The Fe₃C–Nx Site Assists the Fe–Nx Site to Promote Activity of the Fe–N–C Electrocatalyst for Oxygen Reduction Reaction

Fe–N–C materials containing Fe–N x sites have emerged as promising electrocatalysts to substitute precious metal Pt in oxygen reduction reaction (ORR). Nevertheless, in-depth understanding the origin of iron species in Fe–N x sites is essential for the design of promising performance catalysts. Herein, Fe–N–C material composed of Fe and Fe 3 C embedded in bamboo-like nitrogen-doped carbon nanotubes (Fe–Fe 3 C–NCT) have been constructed via a simple pyrolysis strategy and can be used as excellent ORR electrocatalysts. DFT calculations uncover that the interaction between Fe and Fe 3 C could promote the electron density of the center metal iron species, creating a stronger O 2 adsorption and faster ORR kinetics. Furthermore, the oxygen intermediates would more readily dissociate on the Fe–N x sites formed by the coordination of metallic Fe and N. Inspired by these structural characterizations, Fe–Fe 3 C–NCT exhibits a positive onset potential of 0.99 V (vs RHE) and a high diffusion-limited current density of 8.00 mA cm –2 toward ORR, accompanied by an outstanding stability (only 4 mV negative shift after 10 000 cycles). The primary Zn–air battery displays a power density of 195 mW cm –2 and an energy density of 840 mAh g –1 at 10 mA cm –2, much superior to Pt/C (123 mW cm –2, 647.7 mAh g –1 ).