Perspectives and Limitations of Tartaric Acid Diamides as Phase Change Materials for Sustainable Heat Applications

Phase change materials (PCMs) with melting temperatures in the intermediate range (100-220 °C) have recently been in high demand for applications in solar and wind renewable energy storage. Such materials can help advance thermal battery technologies, e.g. Carnot batteries, that can reduce the amount of fossil fuels used to generate electricity, contributing to substantial savings in CO₂ emissions. Recently, polyol esters have been recognized as robust PCMs with high stability and high energy storage density (up to 221 J g^-1), additionally meeting sustainability and circularity criteria, being sourced from inexpensive, biorenewable tartaric acid (TA), which provides H-bonding, boosting the esters' thermal properties. However, the melting points of TA esters, which are below 100 °C, limit their suitability for applications in the intermediate temperature range. In this study, TA diamides are explored as candidates for thermal energy storage with improved melting temperatures ranging from 130 to 190 °C and melting enthalpies up to 173 J g^-1. With the aid of differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and variable-temperature Fourier-transform infrared spectroscopy (FT-IR), various perspectives and limitations of designing TA-derived PCMs for sustainable heat use above 100 °C are investigated.