Читать книгу Hybridized and Coupled Nanogenerators - Ya Yang - Страница 44

WD‐TENGs, which possess the advantages of small scale, low cost, and easy fabrication, can be used as facile power sources to uninterruptedly power some small electronic devices under continuous wind flow. Yang et al. developed a small‐scale wind‐driven TENG, which can be used to power three light‐emitting diodes and an exit sign by harvesting human mouth blowing induced wind energy, as shown in Figure 2.19a,b [32].

Figure 2.18 The self‐powered healthcare monitoring system. (a) Output voltage signals of the TENG. (b) Output current signals of the TENG. (c) Output current signals after using the up‐flow chip. (d) Measured voltage of a capacitor charged by scavenging human nose breathing via the TENG. (e) Photographs before human breath. (f) Photographs of the temperature sensor after using the TENG to scavenge human breath induced air‐flow energy.

Source: Reproduced with permission from Wang et al. [34]. Copyright 2015, American Chemical Society.

Figure 2.19 The wind‐driven electronics light‐emitting diodes. (a) Photographs of lighting light‐emitting diodes via the TENG. (b) Photographs of powering an exit sign via the TENG.

Source: Reproduced with permission from Yang et al. [32]. Copyright 2013, American Chemical Society.

Wang et al. reported a TEG that can harvest flow‐driven mechanical energy to achieve sufficient illumination for reading [33]. As illustrated in Figure 2.20a, 10 light bulbs could be lit up by using TEGs. Figure 2.20b shows that the illumination powered by the TEGs can be used to read printed text in the dark environment. Humidity sensors are very important for food quality inspection and equipment security. Conventional humidity sensors, which are based on metal oxides, porous silicon, and polymers, would attain saturation at high humidity. Environmental humidity can affect the output performance of TENGs. The output voltage decreased with increasing the relative humidity. According to this property, Guo et al. developed a novel humidity sensor based on the airflow‐induced TENG [63]. This sensor can work in a wide humidity range and exhibits several advantages, such as self‐power, multifunction, low cost, and high sensitivity.

Figure 2.20 Photograph of lighting equipment power by the TEGs. (a) Ten spot lights driven by the TENGs. (b) Photograph of the printed text illuminated by the lights in the dark environment.

Source: Reproduced with permission from Wang et al. [33]. Copyright 2015, John Wiley and Sons.

With population growth and industrial development, air pollution has developed into a main problem that threatens human endurance. Currently, air‐purifying methods mainly include filtration, pulsed electron beam, and electrostatic precipitation. These approaches all face respective problems, such as occlusion for filtration and high voltage requirement for electrostatic precipitation. Chen et al. developed a self‐powered clearing system, which consists of a rotating TENG, an electric tank, and tow metal electrodes [76]. This nanogenerator can harvest wind energy and generate an output voltage of about 300 V. The voltage could not generate by‐products such as ozone and NO_X compared to that in traditional electrostatic precipitation. The generated voltage signals were converted into DC electricity through a rectifying bridge, and then connected to two metal electrodes. In this system, SO₂ could be converted to H₂SO₄ by the electrochemical reaction. Hydrogen (H₂), which mainly comes from natural gas and water reduction, is one of desired energy sources because of its high energy capacity. Water splitting where water is converted to H₂ and O₂ needs an external power supply, which makes it economically inefficient. Ren et al. developed a self‐powered water splitting system, which can harvest energy from our living environment for electrolytic water splitting based on a coaxial rotatory freestanding TENG [38]. The hydrogen generation rate of this system is about 6.9685 μl/min in 1 M KOH under a wind speed of about 10 m/s.

