Atomic Engineering of 3D Self-Supported Bifunctional Oxygen Electrodes for Rechargeable Zinc-Air Batteries and Fuel Cell Applications

The oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are cornerstone half reactions involved in many renewable energy technologies. High-density single-atom catalysts maximize the atom utilization and isolated active sites. Furthermore, introduction of pyri-N into the carbon-based nanostructures as an oxygen electrocatalyst creates an abundance of active sites. Here, an innovative strategy is reported based on atomic scale dispersion of Co atoms into the pyri-N enriched carbon nanotube encapsulated Ni nanoparticles grown on 3D electrospun carbon nanofiber nano-assemblies. Notably, the Co_SANi-NCNT/CNF electrocatalyst exhibited excellent OER and ORR activity in terms of low overpotentials and higher half-wave potentials. The atomically distributed Co allows the maximum exposure of active sites on the pyri-N dominated multidimensional carbon skeleton, and synergistic effects with Ni nanoparticles greatly reduced the delocalization around the metal centers and provided an ideal environment for interactions with oxygen intermediates, thus facilitating the 4e⁻ pathway, as evidenced by the DFT calculations. Moreover, Zn-air batteries using a Co_SANi-NCNT/CNF air cathode exhibited a high-power density and admirable specific capacity. This studies may provide an avenue for the rational modulation of single-atom catalysts and cost-effective, large-scale synthesis of bifunctional oxygen electrocatalysts for rechargeable Zn-air batteries and anion exchange membrane fuel cell.