Photothermal Macroporous Lignin Cryogels for Off‐Grid, Continuous Atmospheric Water Collection via Interlayer Heat Recovery

Abstract Sorption‐based atmospheric water harvesting (SAWH) offers a promising solution to water scarcity in arid and infrastructure‐limited regions, yet achieving both high water productivity and energy efficiency remains a significant challenging. Herein, a lignin‐engineered hygroscopic cryogel is reported with a tailored molecular structure designed to enhance both photothermal conversion and swelling. Compared with kraft lignin (KL), regenerated lignin achieves a photothermal conversion efficiency of 56% (1.68× that of KL) and exhibits about fourfold higher swelling in the hydrogel precursor. After LiCl loading, the composite cryogel reaches 1.81 g _water g _sorbent ⁻¹ at 60% RH, a 1.94× improvement over the KL‐based cryogel. To further increase water yield and energy efficiency, a drum‑type SAWH device is developed that incorporates interlayer heat transfer, recovering waste heat from the upper sorbent bed to drive desorption in a lower layer. This design increases the thermal energy efficiency to 48.4% and enhance the daily water yield by 1.49× in indoor tests. Outdoor trials demonstrate stable operation over ten continuous sorption/desorption cycles, producing 66.15 g of water (1439.04 mL _water m _solar ⁻² ), a 31.7% improvement relative to a single‐layer configuration. This work introduces a scalable, off‐grid thermal‐management strategy that significantly improves the efficiency of atmospheric water harvesting in arid environments.