Downward design of solar-driven interfacial evaporators: Beyond the limitation of vertical water delivery in conventional upward evaporators

Solar-driven interfacial evaporation (SIE) represents a promising approach for freshwater production that eliminates the need for fossil fuel inputs. One of the primary objectives of SIE is to achieve a high evaporation rate. To enhance SIE performance, it is advantageous to increase the height of the evaporators, as this expands the evaporating interface. However, many existing evaporators face limitations in water delivery due to the competition between gravity and capillary forces. In this study, we propose a downward design strategy that mitigates this competition, resulting in a larger evaporating interface and higher evaporation rate. Through our experimental setup, we achieved an impressive evaporation rate of 2.01 kg·m−2·h−1 using the downward evaporator, which is 46.7% higher than that of the upward evaporator. When applied to desalination, downward evaporators exhibit excellent anti-salt performance, owing to an ample water supply, thereby enabling prolonged operation without a decline in evaporation rate or observable salt precipitation, even under 2.0-sun illumination. Furthermore, we demonstrate that the downward design strategy allows water bodies, rather than air, to serve as the cold source for condensation, enabling the attainment of a higher temperature gradient and enhanced vapor condensation. We achieved a notable water harvesting rate of 0.76 kg·m−2·h−1 under 1.0-sun irradiation.