NiCo@EG-based composite PCMs with boosted thermal conductivity and photothermal conversion efficiency for solar energy harvesting

The application of phase change materials (PCMs) in solar energy is hampered by challenges such as insufficient photothermal conversion efficiency, low thermal conductivity and leakage. In this study, a novel composite PCMs based on NiCo@EG were prepared to solve the problems of low thermal conductivity, high leakage rate and inefficient photothermal performance. The NiCo@EG is obtained through calcination of the product of Ni-Co-BTC in-situ on expanded graphite (EG). In the composite PCMs, the octadecanol (OD) acts as a latent heat storage unit, the EG retains its porous network structure as an encapsulating skeleton. The nickel and cobalt nanoparticles derived from Ni-Co-BTC bimetallic organic frameworks are uniformly fixed on the surface of the EG, which could not only construct multiple thermal conduction pathways, but also enhance the photon-trapping ability. Benefiting from the synergy effect of nickel, cobalt metal nanoparticles and EG, the prepared OD/NiCo@EG-550 composite PCMs display high latent heat (168.3 J/g), excellent photothermal conversion efficiency (98.71 %), and improved thermal conductivity of 12.873 W/(m·K). Furthermore, the composite PCMs demonstrate exceptional shape stability, thermal stability, and robust thermal reliability. In summary, the high-efficiency photothermal composite PCMs display significant potential in improving the utilization of solar energy.