A common layered manganese oxide mineral has been demonstrated by researchers from Tohoku University and Rigaku Corporation, Japan, to possess superior heat storage and release properties, making it valuable for recycling industrial waste heat. The material exchanges water with the air, allowing it to quickly absorb or release heat.

Heating the manganese oxide mineral containing potassium ions and crystal water to 200︎° C dehydrated the material, imparting the energy needed by stored water molecules to be released into the surroundingHeat is released from the manganese oxide material when water molecules penetrate its layered structure. Source: Norihiko L. Okamoto/Tohoku University atmosphere. When cooled below 120︎° C in a dry container and then exposed to humid air, the now re-hydrated material absorbed water molecules and released its stored heat. As reported in Nature Communications, the material’s energy density is more than 1,000 MJ/m³ and it can be charged and discharged within minutes.

"This 'intercalation' mechanism, where water molecules are reversibly inserted into a layered material, is very advantageous for heat storage," said Tohoku University materials scientist Tetsu Ichitsubo. "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."