Passive Oxide Layer Research Articles

Physical device simulation of dopant-free asymmetric silicon heterojunction solar cell featuring tungsten oxide as a hole-selective layer with ultrathin silicon oxide passivation layer

The dopant-related issues are amongst the major performance bottleneck in crystalline silicon solar cells that can be alleviated via implementation of dopant-free layers. This work presents the implementation of tungsten oxide (WOx) and titanium oxide (TiOx) as hole- and electron-selective films for heterostructure solar cell design whereby n-type Si wafer has been passivated with ultrathin silicon oxide (SiO2) layer. Several designs have been investigated including passivated hydrogenated amorphous silicon (i-a-Si:H) and characterized by evaluating work function, electron affinity, interfacial charge, and layer thickness. The high work function of WOx induces significant upward band bending to permit holes transportation towards anode, whereas, low electron-affinity for TiOx reduces the barrier against electrons at the cathode. Smaller band offsets have been observed against minority carriers for devices that employ passivated i-a-Si:H film. However, incorporating SiO2 significantly improves the energy barrier height against minority carriers that leads to an enhancement in electric field along with reduction in recombination. The best-performance device with an optimum SiO2 thickness of 1 nm numerically validated Voc of 751 mV, Jsc 40.2 mA/cm2, FF 79.7%, and η of 24.06%. A comparative analysis with hole-selective vanadium oxide (V2Ox) demonstrated η of 21.73% limited by the low work function of V2Ox.

Corrosion Behavior of AA2055 Aluminum-Lithium Alloys Anodized in the Presence of Sulfuric Acid Solution

The aim of this work was to evaluate the corrosion behavior of the AA2055 Aluminum-lithium alloy anodized in a sulfuric acid (H2SO4) bath, varying the current density of 0.19 and 1 A·cm−2 and why the sealing solution was water (H2O) and sodium dichromate (Na2Cr2O7). Anodized samples were exposed to a 10 vol.% H2SO4 solution and the electrochemical technique used was electrochemical impedance spectroscopy. Scanning electron microscopy and X-ray photoelectron spectroscopy were employed to characterization of the anodizing layer, determinate morphology and thickness of coatings. The Na2Cr2O7 sealing solution tends to increase the charge transfer resistance and produces a more homogeneous and compact passive oxide layer, and imparts a corrosion inhibition protection to the AA2055. SEM observations indicated that the morphology and thickness of the anodic films formed on AA2055 aluminum-lithium alloy anodized have the best results for both current densities.

Transition metal-based high entropy alloy microfiber electrodes: Corrosion behavior and hydrogen activity

This contribution reveals ultra-high corrosion resistance of high entropy alloys (HEAs), i.e. Ti20Zr20Nb15V15Hf15Ta15 of 1.85 µm yr–1 in alkaline environment, adverting their use for battery/fuel cell components. Formation of several nanometers passive oxide layer confirmed by scanning transmission electron microscopy accounts for corrosion resistance which increases with TiOx content. Cathodic Tafel slope of 67 mV dec–1 and large transfer coefficient of 0.82 obtained for Ti20Zr20Nb20V20Ta20 suggest its use for hydrogen electrocatalysis. High amounts of hydrogen storage, 1.7 wt% in Ti25Zr25Nb15V15Ta20, were confirmed by gas-solid reactions. This HEA also has high corrosion resistance in acidic and saline environments ideal for coatings and surgical tools/implants.

Study on Annealing Process of Aluminum Oxide Passivation Layer for PERC Solar Cells

In this study, Atomic Layer Deposition (ALD) equipment was used to deposit Al2O3 film on a p-type silicon wafer, trimethylaluminum (TMA) and H2O were used as precursor materials, and then the post-annealing process was conducted under atmospheric pressure. The Al2O3 films annealed at different temperatures between 200–500 °C were compared to ascertain the effect of passivation films and to confirm the changes in film structure and thickness before and after annealing through TEM images. Furthermore, the negative fixed charge and interface defect density were analyzed using the C-V measurement method. Photo-induced carrier generation was used to measure the effective minority carrier lifetime, the implied open-circuit voltage, and the effective surface recombination velocity of the film. The carrier lifetime was found to be the longest (2181.7 μs) for Al2O3/Si post-annealed at 400 °C. Finally, with the use of VHF (40.68 MHz) plasma-enhanced chemical vapor deposition (PECVD) equipment, a silicon nitride (SiNx) film was plated as an anti-reflection layer over the front side of the wafer and as a capping layer on the back to realize a passivated emitter and rear contact (PERC) solar cell with optimal efficiency up to 21.54%.

