Effects of reduction methods on the structure and thermal conductivity of free-standing reduced graphene oxide films

In this work, free-standing graphene oxide (GO) films obtained by vacuum filtration were reduced in HI acid or annealed in a confined space to form self-standing reduced graphene oxide (RGO) films. The effects of reduction methods on the reduction degree, microstructure and thermal conductivity of the RGO films were investigated. The RGO films obtained by thermal annealing have higher reduction degree than those treated with HI acid (55%) or treated with the combination of HI acid and 600 °C annealing. The X-ray pole figure measurements show that the orientation degree of GO films after reduction is degraded, and the HI acid reduction results in the worst oriented structure. The in-plane thermal conductivities of the RGO films obtained by thermal reduction are higher than those of films reduced by other methods due to their higher reduction degree and the resulting unfolded structure. However, the differences in the thermal conductivity of the RGO films obtained by thermal annealing at different temperatures are minor, even their reduction degree is enhanced with the increasing of annealing temperature, which is probably due to the generated interspaces between the graphene layers during reduction that greatly limit thermal transport.