Metal–organic frameworks (MOFs) can cool and heat buildings without requiring external electrical inputs, according to researchers who have unlocked new thermal capabilities in the material across a wide range of temperatures. Discovered to possess shape-shifting properties during carbon dioxide adsorption and desorption by University of A Coruña researchers in 2022, these materials now offer a self-regulating solution for green thermal storage and energy-efficient climate control.
How Static Carbon Dioxide Pressure Drives Self-Regulating Thermal Storage
Previous iterations of the technology relied on a swinging pressure to produce thermal effects. However, subsequent studies led by Juan Manuel Bermúdez-García at the University of A Coruña have unveiled a reversed system that maintains a static pressure of carbon dioxide. In this setup, external environmental temperatures trigger the adsorption and desorption of the gas.
“During the day, as temperature rises, carbon dioxide is desorbed, which counterintuitively cools down the MOF, and could cool down our buildings,” Bermúdez-García explains. At night, the process reverses, forcing the material’s pores to readsorb the carbon dioxide and release heat back into the structure.
Claire Hobday, an expert in solid state refrigeration at the University of Edinburgh who was not involved in the study, notes that this represents a novel way to think about utilizing these materials. According to Hobday, heating the MOF at a fixed pressure causes a cooling effect because the material experiences an endothermic phase transition.
Did you know? By fluctuating the fixed gas pressure, researchers can directly alter the charge and discharge temperatures, allowing a single material to adapt to different heating and cooling needs.
Overcoming Climate Adaptability Challenges in Thermal Materials
Traditional thermal storage materials have their transition temperatures predetermined by the energy requirements of the phase change. Shape-shifting MOFs, by contrast, are extremely pressure sensitive, according to Bermúdez-García. Small shifts in static CO2 pressure—ranging between 5 and 25 bar—alter transition temperatures dramatically from –30ºC to 120ºC.
By comparison, current technologies only achieved ranges of 40ºC and typically required pressurization boosts of up to 1000 bar, equivalent to the pressure found in the deepest parts of our oceans, notes Bermúdez-García. This capability solves a significant hurdle in thermal storage adaptability across different climates, a challenge that previously required a myriad of materials.
The MOF functions effectively in environments as diverse as sunny Spain or rainy Scotland, according to Hobday. The system operates within thermodynamic laws while demonstrating a thorough understanding of phase transitions. By absorbing heat at low temperatures and releasing it when pressurized at higher temperatures, the material unlocks energy-efficient industrial applications that usually incur high costs.
Mathematical Modeling and Future Refrigeration Screening
To accelerate the discovery of practical cooling applications, the research team from A Coruña adapted a specialized mathematical model. This theoretical thermodynamic framework predicts critical material properties, including pressure, transition temperatures, and the overall magnitude of the MOF heat-exchange capacity.
In the United States, the National Institute of Standards and Technology maintains a curated catalogue of MOF adsorption isotherms, as Hobday points out. When paired with the simulation model from Spain, these combined resources serve as essential tools for identifying novel shape-shifting MOFs with refrigerant potential.
Frequently Asked Questions
Do metal–organic frameworks require electricity to heat and cool?
How do pressure changes affect the MOF transition temperature?
Small adjustments in static CO2 pressure between 5 and 25 bar can alter the material’s transition temperature dramatically, ranging from –30ºC to 120ºC.
Can the same material be used in different climates?
Yes. Experts note that the material’s adaptability allows it to function effectively across varied environments, such as both sunny and rainy climates, by simply adjusting the fixed gas pressure to meet specific heating and cooling needs.
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