Facile synthesis multifaceted Fe3O4 based on N‑Doped Porous Carbon frameworks for ORR / OER and study of an external magnetic field

Global efforts increasingly focus on developing advanced non-noble metal electrocatalysts for efficient Oxygen Reduction Reaction (ORR) and Oxygen Evolution Reaction (OER), crucial for energy conversion technologies. To address this, we synthesized a novel bifunctional electrocatalyst, Fe3O4 on nitrogen-doped carbon foam (Fe3O4/N-CF) via a very easy single-step pyrolysis of urea, glucose, and a ferric salt in NaCl salt as a template. The multifaceted Fe3O4 nanocrystals were thoroughly characterized by X-ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray Spectroscopy (EDS), and Transmission Electron Microscopy (TEM). This bifunctional Fe₃O₄/N-CF was evaluated for ORR and OER in alkaline media within a magneto-electrochemical system. The application of a magnetic field significantly enhanced the ORR performance, leading to a remarkable ∼50 % increase in current density. This enhancement is not solely due to the well-known magnetohydrodynamic (MHD) effect on mass transport. We observed a crucial kinetic influence, as evidenced by a reduction in the Tafel slope from -75.5 to -68 mV/dec and a positive shift in both the onset and half-wave potentials. This kinetic effect was prominent on the Fe₃O₄/N-CF catalyst, whereas the magnetic field only influenced the diffusion-limited current on the bare N-CF. For OER, the current density for Fe₃O₄/N-CF sharply increased (five-fold at 400 mT), while remaining unaffected on bare N-CF. The Fe₃O₄/N-CF exhibited a minimal bifunctional potential difference (ΔE) of 700 mV at 400 mT, comparable to benchmark catalysts (Pt/C for ORR and IrO₂ for OER, combined: 680 mV). These findings demonstrate a unique synergistic contribution from both paramagnetic O₂ molecules and the magnetic Fe₃O₄ electrocatalyst, highlighting the potential for magnetic fields to not only enhance mass transport but also to modulate reaction kinetics for improved electrocatalytic performance in practical applications.