Accelerating the oxygen adsorption kinetics to regulate the oxygen reduction catalysis via Fe3C nanoparticles coupled with single Fe-N4 sites

• The single-atom Fe catalyst was synthesized by Fe 3 C|Fe-N 4 coupled sites on 1D and 2D doped-carbon structures. • The formed Fe 3 C|Fe-N 4 sites can positively regulate the electronic structure of the Fe center in the catalyst. • DFT calculations indicate that the adjacent Fe 3 C activated single Fe-N 4 sites accelerate the oxygen adsorption kinetics. • The catalyst assembled ZABs manifested a higher power density and better stability than the Pt/C-based ZABs. Manipulating the electronic structure of Fe-N 4 single-sites to accelerate the oxygen adsorption kinetics is a commendable approach to improve the oxygen reduction reaction (ORR) performance of single-atom Fe catalysts but remains a challenge. Here we propose an endogenous regulation strategy to in situ design the single-atom Fe catalyst (Fe 3 C@NCNTs) derived from 1,8-diaminonaphthalene, iron trichloride, and graphitic carbon nitride via Fe-N 4 single-sites strongly coupled with Fe 3 C nanostructures, in which the combination of 1D and 2D doped-carbon structures and the formation of Fe 3 C|Fe-N 4 coupled sites can endow the catalyst with a considerably enhanced electrocatalytic activity and remarkable cycling stability to the ORR in Zn-air batteries. Theoretical calculations further reveal that endogenous Fe 3 C nanostructures can effectively activate the atomically dispersed Fe-N 4 sites, narrowing the energy barriers of the rate-limiting steps of ORR to promote the ORR catalytic performance. This work provides an effective way to in situ tune the electronic structure of metal atoms to boost the ORR performance of single-atom catalysts for electrochemical energy systems.