A Bilayer Electrospun Membrane With Gradient Structure for Long‐Term Stable Moisture‐Driven Energy Generator

Ambient humidity represents a ubiquitous and renewable energy source for next‐generation moisture‐driven energy harvesting, yet achieving stable and long‐term output remains a formidable challenge for practical use in wearable electronics and environmental sensing. Here, we report a high‐performance moisture‐driven energy generator (MEG) that exploits a gradient bilayer electrospun membrane to realize directional moisture transport, resulting in efficient and long‐term stable electricity generation. The device integrates two polyacrylonitrile/sulfonated polyaniline (PAN/S‑PANI) nanofiber layers with different porous structure, an electrostatic‐flocked carbon cloth electrode, and an aluminum electrode. Fixed anionic sites in S‑PANI facilitate cation (e.g., Li + , H + ) transport while suppressing anion (Cl − ) migration, whereas the flocked electrodes promote enhanced water evaporation and directional moisture transport. Benefiting from the rational design, the MEG delivers an output of up to 1.1 V and 3.3 mA . cm −2 under 45°C and >80% relative humidity, representing state‐of‐the‐art performance. Remarkably, after being stored for 180 days, the device still maintained an output voltage of ∼0.7 V and a current above 450 µA, which was sufficient to power calculators and smartwatches. This work offers a promising pathway toward durable, self‐powered, and flexible energy systems.