Assisting Atomic Dispersion of Fe in N-Doped Carbon by Aerosil for High-Efficiency Oxygen Reduction
Tete Zhao, Anuj Kumar, Xuya Xiong, Mang Ma, Yiyan Wang, Ying Zhang, Stefano Agnoli, Guoxin Zhang, Xiaoming Sun
Abstract
Utilizing Zn as a “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 microscopy 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 the carbon substrate was attributed to the heavily doping N and rich oxygen dangling species at the 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) computations suggested that the dangling oxygen ligand on the Fe–N4 moiety could significantly boost the cleavage of OOH* and the reductive release of *OH intermediates, leading to the enhancement of overall ORR performance.