Wood-derived biochar as a matrix for cost-effective and high-performing composite thermal energy storage materials

Abstract

High energy storage density, affordability, and environmental friendliness are the key requirements for materials used in thermal energy storage systems. A new composite thermal energy storage material (TESM) with all these requirements was fabricated by utilizing a biochar matrix. Biochar was derived from the slow pyrolysis of forestry residues, an abundant source of underutilized biomass in Canada. The results of this experimental study indicate that the carbonization conditions of the biomass affect the structure and surface morphology of the biochar and consequently its thermal properties. Amongst the carbonization conditions that were investigated in this study, a peak temperature of 800 °C with a heating rate of 2.5 °C/min yielded a biochar with an energy storage capacity of 508 J/g. This biochar was then used as a matrix for fabricating the composite TESM with salt hydrate. The composite showed high thermal stability after ten hydration/dehydration cycles with an average thermal energy storage capacity of 3795 J/g. The cost of thermal energy storage in this composite was found to be $0.50 CAD /kWh_th.