Sustainable moisture-induced electricity from wood through asymmetric hygroscopic design and radiative cooling

Abstract

As an emerging sustainable energy technology, moisture-electric generators (MEGs) can spontaneously harvest electricity from ubiquitous water vapor. Natural wood, with its abundant oxygen-containing functional groups and anisotropic microchannels, is an ideal material for MEG fabrication. However, most wood-based generators rely on streaming potential driven by evaporation, requiring an external water supply to ensure continuous operation, which significantly limits their practical applications. Here, we present an asymmetric hygroscopic structure based on delignified natural wood, with LiCl and carbon black incorporated into the hygroscopic and hydrophobic sides, respectively. This design maintains a stable internal water content gradient through the dynamic equilibrium of moisture sorption–desorption, enabling continuous directional ion migration and stable output for over 220 h. Delignification enhances hydrophilicity and surface charge density by exposing cellulose nanofibrils. Additionally, the radiative cooling effect of the hygroscopic layer induced by delignification promotes moisture sorption and prevents the collapse of the water content gradient under solar heating. A single device can continuously generate an open-circuit voltage of ∼0.94 V and a short-circuit current of ∼43 µA at 25 °C and 70% RH, with a maximum output power density of ∼29 µW cm⁻³. This work provides a sustainable strategy for developing efficient bio-based MEGs.