Unravelling the High-Activity Nature of Fe-N-C Electrocatalysts for Oxygen Reduction Reaction: The Extraordinary Synergy between Fe-Nx and Fe4N

The scarcity and weak durability of precious metal catalysts are among biggest obstacles to achieving cost-effective electrocatalysts in fuel cells. Hence, it is imperative to develop low-cost non-precious metal catalysts with comparable oxygen reduction reaction (ORR) activity to the precious metal catalysts. Herein, we report a highly effective strategy for facile synthesis of Fe/N-functionalized 3D porous carbon networks. A major advantage of the newly designed catalyst is that ultrafine Fe4N nanoparticles are grown and uniformly mounted on the carbon framework upon pyrolysis treatment at 800 °C, and co-existing with numerous in-situ formed Fe-Nx moieties in the carbon matrix, being evidenced by using X-ray absorption and photoelectron spectroscopy. The new electrocatalysts yield high ORR activity, comparable/superior to that of the state-of-the-art Fe/N-carbon based catalysts reported to date. Specifically, the catalysts show a half-wave potential of 0.890 V and a limited current density of 6.18 mA cm-2, both surpassing the commercial Pt/C. By resorting to the experimental measurements and density-functional theory (DFT) calculations, the synergistic effects between Fe-N4 moieties and the Fe4N support are identified for the first time, which play a key role in boosting catalytic performance of the Fe/N-functionalized porous carbon networks.