Design and study of spin-crossover materials for solid-state cooling

Abstract

The refrigeration and air conditioning industry accounts for roughly 20% of global electricity demand. The contemporary refrigeration system is a vapor compression system. This technology uses hydrofluorocarbon (HFC) refrigerants, which possess global warming potentials up to 14,800 times greater than carbon dioxide. Consequently, solid-state cooling technologies emerge as an interesting, environmentally friendly alternative. These systems take advantage of the inherent caloric effect in solid materials, which undergo reversible entropy changes when an external stimulus is applied. This approach offers significant ecological and operational advantages: it avoids harmful refrigerants and improves overall system efficiency by eliminating the need for mechanical compressors. This work aims to study the caloric effect of spin-crossover compounds, focusing on the understudied elastocaloric effect. Although the barocaloric effect has been proven in spin-crossover compounds, demonstrating their elastocaloric effect is crucial for practical cooling applications. Unlike barocaloric systems that rely on hydrostatic pressure, elastocaloric systems operate with uniaxial stress, which simplifies system implementation for cooling purposes. A specific reported spin-crossover system was chosen to evaluate its potential elastocaloric effect. The compounds were characterized, and a composite synthesis method was established for elastocaloric effect evaluation. Subsequent characterization of the composites confirmed that the spin transition still took place within the polymeric matrix. Several mechanical analyses were made to determine the elastocaloric effect of the composites. Preliminary results were obtained suggesting a possible method for future studies to determine this effect. Based on rational molecular design, new spin-crossover complexes were synthesized to enhance their possible caloric properties. Complete characterization of these systems remains a subject for future studies