Probing cycle stability and reversibility in thermochemical energy storage – CaC2O4·H2O as perfect match?. (1st February 2017)

• Record Type: Journal Article
• Authors: Knoll, Christian; Müller, Danny; Artner, Werner; Welch, Jan M.; Werner, Andreas; Harasek, Michael; Weinberger, Peter
• Is Part Of: Applied energy. Volume 187(2017)
• Page Start: 1
• Page End: 9
• Publication Date: 2017-02-01
• Subjects: Calcium oxalate monohydrate -- Full reversibility -- Cycle stability -- Water vapour concentration -- Chemical heat pump -- Thermochemical energy storage; Power (Mechanics) -- Periodicals; Energy conservation -- Periodicals; Energy conversion -- Periodicals; 621.042
• DOI: 10.1016/j.apenergy.2016.11.053
• Languages: English
• ISSNs: 0306-2619

Abstract

Graphical abstract: Highlights: CaC2 O4 ·H2 O dehydration is fully reversible between 25 °C and 200 °C. Isothermal cycling between hydrate and anhydrate phase can be triggered by the water vapour concentration. High reaction rates and full reversibility demonstrated over 100 cycles. Material shows no ageing effects or reactivity decrease. Abstract: 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 H2 O-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 CaC2 O4 ·H2 O/CaC2 O4 system is perfectly suited for technical application as a thermochemical energy storage medium.