The s...
Figure 16.9 Autonomous energy extractor for TENG. (a) The schematic circui...
Figure 16.10 Output performance of the TENG connecting to PMM. (a) The out...
Figure 16.11 The structure and characteristics of a flexible LIB belt. (a)...
Figure 16.12 Application of a flexible LIB belt. (a) The integrated self‐c...
Figure 16.13 Structure and properties of the kirigami‐based electrode. (a)...
Figure 16.14 Performance of the KP‐SC. (a) CV curves of the six‐unit KP‐SC...
Figure 16.15 Application of the all‐in‐one self‐charging power unit. (a) S...
Figure 16.16 A prototype of self‐powered microsystems. (a) A hybrid energy...
Figure 16.17 Self‐charging smart bracelet for portable electronics. (a) Sc...
Figure 16.18 More examples of harvesters directly driving various actuator...
Figure 16.19 More examples of sensing functions realized by energy harvest...
Chapter 17
Figure 17.1 The first application of an implantable TENG used as the power...
Figure 17.2 A flexible TENG aimed to power a medical laser for osteogenesi...
Figure 17.3 A piezoelectric and triboelectric hybrid nanogenerator (PTNG) ...
Figure 17.4 An innovative implantable TENG with significantly improved in ...
Figure 17.5 A self‐powered and multifunctional iTEAS for real‐time biomedi...
Figure 17.6 A new type of flexible TENG for versatile energy conversion an...
Figure 17.7 A self‐powered wireless body sensor network (BSN) system for h...
Figure 17.8 Results of induced voltage, current, and transferred charge te...
Figure 17.9 Fully in vivo absorbable bioresorbable natural‐materials‐based...
Chapter 18
Figure 18.1 Self‐powered, ultrasensitive, flexible tactile sensors based o...
Figure 18.2 TENG‐enabled body sensor network for self‐powered human heart ...
Figure 18.3 Smart network node based on hybrid nanogenerator for self‐powe...
Figure 18.4 Networks of triboelectric nanogenerators for harvesting water ...
Figure 18.5 Triboelectric nanogenerator as a self‐powered communication un...
Figure 18.6 In vivo self‐powered wireless cardiac monitoring via implantab...
Figure 18.7 Self‐powered wireless smart patch for healthcare monitoring....
Figure 18.8 A universal self‐charging system driven by random biomechanica...
Figure 18.9 High‐efficiency power management and charge boosting strategy ...
Figure 18.10 Structure and performance of fully packaged self‐powered trib...
Figure 18.11 Self‐powered analog smart skin.
Figure 18.12 Stretchable triboelectric–photonic smart skin for tactile and...
Figure 18.13 A self‐powered brain‐linked vision electronic‐skin based on t...
Figure 18.14 Bioinspired tribotronic resistive switching memory for self‐p...
Figure 18.15 Self‐powered real‐time movement monitoring sensor using tribo...
Figure 18.16 Fingertip‐inspired electronic skin based on triboelectric sli...
Figure 18.17 From dual‐mode triboelectric nanogenerator to smart tactile s...
Figure 18.18 Fully stretchable and highly durable triboelectric nanogenera...
Figure 18.19 Self‐powered digital‐analog hybrid electronic skin for noncon...
Chapter 19
Figure 19.1 Self‐powered phenol detection system. (a) A sketch of the trib...
Figure 19.2 The performance of the device. Dependence of (a) the current a...
Figure 19.3 Self‐powered dopamine detection system. (a) Schematic illustra...
Figure 19.4 Self‐powered heavy metal ion detection system. (a) Fabrication...
Figure 19.5 Degradation of AAB. (a) The schematic diagram of the rd‐TENG d...
Figure 19.6 Self‐powered electrodegradation system. (a) Schematic diagram ...
Figure 19.7 Self‐powered air‐cleaning system. Schematic illustrations of t...
Figure 19.8 Self‐powered seawater treatment system. (a) Schematic illustra...
Figure 19.9 Self‐powered water electrolysis units. (a) Schematic diagram o...
Figure 19.10 Self‐powered electrochemical polymerization system. (a) Schem...
Figure 19.11 Self‐powered electrochemical recovery system. (a) Photograph ...
Figure 19.12 The SPAS based on the high‐performance TENG. (a) Schematic im...
