Cost-effective, scalable fabrication of self-floating xerogel foam for simultaneous photothermal water evaporation and thermoelectric power generation

• Self-floating hydrogel foam is prepared by vacuum-assisted water foaming method. • It shows a wide adsorption in solar spectrum and excellent heat management ability. • The hydrogel foam tunes the water state and decreases the evaporation enthalpy. • It exhibits a very high evaporation rate of 3.39 kg m -2 h -1 under 1 Sun irradiation. • Hybrid device generates a thermoelectric power output of 0.63 W m -2 under 1 Sun. Three-dimensional (3D) evaporator has become one of most promising solar absorber/receiver materials for interfacial solar-driven steam generation to efficient global energy and freshwater crises remediation. However, developing 3D evaporators in a green and easy scale-up manner remains a grand challenge. Herein, we pose a cost-effective, scalable, and green foaming method using water as the foaming agent to construct self-floating monolith 3D xerogel foams for synergetic coupling of interfacial solar energy conversion-driven steam generation and low-grade heat-to-electricity conversion. Attributed to its powerful water supply capability, the as-prepared xerogel foam evaporator with porous structure achieves efficient water evaporation without salt accumulation in the course of continuous seawater desalination. Notably, the 3D xerogel evaporator simultaneously achieves an evaporation rate of 3.39 kg m -2 h -1 and the electric power output of 0.63 W m -2 under 1 Sun illumination, surpassing great majority of previously reported solar evaporators. In outdoor experiments, the 3D xerogel evaporator realizes a maximum water collecting rate of 1.2 kg m -2 h -1 and an accumulated output amount of 8.9 kg m -2 during one day. More importantly, six devices connected in series can power small devices like electric fan, calculator and timer. This work provides a cost-effective and easy-to-manufacture vacuum-assisted water-foaming approach for opening up low-cost, high-performance, scalable and durable 3D xerogel evaporators to achieve freshwater and thermoelectric power co-generation in off-grid or remote districts.