Energy harvesting and storage blocks based on 3D oriented expanded graphite and stearic acid with high thermal conductivity for solar thermal application

Photothermal energy conversion and storage based on organic solid-liquid phase change materials (PCMs) show huge potential in conquering discontinuous solar irradiation. It remains a challenge to fabricate integrated devices that take excellent photothermal conversion, heat transportation and energy storage into account. Here, we construct 3D oriented expanded graphite (EG) by compression induced graphite sheet self-assembly, then load the stearic acid (SA) to form oriented PCMs. The in-plane thermal conductivity, thermal response and energy storage density of 3D oriented PCMs are better than those of non-oriented PCMs under the same graphite mass faction and packing density. When the EG content is 20 wt%, the thermal conductivity of the oriented PCMs is 34.2% higher than that of the non-oriented PCMs and latent heat maintains above 159.36 J/g. We further prepare energy storage bricks and coordinate the heat conduction of oriented EG perpendicular to the axial direction of copper tube. The photothermal energy conversion efficiency of the energy storage brick reaches 95.3%, and the average powers during charging and discharging process are 2.1 kW and 2.4 kW, respectively. The design method for solar energy storage device improves the photothermal conversion efficiency, thermal conductivity and energy storage of PCMs, provides a simple and economical strategy for large-scale photothermal applications.