Evaluating the energy consumption, structural, and corrosion resistance properties of photocatalytic TiO2-based PEO coatings on pre-anodized AA2024-Al

In this work, a thorough investigation is carried out to develop plasma electrolytic oxidation (PEO) coatings on pre-anodized AA2024-Al at various concentrations of TiO2 dispersed in a water base electrolyte of sodium silicate, sodium phosphate dodecahydrate, and potassium hydroxide in order to determine the effect of TiO2 incorporation on energy consumption, coating growth, surface morphology, photocatalytic behavior, and associated long-term corrosion resistance properties. The pre-anodization time is controlled to develop a 20.0 ± 1.6 µm thick anodic film, where a reduction of ∼66 % in the energy consumption (kW h m2 µm−1) is observed compared to the PEO developed without pre-anodic precursors, while the addition of TiO2 nanoparticles (Degusa-P25) into the base electrolyte results in reductions of ∼68 %, 64 %, and 51 % for the PEO coatings developed at 2, 5 and 10 g/L TiO2-based electrolyte, respectively. TiO2-based PEO process is found to improve growth rate, coating microstructure with lower porosity and defects, and reduce energy consumption (for a coating of a given thickness). The photocatalytic activity of TiO2 was investigated by photodegrading phenol under simulated sunlight conditions, where the higher concentration of TiO2 nanoparticles affected the phenol photodegradation efficiency, whereas the effectiveness of TiO2 concentration on the corrosion resistance properties of PEO coatings was observed with nearly one-order higher impedance magnitude (after 336 h) than the PEO layer without TiO2.