The influence of passive film characteristics on the critical pitting temperature (CPT) of AISI 316 L stainless steel was investigated. The passive film was formed by potentiostatic polarization in 0.05 M H2SO4 at 0.4 V/SCE for 1 h, while the native film corresponded to the oxide present on freshly polished surfaces. The pre-formed passive film exhibited a higher CPT (similar to 47 degrees C) than the native oxide (similar to 27 degrees C), indicating enhanced resistance to chloride attack. XPS and ToF-SIMS revealed that both oxides possess a bilayer structure, consisting of an Fe-, Mo(VI)-, Ni-, and hydrated Cr-rich outer layer and an inner layer enriched in Cr oxides and Mo(IV). The passive film displays stronger Cr enrichment and improved chemical stability than the native film, which contributes to the higher CPT. ToF-SIMS 3D imaging further demonstrates that pit initiation is associated with nanoscale Fe-oxide clusters embedded within the inner layer, which serve as weak sites for localized breakdown. These inhomogeneities are significantly less prevalent in the passive film, and the presence of molybdenum appears to partially heal such weak spots, resulting in the observed shift of the critical pitting temperature to higher temperature.

The atomic-level structures and energetics of Fe/Cr2O3 and Fe/Fe2O3 metal/oxide interfaces have been investigated by DFT, including the effects of Mo substitution and oxygen vacancy formation. Close examination of Mo substitution revealed that Mo preferentially incorporates at Fe-rich zones and is more stably accommodated in Fe2O3 than Cr2O3. Oxide compression due to the metallic substrate significantly affects substitution energetics. Calculation of oxygen vacancy formation without and with substitution of iron or chromium cations by Mo revealed that the presence of Mo near oxygen sites raises the vacancy formation energies by about 0.3 eV, thus reduces the number of defects in the passive film, limits Cl- ingress (by diffusion in oxygen vacancies) and its ability to degrade the oxide, and therefore enhances corrosion resistance and passivity.. This work elucidates the thermodynamic interplay between spin configuration, oxide termination, Mo incorporation, and vacancy formation in determining interface stability and corrosion resistance of passive films.

The (100)-oriented Fe-18Cr-13Ni model 304 stainless steel surface was exposed to water vapour at very low pressure to study the initial stages of oxidation at room temperature (RT) and 250 degrees C. In situ X-ray photoelectron spectroscopy (XPS) during exposure showed a 2.5 times increase in the initial rate of oxygen uptake upon temperature increase. Angle-resolved high-resolution core-level spectra, recorded at various steps of the reaction, revealed only oxidation of Fe and Cr, leaving Ni unreacted. Growth models, deduced from the careful analysis of spectral changes during water vapour exposure, allowed an estimation of the oxide film thickness and structure. According to these models, at the end of primary growth, the surface is covered with one monolayer of oxide/hydroxide (0.21 +/- 0.02 nm) at RT, while at 250 degrees C, the passive film is twice as thick, with a higher oxide:hydroxide ratio. Compared to O2 exposure experiments performed on the same alloy, water vapour reacted 104 times slower than oxygen. The large reduction in reaction rate is possibly due to the limited dissociation of water on the stainless steel surfaces. This insight improves our fundamental understanding behind the passive film formation mechanism contributing towards producing improved corrosion-resistant surfaces.

