FeNC Electrocatalysts with Densely Accessible FeN 4 Sites for Efficient Oxygen Reduction Reaction

The development of iron and nitrogen co‐doped carbon (FeNC) electrocatalysts for the oxygen reduction reaction (ORR) in proton‐exchange membrane fuel cells (PEMFCs) is a grand challenge due to the low density of accessible FeN 4 sites. Here, an in situ trapping strategy using nitrogen‐rich molecules (e.g., melamine, MA) is demonstrated to enhance the amount of accessible FeN 4 sites in FeNC electrocatalysts. The melamine molecules can participate in the coordination of Fe ions in zeolitic imidazolate frameworks to form FeN 6 sites within precursors. These FeN 6 sites are then converted into atomically dispersed FeN 4 sites during a pyrolytic process. Remarkably, the FeNC/MA exhibits a high single‐atom Fe content (3.5 wt.%), a large surface area (1160 m 2 g −1 ), and a high density of accessible FeN 4 sites (45.7 × 10 19 sites g −1 ). As a result, FeNC/MA shows a much enhanced ORR activity with a half‐wave potential of 0.83 V (vs the reversible hydrogen electrode) in a 0.5 m H 2 SO 4 electrolyte solution and a good performance in a PEMFC system with an activity of 80 mA cm −2 at 0.8 V under 1.0 bar H 2 /air. This work offers a promising approach toward high‐performance carbon‐based ORR electrocatalysts.