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 ) hosted in the micropores of N-doped carbons offer excellent performance for the oxygen reduction reaction (ORR). Achieving a high density of FeN 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 sites is reported. Powder mixtures of microporous zeolitic imidazolate framework-8 and NaCl are first heated to 1000 °C in N , with the melting of NaCl above 800 °C creating a highly porous N-doped carbon product (NC-NaCl). Ferric (Fe ) ions are then adsorbed onto NC-NaCl, with a second pyrolysis stage at 900 °C in N yielding a porous Fe/NC-NaCl electrocatalyst (Brunauer–Emmett–Teller surface area, 1911 m g ) with an excellent dispersion and high density of accessible surface FeN sites (26.3 × 10 sites g ). 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 . When used as the ORR cathode catalyst in a 1.0 bar H -O fuel cell, Fe/NC-NaCl offers a high peak power density of 0.89 W cm , ranking it as one of the most active M-N-C materials reported to date. 4 4 4 2 2 4 4 2 2 3+ 2 −1 19 −1 −2