A Fe Single Atom Seed-Mediated Strategy Toward Fe₃ C/FeNC Catalysts with Outstanding Bifunctional ORR/OER Activities

The discovery of low-cost and high-performance bifunctional oxygen electrocatalysts is vital to the future commercialization of rechargeable zinc-air batteries (ZABs). Herein, a Fe single atom seed-mediated strategy is reported for the fabrication of Fe₃ C species closely surrounded by FeN₄ C active sites with strong electronic interactions built between them and more importantly, creating optimized coordination environment, via subtly adjusting their ratio, for favorable adsorption energies of oxygen intermediates formed during oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Concretely, the voltage difference (ΔE) between the ORR half-wave and OER potential at a current density of 10 mA cm^-2 for the compositionally-optimized FeNC/Fe₃ C-op electrocatalyst is only 0.668 V, endowing itself one of the best bifunctional OER/ORR benchmarks. As a demo, ZABs assembled with FeNC/Fe₃ C-op as the air cathode deliver a remarkable specific capacity (818.1 mAh g_Zn ^-1 ) and a power density (1013.9 mWh g_Zn ^-1 ), along with excellent long-term durability (>450 h). This work extends the methodology to modulate the activity of FeN₄ C atomic site, undoubtedly inspiring wide explorations on the precise design of bifunctional oxygen electrocatalysts.