This study investigates a mild alkaline post-treatment (pH 8-14) strategy to control the Cr(III)/Cr(VI) valence state within Trivalent Chromium Process (TCP) coatings on AA7B04 alloy and improve defect protection. The coating's composition, in-depth valence state distribution, defect response, and electrochemical behavior were characterized using Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) depth profiling, acetic acid salt spray (AASS) testing, electrochemical impedance spectroscopy, and potentiodynamic polarization. Density Functional Theory calculations were performed to interpret the pH-dependent valence transformation, and Life Cycle Assessment (LCA) was used to evaluate the environmental impact. Results show that while the as-prepared TCP coating contains only localized Cr(VI), the post-treatment at an optimal pH of 11 facilitates the uniform generation of CrO42-. XPS analysis indicates that a thickness weighted estimate gives a maximum Cr(VI) content of 0.19 at% in the TCP layer, with depth profiling confirming that the total Cr(VI) content remains well below REACH thresholds. Raman spectra collected after 7 d AASS exposure showed a stronger 856 cm-1 chromate-related band at the scratched region of the post-treated coating. Electrochemical measurements showed that the post-treated coating exhibited 5.2-fold higher film resistance and 5.6-fold higher charge-transfer resistance than the without post-treated TCP coating. The LCA further indicates within the scope of a comparative laboratory-scale assessment, the post-treatment introduced only a modest additional environmental burden, while the Cr(VI) complete-release is only 3.52 & times; 10-6 g per coupon. These results show that alkaline posttreatment is an effective route to regulate chromium valence and improve the protective performance of TCP coatings.

The influence of conversion time on polymeric speciation and protective performance of zirconium conversion coatings (ZrCCs) on aluminium alloy AA5754 was investigated using samples treated in 150 ppm H2ZrF6 at pH 4.6 for 230 s and 480 s. Characterisation combined time-of-flight secondary ion mass spectrometry (ToF-SIMS) with region-of-interest analysis, electrochemical impedance spectroscopy in dilute Harrison's solution after one hour, atomic force microscopy, and contact-angle measurements. ZrCC thickening is conversion-time-dependent, with a preference for growth above intermetallic particles. ToF-SIMS identified monomeric, dimeric, and trimeric zirconium hydroxide fragments, while tetrameric species were detected only at very low intensities, in contrast to previous observations on steel, possibly due to the lower overall pH increase during ZrCC formation. Despite the thicker layer obtained at 480 s, EIS indicated no improvement in corrosion protection compared with the 230 s. Morphological and wettability analyses further showed that the shorter treatment produced a rougher but more compact and uniform coating, which correlates with better short-term protective behaviour. These findings emphasise that compactness and uniformity, rather than thickness or wettability, govern the early protective function of ZrCCs and raise the question of whether tetrameric polymeric forms are required to establish a protective layer, as hypothesised for cold-rolled steel. ToF-SIMS shows ZrCCs contain monomeric, dimeric and trimeric Zr polymeric species.The corrosion performance of ZrCCs matches that of uncoated samples due to cracking near IMPs.A shorter conversion (230 s) yields higher roughness than a longer conversion (480 s).The contact angle shifts from complete wetting to moderate hydrophilicity upon drying.ZrCCs' performance depends more on compactness than on wettability.

Corrosion inhibition of metals in aggressive environments remains a key challenge. Organic inhibitors, especially those with nitrogen, oxygen, or sulfur atoms, are widely studied for their strong adsorption and protective film formation. This review summarizes the classification and adsorption mechanisms of organic inhibitors, followed by recent advances in surface analysis techniques such as AFM, STM, XPS, ToF-SIMS, and Raman spectroscopy, which offer molecular-level insights into inhibitor–metal interactions. Despite progress, challenges remain in capturing dynamic interfacial processes under realistic conditions. Future perspectives highlight the integration of experimental techniques with computational modeling and the development of in-situ platforms for improved inhibitor design.

A mechanism for transpassive film formation in pure Ni in a sulfate environment is proposed based on in situ Raman spectroscopy and electrochemistry-coupled respirometry. Based on potentiostatic respirometry on pure Ni in 0.1 M K2SO4, there is a characteristic time-delay before the onset of oxygen evolution, coinciding with the onset of transpassive film formation upon stepping the potential from passive into the transpassive regime. At the same time, in situ Raman spectroscopy revealed that the transpassive film comprised of NiOOH. It reduced back without any time-delay after returning to open-circuit conditions to a passive Ni(OH)2.

