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C. Knoll, D. Müller, W. Artner, Jan Welch, A. Werner, M. Harasek, P. Weinberger:
"Probing cycle stability and reversibility in thermochemical energy storage - CaC₂O₄.H₂O as perfect match?";
Applied Energy, 187 (2017), 1 - 9.

The dehydration and subsequent rehydration of calcium oxalate monohydrate has yet to find application
in thermochemical energy storage. Unlike for many other salt hydrates, complete reversibility of the
dehydration-rehydration reaction was observed. Additionally, it was found that the rehydration temperature
is strongly affected by the water vapour concentration: Full reversibility is not only achieved at
room-temperature, but, depending on the water vapour concentration, at up to 200 °C. This allows
isothermal switching of the material between charging and discharging by a change of the H2O-partial
pressure. Cycle stability of the material was tested by a long-term stress experiment involving 100 charging
and discharging cycles. No signs of material fatigue or reactivity loss were found. In-situ powder X-ray
diffraction showed complete rehydration of the material within 300 s. The experimental findings indicate
that the CaC2O4.H2O/CaC2O4 system is perfectly suited for technical application as a thermochemical
energy storage medium.

Calcium oxalate monohydrate; full reversibility; cycle stability; water vapour concentration; chemical heat pump; thermochemical energy storage

http://dx.doi.org/10.1016/j.apenergy.2016.11.053