A Three Dimensional Multi‐Layered Sliding Triboelectric Nanogenerator

Recently, a triboelectric nanogenerator (TENG) has been demonstrated to be an effective way to convert mechanical energy into electricity, [ 10 ] with performance depending on the coupling of triboelectrifi cation [ 11 ] and electrostatic induction. [ 10a ] Among the factors that affect the performance of the TENG, the suffi cient charge separation [ 12 ] and the friction area [ 13 ] are the two key factors. For charge separation, it depends on the materials used in the device and we can choose materials (one easy to gain electrons, and the other easy to lose electrons) to increase the output performance. [ 14 ] For the friction area, compared with increasing the size of the device, it is a better choice to extend the device from a 2D planar device [ 15 ] to a 3D device. Here, we develop 3D-TENG, with layer-by-layer stacked polyvinyl chloride (PVC) and aluminum as friction materials, based on an in-plane sliding mode between every two adjacent surfaces. Such a 3D multi-layered structure largely increases the friction area in the same space that contributes to the increase in the transferred charge quantity in the circuit. For a 3D-TENG consisting of 20 layers of PVC and 20 layers of aluminum as friction fi lms, the open-circuit voltage ( V oc ) reaches 800 V, the peak short-circuit current density ( J sc ) of 5.5 mA m −2 and a peak power density of 4.4 W m −2 , a maxiumum charge transfer quantity of 2.6 μC, with a sliding displacement of 15 mm. The results clearly demonstrate that the transferred charge quantity monotonically increases with increasing numbers of friction layers. Furthermore, the transferred charge quantity has a good linear relationship with the sliding displacement in a range of 3–15 mm, which means that 3D-TENG can be used as a selfpowered displacement sensor. 160 commercial light-emitting diode (LED) bulbs are instantaneously lit up because the output power of the 3D-TENG is very high; additionally the power generated by the 3D-TENG can be easily and effectively stored into an energy storage device such as a capacitor. The 3D-TENG takes full advantage of the space and largely improves the output of the TENGs, with great potential in self-powered systems, environmental monitoring, defense technology, and even personal electronics. The basic structure of the 3D-TENG is composed of PVC and aluminum friction fi lms stacking layer-by-layer, as illustrated in Figure 1 a. The digital image of the fabricated device is presented in Figure 1 b. To demonstrate the principle of the device, it is made of 20 layers of PVC and 20 layers of aluminum. Comparing to the previously reported devices, [ 16 ] such 3D-TENG has two advantages. First, it can increase the friction area tens of times compared to the former TENG. Second, since the 3D-TENG can be treated as a large number of individual planar TENGs connected in parallel, it can largely enhance the output current of the device. Nanowires are formed on the surface of PVC fi lms by an inductively coupled plasma (ICP) method (Figure 1 c) to increase the friction area [ 17 ] so the output of the device is expected to be improved. A 30°-tilted view scanning electron microscopy (SEM) image of the nanostructured PVC surface is shown in Figure 1 d, and a higher magnifi cation SEM image is presented as an inset. It is obvious that the PVC nanowires are uniformly distributed on the PVC surface with an average diameter of 100–200 nm and an average length of 500 nm, respectively. The working principle of the 3D-TENG is schematically depicted in Figure 2 a–e step by step. For easily understanding, we note that the PVC and aluminum fi lms fully contacted with each other as the original position (Figure 2 a). At the original position, the PVC and aluminum fi lms are fully overlapped. When the PVC fi lms slide apart from and rub the aluminum fi lms (Figure 2 b), the electrons transfer from the aluminum to the PVC because PVC easily gains electrons while aluminum easily loses electrons, according to the triboelectric series. [ 18 ]