Atomic-scale mechanisms by which chloride ions (Cl ) destabilize cuprous oxide (Cu2O) films and trigger pitting on copper (Cu) remain challenging to resolve under realistic hydration. Here, density functional theory (DFT) calculations and ab initio molecular dynamics (AIMD) simulations are combined to interrogate Cu/Cu2O/water interfaces and to construct a unified solvent-resolved picture of Cl -mediated depassivation. We identify an intrinsic oxygen-layer shielding effect on Cu2O(111) that limits direct water coordination to saturated surface Cu sites and contributes to film stability. Cl destabilizes Cu2O through two coupled steps. Specifically adsorbed Cl attenuates oxygen shielding, activates surface Cu sites, and cooperates with interfacial water to promote localized dissolution-like Cu detachment while perturbing interfacial water organization. This process exhibits a coverage threshold and is insensitive to film thickness. Substitutional Cl at Cu/Cu2O interface migrates upward, draws neighboring coordinatively unsaturated Cu, induces concerted lifting of adjacent saturated Cu, and increases surface-oxygen hydrogen affinity, enhancing hydroxylation and facilitating cathodic reactions. Adsorbed and substitutional Cl act synergistically at subthreshold Cl concentrations with the combined destabilization dependent on Cu2O thickness. Thinner films fail at lower Cl concentrations, whereas thicker films require higher adsorption coverages for breakdown. After film rupture, Cl adsorption on exposed Cu(111) lowers the Cu dissolution barrier and restructures interfacial water, hindering Cu2O re-formation. These results distinguish adsorption- versus substitution-driven roles of Cl and provide an atomistic framework for Cl -induced depassivation and pitting initiation.

Surface pre-treatments play an influential role in the application and performance of conversion protective coatings on aluminium alloys. Among different coatings, trivalent chromium coatings are known to demonstrate enhanced corrosion resistance on pre-treated surfaces. In this work, sandblasting has been investigated as an alternative surface pre-treatment to chemical pickling, with the aim of promoting better adhesion and improved corrosion resistance properties of trivalent chromium coatings on the AA2024-T3 alloy. A surface science approach, using advanced surface analysis and characterisation techniques, is used to evaluate the surface modifications induced by the different pre-treatments. The results show that, although the native oxide layer is removed by each pre-treatment, the chemical composition of the surfaces and the newly formed oxide layer thicknesses differ. Chemical pickling leads to Cu enrichment due to the dissolution of the intermetallic particles, whereas sandblasting results in a reduction in Cu content owing to the fragmentation and redistribution/ejection of these particles. Sandblasting also induces significant surface roughness, along with the formation of a thinner oxide layer. These surface modifications on the sandblasted surface provide favourable conditions for the formation of a less defective and more protective conversion coating.

The mechanisms of 2-mercaptobenzothiazole (2-MBT) adsorption and corrosion inhibition on the aerospace AA2024 T3 aluminium alloy have been investigated using electrochemistry and advanced surface analyses. Electrochemical methods were used to measure the degree of corrosion protection in neutral chloride media, while advanced surface analysis techniques were employed to determine the interfacial interaction and inhibitor action mechanisms. It is shown that 2-MBT effectively inhibits corrosion of the alloy, reducing its susceptibility to corrosion attack and its corrosion rate. Surface analysis, including the use of ToF-SIMS 3-D chemical mapping, confirms 2-MBT adsorption on partially dealloyed intermetallic particles (IMPs) along with the presence of a thin 2-MBT layer on the top-most alloy surface. Chloride ions breakdown the native oxide film, allowing 2-MBT to adsorb on IMPs, thereby inhibiting further localized corrosion on these particles, while the 2-MBT layer on the surface protects the alloy matrix from surface oxidation.

