2, Mechanical Engineering, University of California, Berkeley, Berkeley, California, United States
Thermal storage offers the potential to reduce the amount of waste heat generated by thermal processes and improve overall energy efficiency. Thermochemical storage using reversible reactions has shown considerable potential for high energy density. However, most current thermochemical systems involve the use of at least one gas phase, thus requiring large volumes and reducing energy density. Condensed-phase, particularly all-liquid, thermochemical storage systems are thus highly desirable in order to improve energy density. In this study, we present a computational search for all-liquid thermochemical storage materials based on the Diels-Alder [4+2] cycloaddition reactions. Using high-throughput density functional theory (DFT) calculations, we determined the enthalpy change △Hrxn, entropy change △Srxn, and turning temperature (T* = △Hrxn / △Srxn) of 54 Diels-Alder reactions that had been performed in an aqueous solvent in the literature. We screened this test set for turning temperature, identifying nine reactions with a turning temperature close to the working temperature range of water (-50 - 150 degrees Celsius). Several of these reactions (the exo-reaction between furan and maleimide and the reaction between furan and acrylonitrile) were selectively modified using functional group substitution to generate additional reactions for study. These modified reactions were predicted to display exceptional thermal properties, increasing the heat capacity of water by as much as 58.7% and improving the thermal energy density of water by as much as 33.8%. Gravimetric energy densities as high as 0.5598 MJ/kg were predicted. Experimental work to verify the predicted properties of Diels-Alder reactions are ongoing.