A Novel Composite Material of Hygroscopic Salt Stabilized by Nanocellulose for Thermochemical Energy Storage

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.

Effect of High-energy Milling on the Solid State Formation of Zinc Manganites (ZnxMn3-xO4, 0.5 ≤ x ≤ 1.5) from the System ZnC2O4 · 2H2O-n MnCO3 (n = 1, 1.5 and 2)

By combination of TG/DSC and XRPD measurements it has been shown that zinc manganites form (ZnxMn3−xO4 with 0.5 ≤ x ≤ 1.5) starting from mixtures of zinc oxalate dihydrate and manganese carbonate subjected to mechanical activation by high energy milling. Solid solutions ZnOMn3O4- ZnMn2O4 are the products obtained by the same experimental conditions, when starting from a physical mixture. Furthermore milling, besides changing the enthalpy of dehydration of zinc oxalate, induces a partial formation of amorphous Mn3O4 at r. t. In particular ZnMn2O4 can be prepared by annealing the milled mixture for 18 h at 650 °C while a temperature > 1000 °C is needed to prepare ZnMn2O4 from a physical mixture. Finally, the calorimetric data suggest that the mechanism of the reaction is different in the two kinds of mixtures.