Introduction of eicosane into biochar derived from softwood and wheat straw: Influence of porous structure and surface chemistry

Thermal energy storage using phase change materials (PCMs) has received great attention in a wide range of smart applications. However, the development of shape-stabilized organic composite PCMs is a significant barrier to further advancement. Herein we explore “green” composite PCMs using commercially available biochar materials, derived from two different biomaterials, wheat straw and softwood, at pyrolysis temperatures of 550 °C and 700 °C, and organic PCM, n-eicosane (ES), for efficient thermal energy storage applications. All the composite PCMs exhibited high thermal stability, medium thermal diffusivity, and good chemical compatibility with the composite constituents. Over the phase change temperature range 36.4–40.6 °C, the composite derived from wheat straw biochar pyrolyzed at 550 °C showed the largest latent heat storage capacity of 75.0 J/g due to the high mesopore content of its supporting structure, specific surface area, and active functional groups that enhance the capillary force during PCM adsorption. In contrast, softwood biochar produced at 550 °C had the lowest latent heat storage capacity of 52.0 J/g. The surface functionality, structural characteristics, type of biomaterials, intermolecular interaction between ES and biochars, and pyrolysis temperature play important roles in determining the thermal properties of the as-prepared composite samples.