Switchable Power Generation in Triboelectric Nanogenerator Enabled by Controlled Electrostatic Discharge

As the main energy supply for people's daily life, the energy created by nuclear and coal plays an important role in the history of human development. However, at the same time, they also hinder environmental protection and sustainable development. With the growing awareness of the energy crisis, renewable green energy has been proposed as a promising solution. Among all types of energy, water energy has attracted great interest due to its abundance and recyclability. Humans have developed very well-established methods to harvest large-scale hydropower from waterwheel irrigation in ancient times to the current hydroelectric power generation. For small-scale water such as droplets, triboelectric nanogenerators (TENGs) have emerged as one of the main approaches to convert these ambient mechanical energies into electrical energy. The application of TENGs in droplet energy harvesting has been extensively studied by researchers. However, conventional droplet-based TENGs utilize the periodic sliding of droplets from the friction surface to generate pulsed alternating current (AC), which cannot be directly used as a power source. A rectifier bridge or a power management circuit used to transfer AC into direct current (DC) will greatly reduce the portability of TENGs.<br/>In nature, DC discharge usually occurs during lightning; when the electric charge in the cloud accumulates to a certain strength, it will form a circuit (ie, lightning) by breaking down the air. The lightning tends to require extremely large voltages (several thousand volts), but the required voltage drops dramatically during the breakdown at extremely small distances (only 327V at 7.5 microns). Herein, inspired by the phenomenon of lightning, a droplet-based direct current triboelectric nanogenerator (DDC-TENG) without any rectifier is designed. It utilizes the electrostatic potential generated between the water droplet and the triboelectric layer, and based on the dielectric breakdown mechanism, a small gap is formed between the triboelectric layer and the electrode through photolithography. When the water droplet hits the triboelectric layer, the large voltage generated from the triboelectric layer can break down the air in the gap. Using this mechanism, this sandwich structure single electrode mode DDC-TENG can generate a unidirectional voltage (over 3 V) and unidirectionally transferred charge (maximum 0.63nC) in the periodic motion of droplets. This new design provides a new way to harvest the micromechanical energy of water droplets and directly use them in devices. Moreover, the flexible DDC-TENG produced by using flexible ITO film can be attached to rough and uneven places, which greatly broadens the application area. And due to the increase in the size of the device, the maximum voltage can reach more than 10V, and the maximum current exceeds 160nA.