Ice-templated nanocellulose porous structure enhances thermochemical storage kinetics in hydrated salt/graphite composites

Abstract The freeze-drying technique is employed for the production of novel strontium bromide/graphite/nanocellulose composites for thermochemical heat storage application. The aim is to obtain a better control and stability of salt organization within the composite, while maximizing the air/salt and salt/graphite interfacial areas and enhancing mass and heat transfer associated to the salt hydration and dehydration. A comparison with a conventional wet impregnation method is also reported. The morphology was investigated by means of scanning electron microscopy. Differential scanning calorimetry was employed to evaluate the energy storage density, while hydration kinetics were evaluated at 23 °C and 50% RH. The wet impregnation approach delivered materials with a limited porosity while freeze-drying produced highly porous structures with oriented channels for moisture transport across the composite. The organic binder provided an active contribution to the energy storage process, producing energy storage densities up to 764 kJ/kg, 48% greater than the theoretical value. Freeze-dried nanocellulose composites evidenced a significant increase of 54% in the hydration kinetics, compared to the pristine salt. Based on these results, the freeze-drying of ternary composites based on salt hydrate, graphite and nanocellulose is envisaged as a promising route for the production of fast charge and discharge thermochemical storage systems.