Synergistically promoting proton-coupled electron transfer of oxygen reduction with dual atomic sites on high-curvature carbon onions for highly efficient Zn–air batteries

The oxygen reduction reaction is significantly important for metal-air batteries, yet the sluggish reaction kinetics limited by slow proton-coupled electron transfer has hindered their further application. Here, dual Cr and Fe atoms are incorporated into a high-curvature carbon nano-onion (Onion-CrFe_DSA) to demonstrate significantly synergistic regulation of proton generation and transfer from the dual catalytic centers. The electrochemical measurements confirmed that the dual-site configuration in Onion-CrFe_DSA could enhance the ORR performance with a half-wave potential of 0.916 V and a kinetic current density of 26.45 mA cm^-2. Besides, a high turnover frequency (TOF) of 7.44 s^-1 together with a high mass activity of 51.42 A mg_Fe^-1 are also achieved for the as-obtained dual atomic catalysts. A series of <i>operando</i> techniques, combined with density functional theory calculations, revealed that Cr atoms mainly contribute to water dissociation and proton transfer, while Fe atoms predominantly catalyze oxygen reduction and intermediate conversion. Moreover, the Onion-CrFe_DSA-assembled aqueous and quasi-solid zinc-air batteries achieve impressively high maximum power densities of 314.7 mW cm^-2 and 163.3 mW cm^-2, representing a top-tier Fe-based ORR catalyst. This work proposes a feasible way to enhance the ORR performance by engineering adjacent catalytic centers to cooperatively mediate the proton-coupled electron transfer.