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

The thermal conductivities of the newly synthesized all-sp(2) 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 (k(z)) is one order magnitude higher than that perpendicular direction (k(xy)). This anisotropy is explained by the direction-dependent effective elastic constants. For the size effects, the k(xy) is found to be independent of the hexagon size, while k(z) increases with it. Both k(xy) and k(z) are also validated by the nonequilibrium method. For the pressure effects, this study also reveals an unexpected k(z) 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 k(xy) becomes anisotropic and lower comparing to the three-dimensional graphene with no pressure. These investigations provide important guidance to develop all-sp(2) three-dimensional graphene for energy storage, catalysis, and sensor applications. (C) 2016 Elsevier Ltd. All rights reserved.