Aerogels based on carbon nanomaterials

Carbon nanomaterial-based aerogels have attracted significant interests from both academia and industry due to their extremely low bulk density, tunable surface functionality, high specific surface area, dielectric strength and thermal and electrical properties, and diverse applications. There is currently a lack of understanding of how processing factors would determine the structure-property relationships important to the wide applications of these aerogels. The present work thoroughly examines the preparation, structure, properties and applications of three types of aerogels. Firstly, we briefly review carbon aerogels prepared from the sol-gel of certain organic monomers, where the synthesis and processing conditions determine the structural features, such as pore volume and pore size distribution. Secondly, carbon nanotube (CNT) aerogels made by three methods are discussed to identify their relative advantageous over carbon aerogels in terms of electrical conductivity and mechanical robustness. Finally, graphene aerogels are reviewed, which can be prepared by four routes-template-directed CVD, in situ reduction assembly, template-directing assembly and cross-linking. In comparison with CNT aerogels, graphene aerogels can be made at lower manufacturing costs to achieve appropriate properties meeting various needs. The major applications of these aerogels include flexible energy storage devices and environmental applications, both of which exploit the key characteristics of carbon aerogels such as low density and high porosity, deformability, mechanical robustness, electrical conductivity, adsorption and electro-sorption. Challenges, research opportunities and future applications are also discussed.