Hierarchically Porous Hollow Carbon Spheres for Atmospheric-Pressure Impregnation of Phase Change Materials toward Solar Water Heating

Phase change material (PCM) leveraging solar energy for photothermal conversion and thermal storage represents a common research strategy. However, its practical application is constrained by low thermal conductivity, suboptimal photothermal performance, and the cumbersome vacuum impregnation process. Herein, we propose a novel functional composite PCM with high shape stability and superior photothermal conversion efficiency, comprising hierarchically porous hollow carbon spheres (HPHCS) and polyethylene glycol (PEG). HPHCS exhibits an exceptionally high specific surface area of 2399 m2/g. Its unique hierarchically porous structure enables stable 77 wt % PEG loading under atmospheric-pressure conditions, eliminating the strong dependence on time-consuming vacuum impregnation methods that typically exists for PCM loading in porous carbon matrices. Crucially, the composite PCM with 25 wt % HPHCS demonstrated a 116% enhancement in thermal conductivity compared to pure PEG10000. The unique hollow hierarchical architecture of HPHCS ensured exceptional encapsulation integrity for PEG, with thermal properties and microscopic morphology remaining essentially unchanged after 100 thermal cycles. The composite PCM exhibits excellent broadband light absorption and high photothermal conversion efficiency, demonstrating significant potential for solar water heating applications.