Preparation and electrocatalytic performance of iron based nitrogen doped carbon nanotubes

Abstract

Polypyrrole coated carbon nanotubes (PPy/CNTs) were synthesized by the in-situ chemical polymerization of pyrroles on CNTs. Iron compounds were deposited on the PPy/CNTs to form an Fe-PPy-CNTs composite using ferrous ammonium sulfate as the iron precursor by liquid phase precipitation. Catalysts wherein iron-based compounds were loaded onto nitrogen doped CNTs (FeNCNTs) were prepared by heat treatment of the composites. X-ray diffraction (XRD) analysis shows that the heat treatment of Fe-PPy-CNTs caused the Fe3O4 in the composite to convert to Fe3N and Fe. The FeNCNT700 prepared at 700 °C contains Fe3O4 and Fe. We conclusively show that in both FeNCNT800 and FeNCNT900 that were prepared at 800 and 900 °C, respectively, Fe3N and Fe formed. With an increase in temperature the total amount of nitrogen in the FeNCNTs decreases and the nitrogen containing functional groups convert from pyrrolyic-N to pyridinic-N and graphitic- N. Electrochemical analyses show that the FeNCNT800 and FeNCNT900 that contain Fe3N exhibits good activity toward the oxygen reduction reaction (ORR). Compared with FeNCNT900, FeNCNT800 has better ORR activity and stability because of its larger specific surface area, higher nitrogen content and higher ratio of graphitic-N in the nitrogen containing functional groups. This enhances the oxygen adsorption ability of the catalyst and weakens the O―O bond.