Discovery of Colossal Breathing-Caloric Effect under Low Applied Pressure in the Hybrid Organic–Inorganic MIL-53(Al) Material

Abstract

In this work, “breathing-caloric” effect is introduced as a new term to define very large thermal changes that arise from the combination of structural changes and gas adsorption processes occurring during breathing transitions. In regard to cooling and heating applications, this innovative caloric effect appears under very low working pressures and in a wide operating temperature range. This phenomenon, whose origin is analyzed in depth, is observed and reported here for the first time in the porous hybrid organic–inorganic MIL-53(Al) material. This MOF compound exhibits colossal thermal changes of Δ S ∼ 311 J K –1 kg –1 and Δ H ∼ 93 kJ kg –1 at room temperature (298 K) and under only 16 bar, pressure which is similar to that of common gas refrigerants at the same operating temperature (for instance, p (CO 2 ) ∼ 64 bar and p (R134a) ∼ 6 bar) and noticeably lower than p > 1000 bar of most solid barocaloric materials. Furthermore, MIL-53(Al) can operate in a very wide temperature range from 333 K down to 254 K, matching the operating requirements of most HVAC systems. Therefore, these findings offer new eco-friendly alternatives to the current refrigeration systems that can be easily adapted to existing technologies and open the door to the innovation of future cooling systems yet to be developed.

The importance of crystal size for breathing kinetics in MIL-53(Al)

“…Switchable porous solids are a sub-class of MOFs with adaptable porosity, which undergo stimuli-induced phase transitions between open porous and contracted or even dense phases. 1 Such adaptive materials are currently intensively discussed as promising materials for natural gas storage, 2 CO 2 /CH 4 3,4 and hydrocarbon separation, 5 isotope separation, 6 eco-friendly refrigeration technologies, 7 design of sensors 8 and actuators. 9 The driving force of the phase transitions in MOFs is today well understood in terms of thermodynamics and often experimentally observed phases can be predicted in silico .…”

“…In the first cycle, the np–lp transition rate constant k was calculated as 0.270 s −1 and accelerated in the following cycles reaching a value of 1.236 s −1 . Multiple factors such as the different nucleation mechanism of lp–np and np–lp transition, baro-caloric effects, 7 or differences in diffusion rates of n –butane in lp and np phases may contribute to the differentiation. The nucleation for a structural contraction (lp to np transition) is triggered by adsorption of the n -butane molecules diffusing rapidly into the large pore system.…”

Plastic Avalanches in Metal–Organic Framework Crystals Due to the Dynamic Phase Mixing

“…One challenge of the industrial application of MOFs is the fabrication of MOFs at the commercial scale, because MOFs are usually acquired in the form of loose powders. Thus, MOFs need to be pressed into solid tablets with high density for industrial applications such as heterogeneous catalytic reactions and fluid separations. , In addition, intrinsic responses of MOFs to the mechanical pressure are inevitable in the applications of gas sorption, , shock absorption, , and mechanocalorics, , to name a few. Under these circumstances, understanding the mechanical responses of MOFs under compression is crucial for the shaping process and also the engineering applications of MOFs. , …”

A New Year and 35 Years of Chemistry of Materials

“…Our “35 Voices” initiative will also begin so that we may hear what motivates materials researchers from all over the world. To kick off our 35th year, however, we start by highlighting 35 of the most cited and downloaded manuscripts published in 2022. − …”

“…MXenes and layered dichalcogenides (Table ) − as well as covalent organic framework (COF) materials (Table ) − were also well-represented. The contributions on MXenes include a Methods/Protocols paper that provides practical insights for the synthesis and processing of these exciting materials .…”