Highly‐Efficient Solar Steam Generation with Real Time Salinity Monitoring for Seawater Desalination

Abstract

The annual solar radiation energy is equivalent to 1000 times the energy consumed by all human beings in the same period. [5] Therefore, it is believed that using solar energy to drive water purification is an ideal solution to the increasingly serious shortage of clean water. [6,7] In particular, the latest development of interfacial solar steam generation (SSG) has revived this traditional technology. [8][9][10][11][12] The design of solar evaporator is the key to improving the interfacial SSG efficiency. [13][14][15][16][17][18][19][20] In recent years, various photothermal materials (PTMs) have been developed and used for SSG. The PTMs for SSG can be generally classified into three categories, that is, plasma metals, [9,[21][22][23][24][25] semiconductors, [26][27][28][29] and carbon-based materials, [8,[30][31][32][33][34] which have broadband light absorption covering from visible to near-infrared (IR) and significant photothermal conversion ability. In a typical SSG, photothermal membranes with flat 2D flat shapes are used, which are installed on the air-water interface for water evaporation. [8][9][10] For example, Shan et al. reported an SSG system based on porous reduced graphene oxide (rGO) membrane. The roughness of the light-absorbing surface was designed to enhance the solar light collection capabilities, so as to improve water evaporation efficiency. [10] However, the evaporation rate is only 1.33 kg m −2 h −1 . In addition to the efforts devoted to the development of PTMs with high photothermal efficiency, the thermal management of the SSG system is also very important. An additional layer with low thermal conductivity (such as polystyrene foam) was placed under the PTMs to prevent heat loss into the bulk water, so that to increase the heat used for evaporation of the interfacial water. [35,36] Although significant progress has been made in the above two aspects in recent years, the energy efficiency of the 2D structured PTMs has been pushed to the theoretical limit. [35,37] To further improve the energy efficiency, 3D photothermal structures were proposed and designed. For example, when a 3D cylinder is presented under vertical light irradiation instead of a 2D photothermal surface, the photothermal effect on the top surface drives the interfacial SSG. [38,39] Meanwhile, the sidewall without light irradiation also undergoes a cold evaporation process, thus the temperature of the sidewall is lower than the ambient temperature, and energy can be collected from the environment. [40,41] The advantage of the 3D structure is that the Solar steam generation (SSG) has attracted increasing interest due to its huge potential in seawater desalination. However, SSG performance is not yet satisfactory due to limited photothermal efficiency and crude thermal management. In addition, real-time salinity monitoring is still lacking. Herein, inspired by the transpiration of trees, an umbrella-shaped 3D structure is designed for high-performance SSG. The water evaporation rate under one sun irradiation is as high a...

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