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Highlights • Current developments of nanoscale insight into passive oxide films. • Cr(III) enrichment and its homogeneity at the nanoscale in passive films. • Corrosion properties of grain boundaries in early intergranular corrosion. • Interaction of organic inhibitor molecules with passivated metallic surfaces. Abstract Oxide passive films are a key for the durability of metals and alloys components as well as a central issue in corrosion science and engineering. Herein, we discuss current developments of the nanometer and sub-nanometer scale knowledge of the barrier properties and adsorption properties of passive oxide films brought by recent model experimental and theoretical investigations. The discussed aspects include (i) the chromium enrichment and its homogeneity at the nanoscale in passive films formed on Cr-bearing alloys such as stainless steel, (ii) the corrosion properties of grain boundaries in early intergranular corrosion before penetration and propagation in the grain boundary network, and (iii) the interaction of organic inhibitor molecules with incompletely passivated metallic surfaces. In all three cases, key issues are highlighted and future developments that we consider as most relevant are identified. [ABSTRACT FROM AUTHOR]

Contemporary aspects of corrosion science are reviewed to show how insightful a surface science approach is to understand the mechanisms of corrosion initiation at the atomic and nanometric scales. The review covers experimental approaches using advanced surface analytical techniques applied to single-crystal surfaces of metal and alloys exposed to corrosive aqueous environments in well-controlled conditions and analysed in situ under electrochemical control and/or ex situ by scanning tunneling microscopy/spectroscopy, atomic force microscopy and X-ray diffraction. Complementary theoretical approaches based on atomistic modeling are also covered. The discussed aspects include the metal-water interfacial structure and the surface reconstruction induced by hydroxide adsorption and formation of 2D (hyd)oxide precursors, the structure alterations accompanying anodic dissolution processes of metals without or with 2D protective layers and selective dissolution (i.e. dealloying) of alloys, the atomic structure, orientation and surface hydroxylation of ultrathin passive films, the role of step edges at the exposed surface of oxide grains on the dissolution of passive films and the effect of grain boundaries in polycrystalline passive films acting as preferential sites of passivity breakdown, the differences in local electronic properties measured at passive films grain boundaries, and the structure of adlayers of organic inhibitor molecules. [ABSTRACT FROM AUTHOR]

Atomic level characterization brings fundamental insight into the mechanisms of self-protection against corrosion of metals and alloys by oxide passive films and into how localized corrosion is initiated on passivated metal surfaces. This is illustrated in this overview with selected data obtained at the subnanometre, i.e. atomic or molecular, scale and also at the nanometre scale on singlecrystal copper, nickel, chromium and stainless steel surfaces passivated in well-controlled conditions and analysed in situ and/or ex situ by scanning tunnelling microscopy/spectroscopy and atomic force microscopy. A selected example of corrosion modelling by ab initio density functional theory is also presented. The discussed aspects include the surface reconstruction induced by hydroxide adsorption and formation of two-dimensional (hydr)oxide precursors, the atomic structure, orientation and surface hydroxylation of three-dimensional ultrathin oxide passive films, the effect of grain boundaries in polycrystalline passive films acting as preferential sites of passivity breakdown, the differences in local electronic properties measured at grain boundaries of passive films and the role of step edges at the exposed surface of oxide grains on the dissolution of the passive film. This article is part of the themed issue 'The challenges of hydrogen and metals'. [ABSTRACT FROM AUTHOR]

Abstract: The nanometer scale chemical and structural aspects of ultrathin oxide passive films providing self-protection against corrosion to metals and alloys in aqueous environments are reviewed. Data on the nucleation and growth of 2D anodic oxide films, details on the atomic structure and nanostructure of 3D passive films, the preferential role of surface step edges in dissolution in the passive state and the preferential role of grain boundaries of the passive films in passivity breakdown are presented. Future perspectives are discussed, and exemplified by new data obtained on the relationship between the nanostructure of oxide passive films and their local electronic properties. Atomistic corrosion modeling by ab initio density functional theory (DFT) is illustrated by the example of interactions of chloride ions with hydroxylated oxide surfaces, including the role of surface step edges. Data obtained on well-defined substrate surfaces with surface analytical techniques are emphasized. [Copyright &y& Elsevier]

