Variation of nitrogen species in zeolite-templated carbon by low-temperature carbonization of pyrrole and the effect on oxygen reduction activity†
Nitrogen-doped microporous carbons with various compositions of pyridinic, pyrrolic, and graphitic N species were synthesized by the pyrolysis of pyrrole using Ca2+ ion-exchanged Y zeolite as a template. The Ca2+ ions in zeolite pores served as a catalyst to lower the carbonization temperature, resolving the problems associated with high carbonization temperature, such as inhomogeneous carbon deposition, easy breakage of weak C–N bonds, and preferential formation of thermodynamically stable graphitic N species. The resultant carbons exhibited a 3D microporous structure with high surface area and uniform micropore diameters, as well as high N content (5–6 wt%). Taking advantage of the lowered carbonization temperature, the ratio of the N species was modulated by the carbonization temperature, while a similar pore structure of the carbons was maintained. These N-doped carbons were used to investigate the efficiency of each N species on the electrochemical oxygen reduction, without the influences from the porous structure of the carbons. The results of this electrochemical investigation indicate that the graphitic N was more effective in enhancing the oxygen-reduction performance of the 3D microporous carbons than pyridinic N.