Three-Dimensional Hollow Reduced Graphene Oxide Tube Assembly for Highly Thermally Conductive Phase Change Composites and Efficient Solar–Thermal Energy Conversion

Due to their extraordinary mechanical strength and electrical and thermal conductivities, graphene fibers and their derivatives have been widely utilized in various functional applications. In this work, we report the synthesis of a three-dimensional (3D) hollow reduced graphene oxide tube assembly (HrGOTA) using the same wet spinning method as graphene fibers. The HrGOTA has high thermal conductivity and displays the unique capability of encapsulating phase change materials for effective solar–thermal energy conversion. The HrGOTA comprises layers of moisture-fused hollow reduced graphene oxide tubes (HrGOTs), whose individual thermal conductivity is up to 578 W m–1 K–1. By impregnating 1-octadecanol into HrGOTs, a 1-octadecanol-filled HrGOT phase change composite (PCC) with a latent heat of 262.5 J g–1 is obtained. This high latent heat results from the interfacial interaction between 1-octadecanol and the reduced graphene oxide tube, as evidenced by the shifts in XRD patterns of 1-octadecanol-filled and 1-octadecanol/multiwalled carbon nanotube-filled HrGOTA samples. In addition, 1 wt % multiwalled carbon nanotubes are added to the PCC to enhance visible light absorption. Because of their high thermal conductivity and visible light absorption rates, these new PCCs display high solar–thermal energy conversion and storage efficiencies of up to 81.7%, commensurate with state-of-the-art carbon-based PCCs but with significantly lower carbon weight percentages.