Reversible hydration behavior of CaCl2 at high H2O partial pressures for thermochemical energy storage

• CaCl2/H2O is proposed as gas–solid reaction in thermochemical energy storage.
• De- and rehydration behavior is analyzed with TG measurements in N2/H2O atmosphere.
• Different intermediate hydration steps are identified.
• Cycling stability is demonstrated for 20 cycles.

Compared to other energy storage concepts, thermochemical energy storage stands out with high storage densities and the possibility of heat transformation. However, up to now only few chemical reactions have been characterized sufficiently for this application. In this paper, calcium chloride is analyzed as a possible storage material. CaCl2 is known for its high deliquescence. Its exothermal hydration reaction can be used for storage applications from 80 °C to 200 °C. This paper reports on the hydration and dehydration behavior at different partial vapor pressures. Reversibility, intermediate reaction steps and their stability are studied. The presented results are in good agreement with literature data. The hydration reaction provides good reversibility and cycling stability for 20 cycles. Therefore, CaCl2 can be considered as a reference material for thermochemical storage application in the temperature range studied.