One‐pot emulsion templating for simultaneous hydrothermal carbonization and hydrogel synthesis: porous structures, nitrogen contents and activation

Porous carbons are of interest for a wide range of advanced‐technology ‘green’ energy applications including fuel cells, hydrogen storage, supercapacitors and batteries. Functional groups, heteroatoms and a more accessible hierarchical porous structure would be advantageous for many of these applications. This paper describes the generation of carbonaceous monoliths with hierarchically porous structures and nitrogen functionalities by using a one‐pot, simultaneous combination of hydrogel synthesis and hydrothermal carbonization (HTC) that involves templating within high internal phase emulsions (HIPEs). A carbon monolith with a density of 0.058 g cm−3, a highly interconnected, bimodal porous structure and an apparent specific surface area (SBET) of 101 m2 g−1 was produced by carbonizing a HTC monolith based on 2‐hydroxyethyl methacrylate (HEMA) at 450 °C. SBET of 1540 m2 g−1 was produced through subsequent chemical activation with ZnCl2 at 700 °C, but the overall residual mass (Rm) was only 9 wt%. Direct chemical activation of the HTC monolith, on the other hand, generated SBET of 1250 m2 g−1 and an overall Rm of 28 wt%, corresponding to a higher apparent surface area per mass of HTC monolith. Carbon monoliths with N/C ratios of 0.09 and 0.07 were achieved using nitrogen‐rich monomers (acrylamide and vinylimidazole, respectively) as compared to the HEMA‐based carbon monolith with an N/C ratio of 0.03. This work demonstrates that the hierarchically porous structures and the chemical structures of these highly porous monoliths can be fine‐tuned by modifying the HIPE composition and/or the processing conditions. © 2021 Society of Industrial Chemistry. High internal phase emulsion templating, hydrothermal carbonization, hydrogel synthesis, carbonization and chemical activation generated hierarchically porous carbon monoliths, tunable nitrogen contents and high specific surface areas (to 1540 m2 g−1).