Highly efficient photothermal gel cotton fabricated with MXene and liquid metal particles for solar-driven seawater evaporation and permeable energy generation

Solar evaporators not only convert absorbed solar energy into heat and steam but also generate osmotic energy. Through meticulous interface engineering and water transmission strategies, a photothermal gel consisting of MXene, liquid metal, and polyvinyl alcohol was applied to cotton thread surfaces in this study, resulting in photothermal hydrogel cotton threads with strong hydrophilicity and excellent light absorption rates (> 95 %). These cotton threads were then arranged into an arc, with one end immersed in low-salinity sea water and the other in high-salinity brine, creating a solar evaporator setup. By combining a high-salinity brine collector with a permeation tank equipped with electrodes, commercial Nafion membranes, and simulated saltwater, a series of solar-evaporator-based permeation energy generators was established. The solar evaporator achieved a high evaporation efficiency of up to 4.62 kg m⁻² h⁻¹ when exposed to 1 kW m⁻² of sunshine, producing high-salinity brine and stable water vapor without the formation of surface-bound solid salt crystals during extended use. The permeation generator demonstrated a current of 160 μA and maximum power density of 1.17 W m⁻² after 11 h of illumination. This combination of solar evaporators and osmotic energy generation offers a novel approach to seawater desalination and permeable energy generation.