María Gelpi

One of the major challenges for thermal energy storage (TES) systems based on phase change materials (PCMs)─a key technology for energy decarbonization─is achieving dynamical tunability of their charge and discharge temperatures (Tcharge, Tdischarge). This capability would enable a single material to operate effectively across varying ambient conditions (e.g., different times of day, seasons, or climates) without requiring the use of multiple TES materials. In this work, we present a gas-responsive TES solution based on breathing caloric MOFs, particularly MOF-508b, in which transition temperatures can be widely tuned from −30 to 120 °C (243 to 393 K) by adjusting the surrounding CO2 pressure from 5 to 25 bar under isobaric conditions. More importantly, we demonstrate that this method allows precise control over the thermal hysteresis (|Tcharge – Tdischarge|) and can even reverse the transition temperatures (Tcharge < Tdischarge), which could be highly advantageous for temperature-driven TES applications. These findings pave the way for adaptive thermal technologies in which a single material can respond to different ambient temperatures and diverse storage needs, from cold storage to medium–high-temperature applications. We anticipate that this gas-responsive behavior is not exclusive to MOF-508b and encourage the exploration of other materials exhibiting similar tunable characteristics for adaptive TES applications.

This work discusses two new barocaloric materials, the first 3D printed barocaloric composite in the shape of a gyroid-like heat exchanger, and new potential applications for barocaloric thermal management in hydrogen and Li-ion energy technologies.

Hybrid metal halide materials have attracted significant attention due to their diverse functional properties. In this study, we prepared, characterized, and evaluated the multifunctional properties of two hybrid tetrachloromanganate (II) compounds with the general formula [(CH₃CH₂)₃N(CH₂X)]₂[MnCl₄], where X is Cl or Br. From the structural point of view, these compounds consist of two isolated ionic species with an antifluorite crystal arrangement: 0D tetrahedral [MnCl₂]^2– anions and large, quasi-spherical and polar [(CH₃CH₂)₃N(CH₂X)]⁺ cations. These cations are responsible for the first-order phase transition observed at T_t ~318 K for the Cl-compound and T_t ~343 K for the Br-compound. We investigated various functional properties—specifically dielectric, photoluminescent, and pressure responses—and our results demonstrate that these compounds are highly versatile, exhibiting broad responses to external stimuli. Furthermore, we found that substituting the halogen in the ammonium cations from Cl to Br induces important modifications in their functional properties. In particular, this halogen exchange increases the phase transition temperature, reduces the thermal hysteresis, improves the photoluminescence quantum yield, and enhances the reversible entropy changes under compression-decompression cycles.

Nowadays, materials for energy transition is a key topic in many academic programs in chemistry, natural sciences, and engineering at different levels, especially in advanced undergraduate and postgraduate courses. In this regard, one of the emerging topics is eco-friendly refrigeration and heating solutions based on phase change materials (PCMs). Nevertheless, recent studies show that senior high school and junior university students still find it difficult to relate these phase changes with chemistry. In this work, we have designed visually appealing experiments that use thermal cameras (increasingly affordable) and inexpensive materials, focusing on the physicochemistry of phase transitions and some of their innovative applications.

The hybrid metal halide [(CH₃)₃NOH]₂CoCl₄ exhibits a first-order phase transition at T ∼ 343 K.

Today, ≈20% of the electric consumption is devoted to refrigeration; while, ≈50% of the final energy is dedicated to heating applications. In this scenario, many cooling devices and heat‐pumps are transitioning toward the use of CO₂ as an eco‐friendly refrigerant, favoring carbon circular economy. Nevertheless, CO₂ still has some limitations, such as large operating pressures (70–150 bar) and a critical point at 31 °C, which compromises efficiency and increases technological complexity. Very recently, an innovative breathing‐caloric mechanism in the MIL‐53(Al) compound is reported, which implies gas adsorption under CO₂ pressurization boosted by structural transitions and which overcomes the limitations of stand‐alone CO₂. Here, the breathing‐caloric‐like effects of MOF‐508b are reported, surpassing by 40% those of MIL‐53(Al). Moreover, the first thermometry device operating at room temperature and under the application of only 26 bar of CO₂ is presented. Under those conditions, this material presents values of ΔT ≈ 30 K, reaching heating temperatures of 56 °C and cooling temperatures of −10 °C, which are already useful for space heating, air‐conditioning, food refrigeration, and freezing applications.