Molten NaCl‐Assisted Synthesis of Porous Fe‐N‐C Electrocatalysts with a High Density of Catalytically Accessible FeN4 Active Sites and Outstanding Oxygen Reduction Reaction Performance

Abstract Iron single atom catalysts (FeN 4 ) hosted in the micropores of N‐doped carbons offer excellent performance for the oxygen reduction reaction (ORR). Achieving a high density of FeN 4 sites accessible for ORR has proved challenging to date. Herein, a simple surface NaCl‐assisted method towards microporous N‐doped carbon electrocatalysts with an abundance of catalytically accessible FeN 4 sites is reported. Powder mixtures of microporous zeolitic imidazolate framework‐8 and NaCl are first heated to 1000 °C in N 2 , with the melting of NaCl above 800 °C creating a highly porous N‐doped carbon product (NC‐NaCl). Ferric (Fe 3+ ) ions are then adsorbed onto NC‐NaCl, with a second pyrolysis stage at 900 °C in N 2 yielding a porous Fe/NC‐NaCl electrocatalyst (Brunauer–Emmett–Teller surface area, 1911 m 2 g −1 ) with an excellent dispersion and high density of accessible surface FeN 4 sites (26.3 × 10 19 sites g −1 ). The Fe/NC‐NaCl electrocatalyst exhibits outstanding ORR performance with a high half‐wave potential of 0.832 V (vs reversible hydrogen electrode) in 0.1 m HClO 4 . When used as the ORR cathode catalyst in a 1.0 bar H 2 ‐O 2 fuel cell, Fe/NC‐NaCl offers a high peak power density of 0.89 W cm −2 , ranking it as one of the most active M‐N‐C materials reported to date.