In this work, we developed a Fe₂O₃@ZIF-8 composite precursors and combined with a novel thermal activation treatment under an Ar/H₂ mixture atmosphere (i.e., forming gas), which successfully prepares a highly active Fe-N-C catalyst. ⁵⁷Fe Mossbauer spectroscopy analysis experimentally verified that the catalyst only contains S1 sites. The highly active Fe-N-C catalyst achieved exceptional ORR initial activity in acids, exceeding that of a Pt/C baseline catalyst (60 µg_Pt cm⁻²) in rotating disk electrode (RDE) tests. The MEA tests further verified that the Fe-N-C catalyst's activity is competitive with Pt/C cathode (0.1 mg_Pt cm⁻²) in the kinetic range. Notably, the catalyst demonstrated remarkable activity of 50.8 mA cm⁻² (@0.9 V_iR-free) under H₂-O₂ conditions, exceed the U.S. DOE target. As expected, the catalyst degraded significantly during the stability ASTs.

To increase S1 sites and address the stability issues, we further developed in-situ CVD methods to treat Fe₂O₃@ZIF-8 precursors under forming gas flow but with additional N/C precursors that was put at the upstream sides of the tube furnace. Therefore, additional nitrogen and carbon sources are added to the Fe₂O₃@ZIF-8 precursors during the thermal activation of catalysts. As a results, we can populate the intrinsically stable S2 sites to design highly durable Fe-N-C catalyst. The resulting catalyst presented outstanding stability in both RDE and fuel cell tests. The E_1/2 gained 21 mV after 100,000 cycles of accelerated degradation test (ADT), achieving 0.869 V_RHE at the end of the test, which is close to Pt/C (60 µg_Pt cm⁻²) in acid electrolyte. The current density of MEA at 0.8 V retained unchanged, and the peak power density increased from 454.0 to 512.0 mW cm⁻² in H₂-fuel cell after 30,000 cycles of AST.