Hygroelectric Generator Based on Antisymmetric Modification of Graphene Spheres with Ionic Hydrogels

The moisture-enabled electric generators (MEGs) have attracted wide attention in recent years due to their advantages such as green energy, small size, and simple fabrication process. However, carbon black particles with poor electrical conductivity are often used as the power generation layer in current reports, and their functional group concentration gradient is small, which limits the output power density and working time. In this paper, a high-performance MEG has been designed and fabricated by asymmetric deposition of ionic hydrogels on the surface of graphene spheres. Compared with carbon black particles, graphene spheres have better electrical conductivity. Compared with lamellar graphene, graphene spheres provide larger specific surface area and more abundant nanochannels. Hygroscopic ionic hydrogel captures moisture to provide the water environment (1.32 mg cm –2 h –1 water can be captured at 98% RH). On the other hand, ions can also be directionally transported under the ion concentration gradient to improve the device output performance. The device finally obtains a 0.34 V open-circuit voltage and a 1 μA short-circuit current under 98% RH, and the electrical output has no obvious attenuation even after 5 h of operation. The designed device can not only power the small bulb but also be used as a self-powered humidity sensor to monitor the indoor humidity changes in real time.