PVA–PNIPAM Hydrogel-Based Moisture-Electric Generators with Tunable Pore Structures for Enhanced Power Generation

A hygroscopic layer plays an important role in improving the output abilities of energy generation from ubiquitous moisture, whose mechanism is unclear. Herein, three kinds of hydrogels with different pore structures/functional groups are designed as hygroscopic layers, and a universal strategy was proposed to assemble them into hydrogel-based moisture-electric generators (HMEGs). The hydrogels’ pore structure affects the moisture absorption rate, while the functional groups regulate the diffusion path of water. HMEG’s power generation is a synergistic effect of ionic diffusion and streaming potential, which is closely related to the water diffusion within the material and is not directly related to the amount of moisture absorption. HMEG, which absorbs moisture quickly, stores water efficiently, and releases moisture slowly, has an excellent performance and stable voltage output. Based on this mechanism, HMEG employed the calcium chloride-poly(vinyl alcohol)-poly(N-isopropylacrylamide) (CPVPN), semi-interpenetrating network (semi-IPN) hydrogel as the hygroscopic layer showed an open-circuit voltage as high as 0.34 V and a power density of 33.23 μA cm–3. This study opens a perspective on hydrogel HMEG and provides insights into high-performance HMEG design.