Figure 19.13 Self‐powered cathodic protection system. (a) Schematic diagra...
Figure 19.14 Self‐powered anticorrosion system. (a) The schematic illustra...
Guide
Cover
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Flexible and Stretchable Triboelectric Nanogenerator Devices
Toward Self-powered Systems
Edited by
Mengdi HanXiaosheng ZhangHaixia Zhang
Copyright
Editors
Dr. Mengdi Han
Northwestern University
Center for Bio‐Integrated Electronics
B371, Technological Institute
2145 Sheridan Road
Evanston, IL
United States
Prof. Xiaosheng Zhang
University of Electronic Science and Technology of China
School of Electronic Science and Engineering
B322, Research Building B
No. 2006 Xiyuan Ave
West Hi‐Tech Zone
611731 Chengdu
China
Prof. Haixia Zhang
Peking University
Department of Microelectronics
No. 5 Yiheyuan Road
Haidian District
100871 Beijing
China
Cover Images:
© Iaremenko Sergii/Shutterstock, © piick/Shutterstock
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Print ISBN: 978‐3‐527‐34572‐4
ePDF ISBN: 978‐3‐527‐82014‐6
ePub ISBN: 978‐3‐527‐82016‐0
oBook ISBN: 978‐3‐527‐82015‐3
Preface
Since 1960, electronics has played an important role in modern society, either as computing, sensing devices for information collection or as mobile terminates for data exchange. Further wider applications essentially require overcoming the restriction of traditional rigid, unsustainable power sources, thereby promoting the favorable properties of stability, high‐output, being maintenance‐free, flexibility, or even stretchability for the most sophisticated electronics. Quantitative comparison and qualitative analysis prove that emerging triboelectric nanogenerators (TENGs), invented by Zhonglin Wang of the Georgia Institute of Technology in 2012, can be a powerful and promising approach to address these challenges. Mostly, the TENG is fabricated by polymer‐based materials which make it flexible and stretchable naturally. More than a traditional energy harvester, the TENG can not only scavenge the mechanical energy from an ambient environment, based on the combination of contact electrification and electrostatic induction, but also serve as an active sensor from its rich information output with external stimulation. With all these merits, TENGs are developed as a flexible and stretchable self‐powered system for many applications.
In this book, we introduce in four parts the principle and progress of flexible and stretchable devices based on the triboelectric nanogenerator – the fundamentals of TENGs, approaches to flexible and stretchable structures, self‐powered smart systems, and their applications in various areas. The major contents of each part are listed as follows.
PART I: Fundamentals of triboelectric nanogenerators, including principle, working modes and structures, fabrication technologies, characterization, and power management.
PART II: Approaches to flexible and stretchable, including commonly used materials (0D, 1D, 2D nanomaterials) and unconventional 3D structural design and other recent progresses.
PART III: Self‐powered smart systems, including active and hybrid sensors, smart actuators, electronic skin, and all‐in‐one self‐powered microsystems.
PART IV: Applications of self‐powered smart systems, including biomedical systems, Internet of Things and artificial intelligence, environmental monitoring/protection, etc.
Therefore, this book provides a coherent viewpoint of this attractive field that is difficult to obtain solely by reading individual journal papers. The book also gives comparisons between methods, designs, and materials that typically do not appear in journal publications. The book will act as a resource to those who aspire to further extend either the science and technologies of flexible and stretchable electronics and self‐powered systems or future applications.
This book was written based mainly on numerous journal papers we and our collaborators have authored since 2012. I thank Alice Wonderlab's current and former members and partners who have made countless contributions in relative fields (list not in any particular order): Xiaosheng Zhang, Mengdi Han, Haotian Chen, Zongming Su, Xiaoliang Cheng, Xuexian Chen, Mayue Shi, Hanxiang Wu, Jinxin Zhang, Liming Miao, Yu Song, Bo Meng, Hang Guo, Ji Wan, Chen Xu, Haobin Wang, Wen Liu, Fuyun Zhu, Quan Yuan, Wei Tang, Xuming Sun, Xiuhan Li, Hangbo Zhao, Cunman Liang, Yanyuan Ba, Zhaohui Wu, Danliang Wen, B N Chandrashekar, Smitha A S, Jianbo Fu, and Zijian Song, etc. We thank our collaborators and coworkers worldwide: John A Rogers, Juergen Brugger, Jingfu Bao, Zhongfan Liu, Zhihong Li, Shuxiang Dong, Tianling Ren, and Wei Gao, etc. Particularly, I express my thanks to Prof. Zhonglin Wang for his continuous support and encouragement in the past 10 years, for me Prof. Wang is not just an outstanding scientist in research, a great mentor in career, but also a living model in life.