Abstract: An equilibrium potential–pH (Pourbaix) diagram is presented for sulfur adsorbed on Ag(111). It allows prediction of the E–pH conditions of adsorption of sulfur and hydroxyl on silver surfaces immersed in water containing dissolved sulfur species such as sulfides. The E–pH relations associated with the equilibria between water and adsorbed hydroxyl, and between dissolved sulfur species and adsorbed sulfur are given at 25°C. The E–pH adsorption diagram is calculated for a sulfur concentration of 10−3 molkg−1 and superimposed to the usual Pourbaix diagram for the Sph name="sbnd" />H2O system. It is shown that an adsorbed sulfur monolayer may form on the silver surface in E–pH domains in which usual Pourbaix diagrams predict no stability of the bulk silver sulfide Ag2S. The calculation of stability domains of adsorbed hydroxyl and sulfur allows prediction of the electrocatalytic and corrosion behavior of Ag in water with sulfur species. [Copyright &y& Elsevier]

Abstract: The Cr 2p and O 1s binding energy (BE) levels have been calculated by first principles methods for different models of hydroxylated (0001)-Cr2O3 surfaces. Several surface terminations have been considered. The calculations allow us to reproduce the O 1s shifts between O in oxide and OH groups. It is found that two main effects account for the OH binding energy shifts. On the one hand, the increased covalency of the O–H bond with respect to the Cr–O bond, lowers the electronic O (1s and 2p) energy, and in consequence the BE of the core levels (O 1s) are higher. On the other hand, the lower the OH coordination number, the higher the valence and core levels energy, and the lower the BE. Consequently, mono-coordinated hydroxyls have a binding energy near that of O2− in the oxide (ΔBEOH–O =−0.2–0.0eV). Two-fold coordinated hydroxyls have a slightly higher BE (ΔBEOH–O =+0.3eV). Three-fold coordinated OH groups have a higher binding energy (ΔBEOH–O =+0.6−0.7eV), corresponding to that experimentally measured for OH groups. Finally, water adsorbed above OH groups exhibits a still higher BE (ΔBEHOH–O =+0.9–1.0eV). The ΔBE are slightly under-estimated under the initial state approximation, and overestimated under the final state (Z +1) approximation. [Copyright &y& Elsevier]

Abstract: The principle of equilibrium potential–pH diagrams for two-dimensional layers adsorbed on metal surfaces in aqueous solution is applied to the case of hydrogen and oxygen species electroadsorbed on copper. The conditions of adsorption of species on copper surfaces in water may be predicted from thermodynamic calculations of the equilibrium potentials of the dissolved species/adsorbed species couples and drawing of potential–pH diagrams. Standard chemical potentials for hydroxyl chemisorbed on Cu(111) are derived from recent electrochemical data, while those for hydrogen chemisorbed on Cu(111) are derived from gas phase adsorption data. The E–pH relations associated with the equilibria between water and adsorbed hydroxyl, and between solvated protons and adsorbed hydrogen are given. The possible diagrams showing the E–pH domains of thermodynamic stability of the species adsorbed on a copper (111) surface (H2Oads, OHads and Hads) in water are calculated at 25°C and superimposed to the usual Pourbaix diagram for the Cu–H2O system. [Copyright &y& Elsevier]

The principle of equilibrium potential–pH (Pourbaix) diagrams can be extended to the case of bidimensional layers of species adsorbed on metal surfaces. It allows us to predict the E–pH conditions of adsorption of sulfur and hydroxyl on copper surfaces immersed in water containing dissolved sulfur species such as sulfides, sulfites or thiosulfates. The E–pH relations associated with the equilibria between water and adsorbed hydroxyl, and between dissolved sulfur species and adsorbed sulfur are given at 25 °C. The E–pH adsorption diagrams are calculated for a sulfur concentration of 10−4 mol kg−1 and superimposed to the usual Pourbaix diagrams for the S–Cu–H2O system. It is shown that an adsorbed sulfur monolayer may form on the copper surfaces in E–pH domains in which usual Pourbaix diagrams predict no stability of the bulk copper sulfide. The calculation of stability domains of adsorbed sulfur allows prediction of the corrosion risk for copper-based materials in sulfur-containing aqueous environments. [Copyright &y& Elsevier]

