Phthalocyanine-induced iron active species in metal–organic framework-derived porous carbon for efficient alkaline zinc–air batteries

Abstract

The oxygen reduction reaction (ORR) on the cathode is of great significance in fuel cells and metal–O₂ batteries, which is well demonstrated and highly efficient in nature. Herein, iron phthalocyanine (FePc) is encapsulated into the nanosized pores of a new porous metal–organic framework (MOF) of BMM-14 to give FePc@BMM-14. It shows a series of atomically dispersed Fe-based active species embedded into N-doped Fe@NC(x+y) samples after calcination, where x and y represent the FePc concentration and temperature, respectively. During pyrolysis, the rapid volatilization of Zn contents can further expand the framework to form more loose carbon nanomaterials with abundant active components, including FeN_x and ultrafine Fe-based nanoparticles. Compared to the state-of-the-art Pt/C, the obtained Fe@NC(10+900/1000) exhibits satisfactory ORR performance to give a large limiting current of −5.22/−5.16 mA cm⁻² (0.3 V vs. RHE), small Tafel slope of −51.1/−38.9 mV dec⁻¹, and excellent stability. Meanwhile, the assembled batteries based on the two above catalysts show high activity, indicative of being potential substitutes to those noble metals consolidated by the theoretical calculations. This work demonstrates phthalocyanine-induced Fe-based active species in MOF-derived graphitic carbon as efficient ORR electrocatalysts for zinc–air batteries, which can be extended into the reasonable design and preparation of cost-effective but highly efficient catalysts for various energy-related applications.