The Role of the Magnetic Field Orientation and Strength on the Electrodeposition of Ni-Fe Bifunctional Electrocatalyst for Hydrogen Evolution Reaction and Oxygen Evolution Reaction

Ni–Fe alloys were prepared via electrodeposition from a citrate electrolyte under different magnetic field (MF) strengths (0.1 T, 0.3 T, and 0.5 T) and configurations parallel (B‖) and perpendicular (B⊥) to the electrode surface. The magnetohydrodynamics (MHD) induced by the magnetic field influences their structural, compositional, and electrocatalytic properties. The application of an external homogeneous magnetic field significantly altered the alloy morphology, composition, and crystallinity, which we investigated. Scanning electron microscopy (SEM) and X-ray fluorescence (XRF) studies reflected that moderate MF intensity (0.3 T) led to modest variation in Fe incorporation and produced smoother, denser, and more homogeneous Ni–Fe films, particularly under (B⊥), while high field strength (0.5 T) resulted in surface roughening and compositional nonuniformity. X-ray diffraction (XRD) confirmed that the perpendicular MF enhanced crystallinity and favored (111) and (200) texture growth, while parallel orientation led to weaker and broader diffraction peaks, providing less-ordered growth. Furthermore, slight variations in Fe content were observed with changes in magnetic field strength and direction. Electrochemical measurements demonstrated that the deposited Ni-Fe under various magnetic field conditions modulated both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) in 1 M NaOH. For HER, the lowest overpotential (η10 = −227 mV at 10 mA cm−2) and Tafel slope (120 mV·dec−1) were obtained for the deposited Ni-Fe under (B‖) at 0.1 T, while for OER, the best catalytic performance occurred for fabricated Ni-Fe alloy under (B⊥) at 0.3 T with an overpotential value of (η10 = 320 mV, Tafel = 202 mV·dec−1). The deposited Ni-Fe alloys under both orientations exhibited reasonable stability and durability during a prolonged operation process. Overall, the findings demonstrate that controlling magnetic field orientation and intensity during electrodeposition provides a versatile route to tailor the microstructure and optimize the bifunctional electrocatalytic performance of Ni–Fe alloys for the water-splitting reaction in an alkaline medium.