Iron Oxide Nanoclusters Incorporated into Iron Phthalocyanine as Highly Active Electrocatalysts for the Oxygen Reduction Reaction

摘要

Iron-nitrogen-carbon (Fe-N-C) composites have emerged as active and non-precious-metal electrocatalysts for the oxygen reduction reaction (ORR). Here, we developed a simple process to synthesize FeOx nanoclusters (NCs) incorporated with iron phthalocyanine (FePc) supported on graphene (FeOx/FePc) as highly active electrocatalysts for the ORR by a self-assembly method. The electrochemical activity of FeOx/FePc depends on the loading or size of the FeOx NCs. The best results are obtained on FeOx/FePc with 10wt% FeOx NCs of a size of approximately 2nm and a thickness of approximately 0.6nm, which achieves a half-wave potential of 0.888V and current density of 37.6Ag(-1) at 0.9V (vs. the reversible hydrogen electrode). This is 50mV higher than that of FePc supported on graphene and 64mV higher than that of Pt/C in 0.1m KOH solution at a catalyst loading of 0.1mgcm(-2). X-ray absorption spectroscopy and electrochemical cyclic voltammetry results indicate that the incorporated FeOx NCs interact with the active center of FePc, Fe-N-4, to enhance the electron transition and reversibility of the Fe-III/Fe-II redox couple and promote the kinetics of the ORR. We demonstrate that the nature of the active center of FePc (i.e., Fe-N-4) is related closely to the activity of the Fe-III/Fe-II redox couple.