Voltage-controlled composition tuning of anodic oxide layers on alloy surface using anodization

• Selective anodic layer composition tailoring achieved via voltage tuning. • Voltage determines the dominant driver of anodic oxide formation. • Fe/Cr-rich spinels formed at high voltages in composition ratio-driven regime. • Al 2 O 3 -rich layers emerge at low voltages in oxidation tendency-driven regime. Anodization is a widely employed surface engineering strategy for improving comprehensive performance enhancement, particularly in single-component valve metals. In this study, we extend the anodization approach to a multicomponent system to enable compositional control of anodic layers. Using FeCrAl alloy as a prototype substrate, we demonstrate that the applied voltage can be used to modulate the electrochemical oxidation behavior of individual alloying elements. At high potentials (≥60 V), field-assisted ion mobility and composition ratio dominate, resulting in the preferential formation of Fe 3 O 4 and FeCr 2 O 4 phases, defined as the “composition ratio-dominant” regime. In contrast, lowering the voltage (≤30 V) leads to the introduction of transition and α-Al 2 O 3 phases, governed by the superior intrinsic oxidation tendency of Al, termed the “oxidation tendency-dominant” regime. While precise control of oxide architecture in complex systems also depends on factors such as electrolyte chemistry, alloy composition, and temperature, this work demonstrates that voltage alone can drive the formation of tailored anodic layers. This finding offers a broad applicability for designing compositionally selective oxides with strong potential for widespread impact through fields such as corrosion protection, catalysis, sensing, energy devices, and beyond.