Pore Structures in Carbon Hydrogels and Aerogels

Hydrogels fabricated from natural and synthetic polymers are hydrated cross-linked networks having a wide range of chemical composition and applications. However, aerogels possess large volume, surface area, and porosity but low density in comparison to hydrogels. Carbon-based hydrogels and aerogels are broadly classified into different categories including graphene-based, polymers-based, carbon nanotubes, and biomass-derived materials. Generally, these are synthesized using hydrothermal reactions involving self-assembly, sol-gel method, and chemical cross-linking reactions. The method of synthesis may control the pore size. The hydrogels and aerogels possess numerous uniformly distributed pores over their surfaces ranging from macropores to nanopores. The pore structures in hydrogels and aerogels are generally determined using gas adsorption, scanning electron microscopy, mercury porosimetry, and thermoporometry. The porosity in hydrogels and aerogels can be tuned by controlling certain parameters including concentrations of polymer and cross-linker along with temperature. The interconnected porous structures of carbon hydrogels and aerogels make them promising materials in the areas of health, energy, and the environment. The recent progress of carbon hydrogel and aerogel in the market is mainly focused toward their green production. In the upcoming future, the demand for carbon aerogels in energy storage, electric vehicles, and high-performance composite materials is predicted to be increased to minimize emissions and to reduce dependence on conventional fuel. Currently, these materials find applications in water remediation, adsorption, drug delivery, catalysis, and thermal insulations owing to large active areas being exposed due to the presence of pores. The porous structures allow free charge and mass transfer, leading to efficient applications in supercapacitors. This book chapter focuses on pore structures in various carbon hydrogels and aerogels, the importance of various methods used for the determination of these pore structures, factors affecting the porous structures, and finally the discussion on potential applications of these materials owing to their porous infrastructure.