Pressure-induced thermal changes in solids—barocaloric effects—offer promise for creating solid-state refrigerants as alternatives to conventional volatile refrigerants. Efficient and scalable barocaloric cooling requires materials that undergo high-entropy, reversible phase transitions in the solid state in response to a small change in pressure. Here, we describe a mechanism for realizing a new class of barocaloric materials that feature colossal and tunable barocaloric effects near room temperature. This mechanism is based on conformational order–disorder phase 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 the thermodynamics and kinetics of pressure-induced phase transitions. Through these efforts, we report a library of hybrid materials that feature a combination of large entropy changes, high pressure sensitivity, and ultralow hysteresis, the combination of which leads to colossal reversible barocaloric effects at record-low pressures (&lt; 300 bar). We anticipate that our results should accelerate progress in developing new materials and mechanisms for efficient solid-state cooling and should be of broad interest to researchers in inorganic and materials chemistry, as well as physical chemists studying phase transitions in solids.

Manipulating disorder in metal–organic materials for solid-state barocaloric cooling

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ACS Fall 2022

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