Surface Charge Engineering Toward Flexible Moisture‐Induced Energy Harvesting

ABSTRACT The emerging moisture‐induced energy harvesting technology is promising green power source for a wide range of internet‐of‐things and next‐generation wearable electronics. However, significant challenges remain, including intermittent electric output, bulky integration requirements, and low conformality, inevitably hindering their practical applications. Here, we present a flexible moisture‐induced generator (MEG) fabricated by surface charge engineering via bilateral coating of hygroscopic salt‐loaded polymer and polyelectrolyte on carbon nanotubes. This surface engineering effectively utilizes the ion selectivity of polyelectrolytes and the adsorption characteristics of carbon nanotubes to establish an in‐plane surface charge difference in the device, achieving a sustained voltage of 0.3 V and a short‐circuit current output of 27.5 µA, along with a power density up to 52.5 W m −3 for a single device. Thanks to the lightweight integration potential and wide substrate adaptability, fifty units connected in series deliver a voltage output of ∼11 V at only 1.34 g, sufficient to charge a smartwatch. The flexibility of the device allows it to conform to various surfaces, with a palm‐sized box containing twenty‐five devices generating 5.5 V to power a calculator. This work provides a brand‐new blueprint for global water energy harvesting and applications.