Magnetic Modulation of Co(OH) ₂ Nucleation and Growth for High-Performance OER Electrocatalysis

As part of anthropogenic climate change mitigations against rising CO2 level, the transition to renewable energy sources relies heavily on scalable green hydrogen production via water splitting. Water oxidation, i.e., the oxygen evolution reaction (OER), often suffers from kinetic limitations, which can be overcome by applying an external magnetic field to enhance efficiency and yield. However, the specific effects of magnetic fields (MFs) on the electrodeposition processes of catalytic materials, such as ion movement and deposition kinetics, remain unclear. This study examines the effects of MF on ion movement, nucleation, growth, and deposition kinetics during electrodeposition of cobalt hydroxide (Co(OH)2) films and investigates morphological changes by combining theoretical models of nucleation and growth with electrochemical experiments. Structural analysis confirms that MF-assisted electrodeposition does not significantly alter the Co(OH)2 crystal structure. Instead, a magnetic field increases the nucleation rate and density, reduces charge-transfer resistance, and enhances double-layer capacitance. This indicates the improvement of ion transport and a thinner diffusion layer. MF-assisted films show higher roughness and increased porosity, enabling rapid bubble detachment, which, in turn, preserves the electrochemical active surface area. These results demonstrate a direct link between MF-controlled deposition dynamics, morphology, and improved OER activity, highlighting magnetic-assisted synthesis as a promising strategy for electrocatalyst development.