Assisting Atomic Dispersion of Fe in N-Doped Carbon by Aerosil for High-Efficiency Oxygen Reduction - Carbon4Energy

Utilizing Zn as “fencing” agent has enabled the pyrolytic synthesis of atomically dispersed metal-nitrogen-carbon (AD-MNC) materials for broad electrocatalysis such as fuel cells, metal-air batteries, and water electrolyzers. Yet the Zn residue troubles the precise identification of the responsible sites in active service. Herein we developed a simple aerosil-assisted method for preparing AD-MNC materials to cautiously avoid the introduction of Zn. The combined analysis of extended X-ray absorption fine structure (EXAFS) and aberration-corrected high-resolution transition electron microscope verified the atomic dispersion of Fe species in the as-made Fe-NC sample with a well-defined structure of Fe-N4. Besides, the EXAFS studies indicated the formation of oxygenated Fe-N4 moieties (O-Fe-N4) after the removal of aerosil nanoparticles. Therefore, the immobilization of Fe atoms in carbon substrate was attributed to the heavily doping N and rich oxygen dangling species at aerosil surface. Electrochemical measurements revealed that the as-made Fe-NC material furnished with O-Fe-N4 moieties exhibited excellent oxygen reduction reaction (ORR) performance, characterized by individually indicating 22 mV higher half-wave potentials, with respect to commercial Pt/C catalyst. Density functional theory (DFT) calculations proposed that the O-dangling bond on Fe center, serving as a fifth coordination, could significantly boost the rate-limiting step of reductive release of *OH intermediates, leading to the enhancement of overall ORR performance.