Melt-salt-assisted direct transformation of solid oxide into atomically dispersed FeN4 sites on nitrogen-doped porous carbon

Emerging heterogeneous catalysts with metal atomically dispersed on supports (tentatively termed single-atom catalysts, SACs) exhibit many appealing features in a wide variety of catalytic reactions, such as high activity and nearly 100% atom utilization. However, the synthesis of SACs currently requires not only multiple procedures but also appropriate precursors with special structures. Herein, the molten-salt assistance is presented as an effective means that enables the use of common metal oxides (such as Fe2O3 and Co2O3) and small organic molecules as precursors for the preparation of carbon-supported SACs through one-pot pyrolysis. Molten salts as templates that can be easily removed after synthesis also contribute to the formation of porous and nitrogen-doped carbon with a high specific area. More importantly, benefiting from the strong polarizing force of molten salts, the ionic bonds in oxides can be destabilized at high temperature. Subsequently, metal ions released from solid oxides are transformed into atomically dispersed active sites after being trapped by nitrogen (N) atoms on the carbon support. The as-prepared SAC with atomically dispersed Fe–N4 sites demonstrates high activity, outstanding stability and good methanol tolerance in the oxygen reduction reaction (ORR) in both alkaline and acidic media.