*Small-Scale Energy Harvesting from Environment by Triboelectric Nanogenerators DOI: http://dx.doi.org/10.5772/intechopen.83703*

For versatile scavenging mechanical energy induced from arbitrary mechanical moving objects such as humans, a new mode of triboelectric nanogenerator is first demonstrated based on the sliding of a freestanding triboelectric-layer between two stationary electrodes on the same plane [58]. With two electrodes alternatively approached by the tribo-charges on the sliding layer, electricity is effectively generated due to electrostatic induction. To reduce the direct friction between triboelectric layers for energy loss, a linear grating-structured freestanding triboelectric-layer nanogenerator (GF-TENG), consisting of a freestanding triboelectric layer with grating segments and two interdigitated metal electrodes, was developed for high-efficiency harvesting vibration energy from human walking [59]. As shown in **Figure 4a**, 60 commercial LEDs (Nichia NSPG500DS) can be lighted up instantaneously with the motion of hand sliding under a slow speed and a small displacement. The GF-TENG can also havest energy from the monement of car for powering electronic components on the vehicle (**Figure 4b**). Four identical extension springs are used to suspend and anchore the triboelectric layer, as displayed in **Figure 4c**. Owing to the structure, the obtained GF-TENG can scavenge

#### **Figure 4.**

*A Guide to Small-Scale Energy Harvesting Techniques*

polydimethysiloxane (ppy/PDMS) triboelectric-photodetecting pixel-addressable matrix [48]. The e-skin can directly transmit photodetecting signal into brain for participating in the vision perception and behavioral intervention. Besides visualimage recognitio, more functional sensors including sliding sensor [49], touch screen

In order to satisfy the requirement of self-powered, highly stretchability, and transparency of triboelectric skins, different materials including silicone rubber [53], metal nanowire [54, 55], and conductive polymer [56] are widely studied. To introduce the characteristic of instilling self-healing and further enhance the performance of energy generation, stretch ability, transparency, and slime-based ionic conductors were first used as transparent current-collecting layers of TENG for harvesting mechanical [57]. The ionic-skin TENG consists of a silicone rubber layer with a thickness of 100 ± 10 μm, utilized as the triboelectrically negative material, a slime layer (a crosslinked poly(vinyl alcohol) gel) with a thickness of 1 mm that works as the ionic current collector, and a VHB tape with a thickness of 1 mm as the substrate (**Figure 3a**). **Figure 3b** shows the photograph of the real highly transparent ionic-skin TENG. As depicted in **Figure 3c**, the resulting ionic-skin TENG displays a transparency of 92% transmittance for visible light. The mechanism of the ionicskin TENG is based on the single-electrode mode, wherein human skin and silicone rubber serve as frictional layer, respectively (**Figure 3d**). **Figure 3e** shows the digital photographs of the fabricated ionic-skin TENG suffering various mechanical deformations including uniaxial stretching up to 700% strain as well as folding and rolling. The produced slime exhibits high ionic conductivity due to the presence

) and negative ions (B(OH)4<sup>−</sup>), which is measured using electro-

chemical impedance spectroscopy (**Figure 3f**). Thanks for the series of design, the energy-harvesting performance of ionic-skin TENG is 12-fold higher than that of the silver-based electronic current collectors. Besides, fabricated ionic-skin TENG can recover its property even suffering 300 times of complete bifurcation, exhibiting an

*(a) Schematic diagram of the IS-TENG. (b) Digital photo of the highly transparent IS-TENG. (c) Transmittance spectra of the slime (ionic conductor) and the IS-TENG with respect to a glass slide. (d) Schematic illustration of the working mechanism of the IS-TENG. (e) Digital photos of the IS-TENG under various mechanically deformed states such as axial strain up to 700%, rolled, and folded. (f) EIS measurement* 

[50], pressing sensor [51], and motion sensors [52] are also deeply explored.

**70**

**Figure 3.**

*of the slime (ionic conductor) [57].*

of positive (Na+

autonomously self-healing capacity.

*Applications of GF-TENG for harvesting a wide range of mechanical energy. (a) Harvesting energy from sliding of a human hand. (b) Harvesting energy from acceleration or deceleration of a remote control car. (c) Device structure for noncontact GF-TENG. (d) Harvesting energy from people walking by noncontact GF-TENG and the real-time measurement of Isc. (e) Total conversion efficiency of noncontact GF-TENG for harvesting slight vibration under different load resistances [59].*

the mechanical energy from people's walking motion when it is bonded to human legs (**Figure 4d**). An excellent stability and maxmiun energy conversion efficiency of 85% are realized at a matched load resistance of 88 MU under the noncontact mode (**Figure 4e**).
