Facing the global water shortage challenge, solar‐driven desalination is considered a sustainable technology to obtain freshwater from seawater. However, the trade‐off between the salt cycle and heat localization of existing solar evaporators (SE) hinders its further practical applications. Here, inspired by water hyacinth, a self‐standing and self‐floating 3D SE with adiabatic foam particles and aligned water channels is built through a continuous directional freeze‐casting technique. With the help of the heat insulation effect of foam particles and the efficient water transport of aligned water channels, this new SE can cut off the heat transfer from the top photothermal area to the bulk water without affecting the water supply, breaking the long‐standing trade‐off between salt cycle and heat localization of traditional SEs. Additionally, its self‐standing and self‐floating features can reduce human maintenance. Its large exposure height can increase evaporation area and collect environmental energy, breaking the long‐standing limitation of solar‐to‐vapor efficiency of conventional SEs. With the novel structure employed, an evaporation flux of 2.25 kg m−2 h−1, and apparent solar‐to‐vapor efficiency of 136.7% are achieved under 1 sun illumination. This work demonstrates a new evaporator structure, and also provides a key insight into the structural design of next‐generation salt‐tolerant and high‐efficiency SEs.
The microcellular honeycomb foams can be manufactured via fused deposition modeling (FDM) technology. However, the process often involves complicated pre/post‐treatment. Herein, a novel in situ foaming FDM technology is developed to efficiently fabricate the microcellular polyetherimide (PEI) honeycomb foams with various lattice structures. The extremely low gas diffusivity endows the CO2‐saturated PEI filament with a long‐time printing ability and well printing performance, which is characterized by a long printable time up to 7 days and the formation of microcellular structure within the deposited foam strands. The printed PEI foam parts possess high dimensional accuracy with a relative accuracy (δR) of 1.3–6.4% at the external regions and low internal accuracy with δR of 27.5–48.8%, resulting from the increased nozzle expansion and reduced melt viscosity. An accuracy correction based on the nozzle expansion is effective to improve the dimensional accuracy of the foam parts. The high accuracy control of macro/microstructure and the advantages of green processing and long‐time printing make the in situ foaming FDM technology show great application prospects in the fabrication of hierarchical cellular materials.
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