An estuarine-inspired dual-gradient hydrogel for stable and scalable moisture energy harvesting up to a single-module 100 mA output

Abstract

Moisture energy harvesting holds immense potential for sustained electricity generation, yet its practical deployment is hindered by the inherent instability of water–ion gradients, leading to rapid performance degradation and limited scalability. Here, we present a dual-layer hydrogel platform driven by asymmetric ionic hydration chemistries, creating persistent water–salt gradients for sustained energy harvesting. The system leverages distinct ionic hydration dynamics, where the LiCl layer maximizes ionic dissociation and water adsorption while the Li₂CO₃ layer stabilizes the water content through moderate ionic binding. This water–salt dual gradient design induces persistent osmotic pressure differentials, enabling synchronized water–ion migration and continuous ionic transport. Our platform shows a significant improvement in current density compared to conventional long-duration moisture energy generators (MEGs), achieving a peak current density of 96.4 µA cm⁻² and a power density of 5.06 µW cm⁻², while maintaining stable operation for over 500 h. Additionally, we introduce a highly scalable MEG platform, with an active surface area of 1000 cm², enabling energy harvesting at scales previously unattainable. This work demonstrates a scalable and durable MEG platform capable of sustainable energy generation in diverse environments, paving the way for self-powered wearable electronics, environmental monitoring, and autonomous sensing technologies.