Magnetic-Field-Enhanced Oxygen Evolution in Yttrium-Doped CoFe 2 O 4 Langmuir–Blodgett Nanofilms

Abstract

Pure cobalt ferrite (CoFe2O4) and yttrium-doped cobalt ferrite (CoY0.2Fe1.8O4) nanofilms were fabricated using nanoparticles synthesized via a self-combustion route and assembled through the Langmuir–Blodgett (LB) technique. These nanostructured films were employed as anodes to investigate the effects of Y3+ incorporation in the structure and the application of an external magnetic field on the oxygen evolution reaction (OER). Transmission electron microscopy and X-ray diffraction confirmed a reduction in particle and crystallite size upon Y doping, while X-ray photoelectron spectroscopy evidenced Y3+ incorporation and partial cation redistribution within the spinel lattice. Magnetic measurements indicated ferrimagnetic behavior for both materials, with Y substitution decreasing the saturation magnetization and increasing the coercivity. The LB nanofilms exhibited homogeneous coverage and pronounced in-plane magnetic anisotropy, and were used as anodes for the OER in alkaline media. Y3+ doping significantly improved the OER activity by reducing the overpotential and charge-transfer resistance, whereas the application of a magnetic field further amplified the catalytic response (particularly under in-plane orientation) through the combined effects of spin polarization and Lorentz-force-induced magnetohydrodynamic convection. Remarkably, the magneto-enhancement observed in pure CoFe2O4 nanofilms was comparable to that achieved through Y doping, underscoring the potential of magnetic-field-assisted catalysis as a sustainable strategy to minimize reliance on rare-earth elements while maintaining high OER efficiency. Both electrodes maintained stable activity over prolonged cycling, confirming their structural and electrochemical robustness. This study highlights the dual role of rare-earth doping and magnetic-field effects in tailoring the spin, structural, and electronic properties of spinel ferrite nanofilms for next-generation energy conversion applications.