Tailoring the hetero-structure of iron oxides in the framework of nitrogen doped carbon for the oxygen reduction reaction and zinc–air batteries

Abstract

Rationally constructing hetero-structures of iron species for efficient oxygen reduction reaction (ORR) remains challenging. Herein, an efficient and robust strategy has been developed for building and tailoring FeO_x/Fe hetero-structures. By tuning the temperature of H₂ treatment, highly dispersed FeO_x/Fe hetero-structures with controllable composition and multiple exposed crystal planes have been obtained to increase the electro-conductivity and hydrophilicity for efficient ORR. The resulting as-prepared Fe₂O₃@NC-450 exhibited remarkable ORR activity with an E_onset value of 1.001 V, E_1/2 of 0.838 V and limited current density of 6.71 mA cm⁻², which are superior to those of commercial 20 wt% Pt/C (E_onset = 0.994 V, E_1/2 = 0.828 V, 5.19 mA cm⁻²). Moreover, Fe₂O₃@NC-450 provided a high power density of 156.6 mW cm⁻², which is 2.3 times that of 20 wt% Pt/C (68 mW cm⁻²) in a zinc–air battery test. In addition, Fe₂O₃@NC-450 had a discharge time of 29 h, which is longer than that of 20 wt% Pt/C (23.5 h). This work provides an alternative efficient way to rationally construct hetero-structures of metal oxides and metal for next-generation ORR catalysts and metal–air batteries.