High cross-plane thermal conductivity in graphene films achieved via controlled thermal reduction of graphene oxide and embedding of multi-walled carbon nanotubes

The thermal conductivity graphene films using graphene oxide (GO) as the raw material experience an expansion in interlamellar spacing and weaker compactness attributed to the decomposition of oxygen-containing functional groups during thermal reduction. The process indirectly influences the cross-plane thermal conductivity (K_⊥), resulting in limitations for the potential applications. In this work, a graphene film with high K_⊥ value is achieved by integration of controlled thermal reduction of GO film and the strategic embedding multi-walled carbon nanotubes (MWCNTs) into graphene layers. The results demonstrate that a moderate thermal reduction rate (3 °C min⁻¹) helps to avoid excessive morphological evolution in GO. Simultaneously, the uniformly embedded MWCNTs network acts as bridging structures, which can effectively repair the point defects in graphene and significantly reduce the interlamellar interfacial thermal resistance. After optimization of the thermal reduction process and the MWCNTs loading, the K_⊥ value of the MWCNT-graphene film at room temperature is 23.28 W m⁻¹ K⁻¹, which is 4.82 times higher than that of pristine graphene. This work deepens the understanding of the GO thermal reduction process and offers valuable guidance for the design of advanced graphene composite films with superior cross-plane thermal management capabilities.