High thermal conductive and photothermal phase change material microcapsules via cellulose nanocrystal stabilized Pickering emulsion for solar harvesting and thermal energy storage.

Phase change materials (PCMs) are promising for thermal energy storage due to their high latent enthalpy and constant phase change temperature. However, organic PCMs suffer from leaking, low thermal conductivity, and flammability. Herein, high thermal conductivity, photothermal and flame-proof docosane microcapsules with melamine-formaldehyde (MF) and polypyrrole (PPy) (C-CMFP) were reported with cellulose nanocrystal (CNC) stabilized Pickering emulsion droplets as templates through in-situ polymerization. CNCs showed outstanding C Pickering emulsifying ability with the presence of NaCl and provided ideal templates for C microcapsules. The obtained C-CMFP microcapsules displayed high enthalpy (205.7 J/g), C core ratio (86.1 %), and stability. The C-CMFP microcapsules retained an outstanding enthalpy remaining ratio (98.9 %) after 100 times cooling/heating cycles and could tolerate 100 °C for 12 h without leaking due to the robust hybrid CMFP shell. PPy significantly improved the thermal conductivity and photothermal conversion efficiency of C-CMFP microcapsules. The C-CMFP microcapsules exhibited a high thermal conductivity of 0.683 W/(m·K). The maximum temperature of C-CMFP microcapsules under light irradiation for 18 min was 60.4 °C. Moreover, C-CMFP microcapsules showed superb flame-proof properties. This study provides a facile approach to fabricate high enthalpy, stable, thermal conductive, photothermal, and flame-proof PCM microcapsules for solar harvesting and thermal energy storage.