Rationalization on high-loading iron and cobalt dual metal single atoms and mechanistic insight into the oxygen reduction reaction

Rational design of single-atom catalysts (SACs) with high metal loadings is essential to enhance the sluggish kinetics of oxygen reduction reactions in metal-air batteries and proton-exchange membrane fuel cells (PEMFCs). Herein, an effective plasma engineering strategy to construct Fe/Co dual single atoms densely dispersed on porous nitrogen-doped carbon nanofibers (Fe, Co SAs-PNCF) with a high mass loading of 9.8 wt% is proposed without any acid leaching. The electrocatalyst exhibits superior ORR performances in both alkaline and acidic media (e.g., Eonset = 1.04 V and E1/2 = 0.93 V). The N3-Fe-Co-N3 moieties are identified to be the main active sites by X-ray absorption spectroscopy (XAS) and density functional theory calculations. The in situ XAS and Raman spectroscopy quantitively reveal the decrease in oxidation states of Fe/Co and the increase in bond lengths of the Fe-N/Co-N in the N3-Fe-Co-N3 during the ORR. Benefitting from the high loading of single atoms and enhanced activity, the Fe, Co SAs-PNCF endows the Al-air batteries and PEMFCs with excellent discharge performances, demonstrating promising practical applications. [Display omitted] •The atomic N3-Fe-Co-N3 dual sites with a high mass loading of 9.8 wt% are achieved.•The mass loading is linearly correlated with the defect degree.•Dual single atom sites are confirmed by AC-STEM and X-ray absorption spectroscopy.•In situ XAS and Raman reveal that the N3-Fe-Co-N3 plays an active role for ORR.