Fe, N‑Doped Hollow Porous Carbon Spheres Decorated with Ultrasmall Co NPs as Efficient Bifunctional Electrocatalysts for Rechargeable Zinc–Air Batteries

Developing dual-function electrocatalysts that improve oxygen reduction/evolution reaction (ORR/OER) kinetics and durability is strongly desirable but still challenging. Herein, ultrasmall Co nanoparticles (NPs) embedded into hollow hierarchically porous Fe, N-codoped carbon spheres (denoted as Co/Fe-NC) are prepared through one-step pyrolysis of trimetallic ZnCoFe-ZIFs composites. The hierarchically porous structure of Co/Fe-NC demonstrates that the micropores possess strong capability to O₂ capture and contribute large specific surface area, the mesopores provide numerous channels for the electrolyte infiltration, and the hollow holes allow more available active sites when used as cathodes of Zn–air batteries (ZABs). Consequently, the optimized Co/Fe-NC catalyst demonstrates satisfactory activities with a half-wave potential (E_1/2 = 0.91 V) and onset potential (E₀ = 1.04 V), higher than that of the benchmark Pt/C catalyst (E₀ = 0.90 V and E_1/2 = 0.85 V) for ORR. Moreover, a rechargeable ZAB assembled by the Co/Fe-NC electrode displays a large specific capacity of 836.2 mA h g^–1, a power density of 136 mW cm^–2, and excellent durability (maintaining 99% of its initial activity after 1195 cycles). The outstanding catalytic activity of the Co/Fe-NC is attributed to its multicomponent active dopants (Co, Fe, and N), and hollow hierarchical porous nanostructure.