Vapor-compression based air conditioning has matured over the last century into a highly efficient technology which is essential to modern life. However, the hydrofluorocarbon refrigerants central to this technology are potent greenhouse gases—one to five thousand times more effective than CO<sub>2</sub>. The unintentional release of these refrigerants to the atmosphere during air conditioner installation, maintenance, and disposal is currently responsible for ca. 4% of planetwide global warming and is expected to rise to 10% of all warming by 2050. To eliminate this source of atmospheric emissions, we are focused on developing solid-state barocaloric materials which can serve as direct replacements for hydrofluorocarbons in air conditioners and other heat-pump applications. These solids operate with the same pressure-driven thermodynamic cycle as vapor compressors but utilize a solid-solid phase transition to store and release heat rather than the traditional liquid-vapor transition. Many different compounds have been proposed as possible barocaloric materials, however a combination of low transition pressure sensitivity and high transition hysteresis means that most require impractically high pressures—in excess of 1000 bar—to achieve efficient cooling. We have recently discovered a promising new family of barocalorics: layered halide perovskites with long alkyl ammonium tails. These undergo solid-solid, order-disorder transitions within the alkyl sublattice which are analogous to the melting of simple <i>n</i>-alkanes, albeit confined to two dimensions by the layered perovskite structure. Layered perovskite transitions occur near ambient temperature with high pressure sensitivity and extremely low hysteresis, while maintaining moderately high transition entropies. This combination of properties enables layered perovskites to realize efficient barocaloric cooling with a pressure swing of 200 bar or less, which is achievable with standard hydraulic systems. To demonstrate this in practice, we have designed and constructed a custom barocaloric prototype device and achieved efficient barocaloric cooling at moderate pressures for the first time. I will discuss our current progress, ongoing challenges, and future directions of this work.

Materials for practical solid-state barocaloric cooling: A chemist (re)invents an air conditioner

Fall 2022 abstracts, posters, and presentations will launch in mid-September.

ACS Fall 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.