Honeycomb-like single-atom catalysts with FeN3Cl sites for high-performance oxygen reduction

Abstract

The great interest of Fe-N/C based Zn-air batteries and fuel cells intrigues large numbers of studies on modulating the pore structure for fast mass transport and the electronic structure of atomic Fe centers for enhancing intrinsic activity for oxygen reduction reaction (ORR). A Zn-assisted strategy herein is developed to synthesize a honeycomb-like micro-nanoscale porous Fe-N/C catalyst with atomic FeN₃Cl active sites. Specifically, Zn-guided synthesis of honeycomb-like porous carbon supported ZnO, ZnO-templated assembly of hemin modified ZIF-8 on honeycomb-like carbon and Zn/ZnO-assisted pyrolysis of the ZIF-8 precursor are involved. The synthetic mechanism is revealed by in-situ transmission electron microscopy imaging and in-situ X-ray diffraction analysis. Density functional theory calculations demonstrate FeN₃Cl can prominently lower the ORR energy barrier on the Fe centers, greatly facilitating catalytic kinetics. Hence, high ORR performance, including half-wave potentials of 0.81 ​V in acidic conditions and 0.91 ​V under alkaline media, is achieved. Besides, Zn-air batteries and H₂-O₂ fuel cells base on the resulting catalyst are investigated, also exhibiting excellent battery/cell performances. This study provides a novel strategy for the preparation of honeycomb-like micro-nanoscale porous single-atom catalysts as well as a significant new insight on the catalytic mechanisms, helping to advance in energy devices.