Milliampere level moisture current enabled by a zwitterionic nanocomposite conductive hydrogel

Hygroscopic salt composite hydrogels (HSCHs) offer a promising solution for combating global water scarcity by harvesting atmospheric water. Importantly, this is aided by an interior water gradient that facilitates ion transport, which opens up opportunities for power generation. The current and potential outputs are restricted by inadequate water collection and excessive cross-link density. Herein, a novel zwitterionic nanocomposite conductive hydrogel (ZNCH) is introduced to resist polyelectrolyte changes by leveraging the salt-in effect of cationic and anionic functional groups. The poly-[2-(methacryloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide-based ZNCH endows the HSCH with an enhanced swelling property together with an improved water storage capacity. The adsorption capacity of water reaches 3.0 g g−1 after 10 h of operation at 25 °C and 90% RH. More importantly, ZNCH replaces H bonds with Li bonds under the Hofmeister effect, resulting in the generation of a substantial number of free H+ ions. These endow the ZNCH with highly efficient power generation performance, associating with a short-circuit current of up to 945 μA, a current density of 945 μA cm−1, and an open-circuit voltage of 0.802 V. This work motivates the improvement of materials and devices that convert energy from atmospheric water.