Highly porous chemically modified carbon cryogels and their coherent nanocomposites for energy applications

Abstract

Highly porous carbon cryogels with tunable pore structure and chemical composition were synthesized through controlled hydrolysis and polycondensation reactions using different chemicals as precursors and either NaOH or hexamine (C₆N₁₂N₄) as catalysts. Gelation was followed with freeze drying to preserve the highly porous structure during solvent removal and controlled pyrolysis of the organic hydrogels and subsequent optional activation was performed. In addition, two different approaches were taken to modify the surface chemistry of porous carbon to introduce nitrogen or nitrogen-boron, leading to different porous structures and surface chemistry, as well as electrochemical properties. These carbon cryogels have been characterized and studied for energy storage applications. Specifically, they have been investigated as electrodes for electric double layer supercapacitors, high energy and high power density lithium-ion batteries with vanadium pentoxide deposited inside the pores, porous media for natural gas (methane) storage at reduced pressure, and scaffolds for hydride nanocomposites for greatly improved hydrogen storage. The relationship between processing conditions, chemical composition, pore structure, and energy storage properties are discussed.