Robust and Flexible 3D Photothermal Evaporator with Heat Storage for High‐Performance Solar‐Driven Evaporation

Abstract Solar‐driven interfacial steam generation serves as an alternative strategy to alleviate the emergency of the global freshwater shortage. Compared to traditional 2D evaporators, 3D evaporators have drawn further attention for their excellent evaporation performance. However, large volume 3D evaporators suffer from problems related to higher vulnerability to damage and less portable storage. Worse still, 3D evaporators equally behave poorly in dark conditions. Herein, a robust and flexible 3D hydrogel/fiber evaporator mounted with solid–solid phase change materials (SPCMs) for efficient photothermal desalination is reported. The hydrogel fills the spaces of fibers and not only forms a topology‐like structure to strengthen the sunlight absorption (≈0.1% optical transmittance and ≈10% reflectance), but also reinforces the mechanical strength and elasticity of the evaporator (≈4 MPa tensile strength and ≈23 MPa Young's modulus). Notably, highly thermally‐conductive SPCMs fulfill a dual function under light‐dark conditions, facilitating a 3D evaporator for absorbing energy from high‐temperature environment under daylight, and releasing latent heat to sustain evaporation when light is turned off, ultimately achieving evaporation rates of 3.80 and 0.31 kg m^–2 h^–1 under different conditions. Such a durable 3D hydrogel/fiber evaporator with dramatic evaporation performance opens up promising prospects for freshwater production in remote areas.