(378ae) Computational Screening of Hydration Reactions for Thermal Energy Storage: New Materials and Design Rules

Thermal energy storage (TES) materials offer a unique approach to renewable energy storage. TES materials store energy by absorbing heat when it is in excess and releasing heat when energy is needed. For instance, TES is ideal for thermal energy regulation (e.g., of buildings, textiles, and electronics), waste heat capture, and improving the efficiency of solar energy plants. Of particular interest is storing the energy in hydration/dehydration reactions since this method has the potential to store large amounts of energy in a process that is simple, cost effective, and reversible at moderate temperatures. In the current study, we performed high-throughput, first principles calculations on a set of salt hydrates and metal hydroxides to determine the most promising candidates for TES based on energy storage densities.¹ We selected known compounds from the Inorganic Crystal Structure Database, optimized their structure, and calculated their gravimetric and volumetric energy densities in addition to their operating temperature range. In total, 265 hydration reactions were characterized, and promising reactions were identified for low (<100 °C), medium (100-300 °C), and high (>300 °C) temperature ranges. Many promising reactions identified in the current study have been previously unexplored for TES applications, including the dehydration of CrF₃•9H₂O. Additionally, property-performance relationships were identified using a Pearson correlation matrix. For salt hydrates, performance is highly dependent on the water capacity of the salt hydrate, and, for hydroxides, performance is strongly influenced by ionic properties of the material, such as the electronegativity of the cation. Our work represents one of the largest screening studies involving salt hydrates and metal hydroxides. The results can be used to guide experiments towards the most promising TES materials.

(1) S. Kiyabu, J.S. Lowe, A. Ahmed, and D.J. Siegel, “Computational Screening of Hydration Reactions for Thermal Energy Storage: New Materials and Design Rules,” Chemistry of Materials 2018, 30, 2006-2017