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Page 8 of 47 Zhou et al. Soft Sci. 2026, 6, 10

materials are primarily classified into four categories: inorganic, organic polymeric, biomass, and composite
materials, each leveraging unique structural and performance advantages to contribute critically to the
power-generating layer.

Inorganic materials
Inorganic materials, with their unique structural tunability, high electrical conductivity, and excellent
thermal stability, have emerged as ideal candidates for the power-generating layer in MEGTs. Their high
specific surface area provides the functional layer with abundant sites for water adsorption and ion
dissociation . Ions undergo directional diffusion driven by humidity gradients, while charge separation is
[48]
facilitated by the ion selectivity of nanopores. The mechanical strength and chemical stability of these
materials ensure that the nanostructure of the power-generating layer remains intact during prolonged cyclic
moisture absorption and desorption, guaranteeing stable output performance and extending device
lifespan . GO as an inorganic carbon material, can form proton concentration gradients through structural
[93]
regulation, making it a prominent choice for humidity-powered layers. Early studies by Zhao et al. prepared
GOFs with gradient-distributed Ocfgs via a “moisture-electro-annealing” bias treatment [Figure 3A] .
[94]
significantly enhancing proton gradient-driven effects. The team later employed directional thermal
reduction to fabricate porous GOFs [asymmetric porous GO membrane (a-GOM)] with asymmetrically
reconstructed functional groups, optimizing interfacial and transport behavior . In the same year,
[95]
laser-assisted modulation was used [Figure 3B] to selectively irradiate specific GO regions, forming a
Schottky junction interface and achieving a high-performance power generation unit with output voltage up
to 1.5 V . Gao et al. constructed GO-reduced GO (rGO) heterostructures via localized thermal reduction of
[87]
commercial GOFs, enabling efficient electricity generation by leveraging asymmetric interactions between
water molecules and functional groups in distinct regions . These studies exemplify a mainstream approach
[96]
to enhancing device output through regulation of GO functional groups and electrode asymmetry.

To push the performance boundaries and expand the application potential of humidity-powered devices,
researchers are exploring novel inorganic materials such as MXene , molybdenum disulfide (MoS ) [98,99] ,
[97]
2
and black phosphorus (BP) , leveraging their unique structural and functional properties. MXene provides
[62]
abundant active sites for ion adsorption and migration. Inspired by the “pump effect” of wood, Cai et al.
fabricated a hygroscopic structure with a dual-hydrogen-bond network and wood-like channels via
ice-templating and a controlled lithium chloride (LiCl) process [Figure 3C], achieving a moisture absorption
capacity of 3.12 g·g at 90% RH [100] . MoS , as another class of 2D material, offers design possibilities for
-1
2
humidity-driven power generation . Cao et al. designed a vertical heterojunction structure based on
[99]
2H-MoS (semiconducting) in carbonized silk (2H-MoS /CSilk) and 1T-MoS (metallic) in cotton fiber
2
2
2
(1T-MoS cotton) [Figure 3D], where the induced built-in electric field promotes proton migration and
2
charge collection .
[98]
BP has attracted attention for its tunable band structure and catalytic activity. Liang et al. employed
directional oxygen plasma irradiation to create an oxygen defect gradient on the surface of black phosphorus
aerogel (g-O-BP), enabling spontaneous charge separation in humid environments [Figure 3E] . This
[62]
flexible device, only 160 μm thick, delivered a voltage of 0.25 V and a current density of 0.16 μA·cm .
-2
Hydrophilic carbon cloth electrodes and tape encapsulation were incorporated, further enhancing
mechanical flexibility and practical applicability.

In addition to the materials discussed above, 1D inorganic nanomaterials such as silicon nanowires
(SiNWs) [101] and metal oxide nanowires [102] have attracted attention due to their unique water absorption
properties and oriented nanoscale channel structures. As shown in Figure 3F, a typical device consists of a
SiNWs-based power-generating layer and an asymmetric electrode. Under a humidity gradient, a directional