Green, Safe, Durable, Printed Fabric Hygroelectric Generators for Wearable Systems

Hygroelectric generators, converting energy from moisture into electricity, have attracted great interest due to sustainable and ubiquitous moisture in the environment. However, it is absolutely necessary to replace the fragile and noxious materials reported previously in the hygroelectric generators before real applications for wearables. Herein, a green hygroelectric generator with a high current density is designed for the first time by printing functional materials that are abundant, safe to humans and environments. By engineering printable hydrogel through the synergistic effect of water absorption and ion migration on the fabric, the wearable fabric hygroelectric generators deliver a high open-circuit voltage of 1.2 V with a remarkable short-circuit current density of 1.0 mA·cm^-2, more than 7 times that of most reported hygroelectric generators. The devices show no performance declination after long-term storage and bending tests due to the design of stable hydrogel and robust electrode/hydrogel interfaces. Moreover, the devices with cross-finger structures achieve a facile scalable integration for enhanced electric outputs. Exemplifying applications illustrate the great potential of the printed fabric hygroelectric generators as a direct current power supply for wearable applications. This work sheds light on a novel avenue to design safe and environmentally friendly energy harvesting devices for practical applications.