Discovery of Rapid and Reversible Water Insertion in Rare Earth Sulfates: A New Process for Thermochemical Heat Storage

5 years ago

Discovery of Rapid and Reversible Water Insertion in Rare Earth Sulfates: A New Process for Thermochemical Heat Storage

Kunihiko Shizume, Tetsuya Uda, Naoyuki Hatada

Thermal energy storage based on chemical reactions is a prospective technology for the reduction of fossil-fuel consumption by storing and using waste heat. For widespread application, a critical challenge is to identify appropriate reversible reactions that occur below 250 °C, where abundant low-grade waste heat and solar energy might be available. Here, it is shown that lanthanum sulfate monohydrate La2(SO4)3⋅H2O undergoes rapid and reversible dehydration/hydration reactions in the temperature range from 50 to 250 °C upon heating/cooling with remarkably small thermal hysteresis (<50 °C), and thus it emerges as a new candidate system for thermal energy storage. Thermogravimetry and X-ray diffraction analyses reveal that the reactions proceed through an unusual mechanism for sulfates: water is removed from, or inserted in La2(SO4)3⋅H2O with progressive change in hydration number x without phase change. It is also revealed that only a specific structural modification of La2(SO4)3 exhibits this reversible dehydration/hydration behavior. Water molecules can be inserted in crystalline rare earth sulfates such as La2(SO4)3 without phase change, accompanied by heat release. Since the reaction proceeds rapidly and reversibly upon changing temperature and water vapor pressure in the temperature range 50–250 °C, it will be a promising process for thermal energy storage, especially for low-grade waste heat and solar energy.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/adma.201606569