▎ 摘　　要

Thermal conductivities (k) of different graphene nanosheet (GN)-based heat sinks are investigated within the temperature range of 323-423 K. One- and two-step modified Hummers' methods are adopted to chemically exfoliate GNs from two kinds of carbon precursors: carbon nanotubes (CNTs) and graphite powders. The two-step method offers an improved exfoliation level of GN products, especially for the CNT precursor. Experimental results show that the GN-based heat sinkexfoliated from graphite powders after the two-step approachdelivers an enhanced k value to 2507 W/m K at 323 K, as compared to the others. The k value is found to be a decreasing function of the porosity of the heat sink, revealing the importance of solid/void fraction (i.e., volumetric heat capacity). The improved thermal efficiency mainly originates from the long phonon mean free path and the low void fraction of GN-based heat sinks, thus inducing highly efficient thermal transport in the GN framework.