In addition, I thank my iCAN team, Yiqing Wang, Zhonghua Yu, Baoqin Chen, Jianping Xing, Yalin Ren, Xiangjun Xin, Jiaxin Cui, Sulan Li, Esashi Masayoshi, Chihming Ho, and others. iCAN is the original force in my mind, to make something different, to make something great, and to make something meaningful. With your long‐term support and co‐efforts, we are on the way to make this great dream come true. This book is a demonstration in academy.
Last but not least, I thank my harmonious four‐generation family, my dearest grandmother, and my father and mother, my husband Herbert and my daughter Lily, without their powerful support and full understanding nothing would have come out in my life. This book is my sincere gift to all of you.
Haixia(Alice) Zhang
Microelectronics Department
Peking University
Beijing, China
Part IFundamentals of Triboelectric Nanogenerator
1Overview of Triboelectric Nanogenerators
Xiaosheng Zhang
University of Electronic Science and Technology of China, School of Electronic Science and Engineering, No. 2006, Xiyuan Ave, West Hi‐Tech Zone, Chengdu, 611731, P.R. China
Ambient energy is abundant in the environment and takes various forms, such as solar irradiation [1], thermal gradient [2], mechanical deformation [3], and so on, which can be converted into electricity using ambient energy‐harvesting techniques [4]. The approach to harvesting energy from the environment is one of the ideal solutions to respond to the energy demands of distributed autonomous microsystems, which should be sustainable, renewable, and of high performance [4]. Ambient energy‐harvesting technology provides an attractive future vision to realize fully integrated self‐powered microsystems that overcome the drawbacks of batteries, which currently need to be frequently replaced, or of laying out long wires for power supply [5]. In 2012, a new ambient energy‐harvesting mechanism named triboelectric nanogenerator (TENG) was developed by combining the triboelectrification effect and electrostatic induction [6,7]. This novel technology has proved to be a robust power source to directly power commercial electronics and even regular light bulbs [7]. There has been a remarkable growth of TENG research in the past years due to its unique properties, including high‐output performance, cleanness, sustainability, etc. [8,9]. Mechanical energy from sources such as wind, raindrops, and ocean waves, as well as body motions can be efficiently converted to electric power using TENGs. Therefore, this chapter summarizes the current progress of microenergy technologies and then introduces an overview of TENG.
1.1 Energy Crisis of Microsystems
In the past half century, as the benefit of the rapid development of electronic science and technology, human society gradually changed to automation, both intelligent and digitization, and various electronic devices have become part of our life and are distributed everywhere. The featured size of modern electronic devices becomes smaller year by year down to the millimeter, and even to micrometer levels, which induces a continuous decrease in power consumption down to milliwatts and even to microwatts. Consequently, the great reforms in small‐size and low‐power consumption promote the integration of multifunctional electronic devices to realize microsystems.
Microsystems experienced a blooming development in the past decades resulting from their unique features, i.e. portable, smart, and miniature. However, the further development of microsystems suffered several critical challenges, especially the exploration of appropriate power sources. At present, batteries are still the first option, especially some of the flexible batteries, but the problems of sustainability and pollution caused by batteries cannot be ignored. In the meantime, distributed autonomous microsystems also have some new energy demands such as sustainability, renewability, high performance, and even flexibility or stretchability.
As an essential example of microsystems, Internet of things (IoT) is expected to play an important role in economic and social development of the next generation, as shown in Figure 1.1. Thus, IoT is taken as an example to describe the energy crisis of microsystems [10].
Figure 1.1 Schematic view of the Internet of things (IoT) and its power supply requirements. It is of great significance for the development of IoT to realize the appropriate microenergy source that fits the unique requirements.
