Recent advances in moisture-electric nanogenerators: from moisture-enabled electrification to practical applications

The global energy shortage continues to raise energy prices and cause an imbalance between supply and demand of oil, gas and electricity. This ongoing worldwide energy crisis highlights the urgent need for exploiting more renewable and clean energy from natural resources while simultaneously minimizing the carbon footprint. Moisture-electric nanogenerators (MEGs) have emerged as a novel method for energy harvesting, utilizing the ubiquity, sustainability, and portability of atmospheric moisture, and overcoming regional restrictions for thermal, solar, or mechanical energy inputs. By exchanging intermolecular bonding energy when ionizing moisture into electrical output through deliberately fabricated hygroscopic materials, MEGs can have diverse applications, including self-powered sensors and low-power sources used for humidity sensing, respiration monitoring, etc. This review covers the construction, materials, and mechanisms of the MEGs, the recent progress in cutting-edge innovations in moisture-responsive materials for boosting electrical outputs, followed by discussions of practical MEG applications. The outlook for further development of MEGs is also provided, along with the predicted increase in use cases of this promising clean energy-harvesting approach.