Lorentz Force-Assisted Growth of Romanesco-Like Ni-Fe Nano-Cone Arrays for Enhanced Oxygen Evolution Reaction at High Current Densities

Abstract

Water splitting for producing green hydrogen has been broadly regarded as a major building block for the future sustainable society. Most current studies focus on enhancing the oxygen evolution reaction (OER) rate and catalytic activity by electrodepositing catalysts with various morphologies, while few address the issue of catalyst bubble realease, especially under high current densities where mass transport becomes critical. This study presents a novel approach to fabricate hierarchical Romanesco-like nickel-iron nano-cone arrays (R-NiFe NCAs) via Lorentz-force-assisted electrodeposition under an external magnetic field. This process introduces a high density of line defects to enhance the stability of the cone structure while enriching the surface with step edges and directing the crystal phase evolution towards more stable (111) and (220) facets. The hierarchical nano-cone array exhibits excellent wettability and efficient bubble release properties. Experimental results demonstrate that the R-NiFe NCAs achieve an overpotential of only 199 mV at 10 mA cm-2 and 375 mV at 100 mA cm-2 for OER. When integrated into an anion exchange membrane water electrolyzer (AEMWE), the system remains stable for over 600 hours at a current density of 1 A cm-². Comparative studies of different nano-cone morphologies further confirm the positive role of the Romanesco-like nano-cone with richer surface structure in improving mass transfer, wettability and bubble release.