Transforming Sugars into Salts-A Novel Strategy to Reduce Supercooling in Polyol Phase-Change Materials

Phase-change materials (PCMs) that melt in the intermediate temperature range of 100-220 degrees C can contribute to the utilization of renewable energy. Compounds rich in hydroxyl groups (e.g., sugar alcohols) are promising materials because of their high energy-storage densities and renewability. However, supercooling and poor stability under operating conditions currently exclude them from practical application as PCMs in the pure form. In this study, we explore a new strategy to encourage the crystallization of sugars by introducing Coulombic interactions into their structures. The thermal properties of the first carbohydrate-based ionic compounds studied as PCMs are reported, focusing on a glucose-based cation and four different anions, namely, Br- [NO3](-), [OMs](-), and [BF4](-). Combining alpha-d-glucopyranoside, which typically supercools, with the [NO3](-) anion resulted in a salt system that crystallized readily during heating/cooling cycles. The role of hydrogen bonding in dictating the thermal properties was examined by single-crystal X-ray diffraction and Hirshfeld surface analyses.