Water management by hierarchical structures for highly efficient solar water evaporation

Solar water evaporation is a sustainable and efficient way to produce fresh water. Identifying highly efficient photothermal materials is an important step for achieving high evaporation rates. However, the effects of the water interfacial area are rarely paid any attention, although a few reports have demonstrated high evaporation rates from micro-/nanostructured devices. In this work, we introduce a new term, water mass per unit surface area (WMUA), to connect the water mass and interfacial area. We can regulate WMUA using different commercial porous materials to realize water management in devices, which further affects the evaporation rates. The optimized device is composed of suedette sponge, filter paper, and polydopamine as the water-transportation, water-restrictive, and photothermal materials, respectively, and it achieves an evaporation rate of 1.8 kg m−2 h−1 and energy efficiency of ∼92%. This presents a new strategy for the rational design of device structures and the promotion of evaporation rates, pushing this field into new areas.