Hierarchical Hollow Vascular Fiber Evaporator for Water‑Thermal‑Balanced Solar Evaporation

ABSTRACT Solar‐driven interfacial evaporation promises energy‐efficient and sustainable desalination. Despite the development of various sophisticated 3D evaporators, balancing water‐thermal equilibrium to achieve both high efficiency and salt tolerance remains challenging. Inspired by 1D water transport structures in nature, we engineered an evaporator with multi‐level vertical water channels using hierarchically structured hollow vascular fibers as building blocks. This design enables sustained evaporation even at heights exceeding the rapid water‑transport limit, without salt accumulation. Under solar illumination, the evaporator achieves rapid evaporation rates and exhibits exceptional long‐term stability for high‑salinity brine desalination, with large‐scale channels supplying ample water for evaporation and salt diffusion and micro‐channels serving as thermal pathways to regulate water‐thermal balance. By integrating radiative cooling into a 3D‐printed portable solar water purification device, purified water far exceeding drinking standards is produced from seawater and diverse wastewater streams under natural sunlight, highlighting the potential of the structural design for water‐treatment applications.