A Dual-Function Poly(vinyl alcohol) Hydrogel for Solar Water Production and Thermoelectric Energy Generation

This work addresses the dual challenges of seawater purification and converting low-grade waste heat into electricity, both of which are crucial for sustainable resource management. It presents a combined approach that solves both problems using a self-fabricated device. The device generates a temperature gradient through efficient photothermal conversion by placing thermoelectric hydrogels on top of a photothermal hydrogel. Poly(vinyl alcohol) (PVA) is used as the matrix for the photothermal hydrogel and was selected for its biocompatibility and ease of processing. In order to enhance both the solar-driven water evaporation and photothermal conversion efficiency, ball-milled dititanium trioxide (Ti₂O₃) nanoparticles and carbon nanotubes (CNTs) are incorporated within the PVA matrix. This approach enables a water evaporation rate as high as 3.22 kg m^–2 h^–1. Additionally, PVA also serves as the matrix for thermoelectric gels, which are soaked with a K₃[Fe(CN)₆]/K₄[Fe(CN)₆] redox pair solution to exploit the thermogalvanic acid (TGC) effect. This arrangement enables voltage generation through redox reactions at the hot and cold ends. The obtained excellent thermoelectric properties can be characterized by the ionic Seebeck coefficient (S_i) of 1.48 mV K^–1 and a power density of 9.6 mW m^–2 after nine thermoelectric hydrogels were connected in series. As a result, this dual-functional device simultaneously and effectively purifies seawater and generates electricity. Outdoor testing shows a daily water production of 9.2 kg m^–2 and a stable voltage generation of 130 mV from the thermoelectric hydrogels. This approach advances water purification and energy generation technologies and opens new avenues for innovative applications in renewable energy.