In principle, an IoT system is composed of three main parts: sensing network, interconnection network, and terminal network. The sensing network detects the various changes of environmental factors and transforms them as electronic signals. Subsequently, the electronic signals are transferred to the interconnection network and treated to form control signals. Eventually, these control signals are delivered to the terminal network to drive functional electronic devices to respond to the corresponding changes. Therefore, the sensing network serving as the interface media between environment and client is the essential component of the IoT. The sensing network consists of trillions of sensors, which are widely distributed in the environment, especially in autonomous states.
Consequently, exploring an appropriate power approach for the sensing network is an urgent issue for the rapid development of IoT. Micro energy sources harvesting energy from the ambient have been proven as one of the attractive methods. By using piezoelectric, thermoelectric, photovoltaic effects, etc., microenergy harvesters can accumulate energy in various forms and convert them to electricity to power miniature devices and systems. There micro energy‐harvesting technologies are clean, sustainable, and low‐cost. Moreover, it provides the feasibility to integrate functional electronic components with these microenergy sources.
1.2 Microenergy Technologies
A promising way to satisfy the energy demands of low‐power‐consumption microsystems is to collect energy from the living environment. Because the featured size and the electric output are at milliscale or even microscale levels, the ambient energy‐harvesting technologies are also named as microenergy technologies. They possess attractive advantages to realize fully integrated, self‐powered devices which do not need replacement of batteries or laying out long wires for charging.
Previous research work has exploited several techniques using different mechanisms, such as photoelectric conversion, piezoelectric effect, thermoelectric effect, biochemical effect, etc. These techniques can be used to collect various forms of environmental energy such as light, mechanical change, temperature difference, variation of electromagnetic field, etc.
Herein, we summarize and compare five essential technologies for ambient energy‐harvesting in Figure 1.2 and Table 1.1. Since the specific application area is limited for self‐powered flexible microsystems, only flexible or wearable configurations of these five technologies are emphasized.
Figure 1.2 Summary of technical progress of five promising methods for harvesting energy from the environment.
Source: Reproduced with permission from Zhang et al. [4]. Copyright 2018, Elsevier.
Table 1.1 Comparison of five technologies for ambient energy harvesting.
Source: Reproduced with permission from Zhang et al. [4]. Copyright 2018, Elsevier.
Type
Schematic view
Voltage (V)
Current (A)
Power density (mW/cm
2
)
Efficiency (%)
Pros versus cons
Photovoltaic
(
PV
)
0.5–0.9
100–500
5–30
0.3–46
High output power, continuous DC output, good basis of industrial fabrication
For the flexible organic solar cell, the conversion efficiency is still very low, only works under light
Thermoelectric
(
ThE
)
0.1–1
5–30
0.01–3
0.1–25
Sustainably working as a DC power source, easy to scale down, no moving component
Low conversion efficiency, low output performance, large temperature difference
Electromagnetic
(
EM
)
0.1–10
N/A
N/A
5–90
High conversion efficiency, high current with low voltage, resistive impedance
For wireless power transmission: short range, working at certain frequency; For magnet moving: heavy weight and big size, complexity
Piezoelectric
1–200
0.01–10
0.001–30
0.01–21
Highly sensitive to external excitation, easily integrates and miniaturizes in micro‐/nanoscale
Low conversion efficiency, low output performance, pulse output, high impedance
Triboelectric
(
TrE
)
3–1500
10–2000
0.1–100
10–85
High output and energy conversion efficiency, no materials limitation, remarkable flexibility
Pulse output, high impedance, friction damage
1.2.1 Photovoltaic Effect
The solar cell is one of most popular power sources based on photovoltaic effect. The basic law of photovoltaic effect is that electrons overcome the potential barrier and are excited to a higher energy state by absorbed lights. The frequency of light must exceed a certain range in order to possess sufficient energy to overcome the potential barrier for excitation, and then the separation of charges leads to the establishment of an electric potential [4,11].
So far, solar cells can be divided into five main categories, including multi‐junction cells, single‐junction GaAs, crystalline silicon cells, thin‐film technologies, and emerging others [12]. The first three types possess better performance, with the energy conversion efficiency (ECE) ranging from 21.2% to 46%, and silicon‐based solar cells dominate the commercial market [12]. Nevertheless, because of fragile and nonflexible characterization, it is difficult to apply them in wearable microsystems.
