objective of writing this book is to systematically introduce hybridized and coupled nanogenerators. Understanding of the fundamental mechanism and related technological applications of the hybridized and coupled nanogenerators can be seen in this book. The potential readership includes scientists, engineers, undergraduate and graduate students in materials, physics, energy, nano‐science, and other related fields from science and industry.
First, I would like to thank my postdoctoral supervisor (Prof. Zhong Lin Wang) and doctoral supervisor (Prof. Yue Zhang) for good guidance and strong support in these years. It would not have been possible to achieve this research without their guidance and support. Second, I would like to thank my students for their contributions to this book: my postdoctoral student (Yang Wang), and my doctoral students (Kai Song, Bangsen Ouyang, Ding Zhang, Yun Ji). Third, I would like to thank my current and former group members who have made outstanding contributions to the development of hybridized and coupled nanogenerators: Yingchun Wu, Shuhua Wang, Kewei Zhang, Xiandai Zhong, Xue Wang, Ting Quan, Kun Zhao, Qingbin Zhai, Xi Liu, Yang Wang, Jia Qi, Nan Ma, Yun Ji, Bangsen Ouyang, Kai Song, Tiantian Gao, Qiang Jiang, Bo Chen, Yuanming Wang, Yuting Jiang, Ding Zhang, Rudai Zhao, Xue Zhao, Weiqi Qian. Moreover, I thank my family members for the support and understanding. Finally, I want to acknowledge funding by the Beijing Institute of Nanoenergy and Nanosystems, Chinese Academy of Sciences, the National Natural Science Foundation of China (Grant No. 51472055, Grant No. 61404034), External Cooperation Program of BIC, Chinese Academy of Sciences (Grant No. 121411KYS820150028), the 2015 Annual Beijing Talents Fund (Grant No. 2015000021223ZK32), the Beijing Natural Science Foundation (Grant No. 2154059), the University of Chinese Academy of Sciences (Grant No. Y8540XX2D2), the National Key R&D Program of China (Grant No. 2016YFA0202701), and Qingdao National Laboratory for Marine Science and Technology (Grant No.2017ASKJ01).
Ya Yang, Professor
Beijing Institute of Nanoenergy and Nanosystems,
Chinese Academy of Sciences
School of Nanoscience and Technology,
University of Chinese Academy of Sciences
*E‐mail: [email protected]
Website: http://www.researcherid.com/rid/A-7219-2016
Beijing, China
20 January 2020
1 Overview
1.1 Introduction
Nanogenerators are based on the use of the displacement current of Maxwell as the driving force to convert environmental energies into electric signals, exhibiting various potential applications in wearable electronics, sensor systems, robotics, and other energy‐related science. Prof. Z. L. Wang and coworkers invented the first piezoelectric nanogenerator in 2006 [1], and invented the first triboelectric nanogenerator (TENG) in 2012 [2]. Both these nanogenerators are based on the polarization Ps produced due to the mechanical motions induced electrostatic surface charges, where it is not the electric field produced medium polarization P.
Usually, Maxwell's equations can be expressed by
(1.1)
(1.2)
(1.3)
(1.4)
where D is the electric displacement vector (D = ɛ0E + P). Z. L. Wang added an additional term Ps in D in 2017 [3,4]. Thus, D can be given as
(1.5)
where the polarization vector P is associated with the appearance of the external electric field, while the additional term Ps is associated with the appearance of the surface charges that can be independent of external electric fields [5]. Maxwell's displacement current is then expressed as
(1.6)
where the first term
Various energies such as thermal, mechanical, chemical, and solar energies exist in the living environment. However, the occurrence of these energies depends on some working conditions such as weather or some other factors. The purpose of developing hybridized nanogenerators is to scavenge the different energies at the same time by integrating the different energy scavenging units into a system, so that we can obtain stable and sustainable power supply, regardless of whatever energy is available in the environment [6]. Prof. Z. L. Wang and coworkers invented the first hybrid energy cell in 2009 [7]. The first electromagnetic–triboelectric hybridized nanogenerator has been reported to scavenge one vibration energy by two different energy scavenging units in 2015 [8], which can largely enhance the efficiency of conversion from mechanical energy to electric energy. The existing hybridized nanogenerators are based on effectively stacking individual nanogenerators together in parallel or in series, where the individual nanogenerator has independent device structures and output electrodes. This is not suitable for miniaturization of the device dimension and for massive production. It is highly desirable to utilize multifunctional materials to obtain multi‐effects coupled nanogenerators with the same structure, material, and electrodes. By using piezo–tribo–pyro–photoelectric effects, Prof. Ya Yang and coworkers invented the first coupled nanogenerators in 2015 [9], which have the same materials, the same electrodes, and simultaneous different energies scavenging abilities. This book will give a detailed summary about the design, performance, and applications of the hybridized and coupled nanogenerators.
1.2 Hybridized Nanogenerators
Hybridized nanogenerators are based on integrating the different energies scavenging units into a system for realizing simultaneous multiple energies scavenging, which has two advantages as compared with the reported individual energy scavenging techniques: (i) increasing the total output electric performances; (ii) providing a more stable and sustainable small power source. By integrating the electromagnetic generators (EMGs) and TENGs, the research group of Prof. Ya Yang reported various electromagnetic–triboelectric hybridized nanogenerators to scavenge different types of mechanical energies [8,10–19], where all the hybridized nanogenerators have the same concept of integrating different nanogenerators to scavenge one mechanical energy for realizing obvious enhancement of energy conversion
