Boosted Electrocatalytic Oxygen Reduction Performance of Porous Co-NC Catalysts by the Coexistence of Abundant Co-N₄ and g-N Sites

Cobalt nanoparticles on nitrogen-doped carbon substrates (Co-NC) are excellent oxygen reduction reaction (ORR) electrocatalysts. However, their use is still challenging due to cobalt nanoparticle agglomeration, low-content Co-N₄ active sites, and nonselective types of nitrogen coordination. In this work, enhanced ORR performance was achieved on porous Co-NC electrocatalysts with the coexistence of abundant Co-N₄ and graphitic-nitrogen (g-N) sites, which were prepared for the first time via zinc-mediated 2,6-diaminopyridine (DAP) composite pyrolysis. Thanks to the coexistence of Co-N₄ and g-N sites in this structure and large specific surface area, Co-NC(Zn12)-900 exhibited excellent ORR activity with a half-wave potential of 0.820 V and an onset potential of 0.861 V, which was comparable with the commercial Pt/C catalyst. Co-NC(Zn12)-900 exhibited significantly superior long-term stability compared to Pt/C. For the methanol tolerance test, the current decay performance on the Co-NC(Zn12)-900 catalyst was also considerably better when compared with Pt/C. In addition, the calculation of density functional theory suggested that the coexistence of abundant Co-N₄ and g-N enhanced the degree of 3d-orbital filling while reduced the on-site magnetic moment of the Co centers. This can improve the binding energy of ORR intermediates and thereby substantially intensify the intrinsic activity of the ORR. This work paved the way for applications of non-precious-metal catalysts in technologies associated with energy conversion.