With the development of the industrial internet, wireless sensors, which can be used to apperceive the change in the surrounding environment, have attracted increasing attention in the past decade. Usually, powering wireless sensors needs an external power source such as a Li‐ion battery, which is limited by the capacity of batteries. Electrical energy generated by harvesting wind energy via TEGs can be used in the wireless sensor, according to Wang et al. The output voltage signals generated by the TEG must be reduced to reasonable voltage value, which can be accomplished by the power management circuit, as illustrated in Figure 2.21a [33]. The output voltage signals were decreased to about 12 V, and the current signals were increased to about 0.9 mA, as shown in Figure 2.21b,c. The wireless system consists of a power management circuit, a wireless sensor node, and the TEGs in a transparent gas tube, as shown in Figure 2.21d. The output voltage value could be adjusted to 1.8 V via the power management circuit when the TEG continuity harvest wind energy is about 4.9 S, as shown in Figure 2.21e.

Figure 2.21 The wind‐driven wireless sensor. (a) Schematic diagram of an integral powering circuit. The measured (b) regulative voltage and (c) the current at the transformer output port. (d) Photograph of the self‐powered system. (e) Output voltage of the system.

Source: Reproduced with permission from Wang et al. [33]. Copyright 2015, John Wiley and Sons.

Zhao et al. fabricated a highly efficient TENG, which can harvest wind energy for sustainably powering a wireless smart temperature sensor node [61]. Figure 2.22a shows a photograph of the wireless temperature sensor. A 10 mF capacitor was used to store the energy from the nanogenerator. In the charging stage (process‐1), the capacitor can be charged from 0 to 3.3 V, as shown in Figure 2.22b. The voltage of the capacitor decreased when the sensor stood at the initial stage, and then increased due to the supplement from the nanogenerator. When the TENG was shut down, no electrical energy could be generated, resulting in no temperature data on the screen of the iPhone, as illustrated in Figure 2.22c. When the TENG was working, the temperature sensor can probe the temperature of a human finger, as shown in Figure 2.22d. Lithium ion batteries, which are most effective energy storage devices, have been widely used in numerous electronic devices Jiang et al. used the Li‐ion battery to store electrical energy generated by TENGs [69]. By adjusting the output voltage of the TENG via a power management circuit, the regulative electrical energy can be used to charge the Li‐ion battery, as shown in Figure 2.23a. It was found that voltages of the Li‐ion battery can be increased by increasing the charging time. The voltage of the battery was about 3.6 V, when charged by the TENG for about 40 minutes. Figure 2.23b shows a photograph of the fabricated self‐charging system, which consists of a TENG, a Li‐ion battery, and an LED. The LED can be lit up by the Li‐ion battery, which is charged by the TENG, as shown in Figure 2.23c.

On the other hand, by integrating a WD‐TENG and a pressure‐sensitive elastic polyimide (PI)/reduced graphene oxide (rGO) foam, Zhao et al. fabricated a self‐powered pressure sensor [77]. Figure 2.24a shows a schematic diagram of the self‐powered pressure system. The TENG can generate output voltage signals by harvesting the wind energy. Figure 2.24b shows photographs of the self‐powered pressure system. Figure 2.24c presents four foams with different heights. The resistances of the elastic foam that was connected to the TENG can be changed with the diversification of the external forces, resulting in changes in the measured voltage, as shown in Figure 2.24d.

Figure 2.22 The wind‐driven self‐powered wireless smart temperature sensor. (a) Photographs of the temperature sensor. (b) Charging curve of a capacitor by using the TENG with a PMC. Photographs of the temperature sensor before (c) and after (d) being powered by the TENG.

Source: Reproduced with permission from Zhao et al. [61]. Copyright 2016, American Chemical Society.

Figure 2.23 The wind‐driven self‐charging Li‐ion battery. (a) Charging and discharging curves of the Li‐ion battery via the TENG. (b) Photograph of the self‐charging system. (c) Photographs of lighting up a green LED via the Li‐ion battery charged by the TENG.

Source: Reproduced with permission from Jiang et al. [69]. Copyright 2018, American Chemical Society.

Figure 2.24 The wind‐driven self‐powered pressure sensor. (a) Schematic diagram of the as‐fabricated self‐powered pressure sensor. (b) Photograph of the prepared pressure sensor. (c) Photograph of foams with heights. (d) The output voltage of the foam connected to the TENG.

Source: Reproduced with permission from Zhao et al. [77]. Copyright 2019, John Wiley and Sons.