Tuning the wettability of solar absorbers towards high-efficiency solar vapor generation

As an environmentally-friendly fresh water production method, solar water evaporation plays an important role in solving the shortage of fresh water. Recently, various kinds of solar absorbers have been developed. However, most of solar absorbers are hydrophilic for the sufficient water supply, and less attention has been paid to the effect of absorber's wettability on the evaporation performance. Herein, the effect of wettability of photo-thermal films on the evaporation rates was investigated. The evaporation of the full-wetting film (0.99 kg m⁻² h⁻¹) increased by 5.3% compared to the semi-wetting film (0.94 kg m⁻² h⁻¹) at 1 kW m⁻². Conversely, the evaporation of the full-wetting film (8.77 kg m⁻² h⁻¹) decreased by 8.5% compared to the semi-wetting film (9.58 kg m⁻² h⁻¹) at 13 kW m⁻². The systematic test indicated that the full-wetting film exhibited high evaporation performance at low optical power densities (1–5 kW m⁻²), and the performance of the semi-wetting film was better at high optical power densities (9–13 kW m⁻²). This work provides a new avenue to achieve high evaporation performance by tuning the wettability at different application environments.