Direct solar vapor generation with micro-3D printed hydrogel device

Direct solar vapor generation (SVG) provides a sustainable and eco-friendly solution to the current global water scarcity challenges. However, existing SVG systems operating under natural sunlight suffer from low water yield and high energy requirement of vaporization. New materials with reduced latent heat of water vaporization are in urgent demand to boost SVG process. Herein, we propose a novel strategy to additively fabricate anisotropic hybrid 3D structure from photocurable thermoresponsive p(NIPAm-co-PEGDA) hydrogel on the top of PEGDA foam for SVG. The in-situ post-printing synthesis of iron oxide nanoparticles within the p(NIPAm-co-PEGDA) hydrogel on the top surface, thus introducing anisotropy, is achieved by adding metallic salt precursor into the printing solution. The as-fabricated hydrogel composite structure exhibits superior light absorption properties and rapid capillary-driven water transport through a 3D-printed microchannel network within the hydrogel. As a result, our SVG device achieves an extraordinary water evaporation rate of 5.12 kg m⁻² h⁻¹ under one sun (1 kW/m²). The intrinsic water activation states, in addition to wettability modulation with temperature increase within p(NIPAm-co-PEGDA) hydrogel, plays a critical role in reducing the equivalent vaporization enthalpy and shifting the vaporization to relatively lower temperatures. The proposed hybrid SVG device is feasible, portable, and highly efficient, promising great potential for grand water-energy nexus challenges. (Figure presented.).