Enhanced vapor condensation in bidirectional solar stills using copper foam with multiple nucleation sites

Solar-driven interfacial evaporation, with its zero carbon emissions, low cost, and off-grid characteristics, has become a core solution for seawater desalination and wastewater purification. However, its practical application is still limited by the insufficient freshwater productivity due to the low vapor condensation rate. This study introduces a copper foam (CF)-based bidirectional solar water production (CF-BSWP) device. Utilizing the interconnected networks of CF, the available surface area and nucleation sites for vapor condensation are increased. Furthermore, the CF undergoes hydrophobic modification to suppress the formation of a liquid film, which constitutes a major barrier for continuous vapor condensation. Under 1 sun illumination, the hydrophobic CF-BSWP device achieves a water productivity of 1.20 kg m −2 h −1 and a solar-water efficiency of 80%. Importantly, a 10-hour real-world operation demonstrates an outstanding water yield of 11.07 kg m −2 , suggesting sustainable water production under natural sunlight and fluctuating weather conditions. This work provides an effective and viable solution to harvest the vapor generated in solar-driven interfacial evaporation devices.