Double hydrates salt as sustainable thermochemical energy storage materials: Evaluation of dehydration behavior and structural phase transition reversibility

Abstract

Currently, thermochemical energy storage (TCES) offers the opportunity to relieve the enormous gap of energy demand and supply in the solar energy field. This method has its specific requirements, such as high energy storage density, good thermal stability, high reaction enthalpy, high heat capacity and switched temperature range of thermochemical storage material (TCM) for low to medium temperature building applications. This paper reports the synthesis of blödite-type structure Na2M(SO4)2·4H2O (M = Zn, Mg) and copper kröhnkite phase Na2Cu(SO4)2·2H2O. Their structural and thermal behavior were also investigated to explore a new temperature range using incorporated salts. An evaluation of potential energy storage density, structural reversibility, thermal cycling stability and storage efficiency of double salts compared to pure hydrates salts as TCM was carried out. The preliminary results show a good structural matching of synthesized double salts confirmed by XRD, FTIR, and Raman spectroscopy, while the transition phase investigation since dehydration process was reported by XRD and Raman spectroscopy. Moreover, Na2Zn(SO4)2·4H2O exhibited a suitable charging range temperature (<105 °C), good cycling stability at the first ten hydration/dehydration cycles with an excellent energy storage density of 4.7 GJ m−3 and an interesting theoretical efficiency up to 77.4%.