Unravelling nanoporous anodic iron oxide formation

We studied the formation of self-ordered nanopores in the anodization of iron foils. Different anodization conditions (e.g. water content and applied voltage) were tested, and anodization curves were obtained for each case to establish the optimal parameters for fabricating homogeneous nanoporous films. Samples were characterized by Raman spectroscopy, X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, and high-resolution scanning transmission electron microscopy. Moreover, the bandgap of 2.1 ± 0.1 eV was measured in nanostructured films, and electrochemical impedance spectroscopy measurements were taken at each step. Finally, we propose a mechanism for the formation of iron oxide by anodization that takes into account the chemical reactions involved.The authors acknowledge the financial support of the Intramural Infante and MAT2017-86450-C4-3-R projects. The authors acknowledge the service from the MiNa Laboratory at IMN, and funding from CM (project SpaceTec, S2013/ICE2822), MINECO (project CSIC13-4E-1794) and EU (FEDER,FSE).Peer reviewe