Simultaneously Constructing Asymmetrically Coordinated Cobalt Single Atoms and Cobalt Nanoclusters via a Fresh Potassium Hydroxide Clipping Strategy toward Efficient Alkaline Oxygen Reduction Reaction

Single-atom catalysts based on metal–N–C constituents facilitate oxygen reduction reaction kinetics due to super-high atomic utilization efficiency. However, conventional isolated atoms suffer from coordination symmetry and make less use of electron interaction between adjacent metal sites, which severely impedes its electrocatalytic activity. In response, we creatively issue a feasible potassium hydroxide clipping strategy through breaking up partial Co–N bonding and reconstructing Co–Co coordination, thus simultaneously implanting abundant Co atomic clusters and Co single atoms (SAs) on the surface of covalent organic framework (COF)-derived N-doped carbon nanospheres, which are intertwined by surrounding carbon nanotube (CNT) networks. This elaborately designed Co_AC-SAs/N–C@CNT catalyst combines the benefits of the asymmetrically coordinated Co–N₂ configuration and Co–Co electronic interaction, which exert great influence on local atomic microenvironment of metal sites and, thus, efficiently modulate the electronic structure. Then, the optimized d-band center of Co centers contributes to weakening oxygen intermediate adsorption and to reducing the rate-determining step energy barrier. Meanwhile, because of the unique surface chelation mechanism between COF matrix and Co cations, the as-optimized Co centers are homogenously stabilized on the carbon outermost shell, further maximizing active sites efficiency. As expected, the Co_AC-SAs/N–C@CNT catalyst harvests superior oxygen reduction reaction catalytic kinetics in alkaline medium, surpassing the commercial Pt/C catalyst.