Expanded graphite@octadecanol composite phase change material with photothermal conversion interface

•A hydrangea-shaped CuS was successfully synthesized and uniformly loaded onto cotton yarn to prepare an interfacial material with a photo-thermal conversion function.•18 wt%EG-OC has excellent thermal storage performance and photo-thermal conversion efficiency with phase change enthalpy of 366.8 J/g, thermal conductivity of 2.90 W·m−1·K−1 and photothermal conversion efficiency of 75.11%.•18 wt%EG-OC has excellent shape stability, can be bent and deformed arbitrarily under external forces, and has a certain flexibility. In this study, a CuS with a flower ball shape was synthesized and loaded onto cotton yarn to develop a photosensitive interfacial material with excellent photothermal conversion properties. Four composite phase change materials were prepared by compounding different ratios of expanded graphite (EG) with 1-octadecanol (OC). Finally, four sandwich-shaped photothermal CPCMs with different parameters (6 wt%EG-OC, 12 wt%EG-OC, 18 wt%EG-OC and 24 wt%EG-OC) were prepared by constant pressure molding with cotton yarn loaded with CuS as the outer layer and expanded graphite-octadecane as the sandwich layer. As a safe and stable low-temperature phase change material, OC has great potential for applications such as energy saving in buildings, domestic hot water supply and body heat management. The photothermal CPCMs developed in this study have good thermal storage performance, photothermal conversion efficiency, and thermal stability. The experimental results showed that the enthalpy of melting of 6 wt% EG-OC was 337.8 J/g, the thermal conductivity of solid 24 wt% EG-OC could reach 3.43 W·m−1·K−1, and the photothermal conversion efficiency of 24 wt% EG-OC was 75.92%. A typical daily amount of solar radiation can be stored using 27.19 g (58.01 m3) of 18 wt% EG-OC. This work provides a valuable reference for the study of solar thermal storage applications.