FeNC Electrocatalysts with Densely Accessible FeN<sub>4</sub> Sites for Efficient Oxygen Reduction Reaction
Yazhou Zhou, Guangbo Chen, Qing Wang, Ding Wang, Xiafang Tao, Tierui Zhang, Xinliang Feng, Kläus Müllen
Abstract
Abstract 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.