G-C3N4 Facilitates MOF-Derived with an Ultra-High Fe-N4 Proportion for a Record-Low ΔE of 0.615 V in Single-Atom Catalyst for Rechargeable Zinc-Air Batteries.

In this study, an ultra-high Fe-N4 proportion single-atom catalyst (g-Fe SAC) was synthesized on nitrogen-doped porous carbon using ZIF-7-NH2 as the precursor material. Comprehensive characterization via spherical aberration corrected transmission electron microscope (AC-TEM) and extended X-ray absorption fine structure (EXAFS) confirmed atomic dispersion of Fe species and dominant Fe-N coordination configurations. Density functional theory (DFT) analyses demonstrated that thermally metastable FeN2/FeN3 intermediates undergo structural evolution into stabilized FeN4 motifs through interfacial interactions with g-C3N4-derived molecular frameworks. The Fe-N coordination environment demonstrates pronounced electron localization, resulting in a down shift of the D-band center phenomenon, which facilitates efficient electron transfer and optimizes the rate-determining step in both OER (O* → OOH*) and ORR (OH* → OH-). The potential difference ΔE is as low as 615 mV which represents the most recent record in single atom catalysis, and there are still three reported catalysts that exhibit superior performance compared to this work. However, when assembled into a battery, compared with the FeNC@LDH and FeCo-N3O3, this study shows better results in terms of the number of cycles (1200 cycles) at 10 mA·cm-2, and the reported peak power density of Bi-cat is also inferior to that observed in this research (222.39 mW cm-2) meanwhile.