Epifluorescence microscopy, dissolved oxygen measurements, electrochemical techniques (Voltametry, EIS), ICP-OES, XPS and ToF-SIMS were used to investigate the interactions between Pseudoalteromonas NCIMB 2021 bacteria and a mild steel surface during the first 24 hours of bacterial adhesion, with emphasis on the effect of bacteria on the surface oxide layer modifications. Bacterial colonization significantly reduced the overall corrosion rate, an effect attributed to oxygen consumption limiting cathodic reduction. This protective effect remains as long as bacteria are present, but after removal of the biofilm, an increased susceptibility to localized corrosion is observed in previously colonized surface areas. These areas exhibited chloride enrichment and localized oxide breakdown, leading to enhanced corrosion upon air exposure. This work emphasizes the dual role of bacteria in affecting mild steel corrosion. While bacterial colonization can reduce the corrosion rate, it also induces surface modifications,which were observed and characterized by ToF-SIMS, that promote localized corrosion upon bacterial removal. These findings highlight the importance of understanding the surface modifications that occur during the early stages of biofouling.

The discharge behaviour of Mg-air batteries with pure Mg anodes is presented, highlighting the improved anodic utilization efficiency and specific capacity in sodium acetate (NaOAc) electrolyte over sodium chloride (NaCl) electrolyte. Moreover, only a modest reduction in discharge potential was noted at increased current densities in half-cell tests. NaOAc electrolyte, containting less aggressive acetate ions, enables the formation of a homogeneous and protective oxide layer, in contrast to the chloride ions in NaCl electrolyte, which promote oxide breakdown and localized corrosion. The protective layer formed in NaOAc electrolyte limits Mg degradation, reduces H2 evolution rate, and enhances discharge performance. The surface characterizations by Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS), X-ray Photoelectron Spectroscopy (XPS) and Atomic Force Microscopy (AFM) reveal a denser corrosion layer formed on the surface of pure Mg anode in the NaOAc electrolyte, contributing to improved corrosion resistance and increased anodic utilization efficiency. Full-cell discharge tests using pure Mg, Mg-0.2Ca, and AZ31 alloy show that the anodic utilization efficiency and specific energy are improved in NaOAc electrolyte, particularly for Mg-0.2Ca, with energy density of 2066 Wh/kg at 2 mA/cm2. These findings suggest that NaOAc is a promising electrolyte for improving the performance of Mg-air batteries for different Mg-based anode materials.

The aim of this lecture is to present an overview of insights achieved over a period of nearly 20 years, using EC-STM on different metals and alloys, with a focus on copper, going from well oriented single-crystal surfaces to grain boundaries of micro-crystalline copper, and to the effect of adsorbed organic molecules to inhibit corrosion. On (111) and (001) single-crystal surfaces, EC-STM was instrumental to reveal ordered overlayer structures of adsorbed hydroxyl groups (OH ads ), and copper surface reconstruction. Going beyond adsorption of OH, oxidation of copper at increasing potentials was shown to yield thin layers of crystalline oxides, in tilted epitaxy with the copper surface, with a tilt angle minimizing the interface energy. In an effort to progress towards surfaces of practical use (polycrystals), micro-crystalline copper surfaces were investigated, with the aim of investigating the reactivity of emerging grain boundaries, measuring the depth of corrosion attack at the nanometric scale, as a function of GB misorientation, using EC-STM coupled with EBSD. Re-positioning the location of STM measurements to combine EBSD with STM was a major challenge. The effect of GB orientation was clearly observed. Mitigation of corrosion being a major issue, we then looked at the effect of organic molecules, aiming at understanding the key factors for corrosion inhibition. EC-STM data will be presented, as well as some data from DFT calculations, including modeling adsorption of MBT molecules on locally de-passivated copper surfaces, and at grain boundaries. A selection of 7 references V.Maurice, H.-H. Strehblow, P. Marcus, In situ STM study of the initial stages of oxidation of Cu(111) in aqueous solution, Surface Science 458 (2000) 185-194. doi: 10.1016/S0039-6028(00)00442-8 J.Kunze, V. Maurice, L.H. Klein, H.-H. Strehblow, P. Marcus, In situ STM study of the effect of chlorides on the initial stages of anodic oxidation of Cu(111) in alkaline solutions, Electrochimica Acta 48 (2003) 1157-1167. doi: 10.1016/S0013-4686(02)00826-5 J.Kunze, V. Maurice, L.H. Klein, H.H. Strehblow, P. Marcus, In situ STM study of the duplex passive films formed on Cu(111) and Cu(001) in 0.1. M NaOH, Corrosion Science 46 (2004) 245-254. doi: 10.1016/S0010-938X(03)00140-9 M.Bettayeb, V. Maurice, L. H. Klein, L. Lapeire, K. Verbeken, P. Marcus, Nanoscale Intergranular Corrosion and Relation With Grain Boundary Character as Studied In Situ on Copper, Journal of the Electrochemical Society 165 (2018) C835-C841. doi : 10.1149/2.1341811jes S.Sharma, V. Maurice, L. Klein and P. Marcus, Local Inhibition by 2-mercaptobenzothiazole of Early Stage Intergranular Corrosion of Copper, Journal of the Electrochemical Society 167 (2020) 161504. doi: 10.1149/1945-7111/abcc36 F.Chiter, D. Costa, V. Maurice, P. Marcus, Corrosion inhibition of locally de-passivated surfaces by DFT study of 2-mercaptobenzothiazole on copper, npj Materials Degradation 5 (2021) 52. doi: 10.1038/s41529-021-00198-x F.Chiter, D. Costa, V. Maurice, P. Marcus, Corrosion inhibition at emergent grain boundaries studied by DFT for 2-mercaptobenzothiazole on bi-crystalline copper, npj Materials Degradation 7 (2023) 5. doi: 10.1038/s41529-022-00314-5

