Electrostatic Coordination Salt-Locking and Anisotropic Thermal Highways for Leakage-Free Atmospheric Water Harvesting.

Abstract

Sorption-based atmospheric water harvesting (AWH) offers a decentralized strategy to alleviate global water scarcity. However, the trade-off between high salt loading and structural stability in AWH sorbent materials remains a critical bottleneck. Here, we report a hierarchical composite gel (D-HKPB@LiCl) that addresses the persistent salt-leakage challenge while enhancing solar-thermal efficiency. By integrating sulfated κ-carrageenan (KC) into a thermoresponsive hydroxypropyl cellulose (HPC) matrix, strong coordination between sulfate groups and lithium ions chemically anchors the hygroscopic salts within the polymer network, endowing the system with exceptional cycling stability. To overcome kinetic limitations, directional freezing vertically aligns polydopamine-coated hydroxylated boron nitride (PDA@BNO) whiskers, creating anisotropic thermal pathways with through-plane conductivity of 0.49 W m^-1 K^-1 along the ice-growth direction. This architecture, coupled with the photothermally triggered hydrophobic phase transition of HPC, enables a maximum desorption rate of 3.1 kg m^-2 h^-1 under one Sun illumination. The D-HKPB@LiCl gel exhibits a water uptake of 0.91-4.32 g g^-1 across 30%-90% RH. Outdoor field validation in Lanzhou, China, under challenging winter conditions (average 4.3 °C, <0.5 Sun) using a customized active condensation harvester yields a freshwater output of 0.78 g g^-1, establishing a reliable design framework for high-performance freshwater generation across diverse climatic conditions.