Polyelectrolyte functionalized photothermally active surface charge effective tuned porous wood as ambient evaporation induced hydrovoltaic energy harvesting

Journal article, 2026

Hydrovoltaic energy harvester enables the conversion of low-level water dynamics into electrical energy, offering a promising route for sustainable power generation. Wood is an attractive platform due to its hierarchical porous structure, mechanical robustness, and tunable surface chemistry; however, efficient ambient evaporation–driven performance is limited by insufficient ion selectivity and surface charge density, as well as an incomplete understanding of ion transport and electric double-layer (EDL) overlap in confined nanochannels. Here, we present a pore-size–tunable wood-based hydrovoltaic system with enhanced surface charge density achieved by coating polyelectrolyte-treated iron sulfide (FeS/PSS⁻). The negatively charged PSS⁻ improves ion adsorption and charge separation, while the FeS layer provides strong photothermal effects. By tuning the pore size from ∼20–100 nm, optimized ion selectivity and transport are achieved which is theoretically validated through COMSOL simulation. The optimized device delivers an open-circuit voltage of approximately 289 mV and a short-circuit current of 3.5–4 µA under ambient DI-water evaporation conditions, with stable operation for over 160 h. Under IR-light-assisted evaporation, the output further increases to approximately 454 mV and 20 µA, owing to enhanced photothermal evaporation and accelerated ion transport within the charged porous channels. Under standard solar illumination, the device delivers a high evaporation rate of ∼2.4 kg m⁻² h⁻¹ and an output power density of 11.19 µW cm⁻³ with a salt accumulation self-cleaning characteristic. Moreover, the device boosts its performance under salt solution which is practically useful for large scale applications in seawater. Integrating 8 devices in series delivers a voltage 2.7 V and in parallel 42 µA confirms the reliability and practicality for real-time practical applications. Demonstration takes place by powering light-emitting diodes and portable calculators. This work highlights nanochannel and surface-charge engineering as effective strategies for scalable, ambient hydrovoltaic energy harvesting.