The modifications in corrosion resistance and local surface modifications caused by the colonization of Pseudoalteromonas NCIMB 2021 bacteria on mild steel in artificial seawater were investigated using electrochemical techniques, Scanning Electron Microscopy and Time-of-Flight Secondary Ion Mass Spectrometry. A dual role of these bacteria on corrosion resistance was observed and characterized. While an improvement in corrosion resistance was obtained in the presence of the bacteria, the colonized surface is locally modified and once the bacteria are removed, the previously colonized areas are exposed, leading to enhanced localized corrosion.

The influence of pre-twins on the corrosion behavior of Zr702 alloy was investigated through combined electrochemical and surface analysis techniques, including time-of-flight secondary ion mass spectrometry and X-ray photoelectron spectroscopy. The pre-twinned specimens exhibited increased pitting potential in 1 mol/L NaCl electrolyte. A significant reduction in corrosion current density was demonstrated in 0.05 mol/L H2SO4 electrolyte. Twin boundaries were found critical for promoting the formation of protective passive films. Furthermore, twinning induced orientation rotation, leading to more closely-packed plane {10-10} to be parallel to the sample surface, also contributed to the formation of protective passive films. In addition, pre-twins enhance the hardness and strength as a result of the high density of twin boundaries. These results may provide a new approach to improve the property of Zr alloy.

This study provides a detailed characterization of the AA5083 aluminum alloy, surface, and interface over 6 months of immersion in seawater, employing techniques such as SEM/EDX, GIXRD, μ-Raman and XPS. The purpose was to evaluate the evolution of the biomineralization process that occurs on the Al-Mg alloy. By investigating the specific conditions that favor the in situ growth of layered double hydroxide (LDH) during seawater immersion as a result of biomineralization, this research provides insights into marine biomineralization, highlighting its potential as an innovative and sustainable strategy for corrosion protection.

We report a DFT study of (0001)-oriented Cr2O3 and Fe2O3 surfaces addressing the beneficial effects of Mo on the passivity breakdown of stainless steels in Cl-rich environments. Compared to Cr-rich zones, Fe-rich zones of the oxide barrier layer of the passive film are more prone to adsorbing Cl ions. Mo substitutes preferentially in these Fe-rich zones and favors the cationic vacancy formation to promote selective dissolution, thus curing the weak sites, sensitive to localized corrosion attack. In the Fe-rich weak sites with adsorbed Cl, Mo increases the barrier of O vacancy formation, thus mitigating passivity breakdown by inhibiting Cl penetration.

