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The single‐atom Fe−N−C is a prominent material with exceptional reactivity in areas of sustainable energy and catalysis research. It is challenging to obtain the dense Fe‐N4 site without the Fe nanoparticles (NPs) sintering during the Fe−N−C synthesis via high‐temperature pyrolysis. Thus, a novel approach is devised for the Fe−N−C synthesis at low temperatures. Taking FeCl2 as Fe source, a hydrogen environment can facilitate oxygen removal and dichlorination processes in the synthesis, efficiently favouring Fe‐N4 site formation without Fe NPs clustering at as low as 360 °C. We shed light on the reaction mechanism about hydrogen promoting Fe‐N4 formation in the synthesis. By adjusting the temperature and duration, the Fe‐N4 structural evolution and site density can be precisely tuned to directly influence the catalytic behaviour of the Fe−N−C material. The FeNC‐H2‐360 catalyst demonstrates a remarkable Fe dispersion (8.3 wt %) and superior acid ORR activity with a half‐wave potential of 0.85 V and a peak power density of 1.21 W cm−2 in fuel cell. This method also generally facilitates the synthesis of various high‐performance M−N−C materials (M=Fe, Co, Mn, Ni, Zn, Ru) with elevated single‐atom loadings. [ABSTRACT FROM AUTHOR]

To achieve the Fe−N−C materials with both high activity and durability in proton exchange membrane fuel cells, the attack of free radicals on Fe−N4 sites must be overcome. Herein, we report a strategy to effectively eliminate radicals at the source to mitigate the degradation by anchoring CeO2 nanoparticles as radicals scavengers adjacent (Scaad‐CeO2) to the Fe−N4 sites. Radicals such as ⋅OH and HO2⋅ that form at Fe−N4 sites can be instantaneously eliminated by adjacent CeO2, which shortens the survival time of radicals and the regional space of their damage. As a result, the CeO2 scavengers in Fe−NC/Scaad‐CeO2 achieved ~80 % elimination of the radicals generated at the Fe−N4 sites. A fuel cell prepared with the Fe−NC/Scaad‐CeO2 showed a smaller peak power density decay after 30,000 cycles determined with US DOE PGM‐relevant AST, increasing the decay of Fe−NCPhen from 69 % to 28 % decay. [ABSTRACT FROM AUTHOR]