Bioinspired Self-Floating Hydrogel-Coated Foam for Synergistic Solar Power Generation and Desalination

Abstract Interfacial solar-driven evaporation provides a sustainable route for freshwater generation, but practical implementation remains limited by salt accumulation, insufficient understanding of water/ion transport, and inefficient utilization of the evaporated vapor. Herein, we report an interfacially engineered self-floating hydrogel-coated foam evaporator constructed by anchoring Ketjen black/sodium alginate/tannic acid/Fe3+ networks onto a melamine foam skeleton. The Fe3+ ions serve as multivalent coordination centers, simultaneously interacting with the carboxylate groups of sodium alginate and the phenolic groups of tannic acid, thereby forming a stable hydrophilic coating with enhanced surface wettability and robust interfacial adhesion. The open-cell macroporous foam provides low-resistance water supply pathways, while the hydrophilic hydrogel coating promotes surface-mediated water spreading and salt redissolution. Under 1 sun illumination, the optimized evaporator exhibits an evaporation rate of 3.56 kg m–2 h–1 and a solar-to-vapor efficiency of 92.4%. This performance is attributed to broadband solar absorption, localized heat management, and reduced effective evaporation enthalpy of interfacial water. The evaporator maintains stable evaporation in seawater for 120 h without obvious salt crystallization, mainly owing to capillary rewetting, concentration-gradient-driven ion diffusion, and density-driven brine exchange through the macroporous network. In addition, the device enables simultaneous hydrovoltaic electricity generation using inert electrodes. This work provides a chemically and structurally integrated strategy for solar desalination and water-enabled energy harvesting.