This research explores the use of chromium oxide (Cr2O3) thin layers grown by Atomic Layer Deposition (ALD) as protective coating to enhance the corrosion resistance of 2024 aluminum alloys. In order to obtain sufficiently dense and uniform Cr2O3 layers, the ALD process was tailored in terms of alloy surface pretreatment before the main Cr2O3 ALD process. The corrosion resistance of both Cr2O3 coated and non-coated aluminum alloys was evaluated in a corrosive 0.1 M KOH environment using in situ optical microscopy and ex situ surface analysis techniques, including X-ray Photoelectron Spectroscopy (XPS) and Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) and a neutral environment containing chlorides. Findings revealed that the Cr2O3-coated samples exhibited significantly reduced reactivity, highlighting the excellent corrosion protection provided by the Cr2O3 thin films. Although surface analysis revealed the presence of submicron defects within the Cr2O3 layer, which could act as corrosion initiation sites, the occurrence of these defects was mitigated with increasing Cr2O3 layer thickness. Additionally, after the corrosion test, an enrichment of copper and aluminum oxides at the layer surface was observed, suggesting preferential attack at intermetallic phases in corrosive environment.

With increasing environmental and regulatory pressure to replace toxic chromate- and phosphate-based coatings, zirconium conversion coatings (ZrCCs) have emerged as a sustainable and versatile alternative for the corrosion protection of light metals and steels. Despite their industrial potential, the chemical mechanisms underlying ZrCC formation remain only partially understood—primarily due to Zr complex aqueous speciation, which results in a mixture of mono- and polymeric species and exhibits strong sensitivity to bath composition. Also, a persistent challenge in ZrCC application lies in the broad, often vague operating windows prescribed in commercial bath formulations. These lack substrate-specific optimization and are typically based on proprietary industrial data. In an attempt to elucidate this, we combined corrosion performance assessment based on thermodynamic modelling, statistical modelling - response surface methodology (RSM), advanced surface characterization, and electrochemical analysis to investigate the mechanisms of ZrCC formation on cold-rolled steel (CRS), zinc, and the AA5754 aluminum alloy. Electrochemical impedance spectroscopy (EIS)-derived RSM models (Figure 1) produced highly predictive performance maps and proved a universally applicable tool for ZrCC optimization. This multidimensional approach outperforms traditional one-variable-at-a-time studies by capturing nonlinear and interactive effects. The coating performance in dilute Harrison’s solution was assessed using EIS across various Zr concentrations, pH, immersion times, and substrates. The results demonstrated the need for substrate-specific optimization strategies. CRS (Figure 1a-c) and Zn (Figure 1d-f) required higher Zr concentrations (825–1226 ppm), longer immersion times (430–480 s), and pH 4.0–4.6 1 . In contrast, optimal coatings on AA5754 (Figure 1g,h) formed under lower Zr levels (~150 ppm), shorter immersion times (~230 s), and higher pH (~4.6) due to localized growth on intermetallic particles and associated cracking phenomena 2 . EIS effectively characterized coating behaviour, revealing charge transfer control on CRS and AA5754 and diffusion-controlled corrosion on Zn. Revised Zr–OH and Zr–F thermodynamic predominance diagrams were developed using Specific Ion Interaction Theory to understand the mechanism of ZrCC deposition as a function of pH. These diagrams identified the polymeric tetrameric ion Zr 4 (OH) 8 8+ —an already known building block of amorphous zirconia—as a key species in coating precipitation. The formation of polymeric species strongly supports a sol-gel-like mechanism for ZrCC formation rather than a purely electrochemical one 3 . The thermodynamic postulates were further corroborated using the advanced surface method of Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS). The analysis confirmed the presence of polymerized tetrameric Zr-species in coatings on CRS deposited at pH 4.0, previously established as optimal for high-quality films. In contrast, coatings formed on AA5754 aluminum alloy showed only partial polymerization, with monomeric Zr species dominating the bulk and dimeric/trimeric species near the surface 4 . These substrate-dependent differences correlated with local pH measurements, indicating that a smaller interfacial pH rise on aluminum suppresses further polymerization —findings align with our previous speciation predictions 5 . Further, the effects of halide additives (F⁻ and Cl⁻) were examined in NH 4 HCO 3 -buffered electrolytes. Fluoride is strongly complexed with Zr on both CRS and AA5754, narrowing the passive region on aluminum—a critical consideration for bath formulation. On the other hand, chloride-induced pitting corrosion on AA5754 at elevated concentrations reinforces the need to minimize aggressive anions in ZrCC formulations. For zinc substrates, thermodynamic modelling showed that corrosion behaviour is driven primarily by ionic strength and complexation with bicarbonate at higher pH rather than by halide chemistry directly 6 . These findings underscore the importance of substrate-specific approaches in ZrCC optimization, accounting for distinct interfacial behaviours and coating mechanisms. This, we hope, provides both a deeper mechanistic understanding and a practical roadmap for fine-tuning ZrCC deposition parameters—paving the way for robust, multi-metal conversion coatings. In conclusion, by bridging Zr aqueous and solid speciation, thermodynamic modelling, surface analytics, and electrochemical evaluation, this work lays the foundation for the rational design of next-generation, environmentally responsible Zr-based conversion coatings tailored to the needs of diverse engineering alloys. References Kraš, A., D. Kramar, and I. Milošev, Corros. Sci. 242 (2024): p. 112551, https://linkinghub.elsevier.com/retrieve/pii/S0010938X24007467. Kraš, A., D. Kramar, and I. Milošev, Corros. Sci. 249 (2025): p. 112824, https://linkinghub.elsevier.com/retrieve/pii/S0010938X25001519. Kraš, A., and I. Milošev, J. Electrochem. Soc. 170 (2023): p. 21508, https://dx.doi.org/10.1149/1945-7111/acb9c2. Kraš, A., I. Milošev, A. Seyeux, and P. Marcus, npj Mater. Degrad. 8 (2024): p. 65, https://www.nature.com/articles/s41529-024-00485-3. Kraš, A., “Deposition and Protection Mechanisms of Zirconium-Based Conversion Coatings on Aluminium Alloy, Steel, and Zinc Substrates,” Jožef Stefan International Postgraduate School, 2024. Kraš, A., and I. Milošev, Electrochim. Acta 502 (2024): p. 144819, https://linkinghub.elsevier.com/retrieve/pii/S0013468624010594. Figure 1

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) combined with deuterium labelling (D2O), and X-ray photoelectron spectroscopy (XPS) were applied to investigate the interfacial transport mechanisms of hydroxyls between aqueous electrolyte and outer part of the protective oxide film during passivation of Cr15Fe10Co5Ni60Mo10 multi-principal element alloy surfaces. A ToF-SIMS signal treatment methodology was developed to retrieve the in-depth distribution of deuterated hydroxides in the nanometer-thick surface oxide film. After immersion at free potential or anodic passivation in acidified D2O, the initial bilayer structure is retained. The use of heavy water electrolyte has no effect on the composition alterations induced by passivation. Deuterated species were detected mostly in the outer layer of the surface oxide film. Pure inward hydroxyl diffusion from electrolyte/oxide to oxide/metal interface is excluded from being primarily responsible for oxide film growth induced by anodic passivation. The hydroxyls from the dissolving hydroxide species are retained in the oxide film and participate in forming Cr hydroxide, thus reducing the hydroxyl surface uptake from the electrolyte. This work provides deeper insight into the mechanisms of oxide growth and corrosion protection induced by anodic passivation.