Effect of introducing chemically activated biochar as support material on thermal properties of different organic phase change materials.

Chemically activated biochar with richer pore structure and higher specific surface area is well suited for loading phase change materials (PCMs). However, the effect of structural characteristics and abundant surface functional groups of chemically activated biochar on the thermal properties of PCMs has not been systematically investigated. Here, shape-stable samples were prepared by introducing biochar obtained by activation with different chemical reagents (ZnCl 2 , H 3 PO 4 , KOH, and K 2 CO 3) into three organic PCMs (paraffin, stearic acid, and polyethylene glycol). The results indicated that the biochar activated by KOH possessed the highest specific surface area of 1344.45 m2/g, followed by biochar activated by ZnCl 2 , H 3 PO 4 , and K 2 CO 3 of 1297.35, 1062.74, and 891.38 m2/g, respectively. The loading capacity of KOH-activated biochar was as high as 82.12 %, 83.13 %, and 80.81 % for the three organic PCMs, and the melting enthalpies of corresponding composite PCMs were 163.82, 168.54, and 139.96 kJ/kg. Additionally, the influence degree on the enthalpies of the three PCMs was only 10.84 %, 12.26 %, and 7.74 %, while that of ZnCl 2 and H 3 PO 4 -activated biochar was as high as 53.61 % and 44.22 %, 52.10 %, and 57.74 %, 55.35 % and 45.79 % indicating the two biochar were not suitable as support materials for PCMs. Moreover, ZnCl 2 -activated biochar has the most apparent upgradation on PCMs' thermal conductivity, which could increase the thermal conductivity of the three organic PCMs by 1.318, 1.34, and 1.229 times, respectively, followed by H 3 PO 4 , K 2 CO 3 , and KOH-activated biochar. • Chemically activated biochar had larger specific surface area. • Encapsulation capacity of KOH-activated biochar for organic were significant. • Influence degree of ZnCl 2 and H 3 PO 4 -activated biochar was obvious. • ZnCl 2 -activated biochar had the most apparent upgradation on thermal conductivity. [ABSTRACT FROM AUTHOR]