Ion-selective vermiculite nanochannel membrane with water anchoring effect for efficient energy recovery from water evaporation

Abstract

Evaporation, a fundamental process in water treatment, is often criticized for its high energy damans. Harnessing the natural movement of water through confined capillary channels during evaporation offers a promising approach for energy extraction. Despite this potential, existing systems face significant challenges, including limited energy conversion efficiency, high costs and complex fabrication, which restrict their practical application. In this study, we present a cost-effective two-dimensional (2D) vermiculite nanochannel membrane, fabricated via an environmentally process, for efficient energy harvesting from evaporation. When partially immersed into the water, the vermiculite membrane achieved a stable voltage output of 1 V over two weeks at room temperature. The superhydrophilic vermiculite nanochannels facilitated smooth water molecule entry, while the hydration layer remained firmly anchored, even under varying aqueous conditions. Furthermore, overlapping electric double layers (EDLs) formed within the highly negatively charged nanochannels, enabling excellent proton selectivity. Protons, generated by water dissociation and deprotonation of oxygen-containing functional groups, were efficiently transported through the nanochannels, leading to ion polarization at the electrodes and the generation of a continuous streaming potential. By optimizing the membrane geometry, solution conditions, and evaporation environment, energy conversion efficiency was significantly enhanced. Moreover, connecting three membrane-based devices in series allowed for the successful charging of three parallel-connected 47 μF commercial capacitors to 2.4 V, providing enough power to illuminate an LED. This study underscores the considerable potential of evaporation-driven energy harvesting and lays the foundation for scalable, self-sustaining evaporation systems.