Nano-Fe2O3 guided synthesis of an F,N-coordinated FeCo bimetallic catalyst via H2-mediated reductive pyrolysis for the oxygen reduction reaction

Abstract

To address the critical challenges of insufficient active site exposure, compromised stability, and sluggish mass transport kinetics in non-precious metal catalysts for the oxygen reduction reaction (ORR), a hierarchical FeCo bimetallic catalyst (FN/FeCoNC-H₂-700) was developed through synergistic engineering of ZIF-67 pyrolysis. This strategy integrates hydrogen-induced defect generation, F/N dual-heteroatom coordination, and temperature-controlled phase reconstruction. The introduction of hydrogen reduces Fe₂O₃ to generate highly dispersed Fe nanoparticles, which combine with Co and N to form a stable Co–Fe alloy and Fe–N active centers, concurrently enhancing the graphitization degree of the catalyst (I_D/I_G = 0.93). The synergistic strategy of F/N co-doping increases both the content of the primary active nitrogen-containing species (pyridinic-N) and the electrical conductivity of the catalyst (R_ct = 56.68 Ω). Controlled pyrolysis at 700 °C establishes a hierarchical micro-mesoporous architecture (811.7 m² g⁻¹), facilitating mass transport and active site accessibility. The optimized catalyst demonstrates exceptional alkaline ORR performance, with an onset potential (E_onset = 0.98 V) and a half-wave potential (E_1/2 = 0.88 V) surpassing those of commercial Pt/C, a near-ideal four-electron selectivity (n = 3.99), and remarkable durability (86.31% current retention after 86 400 s) and methanol tolerance. This work establishes a multiscale design paradigm for high-performance bimetallic electrocatalysts in energy conversion technologies.