Emerging direct current triboelectric nanogenerator for high-entropy mechanical energy harvesting

In the era of the Internet of Things (IoT), the provision of sustainable power to distributed, mobile, and low-power-consumption electronic devices is a critical challenge. To overcome this challenge, the triboelectric nanogenerator (TENG), a highly efficient high-entropy mechanical energy harvesting device, was developed in 2012. This device enables the direct conversion of irregular and low-frequency mechanical energy into pulsed alternating current (AC) signals. However, the incompatibility of most electronic devices with AC signals necessitates rectifier circuits or generators that deliver direct current (DC) signals. In recent years, DC-TENGs have undergone extensive development, achieving significant milestones in various application fields while also facing crucial challenges that require solutions. In this review, three categories of DC-TENG devices with distinct operating mechanisms are comprehensively explored: multiphase coupling, mechanical rectification, and air breakdown. Their typical structures and working mechanisms are thoroughly discussed, and specific output performance limitations, along with corresponding optimization strategies, are identified. Furthermore, the applications of DC-TENGs in various scenarios are summarized. Finally, the challenges faced by DC-TENGs and potential solutions are analyzed to guide further advancements in this technology.