By contrast, the latter two classifications show good flexibility by fabricating specific functional materials on polymeric substrates, but their ECEs are still at a relatively low level, with copper indium gallium selenide (CIGS), perovskite, and dye‐sensitized solar cells reaching the highest values of 23.3%, 22.1%, and 11.9%, respectively [12].
1.2.2 Thermoelectric Effect
As is known, the human body itself is a perfect energy source to provide thermal dissipation and physical movement [13,14], which is regarded as an attractive solution to satisfy the power demand of wearable electronics. The thermoelectric effect is employed to transform the energy generated by the thermal dissipation of the human body to electricity. When a temperature difference is applied to thermoelectric devices, an electrical potential that can drive the flow of electrons in the circuit loop to generate the electricity will be established, which is named the Peltier–Seebeck effect [4,15].
Thermoelectric generators can be classified into inorganic and organic. Inorganic thermoelectric generators are made from inorganic materials, such as several alloys and intermetallic compounds based on elements like Bi, Te, Sb, Pb, etc., which are, as a matter of fact, toxic [16].
Organic thermoelectric generators are usually manufactured using conductive polymers (i.e. conjugated polymers and certain coordination polymers) and small molecules (i.e. charge‐transfer complexes and molecular semiconductors) [15]. They have attracted much attention because of the properties of light weight and outstanding flexibility. However, the ECE needs to be strengthened, which is still at a relatively low level of less than 25%. The ECE of the thermoelectric generator is defined as a function of the figure of merit (ZT), average working temperature, and the temperature difference between the hot and cold ends. Thus, compared with ECE, the figure of merit, i.e. ZT = S2σT/k, is more important to characterize the performance of the thermoelectric generator, where S is the Seebeck coefficient or thermopower, σ is electrical conductivity, κ is thermal conductivity, andT is the absolute temperature [17].
1.2.3 Electromagnetic Effect
The electromagnetic effect is a well‐known Faraday's law of electromagnetic induction, which can be traced back to 1831 [4]. It reveals that the voltage induced in a closed loop is proportional to the change rate of the magnetic flux through the annular region. This is the operational principle of a traditional magnetic generator, which is the cornerstone of modern society. The ECE of the magnetic generator can reach 90%, which has a desirable output power. But when we attempt to use it for wearable applications, this traditional magnetic generator is obviously unsuitable because of its heavy weight and large size. Thus, electromagnetic microgenerators were developed by adopting the microfabrication technology, which makes the device miniaturized and partially realizes its flexibility by fabricating flexible coils [18–20]. However, the properties of a hard magnet make it impossible to create fully flexible electromagnetic microgenerators.
Another promising alternative is wireless power transfer (WPT) based on electromagnetic induction, which can be used to transfer electrical power among multiple points without requiring a physical connection [21,22]. The method endows the powered electronics with the maximum freedom, and has been proved as a wireless power source in both laboratory and industry. Although relay coils have been developed to cope with these obstacles, the limitations of power transmission direction and short‐range distance still pose challenges for further applications [23].
1.2.4 Piezoelectric Effect
The piezoelectric generator is an important approach to scavenging biomechanical energy, which has been proved to be a clean energy source [24–26]. The fundamental mechanism is a piezoelectric effect, which, as an electric potential, is established at the end of piezoelectric materials, and under external pressure is a reversible process [24].
Several kinds of materials, including specific crystals, ceramics, polymers, and biological matter, have been discovered to possess piezoelectric property. They can be simply classified into two main categories: inorganic and organic materials. The most well‐known inorganic materials are piezoelectric crystals and ceramics, such as PZT (lead zirconate titanate), BaTiO3 (barium titanate), ZnO (zinc oxide), quartz, etc. [4,27].
The typical organic material is PVDF (polyvinylidene fluoride), which is flexible and suitable for integration with wearable electronics. In order to obtain piezoelectric property, it is necessary to implement a post process of polarization by applying an ultra‐strong electric field, which requires specific equipment and manufacturing processes.
