Composite formation of covalent organic framework crystals and sugar alcohols for exploring a new class of heat-storage materials

We impregnated the sugar alcohols (SAs) erythritol and mannitol (Man) in >0.1 mm single crystals of a covalent organic framework, COF-300, to propose new solid-state heat storing materials. The fusion-freezing cycles of the Man -COF composite occur in a narrow range of 130-155 °C without large or random supercooling, which has been a crucial problem of SAs, indicating the significance of this materials concept. The Man -COF composite displayed two endothermic and two exothermic features in the heating/cooling cycles. We measured the heat transmission properties in detail, based on which we discuss and suggest a postulate on the phase change behaviour of Man in the pores of the COF. The concept of forming composites of covalent organic framework crystals and sugar alcohols (SAs)-green and low-cost phase change materials-has solved the long-standing problem of SAs' strong supercooling, which degrades the stored thermal energy.