Anisotropic and Lightweight Carbon/Graphene Composite Aerogels for Efficient Thermal Insulation and Electromagnetic...

High-performance and lightweight carbon aerogels (CAs) have attracted considerable attention in various fields such as electrochemistry, catalysis, adsorption, energy storage, and so on. However, finding an environmentally friendly and efficient preparation method and achieving a controllable performance of CAs are still a challenge. Herein, a series of anisotropic carbon/graphene composite aerogels were synthesized by unidirectional freezing of polyamic acid ammonium salt/graphene oxide (PAS/GO) suspension followed by lyophilization, thermal imidization, and carbonization. The prepared aerogels presented a tubular pore structure oriented along the freezing direction. The GO dispersed in the polymer matrix reinforced the skeleton of aerogels, which significantly inhibited the volume shrinkage during the preparation process, thus giving low densities of 0.074-0.185 g cm^-3. In addition, the oriented pore structure endowed the composite aerogels with obviously anisotropic heat insulation performance. The radial thermal conductivity was as low as 0.038 W m^-1 K^-1 at the density of 0.074 g cm^-3. When the initial content of GO rose to 20 phr, the resultant aerogels exhibited a high electrical conductivity of about 0.77 S cm^-1 in the radial direction and the electromagnetic interference shielding effectiveness (EMI SE) reached 54.6 dB at the same time. Therefore, this study provided a facile and environmentally friendly method to prepare lightweight and anisotropic carbon aerogels.