P‐1.5: High‐performance indium oxide thin‐film transistors with UV‐treated zirconium oxide passivation layer

P‐1.5: High‐performance indium oxide thin‐film transistors with UV‐treated zirconium oxide passivation layer

Highly Efficient Vacuum-Evaporated CsPbBr3 Perovskite Light-Emitting Diodes with an Electrical Conductivity Enhanced Polymer-Assisted Passivation Layer.

Highly efficient vacuum-deposited CsPbBr3 perovskite light-emitting diodes (PeLEDs) are demonstrated by introducing a separate polyethylene oxide (PEO) passivation layer. A CsPbBr3 film deposited on the PEO layer via thermal co-evaporation of CsBr and PbBr2 exhibits an almost 50-fold increase in photoluminescence quantum yield intensity compared to a reference sample without PEO. This enhancement is attributed to the passivation of interfacial defects of the perovskite, as evidenced by temperature-dependent photoluminescence measurements. However, direct application of PEO to an LED device is challenging because of the electrically insulating nature of PEO. This issue is solved by doping PEO layers with MgCl2. This strategy results in an enhanced luminance and external quantum efficiency (EQE) of up to 6887 cd m-2 and 7.6%, respectively. To the best of our knowledge, this is the highest EQE reported to date among vacuum-deposited PeLEDs.

Design of Grating Al2O3 Passivation Structure Optimized for High-Efficiency Cu(In,Ga)Se2 Solar Cells.

In this paper, we propose an optimized structure of thin Cu(In,Ga)Se2 (CIGS) solar cells with a grating aluminum oxide (Al2O3) passivation layer (GAPL) providing nano-sized contact openings in order to improve power conversion efficiency using optoelectrical simulations. Al2O3 is used as a rear surface passivation material to reduce carrier recombination and improve reflectivity at a rear surface for high efficiency in thin CIGS solar cells. To realize high efficiency for thin CIGS solar cells, the optimized structure was designed by manipulating two structural factors: the contact opening width (COW) and the pitch of the GAPL. Compared with an unpassivated thin CIGS solar cell, the efficiency was improved up to 20.38% when the pitch of the GAPL was 7.5–12.5 μm. Furthermore, the efficiency was improved as the COW of the GAPL was decreased. The maximum efficiency value occurred when the COW was 100 nm because of the effective carrier recombination inhibition and high reflectivity of the Al2O3 insulator passivation with local contacts. These results indicate that the designed structure has optimized structural points for high-efficiency thin CIGS solar cells. Therefore, the photovoltaic (PV) generator and sensor designers can achieve the higher performance of photosensitive thin CIGS solar cells by considering these results.

A comparative study on high-efficient reduction of bromate in neutral solution using zero-valent Al treated by different procedures

Bromate, a toxic by-product of bromide-containing drinking water after disinfecting with ozone, has attracted much attention in the past two decades. Traditional methods to activate zero-valent metals for reducing bromate are to eliminate their surface oxide layer by acid washing. In this work, for the first time, zero-valent Al (ZVAl) was surface treated by the following procedures including soaking, soaking and freeze-drying, soaking and heat-treating, and γ-Al2O3 covering Al particle surfaces (GCAP). It was found that all of above surface treated ZVAls have an obvious high efficiency for bromate reduction relative to pristine ZVAl. The bromate reduction rate is GCAP > soaking Al > freeze-drying Al > soaking and heat-treating Al > pristine Al, and using GCAP just 30 min is taken to completely reduce bromate to bromide in neutral solution. Mechanism analyses revealed that Al surface treating or covered by fine γ-Al2O3 phase can promote the hydration and breakage of Al surface passive oxide layer, resulting in a fast contact of inner Al with outside ions, leading to a high reduction rate of bromate in neutral solution. XPS analyses indicated that there are no bromate or bromide ions adsorbed on Al particle surfaces, implying that there is a high direct donating efficiency of electrons from inner Al to bromate ions in solution. Furthermore, GCAP has a good reusability and >90% bromate can be reduced even it was reused up to 4 cycles.

