As a promising technology to harvest different forms of mechanical energy from environment, triboelectric nanogenerators (TENGs) have great potential application in self-powered sensor, Internet of Things, and large-scale renewable blue energy. For application it is important to further enhance the output power density and efficiency, which depend on the triboelectric charge density quadratically. In this paper, we briefly introduce the approach to improve the charge density and review the progress of achieving ultrahigh triboelectric charge density. In addition, the restricting factors and limitation of triboelectric charge density are investigated by taking Cu-PTFE as the contact surface of TENG as an example, which could provide a research direction for achieving ultra-high charge density of TENG.

Advanced energy technology has been promoting the development of human society. As a new type of energy collector, triboelectric nanogenerator is based on triboelectrification and electrostatic induction. It is a sustainable, stable and green energy supply. However, in the case of weak energy harvesting, the design of triboelectric nanogenerator should be careful, especially in terms of sensitivity and efficiency. This paper outlines a variety of triboelectric nanogenerator designs for weak energy harvesting, as well as the working mechanism and applications, which in turn presents an outlook for medical equipment, sustainable system and security devices.

Compared with triboelectric nanogenerators (TENGs) that simply harvest ambient mechanical vibration energy, the novel hybrid energy cells combined with TENGs are able to harvest multiple forms of energy with a wider operating frequency range and better output performance. In recent years, hybrid energy cells have gradually developed towards miniaturization, portability, and intelligence. This article starts from several categories such as the combination of TENG with solar cells, combination of TENG with electromagnetic generator, combination of TENG with piezoelectric nanogenerator, combination of TENG with various types of power generation, and combination of TENG with other energy cells. The research progress of hybrid energy cells in terms of working mode, structure, energy output, and applications are reviewed, and the challenges faced by hybrid energy cells are discussed. The development prospects of hybrid energy cells are prospected and it is believed that further research in the aspects of integration, high power, and long service life is needed for hybrid energy cells.

Highway and railway as one of the most important means of transportation have made rapid digitalized development but the power supply of sensors has become a bottleneck for further development. In this paper we illustrate that triboelectric nanogenerator (TENG) with dual functions of power supply and high-sensitive sensing plays an important role in self-powered intelligent transportation systems. We also review the application of TENG in intelligent transportation systems in recent years, including vehicle detection, exhaust gas treatment, vibration energy harvesting, wind energy harvesting, etc. Finally, we analyze the challenges for application of TENG in intelligent transportation and prospect the development trend of TENG in materials, information, electronics, machinery, transportation, and other multidisciplinary fields.

With the development and progress of science and technology, the demand of stretchable materials in intelligent robot, electronic skin and other field is increasing. The emergence of stretchable materials can solve the problem of rigidity of intelligent devices and enable intelligent devices to achieve complete flexibility and stretchability. In this paper, some novel stretchable materials such as ultra-thin materials, fabrics and biodegradable materials at present are reviewed, and applications of stretchable materials in stretchable electrodes, energy storage devices and transistor sensors are briefly introduced. It is pointed out that there are some problems in the balance between the conductivity and the extensibility of the tensile material, and the poor air impermeability and comfort of the tensile electrode. Finally, opportunities and challenges in the future are discussed.