Salt melt synthesis of curved nitrogen-doped carbon nanostructures: ORR kinetics boost

摘要

Highlights•The pyrolysis of renewable chitosan dissolved in a salt melt of ZnCl2and LiCl is reported.•The process resulted in curved N-doped carbon nanostructers.•Chitosan carbonized without the melt possesses a plain structure.•LiCl in the empted pores (after ZnCl2evaporation ∼290°C) induces the compressive stress while cooling down to the room temperature.AbstractImplementing metal-free electrocatalysts for the oxygen reduction reaction (ORR) and revealing crucial chemical or topographical parameters driving their activity are vital for the development of power cells. The carbon-based catalysts are very often synthesized through carbonization of biopolymers, in particular, those one containing nitrogen groups such as chitosan. Unfortunately, the resulting carbonaceous materials usually lack specific porosity and exhibit low catalytic activity.Here, we demonstrate that pyrolysis of chitosan in a ZnCl2melt assisted by the presence of LiCl results not only in a highly porous activated carbon material with a specific surface area of 1317.97 m2/g and the total nitrogen content of 6.5%, but also induces unexpected curvature in the grown graphitic layers. This is the first work that shows curved graphene layers obtained from a biopolymer precursor by its pyrolytic decomposition in the melted salt media.On the other hand, a carbonaceous material obtained from chitosan but without the salts has very low specific surface area of 7.8 m2/g, possesses no specific structural features, and contains 4.7% of nitrogen.The electrochemical studies show, that the former material is highly active towards four-electron pathway of the ORR in terms of an onset potential (0.89 VvsRHE) and the turnover frequency (TOFmax = 0.095 e site−1 s−1).We attribute this high catalytic performance to the presence of the pyridinic and pyrrolic sites in the structure. The ORR kinetics is probably further promoted by curvature in the graphitic layers.