Facile distribution of an alkaline microenvironment improves human bone marrow mesenchymal stem cell osteogenesis on a titanium surface through the ITG/FAK/ALP pathway

PurposeOsseointegration at the titanium surface-bone interface is one of the key factors affecting the success rate of dental implants. However, the titanium surface always forms a passive oxide layer and impacts bone marrow–derived mesenchymal stem cell (BMSC) osteogenic differentiation after exposure to the atmosphere, which further leads to poor osseointegration. Given that wet storage helps prevent titanium aging and that weakly alkaline conditions stimulate BMSC osteogenic differentiation, the aim of the present study was to explore whether sodium bicarbonate, a well-known hydrogen ion (pH) buffer, forms an alkaline microenvironment on titanium surfaces to promote BMSC osteogenic differentiation.Material and methodsIn this work, sand-blasted and acid-etched (SLA) titanium discs were soaked in 20 mM, 50 mM, 100 mM, and 200 mM sodium bicarbonate at room temperature for 5 min without rinsing. The influence of this surface modification on BMSC adhesion, proliferation, and osteogenic differentiation was measured. Additionally, cellular osteogenic differentiation–associated signaling pathways were evaluated.ResultsWe showed that titanium discs treated with sodium bicarbonate created an extracellular environment with a higher pH for BMSCs than the normal physiological value for 5 days, strongly promoting BMSC osteogenic differentiation via the activation of integrin-focal adhesion kinase-alkaline phosphatase (Itg-FAK-ALP). In addition, the proliferation and adhesion of BMSCs were increased after alkaline treatment. These cellular effects were most significant with 100 mM sodium bicarbonate.ConclusionThe results indicated that the titanium surface treated with sodium bicarbonate improved BMSC osteogenic differentiation mainly by creating an alkaline microenvironment, which further activated the Itg-FAK-ALP signaling pathway.Clinical relevanceSurfaces modified with 100 mM sodium bicarbonate had the highest initial pH value and thus showed the greatest potential to improve BMSC performance on titanium surfaces, identifying a novel conservation method for dental implants.

Rechargeable aqueous aluminum-FeFe(CN)6 battery with artificial interphase through deep eutectic solution

The application needs of small electronic devices and large-scale power grid storage continuously promote the development of a new battery energy system. Rechargeable metal batteries based on aluminum (Al) are of enormous potential due to the abundant Al reserves, the trivalent charge carrier, high theoretical specific capacity (2980 mAh/g), and volumetric energy density (8046 mAh/cm3). However, the passivating oxide layer on the surface of the Al anode blocks the migration of electrons and ions, resulting in the operation difficulty and irreversibility of aluminum-based batteries. Herein we treated Al anode with a deep eutectic solution (DES) and constructed stable solid interface interphase on its surface, which can effectively prevent surface passivation, improve the chemical properties of the interface, promote ion transfer, and enable aqueous Al batteries with superior electrochemical performance. The assembled symmetric cells with treat Al (TAl) can cycle for more than 300 h with a low overpotential (~0.2 V). The TAl anode coupling with the FPB cathode material to assemble the full cells based on the aqueous electrolyte system can deliver a high discharge capacity of 85 mAh/g and exhibit capacity retention of 58 mAh/g after 150 cycles and an average coulombic efficiency of 97.1% at a current density of 100 mA/g. This work provides a novel surface modification strategy of Al metal anode and demonstrates high stability and cost-effective aqueous Al metal battery system, which suggest the significance for the commercialization of Al-metal batteries and their applications in large-scale energy store.

