Press Releases

DATE2023.12.27 #Press Releases

Keeping it cool under pressure: new material could revolutionize refrigeration technology

Researchers report the largest temperature change ever measured in a solid refrigerant material

December 27, 2023

Research led by Shin-ichi Ohkoshi of the University of Tokyo, in collaboration with Aisin Corporation, University of Tsukuba, Osaka University, and Molsis Inc., demonstrated the refrigeration potential of the inorganic solid compound, RbMnFeCo Prussian blue (rubidium cyano-bridged manganese-iron-cobalt inorganic compound), which exhibited larger temperature changes than previously ever observed. Exploiting solid refrigerants, materials used for cooling, are more eco-friendly than conventional technologies harnessing the thermal properties of gas-liquid phase transitions. As twenty percent of the power generated in electric power plants is used for cooling, applications of new materials in solid-based refrigeration technologies could significantly reduce global environmental issues. The findings were published in the journal Nature Communications.

Cutting-edge refrigeration technologies exploit the reversible thermal effects of changes in fields around solids. For example, changes in pressure (a type of field) can induce changes in the electronic charge state in the material. This leads to a change in its energetical state called the barocaloric effect, which can be leveraged for cooling. One way to evaluate the performance of potential solid refrigerants is to measure their reversible adiabatic temperature change. Adiabatic temperature change occurs when there is a change in pressure without heat entering or leaving the system. Here, the researchers report the largest ever decrease when the temperature dropped from 88 ℃ to 3 ℃ at 560 MPa (about 5500 times the standard atmospheric pressure). The barocaloric effect was also significant (temperature change of 21 ℃) even at a low (90 MPa) pressure. In one cycle of a direct measurement experiment, applying pressure increased temperature by 44 ℃, and releasing pressure decreased temperature by 31 ℃, resulting in a remarkable total change of 75 ℃. Such large temperature shifts around room temperature were made possible by strategically adjusting the cobalt ions in the Prussian blue compound. In addition to its exceptional range, the material also proved robust. It did not show any degradation in performance even after a hundred cycles of applying and releasing pressure.

Its heat transfer efficiency and wide temperature window around room temperature at low pressures make RbMnFeCo Prussian blue a possible candidate for developing solid-based air conditioning and food storage technologies.

Figure: the crystal structure of solid refrigerant RbMnFeCo Prussian blue (lower center), the largest ever reported reversible adiabatic temperature change: 85 K (85 ℃) around room temperature (upper left), the largest directly measured temperature change (upper right), adapted from Nature Communications, 2023, DOI: 10.1038/s41467-023-44350-4.

For more details, please read the article:   
Shin-ichi Ohkoshi, Kosuke Nakagawa, Marie Yoshikiyo, Asuka Namai, Kenta Imoto, Yugo Nagane, Fangda Jia, Olaf Stefanczyk, Hiroko Tokoro, Junhao Wang, Takeshi Sugahara, Kouji Chiba, Kazuhiko Motodohi, Kazuo Isogai, Koki Nishioka, Takashi Momiki, and Ryu Hatano. 2023. Giant adiabatic temperature change and its direct measurement of a barocaloric effect in a charge-transfer solid. Nature Communications. DOI: 10.1038/s41467-023-44350-4