Toward strategical bottom-up synthesis of carbon materials with exceptionally high pyrrolic-nitrogen content: Development of screening techniques

Abstract

Carbon materials with pyrrolic nitrogen are expected to be applied to electrodes and catalysts because of their excellent high charge density and reactivity. However, pyrrolic nitrogen is known to be easily decomposed or changed into other functional groups at high temperatures, causing difficulty in controlling the structure of carbon materials. In this study, carbon materials with exceptionally high percentages (maximum 94%) and contents (maximum 7.0 at%) of pyrrolic nitrogen were synthesized using brominated precursors with pyrrolic nitrogen at 873 K. The positions and the number of introduced bromo groups influenced percentages of pyrrolic nitrogen after carbonization. By combining density functional theory calculations and molecular dynamics simulation with a reactive force field (ReaxFF) in addition to experimental analyses, screening techniques of precursors for preparing carbon material with high percentages of pyrrolic nitrogen were developed. Also, it was revealed that the lowering carbonization temperature by brominating precursors was indispensable for protecting thermally unstable pyrrolic nitrogen and it was also revealed that the presence of bromo groups at the position of carbon atoms far from pyrrolic nitrogen in the precursor was the key to avoid formation of tertiary nitrogen and hydrogenation of pyrrolic nitrogen, resulting in the high percentage of pyrrolic nitrogen.