Nonlinear Dynamics in Alloy Electrodissolution: Modeling and Simulations

The formation of spatiotemporal patterns on electrochemical systems during the electrodissolution of metals depends on the nature of the metal constituent of the electrodes and can present regions with different behaviors, such as bistability and oscillations, for a set of physical-chemical parameters under potentiostatic control. The understanding of the influence of the parameters that govern the dynamics of the electrodissolution system in the emergence of spatiotemporal patterns has already been well studied taking into account its geometry and arrangement of the reference electrode, usually simplifying or neglecting the kinetics of reaction in the counter-electrode. This study aims to expand the complexity of the problem by considering the nature of the metal, changing the composition of the electrodes using metal alloys. The modelling of metal electrodissolution was based on previous works in the literature, in which the potential and the hydronium activity are considered as dependent and representative variables of the system. In this electrochemical system, the following geometries are adopted for the system: the electrochemical cell is cylindrical and the working electrode and counter-electrode are one on each side of this cylinder, having a ring or disc shape and the reference electrode is considered as a point belonging to the system.The activation-passivation transition that occurs in the working electrode is described by a smooth function Heaviside dependent on the Flade potential, as a consequence on the hydronium activity, and double-layer potential. Therefore, the total current density is the sum of two terms: one faradic current density, that is represented by this transition and the other assuming the existence of a capacitive current. In the mass transport of the hydron ions near the electrode we consider a linear diffusional term and a migratory one. The kinetics of the counter-electrode potential has a parameter that depends on the nature of the metal or alloy, from which the electrodes are made, and provides a novel approach to this study.The model takes advantage of the given geometric arrangement and its symmetries to reduce the spatial dimensionality by placing the reference electrode on the cylinder wall. In the case of ring electrodes geometry, it can be imposed that the radial derivative is null on this surface, reducing the evaluation of three spatial variables for cylindrical system: radius (r), angle (θ) and height (z), respectively, to s and z, where s is the arc of circumference. The simulations start with a working electrode entirely passive, and a section of the working electrode is disturbed, calculating the potentials of the system by numerical integration for each time step. A rectangular grid of points was used, and the time integration was done using a Runge-Kutta fourth order method. The disturbance in the initial condition is done considering a small section as activated. This disturbance is reproduced experimentally by scratching away a small portion of a passivating oxide layer. Several assumptions were made regarding the different metal potential in the counter-eletrode kinetics, comparing pure metal and these different ratio of metals in alloys, looking for three different responses to the temporal evolution of the potentials in the system due to these initial conditions: a totally active state, a totally passive state, and a partial active state.In future works, it is intended to validate the model using experimental data during the electrodissolution of alloy electrodes, so that can be applied as a guide in the search for desired spatiotemporal patterns. Figure 1

First Principles, Explicit Interface Studies of Oxygen Vacancyand Chloride in Al2O3 Films on Metal Surfaces for Metal Corrosion Applications

Pitting corrosion is a much-studied and technologically relvant subject. However, the fundamental mechanisms responsible the breakdown of the passivating oxide layer are still subjects of debate. Chloride anions are known to accelerate corrosion; relevant hypotheses include Cl insertion into positively charged oxygen vacancies in the oxide film, and Cl adsorption on passivating oxide surfaces -- substituting for OH-. In this work, we conduct large scale first principles modeling of explicit metal/Al2O3 interfaces to investigate the energetics and electronic structure associated with these hypotheses in connection to atmospheric aluminum corrosion. The explicit interface models allow electron transfer that mimics electrochemical events, and the establishment of the relation between atomic structures at different interfaces and the electronic band alignment. For multiple model interfaces, we find that doubly charged oxygen vacancies, which are key ingredients of the point defect model (PDM) often used to analyze corrosion data, can only occur in the presence of a potential gradient that raises the voltage. Cl- insertion into oxide films can be energetically favorable in some oxygen vacancy sites, depending on the voltage. Cl- substitution of surface hydroxyl groups is energetically unfavorable. We also discuss the challenges associated with explicit DFT modeling of these complex interfaces.Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. This paper describes objective technical results and analysis. Any subjective views or opinions that might be expressed in the document do not necessarily represent the views of the U.S. Department of Energy or the United States Government. Figure 1

Layer Thickness Effect on Lifetime of Copper Oxide Passivated Plasma Etched Copper Line

Previously, authors reported that copper oxide could be a good passivation material for the copper line because it prevented copper diffusion to adjacent layer at the high temperature. In this paper, the copper oxide thickness effect on the electromigration failure mechanism is studied. The copper oxide passivation layer was formed by exposing the copper line to the oxygen plasma in a parallel-plate plasma etcher. The copper oxide passivation layer has a smooth surface and a crystalline structure. The copper line with a very thin copper oxide passivation layer has an electromigration lifetime similar to that of the unpassivated copper line. However, the lifetime deteriorates with the increase of the copper oxide thickness due to the enlargement of the mechanical and thermal stress mismatches between the bulk copper film and the passivation layer. Therefore, the thickness of the copper oxide is critical to the effectiveness of its passivation function.

