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-N_(2) 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 CoAC-SAs/N-C@CNT catalyst harvests superior oxygen reduction reaction catalytic kinetics in alkaline medium,surpassing the commercial Pt/C catalyst.