Integration of atomic Co-N₅ sites with defective N-doped carbon for efficient zinc-air batteries

Transition metal single-atom catalysts have attracted considerable attention for their applicability in electrocatalytic oxygen reduction reactions (ORR), but it is still very challenging to regulate the interaction between the active sites and oxygen-containing intermediates. In this study, atomically dispersed Co-N₅ sites integrated with defective N-doped carbon (Co-N₅/DHC) were developed using a facile templating approach, followed by NH₃ treatment. NH₃ can simultaneously etch inactive amorphous substrates on the surfaces of metal sites and construct intrinsic carbon defects, thereby increasing the number of both metal and metal-free active sites. By bridging the intrinsic carbon defects and metal sites, the optimized Co-N₅/DHC catalyst exhibited significantly improved electrocatalytic ORR performance compared to the pristine Co-N_x/HC sample (cobalt-nitrogen sites anchored on heteroatom-doped carbon). Density functional calculations revealed that the strong interaction between the Co-N₅ sites and carbon defects modified the electronic localization, thus optimizing the binding energy with oxygen-containing intermediates and resulting in significantly improved ORR catalytic activity with a half-wave potential of 0.877 V. In addition, a zinc-air battery assembled with the Co-N₅/DHC as the cathode achieves a maximum power density of 160.7 mW cm⁻² and affords a specific capacity of 766.2 mA h g_Zn⁻¹.