Piezoelectric coefficient, also named piezoelectric constant, is one of the essential parameters to quantify the piezoelectric property of materials, whose variation ranges from tens to thousands. Therefore, the performance of a piezoelectric generator has a direct relation with the piezoelectric property of the selected material. The remarkable linear characteristic between input pressure stimulation and output electric signal makes piezoelectric generators suitable to play the part of self‐powered transducers [5]. It deserves to be mentioned that piezoelectric nanogenerators (PENGs) based on ZnO nanowires have developed vigorously in the past decades [28].
1.3 Triboelectric Nanogenerators
The traditional techniques proposed for microenergy sources are still hindered more or less by the following limitations, such as low output performance, strict environmental requirement, and low conversion efficiency. In 2012, a novel ambient energy‐harvesting technology was developed. Named TENG, it combines triboelectrification effect and electrostatic induction [4,6].
The charge generated at the friction interface of two different materials (i.e. the triboelectric pair) is defined as the triboelectrification effect. Although the observation and description of the electrification effect can be traced back more than 3000 years ago, the question is how to accumulate charges, generate electricity, and minimize the size in an efficient way.
By setting two electrodes on the back surface of a triboelectric couple, electrification effect and electrostatic induction are combined for effective power conversion [4,6]. In the past five years, TENGs have aroused widespread interest due to excellent properties of high‐output performance, low cost, being maintenance‐free, sustainability, and green power performance. In order to strengthen and extend the capabilities of TENGs, a variety of techniques have been developed, and the power density has reached tens of mW/cm2 level [9]. Furthermore, the maximum power conversion efficiency was achieved at 85% [29].
Since the electrification effect exists between nearly all of the two different materials used, this technique has great tolerance with material selection, and plenty of polymers and organic materials can be selected to achieve flexible and even stretchable devices. Besides, micro‐/nanopatterned surfaces are usually adopted to maximize the effective friction area and enhance the output performance, and TENGs serve to emphasize it [30–34].
1.3.1 Principle of Triboelectric Nanogenerators
The original prototype of TENG had a triboelectric pair made of two different materials and two electrodes placed at the back. The operation principle can be described using contact‐separation‐mode TENG, as shown in Figure. 1.3.
Figure 1.3 The working principle of contact‐separation‐mode triboelectric nanogenerators (TENGs). (a) In the beginning, the triboelectric pair made of triboelectric materials 1 and 2 are separated, and the whole device shows an electrically neutral state. (b) When a compressive force is applied, the top structures will move toward the bottom structures and have a friction with each other. Due to the phenomenon of triboelectrification effect, positive and negative charges of equal amount will be generated on the surfaces of triboelectric pair, respectively. (b–d) When the compressive force is removed, the triboelectric pair will separate from each other as a result of the mechanical recovery force. And then, an internal electric potential is established, which changes accordingly as the distance of the triboelectric pair increases and decreases. Consequently, due to the electrostatic induction, opposite charges are generated on the back electrodes, and a current (I) can be detected in the loop resulting from the charges flowing from one electrode to the other. When the triboelectric pair works cyclically, an electric output power will be generated continuously.
Source: Reproduced with permission from Zhang et al. [4]. Copyright 2018, Elsevier.
Firstly, the whole TENG is electrically neutral and the triboelectric pair materials are separate. Under an action of external force, the pair makes contact and generates friction, and then surface charges are generated at the friction interface. Because of the difference in capabilities of losing or capturing electrons during electrification, one material of the triboelectric pair loses electrons and shows positive potential, while another captures electrons and shows negative potential. In principle, the total charge amounts on the surface of the triboelectric pair are equal.
Secondly, after removing the external force, the triboelectric pair separates and an internal potential is established owing to the electrostatic induction. During the separation process, this internal potential will drive charges to flow from one electrode to the other through the connection loop to make the change of electrical potential balanced. And then, a positive current is formed, namely, electricity is generated. This is named the process of separating.
Thirdly, when applying an external force to the TENG again, the triboelectric pair moves toward each other, which will cause charges to flow back due to the opposite change of electrical potential. Thus, a negative current is formed, and this process is named approaching.
Finally, the triboelectric pair makes contact again and there is friction, and then a new cycle begins. Thus, when TENG repeats this separating–approaching cycle, it produces a periodical electric output with positive and negative parts.
The output performances of CS‐mode TENGs were not so advantageous and it remained at a low level of several or tens of volts at the beginning. Subsequently, an arch‐shaped geometry design was introduced, whereby surface roughness was increased. It significantly expanded the output voltages and power densities of CS‐mode TENGs to hundreds of volts and several mW/cm2 [9].
