Densely Populated Macrocyclic Dicobalt Sites in Ladder Polymers for Ultralow Overpotential Oxygen Reduction Catalysis

Abstract Dual-atom catalysts (DACs) with synergetic dinuclear active sites, have the potential to break the linear scaling relationship of the well-established single-atom catalysts for oxygen reduction reaction (ORR); however, the design of DACs with rationalized local microenvironment for high activity and selectivity remains a blind area and is great challenge. Herein, we reported a design of bisalphen ladder polymer with well-defined densely populated binuclear cobalt sites that in suit growth on Ketjenblack substrates (CoCo-BiSalphen@KB). The strong electron coupling effect between the fully-conjugated ladder structure with carbon substrates induces the low-to-high spin transition for the 3d electron of Co(II), activating O-O bond through the side-on overlapping and enhancing the electron transfer between the cobalt center and reactants/intermediates. In situ techniques and density functional theory calculations revealed the dynamic evolution of Co2N4O2 active sites and reaction intermediates. In alkaline conditions, the catalyst presented impressive ORR activity featuring an ultrahigh onset potential of 1.10 V and a remarkable half-wave potential of 1.00 V, insignificant decay after 30,000 cycles, which pushes the overpotential boundaries of ORR electrocatalysis to an unprecedented low level. This work provides a new platform for designing high-efficiency dual atom catalysts with well-defined coordination and electronic structures in energy conversion technologies.