Structure and thermal property relationships in the thermomaterial di-n-butylammonium tetrafluoroborate for multipurpose cooling and cold-storage

Abstract

Nowadays around 46% of food production around the world requires refrigeration, which is generally provided either by active vapour-compression (based on refrigerants with liquid–gas transitions) or passive cold-storage (based on solid-to-liquid phase change materials, SL-PCMs). However, in order to avoid fluid losses during the transitions, new thermomaterials with solid–solid transitions are desired for both applications. In this work, we find that [DBA][BF₄] (DBA = di-n-butylammonium) is a promising thermomaterial with solid–solid phase transitions. This compound presents thermal properties of great interest not only for active barocaloric refrigeration, but also for passive cold-storage, which make this a unique multipurpose thermomaterial. The observed cold-storage capacity is very close to that of commercial SL-PCMs (E ∼ 135 kJ kg⁻¹), while the pressure-induced thermal changes (ΔS ∼ [200–270] J K⁻¹ kg⁻¹) are superior to those of most barocaloric materials, operating under lower pressures (p ∼ [500–1000] bar). Moreover, the operating temperature range of this material is very adequate for food preservation (250–310 K), which is a great advantage over most barocaloric materials. Beyond the thermal properties, we perform deep structural characterization, which reveals a progressive structural disorder of the [DBA]⁺ cations and [BF₄]⁻ anions as the origin of such thermal properties, which will help the future rational design of enhanced thermomaterials.