Biomass-derived polyol esters as sustainable phase change materials for renewable energy storage†

Innovative thermal battery technology has the capability to revolutionize the renewable energy storage market. Its cost-effectiveness, scalability, contribution to CO₂ reduction, and lack of reliance on rare earth metals set it apart. Nevertheless, the overall efficiency and sustainability of this technology hinge on crucial factors such as the sources, performance, and cost of the associated phase-change material (PCM). Fatty acid esters with biorenewable origins meet the sustainability criteria yet are limited to low-temperature applications (mostly <70 °C). In this study, we explored a new strategy to fine-tune the operating temperature of esters by adding hydroxyl groups, which are capable of forming H-bonds, positively affecting crystal packing and boosting their thermal properties. OH-group-rich, and biorenewable tartaric and mucic acids were employed as the core of fatty acid esters. Combinations of tartaric acid and fatty alcohols gave sustainable PCMs (confirmed by green chemistry metrics) with high melting enthalpies up to 221 J g⁻¹, improved melting temperatures up to 94 °C, and high stability demonstrated over more than 500 cycles. With the aid of Fourier-transform infrared spectroscopy (FTIR), synchrotron single-crystal X-ray diffraction, and Hirshfeld surface analyses, we obtained insights into the molecular interactions dictating the extraordinary thermal properties of sugar acid-derived esters, which could be feasible as PCMs for sustainable and inexpensive energy storage.