Researchers in Japan have shown that a common material is excellent at storing and releasing heat, which could make it useful for recycling industrial waste heat. The material exchanges water with the air, allowing it to quickly absorb or release heat.

The material in question is a layered manganese oxide mineral, which contains potassium ions and crystal water. That makes it a type of birnessite, a common natural mineral that’s showing promise in energy storage and as a catalyst for hydrolysis.

For the new study, researchers at Tohoku University and the Rigaku Corporation found that the material also works well for heat storage. The team made the material as a black powder, then used X-rays and transmission electron microscopy to study its crystal structure while the material was being heated and cooled.

The researchers found that the material was excellent at storing and releasing heat, through a mechanism known as water intercalation. Essentially, when the material is exposed to enough heat the water molecules stored inside it gain energy and are released to the air around it. This now-dehydrated material effectively stores that heat energy until it’s rehydrated with humid air, at which point it absorbs water molecules and releases the heat again.

“This ‘intercalation’ mechanism, where water molecules are reversibly inserted into a layered material, is very advantageous for heat storage,” said Tetsu Ichitsubo, corresponding author of the study. “It is very fast, reversible and the material’s structure is well maintained. Also, oxygen in the atmosphere doesn’t degrade the layered manganese oxide crystal and water doesn’t dissolve it. This makes it an excellent candidate for waste-heat reuse in industrial settings.”

In this case, the material was heated to 200 °C (392 °F) to trigger the dehydration, and cooled to 120 °C (248 °F) to release its stored heat on exposure to humid air. The material’s energy density is more than 1,000 MJ per m³, has a long lifetime, and it can be charged and discharged within minutes.

The researchers say the material could be useful for capturing and reusing energy lost as waste heat during industrial processes.

The research was published in the journal Nature Communications.

Source: Tohoku University