Credit: Advanced Functional Materials (2025). DOI: 10.1002/adfm.202419710
As artificial intelligence (AI) and smart gadgets become more common, our need for reliable power sources grows. Renewable energy options like solar and wind are great, but they depend on specific conditions. A research team led by Professor Dong-Myeong Shin from the Department of Mechanical Engineering at the University of Hong Kong (HKU) has developed a novel moisture-activated electricity generator (MEG) that offers a fresh, eco-friendly way to generate electricity—just from moisture in the air.
Their findings have been published in the journal Advanced Functional Materials in an article titled "Long-Lasting Moisture Energy Scavenging in Dry Ambient Air Empowered by a Salt Concentration-Gradient Cationic Hydrogel."
How the new MEG technology works
These moisture-activated generators (or MEGs) work by creating a flow of ions—charged particles—inside a special gel, generating power naturally. But current versions face challenges: they don't last long (less than 16 hours), have high internal resistance, and only work well in very humid conditions.
Professor Shin and his team have overcome those hurdles. They developed a salt-concentration-gradient cationic hydrogel for MEG, promising lower energy loss and higher output even in conditions of low relative humidity.
This innovative salt-concentration gradient cationic hydrogel is synthesized via gelation with a cationic polymer, plasticizer, and salt. The two-step heating process induces salt segregation and flow during gelation, establishing a concentration gradient inside the hydrogel. The engineered gradient exhibits a key role for outstanding electric power performance across a wide range of relative humidity conditions (42.1 mWm-2 at relative humidity (RH) 80%, and 13.8 mWm-2 even at RH 30%), which can cover 97% of the area on Earth, based on the worldwide relative humidity map in 2023.
Performance and potential applications
Furthermore, the hydrogel contains plenty of free ions that create conductive pathways, diminishing the internal resistance to up to 2k ~ 4k ohms, the same as the level of typical commercial electronics (~ 1k ohm). This implies the MEG can power small electronics directly, without extra components like transistors or resistors.
The efficiency of the MEG's open-circuit voltage can remain unchanged for 50 days, with no observable degradation in the environment (~ 50% RH). The team successfully tested the function of the MEG in operating electrical devices such as a smart window requiring high working voltage (~40V), in a humid environment.
"We believe this innovation sharply enhances the feasibility of a sustainable self-powered system in real-world environments," said Eunjong Kim, the first author of the paper.
Professor Shin added, "Sustainable self-powering removes the last bulky piece in compact systems, the external power stage. Our MEG suggests a practical path to shrinking the size of devices while extending their lifespan, from indoor sensors to wearables and building-integrated electronics."
Provided by The University of Hong Kong