Moisture Adsorption‐Desorption Induced Ion Reciprocating Diffusion in Zwitterionic Polymer for Alternating‐Cycle Power Generation

Abstract The vast majority of moisture‐enabled electric generators (MEGs) operate based on the directional migration of ions caused by moisture adsorption. After moisture absorption, the gel gradually becomes water‐saturated, and the gas‐liquid phase transition ceases, resulting in a limited energy output duration. Utilizing fluctuating humidity to induce alternating moisture adsorption and desorption presents a promising strategy to produce periodic and sustained electrical output. Nevertheless, the reverse migration of ions during water desorption is hindered by intricate electrostatic interactions, hydration effects, and steric constraints at the polymer‐water interface. The unidirectional ion transport leads to ion accumulation, which restricts further enhancement of device longevity. Thus, there is an urgent need to explore the strategy of polymer‐water interface design so as to enable the migration of ions following water. In the present work, a zwitterionic gel P (DMAPS‐co‐AM) is soaked in LiCl solution to construct the hygroscopic layer, and free Na ions are introduced at the electrode‐gel interface. Since the zwitterionic gel preferentially binds to LiCl, it effectively screens the interactions between the polymer matrix and Na ions, thereby facilitating the migration of Na in water. When the device operates under alternating high‐humidity (93%RH) and low‐humidity (15%RH) conditions, reversed ion diffusion occurs, indicating that ions move in the gel following water molecules. The mechanism investigation of the zwitterionic interface affecting ion back‐migration performance provides a new idea for the design of more efficient MEGs in the future.