The authors from Yonsei University and the Korea Institute of Industrial Technology, led by Professors Cheolmin Park and Jin Kie Shim, argue that cellulose offers a convergence of properties rarely found together in energy materials. Cellulose is hydrophilic, mechanically robust, hierarchically porous, and fully biodegradable. Instead of relying on synthetic polymers or environmental‑risk nanomaterials, cellulose enables hydrovoltaic systems that could be engineered for end‑of‑life sustainability.

The review organizes cellulose-enabled hydrovoltaic energy generators into four mechanism families: moisture energy generators, evaporation energy generators, osmotic energy generators, and droplet energy generators. This classification helps compare device concepts that look similar at the macro scale but differ fundamentally in how charge is separated and transported at interfaces.

Technically, the work emphasizes cellulose’s surface molecular chemistry—especially the three hydroxyl groups within each anhydroglucose unit. These functional groups modulate electric double layer (EDL) formation at cellulose–water interfaces and tune ion mobility through nanochannel networks. The paper connects performance to microstructure: when charged transport pathways shrink toward the Debye length, EDL overlap can support near single–charge‑carrier transport, boosting conversion efficiency.

Multiple mechanisms are highlighted. Evaporation-driven streaming potentials can arise from charged nanochannels. Moisture gradients promote ion diffusion. Salinity gradients enable ion exchange through Donnan effects. And droplet interfaces can trigger charge displacement similar to interfacial electrokinetic processes.

Reported device metrics span impressive ranges. Moisture energy generators reach open‑circuit voltages up to 1.15 V and power densities as high as 32.59 mW cm⁻². Evaporation energy generators can deliver sustained DC output, including biomimetic architectures where delignified wood produces ~1 V driven primarily by capillary evaporation. Osmotic energy generators cover 0.1–95 W m⁻² under salinity gradients, with optimized membrane pairs achieving cation transference numbers above 0.97. Droplet energy generators leverage natural leaf‑inspired structures to produce ~1.3 V from single droplet impacts, while artificial superhydrophobic cellulose interfaces have been reported to reach ~16 V.

Beyond lab performance, the review outlines why cellulose hydrovoltaics could become a platform for practical electronics. Wearable formats may power calculators, charge coin cells, and enable wireless environmental sensing using ambient humidity or perspiration. Smart packaging could use cellulose-based moisture harvesting for battery-free freshness monitoring. Large-scale approaches—such as floating cellulose aerogels on water bodies—suggest distributed renewable generation.

The authors also lay out a roadmap for making these systems truly useful: AI-assisted materials design, hybridization with triboelectric or photovoltaic components, and rigorous life-cycle assessment to confirm that “sustainable” remains sustainable from synthesis to disposal.

Subject of Research: Cellulose-enabled hydrovoltaic energy generation (mechanisms and device integration)
Article Title: Cellulose‑enabled Hydrovoltaic Energy Generation: from Molecular and Materials Design to Device Integration
News Publication Date: 22-Jun-2026
Web References: http://dx.doi.org/10.1007/s40820-026-02243-3
References: Nano‑Micro Letters (Review article) — 10.1007/s40820-026-02243-3
Image Credits: EunAe Shin, Guangtao Zan, Kaiying Zhao, Shengyou Li, Gwanho Kim, Minji Kwon, HoYeon Kim, Jin Kie Shim, Cheolmin Park.

Keywords

Materials, Hydrovoltaic energy, Cellulose, Energy harvesting, Electric double layer, Osmotic generation, Evaporation-driven power, Droplet electrification, Wearable sensors

In a new study, researchers introduce a vertical microrod generator (VMG) designed to change how fluids move at the microscale. Instead of relying on random streaming, the VMG creates a directional Laplace pressure gradient—an engineered pressure difference that encourages fluid to travel rapidly along the device in a chosen direction.

The key advance is how VMG achieves transport without the usual drag-dominated losses. With the flow accelerated by the Laplace pressure gradient, ion transport becomes “quasi-ballistic,” meaning ions move with fewer scattering events than expected in conventional, diffusive regimes. This shift helps the system maintain a more efficient conversion of evaporative energy into electrical output.

A machine-learning-guided design process helps optimize the microrod geometry and operating conditions, targeting the fluid-dynamics and electrokinetic balance needed for high performance. The result is a generator that not only performs better, but does so in a more controllable manner than earlier approaches.

According to the report, the VMG reaches a 21.5% power conversion efficiency. It also delivers 14.3 W m⁻² of power density, a notable step toward making atmospheric thermal harvesting more competitive with low-power off-grid needs.

Durability is another crucial factor for real-world deployment. The VMG maintains stable performance over 30 days under ambient conditions, suggesting that the device does not quickly degrade or lose its fluid-routing advantages over time. Performance also holds strong across environmental variation, retaining over 20% efficiency despite a 30 K ambient temperature span.

To show practical relevance, the researchers integrate VMG arrays capable of powering commercial electronics, including emergency lighting and 36 W ceiling lamps. Such demonstrations highlight how a microrod-based architecture could scale from lab prototypes to useful energy systems.

Overall, the work presents a promising pathway for converting low-power-density atmospheric thermal energy into reliable electricity by combining pressure-gradient engineering with quasi-ballistic ion transport. If the approach scales cleanly, it could help unlock a new class of dependable, low-maintenance power sources.

Subject of Research: Atmospheric evaporation-driven electricity generation via electrokinetic ion transport
Article Title: Quasi-ballistic ion transport in a vertical microrod enabling efficient evaporation-driven power generation
Article References: Wu, M., Wang, T., Zhang, J. et al. Quasi-ballistic ion transport in a vertical microrod enabling efficient evaporation-driven power generation. Nat Energy (2026). https://doi.org/10.1038/s41560-026-02117-3
Image Credits: AI Generated
DOI: https://doi.org/10.1038/s41560-026-02117-3
Keywords: evaporation-driven power generation; vertical microrod generator; Laplace pressure gradient; quasi-ballistic ion transport; streaming potential; machine learning-driven design