Effect of Tribological Properties on Boron Carbide and CNT Reinforced Copper based Composites

The study focuses on the influence and contribution of multi-walled Carbon-Nano tube (MWCNT) and boron carbide (B4C) to the tribological properties of copper matrix composites. The Samples are prepared using ultrasonic assisted stir casting for different weight fractions. The tribological properties like wear and corrosion studies been carried out according to ASTM standards. Wear rate increased with the increase in speed and load for every combination of the composite. However, with CNT being the main reinforcement with addition of CNT wear rate has reduced marginally. Addition of Boron Carbide also to some extent decreased the wear rate but CNT plays a major role in reducing the wear rate. Corrosion studies of the composite materials is carried out by Weight loss corrosion techniques, it is clearly evident from the critical analysis of the results that with the addition of reinforcements to the composite material, the corrosion rate in weight loss corrosion technique decreases drastically with the duration of time, this is due to the formation of a passive oxide layer on the composite specimen.

NanoSIMS analysis of hydrogen and deuterium in metallic alloys: Artefacts and best practice

Hydrogen embrittlement can cause catastrophic failure of high strength alloys, yet determining localised hydrogen in the microstructure is analytically challenging. NanoSIMS is one of the few techniques that can map hydrogen and deuterium in metal samples at microstructurally relevant length scales. Therefore it is essential to understand the artefacts and determine the optimum methodology for its reliable detection. An experimental methodology/protocol for NanoSIMS analysis of deuterium (as a proxy for hydrogen) has been established uncovering unreported artefacts and a new approach is presented to minimise these artefacts in mapping hydrogen and deuterium in alloys. This method was used to map deuterium distributions in electrochemically charged austenitic stainless steel and precipitation hardened nickel-based alloys. Residual deuterium contamination was detected in the analysis chamber as a result of deuterium outgassing from the samples, and the impact of this deuterium contamination was assessed by a series of NanoSIMS experiments. A new analysis protocol was developed that involves mapping deuterium in the passive oxide layer thus mitigating beam damage effects that may prevent the detection of localised deuterium signals when the surface is highly deuterated.

Assessment of biocompatibility of novel TiTaHf-based high entropy alloys for utility in orthopedic implants

This paper presents the findings of experimentally observed corrosion response of novel TiTaHf-based high entropy alloys (HEAs) in fetal bovine serum (FBS) to evaluate their biocompatibility in presence of proteins and potential to be used as implant materials. Particularly, TiTaHfNb, TiTaHfNbZr and TiTaHfMoZr HEAs were subjected to static immersion experiments in FBS media, and both the HEA samples and the immersion fluids underwent thorough characterization. The findings presented herein show that Zr and Mo addition to the TiTaHf solid solution increased the total ion release from the resulting HEAs in FBS, while the TiTaHfNb HEA became prominent in terms of biocompatibility owing to the reduced ion release in FBS. Moreover, hydroxy apatite (HA) formation was evident on the surfaces of all three HEAs upon immersion in FBS, indicating the potential of the three TiTaHf-based HEAs to form desired binding with the human bone. Considering the fact that passive oxide layer formation facilitating lower susceptibility to corrosion in long-term applications was also observed in the studied HEAs, further elaboration on their mechanical and biological responses is warranted for the sake of a comprehensive assessment regarding their utility as orthopedic implant materials.

Novel cost-effective approach to produce nano-sized contact openings in an aluminum oxide passivation layer up to 30 nm thick for CIGS solar cells

This work presents a novel method of local contact openings formation in an aluminum oxide (Al2O3) rear surface passivation layer by the selenization of the lithium fluoride (LiF) salt on top of the Al2O3 for ultra-thin copper indium gallium (di)selenide (CIGS) solar cells (SCs). This study introduces the potentially cost-effective, fast, industrially viable, and environmentally friendly way to create the nano-sized contact openings with the homogeneous distribution in the thick, i.e. up to 30 nm, Al2O3 passivation layer. The passivation layer is deposited by atomic layer deposition, while the LiF layer is spin-coated. Selenization is done in the H2Se atmosphere and the optimal process parameters are deduced to obtain nano-sized and uniformly allocated openings as confirmed by scanning electron microscopy images. The contact openings were produced in the different thicknesses of the alumina layer from 6 nm to 30 nm. Furthermore, the Al2O3 rear surface passivation layer with the contact openings was implemented into ultra-thin CIGS SC design, and one trial set was produced. We demonstrated that the created openings facilitate the effective current collection through the dielectric Al2O3 layer up to 30 nm thick. However, the upper limit of Al2O3 thickness in which the contact openings can be created by the described method is not established yet. The produced passivated CIGS SCs show increased external quantum efficiency response due to the optical enhancement of the passivated cells. However, the production of SCs on the Al2O3 passivation layer with the openings created by selenization of LiF is not optimized yet.

