Molten salts stand out as excellent thermal energy storage (TES) materials for medium-high temperature applications, including renewable energies like concentrated solar power systems. However, these salts commonly exhibit energy efficiencies below expectations, are highly corrosive to the containers, and can present liquid leakage in their molten state, compromising their storage capabilities. Here, highly macro-porous (~93 %) three-dimensional (3D) expanded vermiculite (EV) supports have been additive manufactured (AM) by robocasting using a strategy based on the combination of optimized patterned architectures with the addition of activated carbon, as pore former, to the printable EV inks. The resulting 3D EV supports have been infiltrated with molten sodium nitrate, leading to 3DTES with an outstanding thermal energy storage efficiency of ~90 %, maintained after thermal cycling, and an energy storage density of 613 J·g−1. These 3DTES present low supercooling degree (2.7 °C), good thermal conductivity (~1.0 W·m−1·K−1), and high corrosion and mechanical resistances (compressive strength of ~46 MPa) despite their lightness (~1.6 g·cm−3). The patterned EV support based on sinusoidal-shaped porous struts keeps the molten salt fully encapsulated into the 3D structure and avoids the liquid leakage. These findings encourage the use of AM to develop novel TES materials able to overcome the drawbacks of phase change materials for energy applications. © 2023

This work was supported by the Grant PID2021-125427OB-I00 funded by MCIN/AEI/10.13039/501100011033 and by “ERDF A way of making Europe”, and by the Grant EIN2020-112153 funded by MCIN/ AEI/10.13039/501100011033 and by “European Union NextGenerationEU/ PRTR”.

Supplementary data to this article can be found online at https://doi. org/10.1016/j.est.2024.111108.

Peer reviewed