Thermal transport properties of all-sp2 three-dimensional graphene: Anisotropy, size and pressure effects

The thermal conductivities of the newly synthesized all-sp2 three-dimensional graphene are investigated by equilibrium molecular dynamics simulations in this work. It is found that the thermal conductivity parallel to the honeycomb axis direction (kz) is one order magnitude higher than that perpendicular direction (kxy). This anisotropy is explained by the direction-dependent effective elastic constants. For the size effects, the kxy is found to be independent of the hexagon size, while kz increases with it. Both kxy and kz are also validated by the nonequilibrium method. For the pressure effects, this study also reveals an unexpected kz reduction with increasing pressure. A critical pressure is found to be 0.65 GPa. Beyond this critical pressure, the three-dimensional graphene breaks its crystal symmetry, leading to the in-plane kxy becomes anisotropic and lower comparing to the three-dimensional graphene with no pressure. These investigations provide important guidance to develop all-sp2 three-dimensional graphene for energy storage, catalysis, and sensor applications.

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