Development and characterisation of an alginate and expanded graphite based composite for thermochemical heat storage

Thermochemical heat storage is one of the most attractive technologies to store heat from solar thermal energy or waste heat from industrial processes for its high energy density and long-term storage capability. This research presents a novel expanded graphite/alginate polymer matrix encapsulated with hydrated salts as highly efficient thermochemical heat storage materials. Through the simple synthesis method, the composite material can be sized and shaped to fit multiple applications, and be easily scaled where needed. Through the reversible hydration and dehydration reaction, the incorporated CaCl₂ salt can store and release heat. Thermal energy from solar thermal generators or low grade waste heat sources (< 200 °C) is appropriate for the dehydration of CaCl₂. A salt loading value of 84% has been achieved with visible porosity maintained. Static heat is used to study the charge reaction, whereas a flow of humid air through a packed bed is used to study the discharge reaction where temperature uplifts between 10–14 °C were observed. A vermiculite/CaCl₂ composite is used as a comparison in both reactions. Additionally, bulk density, surface porosity, surface area, moisture sorption and thermal conductivity are considered. The results show that the novel composite materials developed in this study can achieve better packing density and comparable energy density comparing to the conventional vermiculite/CaCl₂ composite, but with higher thermal conductivity leading to enhanced energy efficiency. Graphical Abstract: [Figure not available: see fulltext.].