Electrochemical Electron Transfer Heterogeneity on Polycrystalline Titanium

The electrochemical behavior of polycrystalline titanium (Ti) is important for applications in defense, energy, and biomedicine, yet the factors governing local electron transfer activity remain poorly understood. Here, voltammetric scanning electrochemical cell microscopy (SECCM) employing a 500 nm nanopipette was used to investigate the [Fe(CN) ₆ ] ^3−/4− redox reaction on passive Ti surfaces. Spatially resolved linear sweep voltammograms were correlated with colocated scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, and electron backscatter diffraction analyses. Three surface preparation methods—electropolishing, ion beam milling (IBM), and HF chemical etching—were examined to evaluate the influence of surface morphology and interface chemistry on electron transfer kinetics. In contrast to microscale measurements, nanoscale SECCM resolved local electrochemical heterogeneity across the Ti surface. No clear correlation was observed between electron transfer kinetics and grain orientation or grain boundaries, indicating that the ambient‐formed TiO _x passive film largely masks microstructural effects. Electropolished and IBM‐treated surfaces exhibited similar electrochemical behavior, whereas HF‐etched Ti showed substantially more negative half‐wave potentials and broader activity distributions, consistent with a more heterogeneous and electronically blocking passive surface. These findings highlight the dominant influence of surface preparation on the electrochemical properties of ambient‐formed TiO _x films.