Densely populated macrocyclic dicobalt sites in ladder polymers for low-overpotential oxygen reduction catalysis

Dual-atom catalysts featuring synergetic dinuclear active sites, have the potential of breaking the linear scaling relationship of the well-established single-atom catalysts for oxygen reduction reaction; however, the design of dual-atom catalysts with rationalized local microenvironment for high activity and selectivity remains a great challenge. Here we design a bisalphen ladder polymer with well-defined densely populated binuclear cobalt sites on Ketjenblack substrates. The strong electron coupling effect between the fully-conjugated ladder structure and carbon substrates enhances the electron transfer between the cobalt center and oxygen intermediates, inducing the low-to-high spin transition for the 3 d electron of Co(II). In situ techniques and theoretical calculations reveal the dynamic evolution of Co 2 N 4 O 2 active sites and reaction intermediates. In alkaline conditions, the catalyst exhibits impressive oxygen reduction reaction activity featuring an onset potential of 1.10 V and a half-wave potential of 1.00 V, insignificant decay after 30,000 cycles, pushing the overpotential boundaries of ORR electrocatalysis to a low level. This work provides a platform for designing efficient dual-atom catalysts with well-defined coordination and electronic structures in energy conversion technologies.