Tuning the spin state of the iron center by FePc/Mg(OH)2 heterojunction boosting oxygen reduction performance

Iron phthalocyanine (FePc) is a promising non-noble metal catalyst for oxygen reduction reaction (ORR). While, with the plane-symmetric FeN 4 site, the ORR activity of FePc is generally low due to its low ability to adsorb and activate O 2 . Herein, we anchor FePc on Mg(OH) 2 / N -doped carbon nanosheets building the ternary plate-like catalyst FePc/Mg(OH) 2 /NC. Theoretical and experimental results show that due to the formation of FePc/Mg(OH) 2 heterojunction, the electron spin state of the monodisperse iron active site ranges from medium spin (MS, t 2g 5 e g 1 ) to low spin (LS, t 2g 6 e g 0 ), enhancing the adsorption with oxygen-containing intermediates, thereby improving the dynamics of the oxygen reduction reaction. As a result, FePc/Mg(OH) 2 /NC catalyst exhibits an outstanding performance (E 0  = 1.02 V, E 1/2  = 0.91 V) for ORR, superior to the commercial Pt/C electrode (E 0  = 1.01 V, E 1/2  = 0.85 V) and FePc/NC (E 0  = 0.97 V, E 1/2  = 0.87 V) under the alkaline conditions. This work offers a new way for the rational design of effective Fe N C catalysts with the support of metal oxides/hydroxides.