was fixed. The side view of the fabricated plate‐based TEG shows that the device is small, with the dimensions of 22 mm × 10 mm × 57 mm (Figure 2.4b). Figure 2.4c shows the front view of the device, with a thickness of about 2 mm.
Figure 2.3 Sketches illustrating the electricity generation process (a–f) in plate‐based TENG.
Source: Reproduced with permission from Yang et al. [32]. Copyright 2013, American Chemical Society.
Figure 2.4 Diagram of the enhanced plate‐based TEG. (a) Schematic diagram of the TENG. (b,c) The side and front views of the TEG. (d) Sketches illustrating the electricity generation process in enhanced plate‐based TENG.
Source: Reproduced with permission from Wang et al. [33]. Copyright 2015, John Wiley and Sons.
The working mechanism of the enhanced plate‐based TEG is schematically depicted in Figure 2.4d. At the initial state, both TEG‐1 and TEG‐2 are in the static condition, resulting in no output signals (Figure 2.4d(1)). When the Al electrode contacts with the top PTFE film in the TEG‐1, electrons will be transferred due to different triboelectric series, and their surfaces will respectively form positive charges and negative charges. This process will generate a balance due to the nature of the insulator, leading to no output signals (Figure 2.4d(2)). When the distance between the Al electrode and the Kapton film was increased under the external force, the balance was broken, which could generate the current signal through an external load in the TEG‐1, as shown in Figure 2.4d(3). The electrostatic induced charges disappeared when a new balance is built, as descripted in Figure 2.4d(4). In this state, the surface of the Al electrode forms positive triboelectric charges, and the surface of the bottom PTFE film forms negative charges in TEG‐2. Increasing the distance between the Al electrode and the bottom PTFE can induce two output signals in TEG‐1 and TEG‐2 due to electrostatic induction.
2.3.1.3 Elasto‐aerodynamics‐Driven TENGs
Under high wind speed, enhancing the stability of the devices is very important because of complex factors, such as buffeting, vortex shedding, galloping, and flutter. There are some natural mechanical problems in the vibrating plate‐based TENGs due to a combination of bending and torsion. To increase the stability and output performances of TENGs, elasto‐aerodynamics‐driven TENG was developed, which consists of a Kapton film, two PTFE films, and Cu electrodes (Figure 2.5a) [34]. Figure 2.5b shows the front view of the device.
The working mechanism of the elasto‐aerodynamics‐driven TENG is schematically depicted in Figure 2.5c. Owing to couple triboelectrification and electrostatic induction, alternating electrons can flow between Cu electrodes. At the initial state, the TENG is in static condition, resulting in no output signals. When the Cu electrode makes contact with the top PTFE film because of wind‐induced vibration, electrons are transferred due to different triboelectric series, and their surfaces will respectively form positive and negative charges. When the distance between the Cu electrode and the PTFE film increases under the external force the balance is broken, leading to the generation of the current signal through an external load. The electrostatic‐induced charges disappear when a new balance is built between the Cu electrode and the PTFE film. In this state, the surface of the Cu electrode forms positive triboelectric charges, and the surface of the bottom PTFE film forms negative charges. Subsequently, the charges on the top electrodes and the bottom electrodes can flow respectively in the external circuits due to the electrostatic induction.
2.3.1.4 Others
To harvest wind energy in our living environment, Xie et al. produced a TENG based on a rotary‐driven mechanical structure, which consists of a shaft, a flexible rotor blade, and two stators [35]. The triboelectrification and electrostatic induction effects in this TENG can be generated by utilizing a hybridization of the contact‐sliding‐separation‐contact processes. Zhang et al. developed a single‐electrode cylindrical TENG to harvest wind energy, which consists of a cylinder, a cylinder tube coated with PTFE [36]. The electric energy generated by this TENG can be used to power wireless sensors. Bae et al. reported a flutter‐driven TENG based on a flexible flag and a rigid plate and studied three contact modes (single, double, and chaotic) to increase the performance of the TENG [37]. Ren et al. designed a coaxial rotatory freestanding TENG, which consists of a stator and a rotator. The stator was made of an acrylic column coated with polyvinylidene fluoride (PVDF) nanofibers membrane, and the rotator was made of another acrylic tube with Al tapes [38].
The TENG arrays could enhance the efficiency of harvesting wind energy. Quan et al. reported double‐side‐fixed TENG arrays based on the coupling of triboelectric frication and electrostatic induction. The TENG arrays were connected in parallel by copper wires. These TENGs consist of top and bottom PTFE/Ti/Al patches and a vibrational Al/Ti/Kapton/Ti/Al film [39]. To enhance the performance and reduce a typical rigid friction of common TENG for harvesting wind energy, Wang et al. reported a composited structure, which consists of an anemometer TENG based on freestanding mode and a wind vane TENG based on single‐electrode mode [40]. The anemometer TENG was made of wind cups, rotator, and stator. Wind energy harvested through the wind cups can be used to drive the rotator. The FEP film used as a triboelectric surface was coated on the rotator. The wind vane TENG was made of a vane connected with a pie‐shaped rotator and a compass coated with Cu electrodes.
Figure 2.5 Diagram of the elasto‐aerodynamics‐driven TENG. (a) Schematic diagram of the TENG. (b) The front view of the TEG. (c) Sketches illustrating the electricity generation process in the elasto‐aerodynamics‐driven plate‐based TENG.
Source: Reproduced with permission from Wang et al. [34]. Copyright 2015, American Chemical Society.
Wind‐driven generators normally can harvest wind in a single direction, which reduces the efficiency of wind energy utilization. To solve this problem, Zhang et al. developed a flexible and transparent TENG, which can harvest natural wind in discretional blowing directions [41]. The TENG was made of massive freestanding polymer strips similar to a forest morphology. When the wind blows, the strips comprised of indium tin oxide (ITO) with polyethylene terephthalate (PET) thin film could sway independently. Harvesting wind energy at a high altitude is difficult for normal wind‐driven generators. Recently, Zhao et al. reported a woven TENG flag based on the interlaced interactions between the Kapton film and a conductive cloth, realizing collection of high‐altitude wind energy [42]. The conductive belts were made of polyester textiles coated with Ni and Kapton film‐sandwiched Cu belts.
2.3.2
