<br/>Barocaloric materials—which undergo thermal changes in response to applied hydrostatic pressure—can be used to drive solid-state cooling cycles that offer an environmentally friendly alternative to vapor compression refrigeration. Efficient barocaloric cooling requires materials that undergo reversible phase transitions with large entropy changes, high sensitivity to hydrostatic pressure, and minimal hysteresis, the combination of which has been challenging to achieve in existing barocaloric materials. Here, we describe a mechanism for realizing a new class of materials that feature colossal and tunable barocaloric effects. This mechanism is based on conformational order–disorder transitions of long-chain organic molecules—confined in space—that give rise to large changes in volume and entropy. Additionally, we demonstrate how the synthetic tunability of this system can be leveraged to control structural and chemical factors that influence the thermodynamics and kinetics of pressure-induced phase transitions. Through these efforts, we report a library of materials that feature a combination of colossal entropy changes, high barocaloric coefficients, and ultralow hysteresis. Further, the excellent processability of these materials, in combination with their unique mechanical properties, offers particularly simple strategies for harnessing barocaloric effects in prototype cooling devices across length scales. We anticipate that these results will help facilitate the development of barocaloric cooling technologies and further inspire new materials and mechanisms for efficient solid-state cooling.

Manipulating and understanding barocaloric effects in metal–organic materials

ACS Spring 2022

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