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conductive fabric electrodes, a complete device structure can be obtained, suitable for applications requiring
air permeability, high stability, and wearable electronic patches. Yang et al. reported a self-sustaining wet
electric generator based on 1D negatively charged nanofibers and 2D conductive nanosheets [Figure 9A],
capable of continuously generating direct current from atmospheric humidity . A CA-crosslinked bacterial
[142]
cellulose sulfate nanofiber/rGO (CA-BCSNF/rGO) film was placed between the upper and lower electrodes.
The composite power generation layer improves performance compared to single-material layers. Zhang
et al. designed a flexible BC/MWCNT bilayer film using vacuum filtration, demonstrating its working
mechanism . The continuous moisture concentration difference maintained by this heterostructure is the
[143]
key factor enabling high humidity performance and sustained power generation. Similarly, Li et al. prepared
a BC/rGO thin film with a heterostructure via vacuum filtration. The top and bottom layers differ in Ocfg
content, creating a moisture gradient that enhances device performance . Li et al. developed an asymmetric
[144]
patterned cellulose nanofiber (CNF)/GO composite film by vacuum filtration, improving moisture
adsorption capacity and transmission rate . Yan et al. prepared a mixed film by combining inorganic CDs
[145]
suspension with PSS and PVA aqueous solution, where the CDs enhance the mechanical properties of the
polymer film . A heterojunction-based power generation layer was fabricated using reconstructed natural
[146]
vermiculite and oxidized MWCNTs treated with nitric acid [147] . In Figure 9B, lithium ions and sulfonate
groups were simultaneously incorporated into a hydrogel system, leveraging their molecular synergy to
construct a functional polymer network [148] . This design enhances mechanical strength, proton dissociation
efficiency, and proton transport pathways. To overcome the limited spatial deformation of traditional rigid
layers, He et al. constructed a stretchable moisture electric generator (s-MEG) using a reversible cross-linked
double-network ionic gel (SIG) and Ag-conductive fabric, exhibiting high stretchability, self-healing, swelling
resistance, wet adhesion, and ultra-high strain tolerance [Figure 9C] [149] . Wu et al. developed a
high-performance double-layer polyelectrolyte ionic paper conductor, capable of dual-function output of V oc
and I sc [150] . Liu et al. combined hydroxyapatite nanowires coated with tannic acid and PVA hydrogel with
waste anaerobic ammonium oxidation activated sludge, significantly improving device stability [151] . Zhou
et al. developed a high-toughness, flexible nanocomposite film composed of activated aramid nanofibers
(aASA) and SA, combining bionic design with interface activation technology to achieve high power
generation efficiency [Figure 9D] [152] . Huang et al. used poly(4-styrene sulfonic acid) (H-PSS)-mediated
polyelectrolyte as the power generation layer and a heterogeneous inert electrode as the polar plate,
developing a high-performance device that can be integrally 3D printed [Figure 9E] . This device combines
[153]
machinability and mechanical strength, promoting directional ion migration under the synergistic effect of
moisture and ion concentration gradients.

3D structure
In the structure of MEGT electric generation layers, 3D configurations are also common, primarily including
porous and heterogeneous structures. The high porosity and interconnected channels of 3D porous
structures significantly enhance the material’s moisture absorption capacity and establish a stable internal
humidity gradient. Multi-layer heterostructures support functional layer integration and are compatible with
fibers, films, printed electrodes, and other processes, promoting the development of flexible, wearable, and
miniaturized devices. Shuang et al. constructed [metal N/O] water-absorption active sites based on chemical
coordination between metals and hydroxyl or amino groups, enabling efficient capture of water from air and
its conversion to liquid water for storage [154] . Kim et al. developed a functional Fumion FAA-3 porous
hydrogel hygroscopic electrolyte with a salt concentration gradient, leveraging the synergistic effects of water
flow, auxiliary anion migration, and cationic gels [155] . Using the ultra-low density, high-efficiency water
transport, and sustainability of CNF aerogels, Zhu et al. introduced Al(III) to prepare water-driven devices,
improving overall hygroscopicity and stability . Similarly, the porous structure of CNFs/SA@Ca/moisture
[156]
adsorption complex-photothermal modification (MAC-P) aerogels prepared by Wang et al. provides strong
capillary forces and effectively retains water [157] . Additionally, Zhang et al. fabricated a double-gradient