Photothermal hygroscopic hydrogel for simultaneous generation of clean water and electricity

Harvesting water from the air using adsorbents and obtaining fresh water by solar-driven desorption is considered as one of the most effective ways to solve the freshwater crisis in arid and desert regions. Based on a simple and low-cost photothermal hygroscopic hydrogel, a new strategy is proposed to boost solar energy efficiency by coupling solar-driven atmospheric water harvesting technology with thermoelectric power generation technology in this paper. Photothermal hygroscopic hydrogel ink PAM-CaCl2 is prepared by in situ polymerization using Acrylamide as monomer, Ammonium persulfate as thermal initiator and CaCl2 as hygroscopic component. During the day, the photothermal hygroscopic hydrogel absorbs solar energy and evaporates its own internal water to obtain fresh water. Simultaneously, the residual waste heat is utilized to power the thermoelectric panel, which produces electricity based on Seebeck effect. At night, the hydrogel harvests water molecules in the air to achieve regeneration. This hybrid system can achieve a water production rate of 0.33 kg m−2 h−1 and an additional electrical energy gain of 124 mW m−2 at 1 kW m−2 solar intensity. Theoretical model of the hybrid system is developed to understand the heat flow and thermoelectric generation process. The results provide new insights into energy and freshwater replenishment options in arid or desert areas with abundant solar energy.