A Universal Approach to Construct Surface-Enriched Metal-Nitrogen Sites in Carbon Matrix toward Oxygen Reduction

Metal-nitrogen (M-N) moieties are recognized as the most active sites in metal-nitrogen codoped carbon catalysts (M-N/C) toward the oxygen reduction reaction (ORR). Controllable construction of the M-N sites and effective exposure of them at the catalyst-electrolyte interfaces are critical for the high-efficiency electrocatalysis of oxygen reduction. Herein, a universal synthesis strategy is developed to construct surface-enriched and highly dispersed M-N sites of various metal centers (including Co, Fe, Cu, Ni, Mn, and Bi) in M-N/C by utilizing a prefabricated pyridine-nitrogen-rich carbon matrix to anchor the metal ions from the corresponding metal chloride vapors. All the as-synthesized M-N/C catalysts demonstrate outstanding ORR activities and excellent long-term stability, among which the optimized Co-N/C exhibits an exceptional ORR half-wave potential (E_1/2) of 0.900 V vs RHE (V_RHE) and only 6% current loss after testing at 0.60 V_RHE for 16 h in a 0.1 mol L^-1 KOH solution. This work opens new possibilities for the fabrication of high-performance M-N/C catalysts with various metallic centers or even multiple kinds of metallic centers for different applications.