铁基氮掺杂碳纳米管制备及其电催化性能

利用化学原位聚合法制备聚吡咯包覆碳纳米管, 然后以硫酸亚铁铵盐为铁前驱体, 采用液相沉淀法制备聚吡咯-碳纳米管-铁化合物复合材料(Fe-PPy-CNTs), 通过对复合材料Fe-PPy-CNTs 热处理, 成功制备出铁基氮掺杂碳纳米管催化剂FeNCNTs. X射线衍射分析表明, 热处理使Fe-PPy-CNTs 复合物中Fe₃O₄向Fe₃N和Fe转化, 700 ℃热处理制备的FeNCNT700中铁主要是Fe₃O₄相, 但也有Fe相. 800和900 ℃热处理制备的催化剂FeNCNT800和FeNCNT900则明显有Fe₃N和Fe形成. 随着热处理温度升高, FeNCNTs 催化剂氮含量降低, 其含氮官能团也由吡咯型氮向吡啶型和石墨型氮转化. 电化学分析表明, 含有Fe₃N 的FeNCNT800 和FeNCNT900催化剂具有明显的氧还原催化活性, 其中, FeNCNT800因其具有高的比表面积、高的氮含量和高比例的有利于增强氧吸附能力和弱化O―O键的石墨氮官能团, 而表现出优于FeNCNT900氧还原催化活性及稳定性.

Preparation and Electrocatalytic Performance of Iron Based Nitrogen Doped Carbon Nanotubes

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 ℃ contains Fe₃O₄ and Fe. We conclusively show that in both FeNCNT800 and FeNCNT900 that were prepared at 800 and 900 ℃, 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.