Unveiling Low Temperature Assembly of Dense Fe‐N4 Active Sites via Hydrogenation in Advanced Oxygen Reduction Catalysts

Abstract 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‐N 4 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 FeCl 2 as Fe source, a hydrogen environment can facilitate oxygen removal and dichlorination processes in the synthesis, efficiently favouring Fe‐N 4 site formation without Fe NPs clustering at as low as 360 °C. We shed light on the reaction mechanism about hydrogen promoting Fe‐N 4 formation in the synthesis. By adjusting the temperature and duration, the Fe‐N 4 structural evolution and site density can be precisely tuned to directly influence the catalytic behaviour of the Fe−N−C material. The FeNC‐H 2 ‐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.