Three-Dimensional Porous Fe-N-C Derived from Iron-Citrate-Functionalized Melamine Foam as a Highly Active Oxygen Reduction Catalyst for Zn-Air Batteries

A facile method to prepare Fe-N-C catalysts with a 3D porous structure is reported, where melamine foam is used as the self-sacrificed template, and citric acid (CA) and iron salts are used as the precursors. The morphology and chemical valence state of the surface elements of the catalyst are characterized. Cyclic voltammetry (CV), liner scanning voltammetry (LSV), and electrochemical impedance spectroscopy (EIS) are used to evaluate the catalytic performance on the oxygen reduction reaction (ORR). The catalyst CA-Fe/MF-N900 (calcinated at 900 degrees C) exhibits the best ORR performance. In alkaline electrolyte, the ORR current starts at 0.98 V versus reversible hydrogen electrode (RHE). The half-wave potential (E-1/2) is 0.83 V versus RHE, and the limiting current density reaches 5.3 mA cm(-2). After 1000 cycles, E-1/2 merely shifts negatively by 7 mV. The Zn-air battery fabricated with the CA-Fe/MF-N900 as the cathode catalyst displays outstanding discharging performance with peak power density of 158 mW cm(-2) and long-term stability. The enhanced catalytic activity can be attributed to the advanced 3D interconnected porous architecture of the Fe-N-C catalyst, which can not only accommodate abundant active sites but also significantly reduce the mass/charge transfer resistance.