The Fe<sub>3</sub>C–N<sub><i>x</i></sub> Site Assists the Fe–N<sub><i>x</i></sub> Site to Promote Activity of the Fe–N–C Electrocatalyst for Oxygen Reduction Reaction
Ying Wang, Lei Wang, Ying Xie, Miaomiao Tong, Chungui Tian, Honggang Fu
Abstract
Fe–N–C materials containing Fe–Nx 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–Nx sites is essential for the design of promising performance catalysts. Herein, Fe–N–C material composed of Fe and Fe3C embedded in bamboo-like nitrogen-doped carbon nanotubes (Fe–Fe3C–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 Fe3C could promote the electron density of the center metal iron species, creating a stronger O2 adsorption and faster ORR kinetics. Furthermore, the oxygen intermediates would more readily dissociate on the Fe–Nx sites formed by the coordination of metallic Fe and N. Inspired by these structural characterizations, Fe–Fe3C–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).