Ultrahigh specific surface area of graphene for eliminating subcooling of water

Graphene is widely utilized because of its exceptional properties, such as strong mechanical strength, low weight, nearly optical transparency, and excellent conductivity of heat and electricity. In this study, we used the ultrahigh specific surface area of graphene due to its inherently two-dimensional nature to reduce the subcooling of freezing of a phase change material. The results enable graphene's application in energy storage using the latent heat of phase transition. The need for subcooling to freeze water was eliminated completely with the suspension of a very low mass fraction (0.020 ± 0.001 wt%) or surface area concentration (0.070 ± 0.003 m2/ml) of graphene. Compared to nanoparticles of SiO2 and TiO2 with the same mass fraction suspended in water, flakes of graphene led to freeze water at a much smaller subcooling degree, and shorter total freezing time. The addition of surfactants can improve suspension stability and further reduce the degree of subcooling, but it also slightly increases the total freezing time. Graphene flakes are more suitable than spherical oxide nanoparticles for use as nucleating additives in water.