A thinned cross-sectional TEM sampl

A thinned cross-sectional TEM sample was prepared using a focused ion beam (FIB, Helios Pegasus). Electrochemical impedance spectroscopy (EIS) was used to evaluate the anti-corrosion performance of the Ce conversion coating and TiO2 photocatalytic layer. EIS was performed using a Gamry Reference 600 with PCI4 Controller (Gamry Instruments, Inc., USA) during immersion in 3.5% NaCl solutions. A three-electrode arrangement was used and consisted of a saturated calomel reference electrode, a graphite rod as the counter electrode, and the exposed sample as the working electrode with a surface area of 13 cm2. The impedance measurements were operated at an open circuit potential with applied 10 mV sinusoidal perturbations in the frequency range of 10−2 to 105 Hz with 10 steps per decade