Bioinspired topological design with unidirectional water transfer for efficient atmospheric water harvesting

Abstract

Sorption-based atmospheric water harvesting (SAWH) followed by solar-driven desorption is emerging as a promising energy and cost-effective solution to alleviate the worldwide freshwater scarcity. To achieve efficient atmospheric water harvesting, a SAWH system with low water transfer resistance and high sorption-desorption kinetics that integrates photothermal properties is demanded. Herein, inspired by nature, a sodium alginate (SA)-based SAWH hemisphere with spatially centripetal conical channels loaded with CaCl
₂ crystals is designed. The device demonstrates unidirectional water transfer properties and high moisture absorption capacity. To enable solar-driven water desorption, the device is engineered with a photothermal layer by chelation of tannic acid (TA) with Fe
³⁺. The multifunctional SAWH device with a special channel structure presents a superb water absorption of 0.90-2.29 g g
⁻¹ within a wide range of relative humidity (RH) (40-90%) and a fast solar-driven water desorption rate of 1.77 kg m
⁻² h
⁻¹ under one sun illumination. In outdoor tests, 82.3% of the water absorbed overnight could be released during the daytime under natural sunlight, achieving an ultrahigh daily water production of 3.72 L per m
² that is superior to that of most previously reported all-in-one SAWH systems. This proposed design strategy provides an effective solution for collecting water from the air by SAWH followed by solar-driven water desorption.