Novel 3D thermal energy storage materials based on highly porous patterned printed clay supports infiltrated with molten nitrate salts

One of the main drawbacks of phase change materials (PCM) to be employed as thermal energy storage (TES) systems in energy applications, such as concentrated solar power (CSP), is the liquid leakage, which considerably reduces the storage efficiency. To overcome this issue, a novel approach is presented, which is based on the development of three-dimensional (3D) engineered TES structures (3DTES) formed by highly porous patterned 3D printed low-cost clay supports (up to ~85% of total porosity) that are infiltrated with a molten sodium nitrate salt. Expanded vermiculite supports are additive manufactured by robocasting, a direct ink writing technology, using clay aqueous inks with a pseudoplastic behavior. 3DTES are lightweight (~1.8 g·cm−3), easy to handle, mechanically robust (~68 MPa) and exhibit high PCM encapsulation capacity (~78%), avoiding the molten salt leakage. Furthermore, they present an enthalpy of fusion of ~136 J·g−1, excellent thermal stability, and high thermal energy storage efficiency (~80%) and thermal conductivity (1.27 W·m−1·K−1), which is indicative of a great charging-discharging ability. The results open new opportunities through the 3DTES approach to manufacture promising affordable materials with outstanding performance for CSP applications.