High dispersion and oxygen reduction reaction activity of Co₃O₄ nanoparticles on platelet-type carbon nanofibers

In this study, platelet-type carbon nanofibers prepared by the liquid phase carbonization of polymers in the pores of a porous anodic alumina template were used to prepare the Co₃O₄/carbon electrocatalysts. For comparison, Co₃O₄ nanoparticles were also deposited on multiwall carbon nanotubes (MWCNTs). Both the nitrogen-free platelet-type carbon nanofibers (pCNFs) and the nitrogen-containing analogue (N-pCNFs) exhibited better dispersion and higher amount of deposited Co₃O₄ nanoparticles compared to the MWCNTs. In addition, many individual Co₃O₄ nanoparticles were deposited separately on pCNF and N-pCNF, whereas aggregated deposition was commonplace on MWCNTs. The results indicated that the side wall of the pCNFs, which consisted of carbon edge planes, was the preferential nucleation site of Co₃O₄ nanoparticles rather than the basal planes of carbon that predominated the surface of the MWCNTs. The oxygen reduction reaction (ORR) activity of the Co₃O₄/pCNF composite in 0.1 mol dm^-3 KOH solution was better than that of Co₃O₄/MWCNTs. The N-pCNF further enhanced the ORR activity of the Co₃O₄/pCNFs even though the dispersion and supported amount of Co₃O₄ nanoparticles were negligibly affected by the presence of the nitrogen species. Synergistic interactions of the Co₃O₄ nanoparticles with N-doped CNFs contributed to the increased ORR activity.