# Research Progress in Fluid Energy Collection Based on Friction Nanogenerators
## 4 Summary and Outlook
This article starts with the nanogenerator material that requires two or more friction layers with high electronegativity to create the induced electromotive force acquired by contact and electrostatic induction in response to a mechanical movement. This section introduces the triboelectric sequence that is necessary for nanogenerators. Generally speaking, choosing friction materials necessitates choosing two or more materials in the sequence in which it is simple to gain electrons and easy to lose electrons in order to offer the highest feasible energy conversion rate. Second, the fundamental theory behind the nanogenerator--the second term of Maxwell's displacement current that has been \"ignored\" for a long time is briefly presented and its working principle is examined. This paper introduces the four basic modes that are currently commonly used in nanogenerators: single electrode type, independent layer type, vertical contact separation type, and horizontal sliding type. To present the research development of nanogenerators in the area of fluid energy collection, energy collection can be separated into wind energy and water flow wave energy based on the collected fluid medium and the structural design of the generators. The advancements in fluid energy harvesting-based nanogenerator research highlight some issues and provide remedies from earlier studies. At the moment, the investigation of a significant number of nanogenerators is plagued by a number of flaws that need to be fixed. Firstly, the coupling structure of gas flow and coupling devices or wave and coupling devices is the primary focus of current energy harvesting research in nanogenerators. Though a lot of progress has been achieved in the mechanical structure, research on semiconductors and triboelectric materials is still insufficient. Especially, after multiple wear and tear, the mechanical tensile strength and mechanical strength may suffer from attenuation [99]. Second, although one of the development trends is to work with the network to create a large-scale network for nanogenerator power generation, the energy reserve and power management systems of nanogenerators have not yet reached a very mature state following the networking. This is because the power generation power of nanogenerators is currently relatively low. The coordination of the power generation network and the circuit must be studied when TENG constructs a power generation network or adopts an excitation circuit. Not only would improper use of excitation and power management circuits fail to optimize the efficiency of each TENG, but it may also result in a decrease in the total power output. As a result, research on TENG network excitation and power management circuits is also ongoing. Thirdly, in order to attract more researchers to the topic, equations or theories pertaining to the dynamics of nanogenerators should be substantially simplified. Ultimately, the development of nanogenerators requires dependability. In the TENG network that collects ocean wave energy, the transmission line should have sufficient wind and wave resistance, the link between the transmission line and the TENG should have fatigue tolerance, and the power attenuation of long-distance transmission should be carefully checked. The development of nanogenerators is motivated by the fact that they are maintenance-free after a specific design life, and if they are not dependable enough and need human maintenance, the value of nanogenerators will not be completely embodied. Thus, in the realm of semiconductors, the design of ordinary semiconductor devices might be compared to the design of nanogenerators for energy harvesting. Transistor principles inspired the fabrication of OCT-TENG, which has triboelectric enhancement with reverse charge enhancement. The porosity and pore depth of the functional rubber film can be controlled.