Two Types of Single-Atom FeN<sub>4</sub> and FeN<sub>5</sub> Electrocatalytic Active Centers on N-Doped Carbon Driving High Performance of the SA-Fe-NC Oxygen Reduction Reaction Catalyst
Xiao Liang, Zeyu Li, Hong Xiao, Tengfei Zhang, Peng Xu, Hang Zhang, Qiuming Gao, Lirong Zheng
Abstract
A novel SA-Fe-NC single-atom catalyst is prepared via a spatial isolation strategy. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) analysis indicates that Fe atomically disperses on SA-Fe-NC. Both X-ray photoelectron spectroscopy (XPS) and X-ray absorption near-edge spectroscopy (XANES) analyses show that the Fe3+/Fe2+ ratio is 0.3/0.7. Extended X-ray absorption fine structure (EXAFS) fitting presents that the isolated Fe is coordinated with 4.4 N atoms on average, corresponding to the coexistence of Fe–N4 (60%) and Fe–N5 (40%). The SA-Fe-NC electrochemical catalyst presents high ORR activity (Eonset/E1/2 = 1.04/0.88 V vs reversible hydrogen electrode (RHE) and JL = 5.62 mA cm–2), superhigh durability (no obvious loss after 30 000 cycles), and absolute tolerance to methanol in alkaline media. The SA-Fe-NC-based primary Zn–air battery (ZAB) shows a high specific capacity of 806 mAh gZn–1, a high energy density of 1048 Wh kgZn–1, and a high power density of 164 mW cm–2 due to the high electrocatalytic activity of SA-Fe-NC. The ZAB shows a superlong lifetime of 320 h at 10 mA cm–2 resulting from the superhigh stability of the SA-Fe-NC catalyst.