Controlled Synthesis And Performance Studies Of The Anisotropic Graphene Aerogels

Graphene aerogels exhibit not only the properties of traditional aerogels(low density, large open pore, high specific surface area, etc), but also the characteristics of graphene, such as excellent mechanical property, high electrical and thermal conductivity, possessing potential applications in the fields of energy storage/conversion, catalysis, environmental remediation, and sensing devices, etc. This work focuses on the ordering phase-transformation from liquid phase into the 3D solid graphene porous materials; controlled synthesis, performances and applications investigation of the anisotropic graphene aerogel. Based on the graphene oxide liquid crystal(GO-LC), we introduced the hydrogen bond promoter by vapor diffusion into the GO-LC, and then synthesized a series of anisotropic graphene aerogels(AN-GAs) with aligned porous network. Physical properties and practical performances of the AN-GA have also been analyzed in detail. The main results are summarized as follows:(1), The ordering phase-transformation from graphene oxide liquid crystal into 3D ordered solid materials was realized and the macroscopic ordered GO hydrogels/aerogels were obtained. A new sol-gel process was proposed by introducing hydrogen bond promoter into the GO-LC system via the vapor diffusion method, where dynamic hydrogen bond networks will be in situ “freezed”. The sol-gel process, the alignment of porous network, and the aligned arrangement of graphene sheets were confirmed by Micro-IR、POM、TEM、 SEM、Raman、XRD and Compression test, etc.(2), Based on the uniform gelation of GO-LC with the solid hydrogen-bonding network, we designed and obtained the anisotropic graphene aerogel by introducing the situ-reduced process via the ion diffusion. The AN-GA posses aligned porous network(aligned pore channels/walls) and can exhibites different macroscopic shapes and direction-related properties, optimizing the exhibition of the graphene in macroscopic materials. SEM、TEM、XRD and Raman were used to characterized the arrangement of graphene sheets and the porous network; Compression test, LFA and Four-probe method were conformed to the anisotropic properties, such as the mechanical, thermal conductivity and electronic conductivity, the corresponding working-model was provided to explain the principle of the anisotropic properties. The aerogels exhibit high thermal conductivity(1.9 W/m K) and electron conductivity(345 S/m) in the axial direction, 8-9 times of the thermal conductivity and 4-5 times of the electron conductivity in the radial direction. Furthermore, the AN-GA has the fast electron-thermal and photo-thermal effect, and can be served as a multi-functional molecular heater.(3), The electron- and photo- driven phase change composites(PCCs) can be obtained by introduce the paraffin into the AN-GA, the PCCs exhibit high crystalline, anisotropic thermal conductivity, high latent heat, excellent reversibility and stable shape, etc. SEM and XRD were used to investigated the structure of the PCCs; TG and DSC were used to characterize the thermal properties(thermal conductivity, latent heat, phase change behavior, and its reversibility, etc) of the PCCs, and a high thermal conductivity(2.99 W/m K) in the axial direction was obtained, about three times of the radial direction. Furthermore, we design and obtained the different energy system for different latent heat storage types depending on the anisotropic thermal properties and structure: selected the cylindrical PCCs for electron-heat(85%) by used the high thermal/electron conductivity during the aligned pore walls of AN-GA; selected the rectangle PCCs for photo-heat(77%) conversion and storage by used the 2D plane of graphene in AN-GA that have a high photo receive area.