Catalytic Carbon Derived from the Pyrolysis of Ionic Liquids with/without Carbon Support
Authors: Poudel Pitambar , Marshall Aaron Timothy 
Published: December 2024

Carbon is an interesting material with important applications in both fundamental and applied research due to its wide availability in different physical forms, high electrical and thermal conductivities, chemical inertness, and low density.1–3 For example, carbon is commonly used as an electrode material for batteries4,5, supercapacitors6, and fuel cells7 as well as an effective support material for catalysis,8–11 gas storage12 and separation technologies.13 Conventionally, polymeric synthetic and natural precursors14–17 such as phenolic resins, heterocyclic compounds, polyacrylonitrile, coal and pitch are used to prepare carbon using high-temperature pyrolysis. However, this approach leads to crack and/or foam formation when attempting to coat substrates with carbon using this pyrolysis approach.13,14 Previously, high yields of nitrogen-doped carbon were efficiently formed from nitrile-functionalized ionic liquids (ILs) through precursor-controlled thermolysis.18 Herein, we develop a strategy of carbonization of our crosslinked nitriles containing IL samples at an optimized heating rate and with or without the addition of commercial carbon supports to obtain a higher yield of functional carbons for electrochemical applications.

To understand the influence of adding pre-made carbon supports, the carbonization of ILs is performed with and without carbon addition at 1000 °C at different heating rates. This method is important to tune the amount of carbon support with crosslinked ILs during their thermal carbonization at favorable heating rates. The influence of adding pre-made carbon, such as carbon black powder, graphene nanoplatelets, and diamond nanopowder, on the carbonization of ILs is also studied. Our thermal analysis demonstrates that carbonizing ILs in the presence of carbon support have mixed results, either increasing, decreasing, or not changing the yield of carbon from the ILs. Notably, our designed IL [{bis(dimethylamino)mono(allylmethyllamino)}cyclopropenium] [dicyanamide] exhibits a very low yield of carbon (almost zero) without adding carbon support, however in the presence of carbon support, the carbonization is catalyzed towards a higher yield due to formation of dimer or polymer from its fragments at ˃ 400 °C. It is also found that synthesized carbons are electrochemically active for [Fe(CN)6]4-/[Fe(CN)6]3- redox system and are further characterized by X-ray photoelectron spectroscopy, scanning electron microscopy/energy dispersion spectroscopy to confirm the presence of heteroatoms in the obtained carbon.

The outlook of this work is to design the correct recipe of ILs to effectively coat carbon- or graphite felts to produce active and heteroatom-doped carbon material on the surface of macroscopically porous carbon substrates. Such electrode materials can be used as electrocatalysts in desired applications such as supercapacitors19–23 and vanadium redox flow batteries.24–27 This comprehensive study also provides insights into the decomposition mechanism of task-specific ILs during pyrolysis and highlights the potential of resulting carbon materials for various applications, particularly in energy storage and catalysis.

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