Single-atom cobalt with asymmetric coordination environment on ionic porous organic framework for efficient oxygen reduction

Precisely modulating active sites to achieve high-performance catalysts remains a significant challenge but is critical to metal-air batteries and fuel cells. In this study, core-shell structured Co-TPG-IPOF/KB containing single cobalt (Co) atoms are anchored onto a 1,3,5-triformylphloroglucinol (TPG)- based ionic porous organic framework (IPOF) coated on Ketjenblack carbon (KB) was prepared through in-situ Schiff-base condensation. Systematic experimental characterizations reveal that KB cores provide abundant mesopores and greatly increase the accessible surface area from 48 to 614 m 2 g -1 , and the Co 2+ active sites are asymmetrically coordinated and uniformly dispersed upon the surface rather than inside the bulk. These remarkable structures enable Co-TPG-IPOF/KB to exhibit excellent oxygen reduction reaction (ORR) performance with a half-wave potential of 0.842 V, superior durability and methanol tolerance, and a favorable four-electron (4e - ) pathway, and therefore Zn-air batteries catalyzed by Co-TPG-IPOF/KB achieved considerably improved maximum power density (189 mW cm -2 ), specific capacity (727 mAh g zn -1 ), and cycling energy efficiency, superior to the benchmark Pt/C catalyst.