Moisture‐Driven Hydrogel Power Source with Asymmetric Ion Adsorption for Flexible Electronics

The hydrogel‐based power source represents a compelling example of generating electricity from green energy. Recent advances have introduced various hydrogel‐based electric generators that operate through external stimuli or utilize ionic interfacial regulation. However, most devices still encounter significant challenges, such as the requirement for continuous stimulation, limited output performance, complex integration processes, and poor conformability of conventional designs, hindering their practical application in wearable electronics. Here, a hydrogel‐based power source is proposed that produces electricity by exploiting moisture‐induced ion gradients and differential ion absorption driven by charge‐asymmetric electrodes. The constructed device with flexible structure can generate a continuous voltage output of 0.45 V for 4 000 min and a current output of 12.3 µA cm −2 along with a power density up to 7.7 W m −3 for a single unit. The flexibility of the device allows it to conform to be attached to various surfaces, thus allowing the overall flexibility and folding into a small scale during the integrated process. Benefit from the miniaturized design, with a palm‐sized folding integrated device containing sixteen devices that can directly power a calculator. This work provides a brand‐new blueprint for a hydrogel‐based energy harvester suitable for flexible electronics.