Spontaneous Dropwise Wicking for Scalable Integration of Salt-Loaded Nanoporous Sorbents

Salt-loaded nanoporous solids are an emerging class of materials that combine the superior water uptake capacity of hygroscopic salts with the porosity and vapor accessibility of nanoporous sorbents. This composite strategy offers a promising pathway for advancing sorption-based atmospheric water harvesting (AWH) and thermal energy storage (TES) applications. However, the presence of salt and the loose-powder form factor of these materials pose significant challenges for practical device integration. Effective incorporation into mechanically robust and vapor-accessible substrates is critical for realizing scalable, durable, and high-performance sorbent modules. In this work, we develop a dropwise-wicking (Dropwick) methodology to integrate salt-loaded sorbents into three-dimensional porous metal foams, leveraging the substrate's mechanical stability and thermal conductivity while preserving fast vapor diffusion kinetics. Unlike conventional dip coating, Dropwick combines precise dropwise deposition with spontaneous capillary-driven wicking, enabling controllable and efficient sorbent integration. Here, we establish a unified physical modeling framework to guide Dropwick operation based on dimensionless numbers that capture key competing effects such as surface wetting, capillary flow, viscous drag, solvent evaporation, and particle dispersion. Using salt-loaded hierarchical silica (LiCl@HSPEG) as a model system, we then experimentally demonstrate Dropwick integration as guided by the predictive model. These successful samples exhibit uniform, scalable coatings while preserving, and even exceeding, the intrinsic sorption performance of state-of-the-art salt-loaded sorbents. This work provides a versatile strategy for bridging material-level properties with device-level requirements in AWH, TES, and related energy systems.