# Research Progress in Fluid Energy Collection Based on Friction Nanogenerators
## 3 Optimization of Fluid Energy Harvesting Devices
### Material and Structural Optimization  
The application environment of fluid energy collection devices based on triboelectric nanogenerators is often in deserts or oceans [82], which means that the frequency of manual maintenance cannot be too high, and high-frequency maintenance will bring high labor costs. The presence of mechanical wear may significantly reduce the service life of an energy harvesting device, so choosing better materials is the lifeblood of an energy harvesting device. Better materials need to be more wear-resistant, referring to the triboelectric sequence [83], to be able to produce long-lasting, high-energy output power. The stability and corrosion resistance of inorganic materials are due to organic materials. In 2023, [PERSON] et al. studied the contact polarization effect between metal electrodes and inorganic materials and found that the electron transfer mechanism is the basis of the charge transfer mechanism for contact charging. The work function of the dielectric layer and atomic species on the metal has an important influence on the charge transfer process when contacting the metal. The friction layer is made of inorganic single crystals, which greatly expands the application of inorganic materials in fluid energy harvesting devices [84]. [PERSON] et al. discovered that rabbit hair has the function of reducing frictional resistance, and introduced rabbit hair to the improvement of fluid energy collection devices to design SCRTENG. When rabbit fur and FEP work together, rabbit fur not only plays a role in reducing friction but also provides more frictional charges and enhances the output power of the fluid energy collection device [85]. The existence of friction pairs that play a non-positive role will definitely shorten the life of the mechanical structure. The friction material is made into a brush shape, which greatly reduces the wear between materials. A dual-mode and frequency-doubled TENG with ultra-high durability and efficiency through elastic connection and soft contact design is used for ultra-low frequency mechanical energy harvesting. By introducing springs and flexible dielectric fluff into a novel pendulum structural design, the TENG's surface tribocharge is replenished in a soft contact mode under intermittent mechanical excitation, while the robustness and durability are enhanced in a non-contact operating mode, as shown in Figure 12a,b [86; 87]. Similarly, the use of liquid lubrication effectively reduces the wear between friction media. [PERSON] et al. proposed a liquid lubrication-facilitated TENG, namely LP-TENG. The reasonable design of the voltage balance rod can obtain an energy output density of 87.26 W/m\({}^{2}\) under the low-frequency disturbance of 2 Hz by using the space charge accumulation effect. This energy output density makes the output power of LP-TENG comparable to that of solar panels, as shown in Figure 12c [88]. The use of pendulum structures, flutter structures, etc., is all prepared to reduce friction pairs. However, another way to reduce frictional losses is to adopt a structural model of solid-liquid contact and solid-gas contact. At present, the most studied mode is solid-liquid contact, and its general structure is to use a solid container of a specific shape, such as an optional FEP, whichencapsulates special liquid and metal electrodes according to the topological shape of the container. Figure 12: **(a,b)** Pendulum TENG with non-contact structure. Among them, (i) is the initial state, and the system has no charge transfer; (ii) is stimulated by vibration, causing the brush to start shaking; When reaching position (iii), PTFE accumulates a large amount of negative charges; Similarly, when reaching position (iv), the brush swings in the opposite direction, producing the opposite current. Reprinted with permission from Ref. [86]. Copyright, 2021 Wiley-VCH GmbH. Reprinted with permission from Ref. [87]. Copyright, 2019 Elsevier Ltd. (**c**) TENG with self-lubricating properties at the friction working interface.