Pyrazine–nitrogen–rich exfoliated C4N nanosheets as efficient metal–free polymeric catalysts for oxygen reduction reaction

Herein, we for the first time demonstrate the synthesis of exfoliated C4N nanosheets via a top–down approach and exploit their use as a new class of organic polymeric catalyst for the oxygen reduction reaction (ORR). The obtained C4N nanosheets are semi–conductive with a small band gap of 1.41 eV and contain abundant pyrazine–nitrogen moieties uniformly distributed throughout C4N. Density function theory calculations reveal that the intramolecular charge transfer induced by pyrazine–nitrogen in C4N enables effective charge redistribution to activate the conjugated structure and facilitate the oxygen adsorption, while the exfoliated sheet–like C4N formation renders improved electrochemical active surface area and results in high exposure of active sites. As a result, despite the bulk C4N is not active, the sheet–like C4N yield markedly improved ORR performance, even on a par with the commercial Pt/C catalyst. Our recent findings not only enrich the family members of two–dimensional conjugated polymer nanosheets but also open up new opportunity to explore new metal–free organic polymeric materials for efficient oxygen reduction catalysis and beyond.