Approach of Designed Imidazole-like Active Sites of Graphitic Catalysts from Selected Sources towards Efficient Oxygen Reduction

Abstract

A novel method was carried out for investigating the growth of N-doped nanoporous graphitic structures from thermal pyrolysis. N-doped catalytic active centers were optimized by inheriting structure of 4-Methylimidazole.In three kinds of methylimidazoles, the weakest bond is between methyl and heterocyclic structure, according to calculation of bond energy by using density functional theory. Thus the methyl group was first broken in the pyrolysis, leading to they were prone to incomplete thermal pyrolysis, because the reaction time was only a few seconds in their floating catalytic pyrolysis; the rest of methylimidazoles formed clusters, and then their free radicals made clusters linked to graphitic structure, which led to 4-imidazole like (MIL) catalytic active centers formed. X-ray photoelectron spectroscopy analysis revealed that more than 50 % N-doped structure were imidazole-like structure among catalysts prepared from methylimidazoles. According to rotating ring-disk electrode tests and DFT calculations, the 4-MIL catalytic structure exhibited the highest catalytic activity among three catalysts prepared from methylimidazoles: the onset potential of 4MIL-GNCs was close to 20 % commercial Pt/C (0.94 V vs. 0.96 V (RHE)). The 4-MIL-GNCs had high electron transfer number (n=3.73) and high kinetic current density Jk = 7.12 mA cm-2 at 0.6 V; the rate determining step of 4-MIL-GNCs had the lowest energy barrier in oxygen reduction among catalysts prepared from methylimidazoles (0.67 vs. 0.79 and 1.16 eV).