Synthetic Design of Barocaloric Materials from the Bottom-Up

The refrigerants in used billions of cooling systems are potent greenhouse gases that inevitably leak into the environment during repair or decommissioning, accelerating the ongoing climate crisis. Thus, we must develop innovative and eco-friendly cooling solutions to regulate temperatures everywhere from our homes to shipments of food and medicine. To this end, emissions-free cooling platforms based on caloric materials have emerged as a viable alternative, wherein the latent heat of solid-solid phase transitions may be used for thermal regulation for heat pump or cooling technologies. In particular, barocaloric materials, which exhibit pressure-induced solid-solid phase transitions, hold great promise as alternative cooling platforms. However, barocaloric materials generally require high operating pressures to realize reversible cooling cycles, hindering their implementation into or alongside existing heating, ventilation, and air-conditioning infrastructure. These high operating pressures typically result from both thermal hysteresis and low pressure sensitivity of such phase transitions.<br/>In this work, we aim to elucidate the underlying structure-property relationships that dictate solid-solid phase transition behavior, namely hysteresis and pressure sensitivity, through systematic molecular variations in layered material platforms, wherein inorganic sheets act to confine alkyl chains that undergo order-disorder transitions. Such variations include changes in interaction strength between the inorganic sheets and alkyl chains (<i>e.g.,</i> covalent to electrostatic) as well as the packing density of alkyl chains arising from unique layer templates. Morevoer, we aim to improve the moisture and thermal stability of these materials through deliberate choice of layer composition and removal of halide ions. Finally, we aim to improve potential scalability through reduction in material cost and synthetic complexity based upon a wide screening of layered material families. The insights gleaned from this investigation aim to guide the design of next-generation, emissions-free cooling based on barocaloric materials.