Solar Evaporator Turns Seawater to Drinking Water

Abstract

Freshwater scarcity demands innovative solutions that combine efficiency, durability, and scalability. Here, CuMnCrO4 (CMCO), is presented as a ternary spinel oxide photothermal absorber introduced for the first time in solar desalination, synthesized via co-substitution of Mn3O4 with Cu and Cr. This multi-cation design narrows the bandgap from 2.3 to 1.49 eV, markedly enhancing solar absorption across the visible and near-infrared spectrum and enabling efficient light-to-heat conversion. Unlike conventional carbon or single-oxide-based systems, CMCO demonstrates record-high evaporation performance of 4.1 kg m−2 h−1 under 1-sun, positioning it among the most efficient oxide-based ISSG materials reported to date. Equally novel is the integration of CMCO with a cotton fabric substrate and hydrophobic polyester strips in an inverted U-shaped configuration, which ensures continuous water wicking, localized salt separation, and mechanical robustness. This architecture delivers stable operation over three weeks without salt accumulation, overcoming a long-standing challenge in ISSG. Furthermore, the system retains high efficiency under strongly acidic/alkaline conditions and in oil- or dye-contaminated water, demonstrating unique resilience rarely reported in solar desalination systems. Finally, the modular design enables straightforward scalability from laboratory-scale strips to large-area panels. Together, these advances establish CMCO-based systems as a new materials platform for practical, durable, and scalable solar desalination, offering a sustainable pathway toward addressing global water scarcity.

A research team, affiliated with UNIST has unveiled a new technology that can convert seawater into clean drinking water using only sunlight, without any external power source. This breakthrough could play a crucial role in solving water shortages in developing countries and remote island communities where electricity is often unavailable.

Led by Professor Ji-Hyun Jang from the School of Energy and Chemical Engineering at UNIST, the team announced the successful development of a ternary oxide-based evaporator capable of efficiently using solar energy to drive evaporation. When placed on seawater, the device heats the water, causing it to evaporate and then condense into fresh drinking water-all without needing electricity.

Their experiments showed that a 1-square-meter (1 m²) setup can produce about 4.1 liters of clean water in just one hour. That is nearly seven times the natural evaporation rate of seawater, making it the fastest oxide-based evaporator reported so far.

What makes this possible is a new kind of photothermal material-substances that absorb sunlight and convert it into heat. This material is coated onto the surface of the evaporator, enhancing its ability to turn sunlight into thermal energy.

The researchers achieved this by replacing parts of manganese in a corrosion-resistant manganese oxide with copper and chromium, creating a new ternary oxide. By carefully adjusting the material's composition through a process called bandgap engineering, they made it capable of absorbing almost the entire solar spectrum-from ultraviolet to near-infrared light-covering 97.2% of sunlight. Unlike typical oxide materials that mainly absorb visible light, this new material captures and converts a much broader range of sunlight into heat.

The result is a surface temperature that can reach up to 80°C, significantly higher than previous manganese oxide-based materials, which topped out around 63°C or 74°C with copper-manganese oxides.

The device's design also addresses a common challenge in solar desalination: salt buildup. It features an inverted U-shape, with the photothermal coating on the part that absorbs water. The structure includes water-wicking fiber materials and hydrophobic polyester fabric, which help draw water efficiently and allow salt ions to flow away, preventing salt accumulation on the surface.

Professor Jang explained, "We have fundamentally improved the light absorption range and the photothermal efficiency of oxide materials, which allowed us to develop a high-performance, durable evaporator. Its scalability and stability mean it could be a practical solution to real-world water shortages."

The research was published online in Advanced Materials on December 16, prior to its official release, and was supported by various grants, including the ERC Project of the Engineering Research Center for Microplastic through Bio/Chemical engineering Convergence Process, the Brain Pool Program (BP), and the InnoCORE program of the Ministry of Science and ICT (MSIT), as well as the Mid-Career Research Program.

Journal Reference

Rana Muhammad Irfan, Sungdo Kim, Jin Young Lee, Ji-Hyun Jang, "Scalable Solar Evaporator Based on Bandgap Engineered CuMnCrO4 Spinel Oxide with Salt-Resistant Property for Contaminated Seawater," Adv., Mater., (2025).