Two Types of Single-Atom FeN4 and FeN5 Electrocatalytic Active Centers on N-Doped Carbon Driving High Performance of the SA-Fe-NC Oxygen Reduction Reaction Catalyst

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 Xray photoelectron spectroscopy (XPS) and X-ray absorption near-edge spectroscopy (X-ANES) 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-N-4 (60%) and Fe-N-5 (40%). The SA-Fe-NC electrochemical catalyst presents high ORR activity (E-onset/E-1/2 = 1.04/0.88 V vs reversible hydrogen electrode (RHE) and J(L) = 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 g(Zn)(-1), a high energy density of 1048 Wh kg(Zn)(-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.