CoFe2O4/CoFe loaded 3D ordered hierarchical porous N-doped carbon for efficient oxygen reduction in Zn-air battery and hydrogen evolution

Abstract

Optimizing active sites and enhancing mass transfer capability are of paramount importance for the improvement of electrocatalyst activity. On this basis, CoFe₂O₄/CoFe nanoparticles (NPs) loaded N-doped carbon (NC) that featured with interconnected three-dimensional (3D) ordered porous hierarchies (3DOM FeCo/NC) are prepared, and its electrocatalytic activity is studied. Due to the open structure of 3D ordered macro-pores that greatly improves the mass transfer capacity of the catalytic process and enhances the utilization of active sites inside the catalyst, as well as the uniform distribution of Fe and Co bimetallic sites on the porous skeleton, 3DOM FeCo/NC exhibits superior bi-functional catalytic activities for both hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR). The overpotential of HER is lower than that of commercial Pt/C when performed at high current density (>235 mA cm⁻²) in 1.0 M KOH, and the half-wave potential (0.896 V) of ORR in 0.1 M KOH is also superior to that of 20% commercial Pt/C and most other similar catalysts. The effective utilization and synergistic effect of CoFe₂O₄ and CoFe hetero-metallic sites remarkably enhance the electrocatalytic activity. Furthermore, 3DOM FeCo/NC is assembled as an air electrode in Zn-air battery, and exhibits satisfactory maximum power density, open-circuit voltage, and charge/discharge stability over benchmark Pt/C + IrO₂. This work contributes new insights into the design of transition-metal-based multifunctional catalysts, and has great potential for energy conversion and storage.