Enhancing vapor condensation in interfacial photothermal evaporation using hydrophobic copper foam

Solar-driven interfacial photothermal evaporation stands out as a green and sustainable desalination technology recognized as one of the most promising solutions to the global freshwater crisis. Despite notable progress in evaporation performance, the issue of low clean water production rates remains a pivotal challenge. This work reports a downward solar water production (DSWP) device that employs hydrophobic foam copper to enhance vapor condensation, utilizing a non-breathable Janus evaporator (NBJE) with an evaporation rate of 1.45 kg m −2 h −1 and a solar thermal conversion efficiency of 96 %. The NBJE is uniquely designed to allow vapor diffusion downward and condense within the bottom aluminum alloy condenser, effectively solving the light loss caused by top condensation droplets in traditional solar stills. Additionally, an HCF was embedded in the bottom condenser of the device, increasing vapor condensation sites and promoting the accumulation of liquid on its condensation surface, thereby eliminating the influence of the surface water film formed after vapor condensation on subsequent vapor condensation. By adjusting the position where the HCF was embedded, further optimizes the condensation displacement of vapor diffusion downward, significantly enhancing the efficiency of solar vapor-to-water conversion. Under 1 sun illumination, the DSWP device achieves a water productivity of 0.84 kg m −2 h −1 with a solar vapor-to-water conversion efficiency of 56 %. Series experiments with varying salinities and outdoor testing demonstrate that the DSWP device exhibits remarkable salt resistance and the potential for high-efficiency solar water production. This research provides fresh perspectives on the design of water collection structures for solar-driven interfacial photothermal evaporation, offering a viable solution to the global freshwater shortage.