Identical-Location SEM/EBSD Reveals Different Microstructure-Dependent Reconstruction of Fe, Co, and Ni Electrodes during Alkaline Oxygen Evolution Reaction

The oxygen evolution reaction (OER) on transition-metal electrodes involves dynamic surface reconstruction, but how the microstructure of metallic pre-catalysts controls this process remains insufficiently resolved. Here, polished polycrystalline Fe, Co, and Ni discs were investigated as alkaline OER anodes by tracking identical surface regions over 3000 activation cycles in 1 M KOH. Correlative identical-location scanning electron microscopy (IL-SEM) and electron backscatter diffraction (EBSD), including kernel average misorientation mapping (KAM), were complemented by energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and time-of-flight secondary ion mass spectrometry (ToF-SIMS) to link OER activation-induced surface restructuring with local morphology, crystallography, stored deformation, and near-surface chemistry. The three metals exhibited markedly different reconstruction pathways. Fe rapidly deactivated and developed a heterogeneous passivation layer thin enough to preserve EBSD visibility, consistent with dissolution/etching and patchy, non-continuous oxide formation. Notably, low-KAM {101} grains were affected the least. Co underwent largely microstructure-independent roughening and developed oxygen-rich micrometre-scale hexagonal platelets, consistent with Co hydroxide/oxyhydroxide formation via dissolution–redeposition, while retaining the EBSD signal after activation. In contrast, Ni formed a relatively thick, porous, large-scale interlaced nanosheet layer of Ni-based oxyhydroxide that completely blocked the EBSD signal, with film growth promoted at grain boundaries and modulated by crystallographic orientation. After activation cycling, the OER activity followed the order Ni > Co > Fe, with overpotentials of 261, 331, and 489 mV at 5 mA cm⁻², respectively. These correlative identical-location electron microscopy observations demonstrate that alkaline OER activation of Fe, Co, and Ni metallic anodes proceeds through distinct electrochemical reconstruction pathways involving different contributions from local oxidation, dissolution/etching, precipitation or redeposition, and porous oxyhydroxide growth. The local progression of these pathways can be governed by crystallographic texture, grain boundaries, and processing-induced deformation.