Water vapor oxidation of SiC layer in surrogate TRISO fuel particles

Under accidental conditions for high temperature gas-cooled reactors (HTGR), the SiC layer in tri-structural-isotropic (TRISO) fuel particles can be exposed to water vapor. In this study, oxidation behaviors of surrogate TRISO fuel particles were investigated in a He-20 vol% water vapor mixed atmosphere at temperatures up to 1600 °C. The growth of the crystalline oxide passivation layer with cracks and pores followed a parabolic law with time, where the maximum was 2.3 μm at 1600 °C. The oxide layer and the SiC surface under the oxide became flattened with increasing temperature, as a function of the silica viscosity and the diffusion path of water vapor. Volatilization of the oxide layer was analyzed using a mechanistic model that an inert gas in oxidizing atmospheres could influence the magnitude of volatilization. The fracture load and strength of the oxidized and thinned SiC layer were numerically estimated to decrease from 2.27 to 1.69 N and from 317 to 299 MPa, respectively, with the SiC thickness decrease from 35 to 32 μm. This prediction indicates that the oxidized SiC layer should retain fission products. Additionally, the mechanical integrity of each layer in the TRISO fuel particle after oxidation was evaluated. The results in this work provide important data for the safety analysis of accidental scenarios in HTGRs.

Analysis of the Polypropylene-Based Aluminium-Air Battery

Global energy demand is rising due to the rapid development and adoption of new technologies in every sector. Hence, there is a need to introduce a clean energy source that does not cause damage to the environment. Aluminium-air battery with its high theoretical specific volumetric capacity is an exciting alternative for post-lithium energy storage and has been at the forefront of energy research for years. However, the conventional aqueous electrolyte-based aluminium-air battery with bulky liquid storage, parasitic corrosion of aluminium in contact with the electrolyte, and formation of a passive oxide or hydroxide layer has precluded its widespread application. In order to achieve successful simplification and cost-effectiveness, a novel idea of a polypropylene-based aluminium-air battery is proposed. In this work, a polypropylene-based aluminium-air battery was constructed using aluminium foil as an anode, carbon fiber cloth as an air-cathode, and Polypropylene and Kimwipes as the separator. The effects of the electrolyte concentration on the aluminium-air battery were investigated and analyzed using various discharge currents. The study showed that the performance of the polypropylene separator is better than that of the Kimwipes separator. The battery capacity is negatively correlated with the concentrations of the electrolyte. At a discharge current of 30 mA, the aluminium-air battery has a specific capacity of 375 mAh g−1 when 1 M of potassium hydroxide was used as electrolyte.

First Principles, Explicit Interface Studies of Oxygen Vacancy and Chloride in Alumina Films for Corrosion Applications

Pitting corrosion is a much-studied and technologically relevant subject. However, the fundamental mechanisms responsible for the breakdown of the passivating oxide layer are still subjects of debate. Chloride anions are known to accelerate corrosion; relevant hypotheses include Cl insertion into positively charged oxygen vacancies in the oxide film, and Cl adsorption on passivating oxide surfaces, substituting for surface hydroxyl groups. In this work, we conduct large-scale first principles modeling of explicit metal/Al2O3 interfaces to investigate the energetics and electronic structures associated with these hypotheses. The explicit interface models allow electron transfer that mimics electrochemical events, and the establishment of the relation between atomic structures at different interfaces and the electronic band alignment. For multiple model interfaces, we find that doubly charged oxygen vacancies, which are key ingredients of the point defect model (PDM) often used to analyze corrosion data, can only occur in the presence of a potential gradient that raises the voltage. Cl− insertion into oxide films can be energetically favorable in some oxygen vacancy sites, depending on the voltage. We also discuss the challenges associated with explicit DFT modeling of these complex interfaces.