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.
In this work, we introduce a new family of barocaloric hybrid organic-inorganic compounds with colossal barocaloric effects. The here reported hybrid materials, [(CH3)3(CH2Cl)N]FeCl4 and [(CH3)3S]FeCl4, exhibit a molecular structure composed by discrete inorganic anions and organic cations with weak elestrostatic interactions. Our calorimetric studies reveal colossal barocaloric effects of similar magnitude than organic plastic crystals (ΔS > 100 J K-1 kg-1) near room temperature and under smaller pressures (p ≤ 1000 bar), which leads to higher barocaloric strengths. Furthermore, these materials exhibit densities similar to barocaloric hybrid perovskites enhancing the volumetric barocaloric effects (ΔS ~ 200 J K-1 l-1), which could provide more compact cooling devices. Therefore, the colossal values of the mass and volumetric barocaloric effects and large barocaloric strength, in addition to the low working pressure and near-room-temperature operation, offer a new family of compounds to further explore in the search for improved barocaloric materials.
In this work, we design, build, and test one of the very first barocaloric devices. The here presented device can recover the energy generated by an individual’s footstep and transform it into barocaloric heating and/or cooling. Accordingly, we present an innovative device that can provide eco-friendly and gas-free heating/cooling. Moreover, we test the device by measuring a new barocaloric organic polymer that exhibits a large adiabatic temperature change of ~2.9 K under the application of 380 bar. These results pave the way towards novel and more advanced barocaloric technologies and provide a simple and low-cost device to explore new barocaloric materials.
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