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.