The fundamental mechanism for enhancing output by increasing surface roughness is to maximize the effect friction area, and more surface charges can therefore be generated [30]. As for the arch‐shaped optimization, the basic rule of output enhancement can be roughly described by introducing a capacitance equivalent mode [35]. Assuming the surface charges (Q) are constant, the potential difference (U = Q/C) between two electrodes increases sharply when the capacitance (C) decreases sharply due to the stronger mechanical restoring force from the arch‐shaped design. The CS‐mode TENGs have the advantage of high output voltage, and their simple geometric structure makes for easy utilization, for instance, to convert most mechanical energies, such as pressing, impacting, bending, shaking, vibration, etc. However, using them for harvesting mechanically rotational energy is hard to achieve, and the frequency effect study also figured out that the CS‐mode TENGs are not suitable for high‐frequency applications [30].
1.3.2 Key Factor: Triboelectric Series
TENG development is based on the progress of materials. As described in Section 1.3.1, the key of electrification is the ability difference of losing or capturing electrons between the triboelectric pairs. Basically, if the ability relative difference of triboelectric pairs becomes larger, then the output performance of fabricated TENG becomes better as a result of the enhancement of generated surface charges. A table of triboelectric series, which qualitatively points out these ability differences, was established, and is summarized in Table 1.2.
Table 1.2 Triboelectric series of different materials.
Source: Reproduced with permission from Zhang et al. [4]. Copyright 2018, Elsevier.
Triboelectric series
No.
Materials
No.
Materials
No.
Materials
POSITIVE
1
Aniline–formol resin
17
Styrene‐acrylonitrile copolymer
33
Polyacrylonitrile
2
Polyformaldehyde 1.3–1.4
18
Styrene‐butadiene copolymer
34
Acrylonitrile‐vinyl chloride
3
Ethylcellulose
19
Wood
35
Polybisphenol carbonate
4
Polyamide 11
20
Hard rubber
36
Polychloroether
5
Polyamide 6‐6
21
Acetate, Rayon
37
Polyvinylidene chloride (Saran)
6
Melanimeformol
22
Polymethyl methacrylate (Lucite)
38
Poly(2,6‐dimethyl polyphenyleneoxide)
7
Wool, knitted
23
Polyvinyl alcohol
39
Polystyrene
8
Silk, woven
24
Polyester (Dacron) (PET)
40
Polyethylene
9
Polyethylene glycol succinate
25
Polyisobutylene
41
Polypropylene
10
Cellulose
26
Polyurethane flexible sponge
42
Polydiphenyl propane carbonate
11
Cellulose acetate
27
Polyethylene terephthalate
43
Polyimide (Kapton)
12
Polyethylene glycol adipate
28
Polyvinyl butyral
44
Polyethylene terephthalate
13
Polydiallyl phthalate
29
Formo‐phenolique, hardened
45
Polyvinyl chloride (PVC)
NEGATIVE
14
Cellulose (regenerated) sponge
30
Polychlorobutadience
46
Polytrifluorochloroethylene
15
Cotton, woven
31
Butadiene‐acrylonitrile copolymer
47
Polytetrafluoroethylene (Teflon)
16
Polyurethane elastomer
32
Natural rubber
The triboelectric series table is essential for constructing high‐performance TENGs, since it quantitatively figures out the relative ability difference of losing/capturing electrons during the triboelectrification effect [36]. If the triboelectric pairs have a larger difference in this table, it means that it is easier for electrons to transfer from one to the other during the triboelectrification effect.
1.3.3 Material Progress of Triboelectric Nanogenerators
In the past few years, great progress was made in different triboelectric pairs for TENGs, as listed in Table 1.3. In this table, the materials in the left column, highlighted in yellow, indicate that they are easy to lose electrons and show positive potential. The materials in the top row, highlighted in blue, indicate that they are relatively easy to capture electrons and show negative potential.
Table 1.3 The configuration of triboelectric pairs (up to October 2017).
