Iron and nitrogen co-doped carbon nanotube@hollow carbon fibers derived from plant biomass as efficient catalysts for the oxygen reduction reaction

The present paper reports on the preparation of novel iron and nitrogen co-doped carbon nanotube@hollow carbon fibers (denoted as Fe/N/CNT@PCFs) by pyrolysis of the natural product catkin, FeCl₃ and melamine. The experimental results show that: (1) melamine and FeCl₃ doped into precursors have hugely enhanced the content of doped nitrogen in Fe/N/CNT@PCFs; (2) Fe elements have catalyzed the growth of abundant CNTs along both the inner and outer walls of Fe/N/CNT@PCFs affording abundant porous structures and a larger BET specific surface area; (3) Fe elements have also facilitated the transformation of inactive oxidized N species to the highly active pyridinic-N, pyrrolic-N, and Fe-N clusters for Fe/N/CNT@PCFs, thereby improving the ORR electro-catalytic activity of the as-prepared Fe/N/CNT@PCF catalyst. On the other hand, the typical RDE and RRDE detection results have proved that the ORR catalyzed by the as-prepared Fe/N/CNT@PCF catalyst is mainly by 4e^- reduction accompanying higher durability of the ORR electro-catalytic activity and more excellent methanol tolerance compared with the commercial Pt/C catalyst. The relatively simple synthesis approach, the cheap precursor materials, and excellent ORR catalytic efficiency of the Fe/N/CNT@PCF catalyst make it promising for low-temperature fuel cells.