Uncovering internal water-flux and surface-potential dominance in Hydrogel Moisture-Enabled Power Generation: Mechanistic Insights and Performance Enhancement

Ambient humidity is an abundant yet underexploited energy reservoir, and its sustained conversion mechanisms remain elusive. This study employed single-layer, bilayer and ion-selective designs, in combination with Kelvin-probe force microscopy and molecular-dynamics simulations, to delineate the fundamental physics of hydrogel-based moisture-enabled generators (MEGs). We demonstrate that continuous, directional water flux—rather than ion migration—governs electricity generation: the transport of 1 g of H₂O through the hydrogel network yields ≈ 7.6 µA h, and vapor-phase migration alone sustains output over hours to days. Interrupting water transport (e.g., via carbon-membrane insertion or device sealing) extinguishes the current instantly. Moreover, the open-circuit voltage scales with the internal surface-potential gradient: increasing this gradient from 31.3 mV to 810.7 mV elevates the output by 2.5 times. Guided by these findings, we introduced a co-optimization strategy that simultaneously enhances water transport and amplifies the potential gradient, thereby achieving a 30–50% increase in output performance (from 0.6 to 0.93V). Surface evaporation contributes solely by sustaining water flux, whereas triboelectric effects are negligible. This work establishes a quantitative mechanistic framework and delivers clear design principles for robust, high-efficiency MEGs, paving the way for self-powered sensors, portable electronics and distributed energy-harvesting platforms.