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Water and ion channels are crucial for moisture energy harvesting, requiring precise pore design for mass transfer control. However, the key challenge lies in managing the localized assembly process of membrane materials to arrange them orderly, forming confined mass transfer pathways and stable solid-liquid interfaces. This is essential for exploring the interrelationship among channel morphological characteristics, mass transfer dynamics, and device power generation performance. This work proposes the use of freeze-assisted salting-out to meticulously construct hydrogel bilayer membranes with micro-meso-macroporous oriented channels and asymmetric charge characteristics. The produced polyvinyl alcohol/MXene hydrogel devices achieved a Voc × Jsc of 11.4 μW cm−2 (pure hydrovoltaic effect) and 146 μW cm−2 (with active electrodes) at 25 °C, 45%RH, surpassing most moisture-based generators. In addition, the power generation performance is highly consistent with the Hofmeister series, with stronger salting-out effect to obtain more micropores and mesopores, and ice crystal growth can help obtain ordered macropores. It has faster water transport rate, higher ionic conductivity, better ionic selectivity, and stronger channel stability than traditional moisture-based power generation membranes. This relationship between pore tuning from salt ions and device power generation performance provides a design basis for the development of high-performance moisture-based power generators. The regulation of water and ion channels is crucial for moisture energy harvesting. The authors adopt a directional freezing-assisted salting-out method to finely adjust the cross-scale pore structure of ion channels, achieving efficient moisture energy harvesting.
Wang et al. (Wed,) studied this question.