Molecular template engineering hierarchical porous Fe–N-C with tunable Fe3O4 particle size for efficient oxygen reduction reaction

Abstract

Synergistic effect between M-N_X sites and M_XO_Y particles in hierarchical porous M–N-C catalysts holds great promises in boosting oxygen reduction reaction (ORR). In this work, 1,4-dicyanobenzene was utilized as a molecular template to prepare the hierarchical porous Fe–N-C catalysts with size-tunable Fe₃O₄ particles for enhanced ORR in Zn-air battery. The as-prepared Fe₃O₄#Fe–N/C_DB0.1 owned a half-potential of 0.90 V vs RHE, exceeding that of commercial 20%Pt/C (E_1/2 = 0.82 V vs RHE), showing a maximum power density of 321 mW cm⁻² in a homemade Zn-air battery. Density functional theory (DFT) calculations indicate that the electronic interaction between Fe₃O₄ and Fe-N₄ sites enhances the adsorption energy of *OOH, effectively optimizing the energy barrier for *O formation, significantly reducing the limiting energy barrier. Such superior ORR activity in Fe₃O₄#Fe–N/C originated from the optimized hierarchical pores and synergistic effect between Fe-N_X sites and Fe₃O₄ particles. This work provides a new and facile template strategy for engineering hierarchical porous carbon-based materials to achieve highly efficient catalytic reactions.