Salt impregnated desiccant matrices for ‘open’ thermochemical energy storage—Selection, synthesis and characterisation of candidate materials

• A list of materials is provided for ‘open’ thermochemical energy storage (TES).
• Characterisation of materials provided their hygrothermal and porous properties.
• Characterisation enables future linking of material performance to its properties.
• Vermiculite with CaCl2 or LiBr show the best potential for ‘open’ TES.

A selection of hygroscopic salts and desiccant matrices (salt in matrix, SIM) were chosen from the literature as candidate materials for open thermal energy storage (TES) systems. The aim of the paper was to narrow this selection through the application of selective criteria to those that had a high affinity of each working pair to each other, were environmentally stable, had low raw material costs with high availability, a low regeneration temperature for charging (<130 °C), a high temperature lift during reaction, high cyclic efficiency and high energy density. Candidate materials included silica gel, zeolite, activated carbon and vermiculite as matrices with CaCl2, MgSO4, Ca(NO3)2, LiNO3 and LiBr as salts. Scanning electron microscopy was used to verify salt presence. The pore geometry and structure was mapped through the use of nitrogen (N2) physisorption with application of both Brunauer–Emmett–Teller and Barrett–Joyner–Halenda analysis, gas pycnometry and gravimetric testing. The hygrothermal properties were characterised using modified transient plane source, differential scanning calorimetry and modified dynamic vapour sorption (DVS) techniques. Vermiculite with either lithium bromide (SIM-3e) or calcium chloride (SIM-3a) appear to have significantly higher TES potential when compared to both the raw desiccants and the other SIM's.