Abstract
Thermochemical energy storage is promising due to its advantages of high-energy density and low-self discharging. One promising reaction material is the hydration and dehydration of hygroscopic salts. However, many pure salts have poor cycle stability. The present work investigates the development of a new composite material for thermochemical storage by impregnating a framework of crystalline nanocellulose (CNC) with calcium chloride (CaCl2) Various weight ratios of CNC:CaCl2 were prepared by dispersing the salt and CNC in deionized water and using mechanical stirring and ultrasonication processes followed by drying at ambient temperature. The attachment of the salt to the CNC was determined by TEM and FTIR analyses. The enthalpy of dehydration and water uptake were measured. The stability of the composite material was determined by subjecting it to multiple cycles. The results show that the nanocellulose binds to the salt crystals and provide a nano-scale architecture to stabilize the salt. The CNC-salt material shows improved energy density and stability compared to pure salt. For example, for the given hydration conditions, the specific enthalpy of dehydration for the formulation 1:2 weight ratio of CNC to salt is 117 J/g while for the pure CaCl2 the enthalpy of dehydration is 86 J/g. Thus, the CNC-salt material shows ∼1.36-x improvement in energy density. Additionally, over the course of multiple cycles, that caused the pure CaCl2 to deliquesce, formulations of the CNC-salt material retained their structural integrity and energy density.
