Superior oxygen reduction electrocatalysis enabled by integrating hierarchical pores, Fe3C nanoparticles and bamboo-like carbon nanotubes

Abstract

Hierarchical porous carbon nanostructures doped with nitrogen or other active elements have been demonstrated to be of importance in enhancing the oxygen reduction reaction (ORR) activity. However, their intrinsic limited active sites usually make them exhibit lower ORR activity than commercial Pt/C. In order to solve well this challenging issue, herein we develop a simple method for encapsulating more electrochemically active Fe₃C nanoparticles (NPs) into the channels of bamboo-like carbon nanotubes (bCNTs) with interesting 3D hierarchical micro-, meso- and macropores by impregnating the bCNTs with a Fe(NO₃)₃ solution, followed by the calcination of the composite under a N₂ atmosphere. The resulting bCNT/Fe₃C hybrid electrocatalysts with much more active sites exhibit excellent ORR activity in acidic media with the half-wave potential of 0.710 V comparable to the commercial Pt/C catalyst (0.782 V). Furthermore, they show very high ORR activity in 0.10 M KOH with the half-wave potential of 0.879 V, 67 mV more positive than that of the Pt/C catalyst. Most importantly, the as-prepared new catalysts are very stable for ORR in both acidic and alkaline solutions with almost no ORR polarization curve shift after 3000 cycles, much better than that of the Pt/C catalyst. To the best of our knowledge, our new bCNT/Fe₃C catalyst is the best non-noble-metal catalyst ever reported for ORR under both acidic and alkaline conditions. The present work highlights the important roles of introducing more stable Fe₃C NPs and hierarchical micro-, meso- and macropores as much more active sites in maximizing the ORR electrocatalysis performance.