Fine Co nanoparticles encapsulated in N-doped porous carbon for efficient oxygen reduction

Nowadays, it has become necessary to develop a new green energy technology (such as fuel cells) to solve the energy crisis and environmental pollution. Because the oxygen reduction reaction is an important process of fuel cells, it is inevitable to develop a high efficiency catalyst for the reaction. Recent studies have found that agglomerated and over-sized metal nanoparticles may severely affect the oxygen reduction reaction activity of catalysts. In this study, through controlling the acid pickling time of Co@NPC, which is obtained by one-step calcination of ZIF-67 in N-2, a catalyst of fine Co nanoparticles encapsulated in N-doped porous carbon was prepared. Many characterizations, such as high resolution transmission electron microscopy, selected area electron diffraction, elemental mapping, and energy dispersive spectrometry, were performed, and the results indicate that the Co@NPC-acid pickling with a 12 h catalyst produced fine and uniform Co nanoparticles and a complete original frame structure. Although the method to prepare the catalyst is simple, the electrochemical characterizations of the two catalysts indicate that the electrocatalytic ORR performance of the Co@NPC-acid pickling is better than that of Co@NPC, and the Co@NPC-acid pickling with a 12 h catalyst can be comparable with that of the commercial Pt-C in an alkaline environment. In addition, the catalyst showed an excellent stability and methanol resistance than the commercial 20 wt% Pt-C.