Currently, the widely used materials are PTFE (polytetrafluoroethylene), PDMS (polydimethylsiloxane), PI (polyimide), and FEP (fluorinated ethylene propylene), composed of 14, 11, 11, and 8 triboelectric pairs, respectively, as shown in Table 1.3. The main reason is that they occupy the bottom‐tier levels in the triboelectric series, which leads to their outstanding abilities of capturing electrons during the electrification effect. The sequence of electron‐capturing ability is listed as PTFE > PDMS > PI [7], and FEP is almost like PTFE with little difference in molecular structure.
Among known materials, PTFE, also known as Teflon, has the strongest ability to capture electrons, and possesses ultrastable chemical and physical properties. PDMS is a kind of biocompatible material which can be micro‐/nanopatterned easily using the molding cast process, and it also maintains a good stretchable capability. PI, also known as Kapton, can be processed into elastic thin films and made to work under high‐temperature conditions.
Regarding the negative part of triboelectric pairs, materials can be classified into four groups: metals, oxides, polymers, and others. Metals can work as triboelectric pairs and electrodes at the same time [37–39], which simplifies the structure of TENGs. Oxide compounds are widely used, including ITO (indium tin oxide), TiO2, Al2O3, SiO2, and graphene oxide. Among the rest, ITO exhibits a unique feature of conductivity and an outstanding property of transparency [40]. Polymers are the most important type of triboelectric materials; therefore, TENG is also called organic nanogenerator, which is firstly used to collect mechanical energy as organic materials [7].
One of the most attractive benefits of TENG is its tolerance to the material selection, since almost all of the two different kinds of materials are able to generate the electrification effect. Therefore, as is shown in Table 1.3, there are a great number of triboelectric pairs made up of different materials. However, the electrical performance of fabricated TENG depends on the ability difference of losing or capturing electrons. From this point of view, the materials are expected to possess the excellent electrical property of easily losing or capturing electrons. Exploring novel triboelectric materials still exists as an important research topic. In addition, triboelectric materials are expected to achieve excellent flexibility or even stretchability, environmental friendliness, or even biocompatibility, which fulfills the demand for constructing flexible and wearable self‐powered microsystems.
1.3.4 Challenges of Triboelectric Nanogenerators
So far, the rapid development of TENG is still confronted with two challenges: one is the requirement to enhance power density, and the second is to simplify the structure to realize easier integration. Although simply enlarging the size can enhance the output power of TENG, the area power density remains constant, which is closely relevant to the fundamental mechanism of the triboelectrification effect, especially the triboelectric series that qualitatively depends on the ability of the triboelectric pair to lose or capture electrons [4]. Moreover, although four types of TENGs with different working principles have already been developed [4], such as contact‐separation mode and relative‐sliding mode, integrating TENG with other components to realize fully integrated self‐powered microsystems still requires a lot of effort.
1.4 Summary
Through the abovementioned analyses and comparisons, we can summarize that TENGs possess much more attractive potentials and are considered as one of the promising ambient energy‐harvesting approaches. In the latter part of this book, we summarize the emerging technology of TENG which serves as an important component of self‐powered flexible and wearable microsystems, including the innovation of working principle and material selection, the functionalization of sensing and actuating, and the future development direction of the all‐in‐one concept.
Abbreviations
CNT
carbon nanotubes
CS
contact‐separation mode
ECE
energy conversion efficiency
EM
electromagnetic
EVA
ethylene‐vinyl acetate
FEP
fluorinated ethylenepropylene
FS
free‐standing mode
IoT
Internet of things
ITO
indium tin oxide
PCL
poly(caprolactone)
PDMS
poly(dimethylsiloxane)
PE
polyethylene
PET
polyethylene terephthalate
PFA
polyfluoroalkoxy
PHB/V
poly(3‐hydroxybutyricacid‐
co
‐3‐hydroxyvaleric acid)
PLGA
poly(
L
‐lactide‐
co
‐glycolide)
PMMA
poly(methyl methacrylate)
PP
polypropylene
PPy
polypyrrole
PU
polyurethane
PV
photovoltaic
PVA
poly(vinyl alcohol)
PVC
polyvinyl chloride
PVDF
polyvinylidene fluoride
PZT
lead zirconate titanate
RS
relative‐sliding mode
SE
single‐electrode mode
TENG
triboelectric nanogenerator
ThM
thermoelectric
WPT
wireless power transfer
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