A flexible droplet-based triboelectric-electromagnetic hybrid generator for raindrop energy harvesting

Dispersed raindrop energy harvesting has recently attracted extensive interest owing to the huge amount of energy contained in the water. However, most raindrop-based electromagnetic generators (EMGs) and triboelectric generators (TEGs) are unable to efficiently convert raindrop energy into electricity due to the rigid, bulky, and complex structures of EMGs with low output voltage, as well as the unstable and low current output of TEGs. Herein, we developed a flexible droplet-based triboelectric-electromagnetic hybrid generator (D-TEHG) including a droplet-based electromagnetic generator (D-EMG) and a droplet-based triboelectric generator (D-TEG) for efficiently harvesting raindrop energy. A flexible magnetically responsive hydrophobic film (MRHF) fabricated by a simple spray coating method was used in a hybrid power output system for raindrop energy conversion, serving as a "spring-like" structure for contacting and separating the electrodes in the D-TEG part, and as an excitation structure for moving the coil in the D-EMG part. When the D-TEHG was excited by a water droplet, the vibration of the elastic film induced the contact and separation of the two electrodes in the D-TEG part and the magnetic flux change through the coil in the D-EMG part, thus generating a dual electrical signal. When a 58.2 µL droplet was dropped from a height of 50 cm and impacted the D-TEHG, the D-TEG generated a peak open-circuit voltage (VOC) of ∼3.01 V and the D-EMG output a peak short-circuit current (ISC) of ∼11.21 mA. The integrated D-TEHG could generate high-performance power for charging capacitors and driving "DUT" LED arrays. By employing advanced flexible materials and structures, the hybrid generator might open up an avenue that makes efficient collection and utilization of large-area raindrop energy a reality.