A hemispherical triboelectric nanogenerator for continuous droplet energy harvesting via electret field-driven polarization

Harvesting energy from water droplets offers a promising route to power decentralized electronics, yet conventional triboelectric nanogenerators (TENGs) are limited by intermittent output and reliance on repetitive mechanical contact. Here, we present a hemispherical TENG (H-TENG) featuring a breakthrough dual-electrode configuration that enables high-efficiency continuous energy extraction from a single moving droplet. The device operates via a two-phase mechanism: initial contact electrification followed by sustained electret-field-driven polarization. As the droplet oscillates, the friction layer accumulates charges and evolves into a permanent electret, producing a stable electric field that polarizes subsequent droplets without direct contact. This design eliminates the inherent intermittency of conventional TENGs and allows infinite energy conversion cycles under wave-like motion. The hemispherical structure is ideally suited for scalable blue energy harvesting from ocean waves. Through systematic experimental and theoretical analysis, we demonstrate the essential roles of droplet kinetics, ion-mediated interfacial effects, and optimized device geometry in enhancing performance. This work offers a robust, material - structure-integrated strategy toward sustainable droplet-based energy harvesting, with significant potential for applications in self-powered marine systems and large-scale renewable energy conversion.