Surface spectroscopy analysis and electrochemistry were applied to study the effects of surface preparation by vibratory polishing on the passivity of stainless steel 304L surfaces. Compared to grinding by traditional mechanical polishing, vibratory polishing promotes the enrichment of Cr(III) oxide and hydroxide species in the duplex chemical structure of the surface native oxide film by enhancing selective Fe oxidation and dissolution. As a result, spontaneous passivity, tested in aggressive sulphuric acid electrolyte, is enhanced. However, in the absence of enrichment in Mo(IV) and Mo(VI) species in the passive film, the Cr enrichment does not enhance passivity upon anodic polarisation nor increase the resistance to Cl-induced passivity breakdown and initiation of localised corrosion in accelerated testing conditions. The results provide comprehensive insight into the mechanisms underlying the passivity enhancement of stainless steel by surface engineering. [ABSTRACT FROM AUTHOR]

N‐Heterocyclic carbenes (NHCs) have drawn considerable interest in the field of nanomaterials chemistry as highly stabilizing ligands enabling the formation of strong and covalent carbon–metal bonds. Applied to gold nanoparticles synthesis, the most common strategy consists of the reduction of a preformed NHC‐AuI complex with a large excess of a reducing agent that makes the particle size difficult to control. In this paper, we report the straightforward synthesis of NHC‐coated gold nanoparticles (NHC‐AuNPs) by treating a commercially available gold(I) precursor with an easy‐to‐synthesize NHC‐BH3 reagent. The latter acts as both the reducing agent and the source of surface ligands operating under mild conditions. Mechanistic studies including NMR spectroscopy and mass spectrometry demonstrate that the reduction of gold(I) generates NHC‐BH2Cl as a by‐product. This strategy gives efficient control over the nucleation and growth of gold particles by varying the NHC‐borane/gold(I) ratio, allowing unparalleled particle size variation over the range of 4.9±0.9 to 10.0±2.7 nm. Our strategy also allows an unprecedented precise and controlled seeded growth of gold nanoparticles. In addition, the as‐prepared NHC‐AuNPs exhibit narrow size distributions without the need for extensive purification or size‐selectivity techniques, and are stable over months. [ABSTRACT FROM AUTHOR]

X‐ray photoelectron spectroscopy analysis was applied to investigate the thermal stability under ultra‐high vacuum environment of the surface oxide film formed by electrochemical passivation of a newly designed Cr15Fe10Co5Ni60Mo10 (at.%) multi‐principal element alloy and providing the alloy superior localized corrosion resistance compared to conventional stainless steels and alloys. A spectral decomposition methodology involving the subtraction of Auger peaks overlapping the Fe 2p and Co 2p core level regions was applied for quantification of the oxide film composition and thickness. The results show that, at 100°C, the passive oxide film is mainly dehydrated and dehydroxylated. Obvious loss of Ni hydroxide and conversion of Mo (VI) to Mo (IV) species are observed at 200°C, with further reduction of Mo species to Mo (III) observed at 300°C. In this temperature range, the total cation quantity in the oxide film remains stable despite the compositional alteration. At 400°C, Cr (III) oxide forms at the expense of Fe and Mo oxides, resulting in an oxide film essentially consisting of chromium oxide. At 500°C, Cr (III) oxide is eliminated, making the passive film unstable at this temperature. Possible Cr oxide removal mechanisms are discussed. [ABSTRACT FROM AUTHOR]

Modeling the growth and failure of passive oxide films formed on stainless steels is of general interest for the use of stainless steel as structural material and of special interest in the context of life time extension of light water reactors in nuclear power plants. Using the DFT+U approach, a theoretical investigation on the resistance to failure of the chromium-rich inner oxide layer formed at the surface of chromium-containing austenitic alloys (stainless steel and nickel based alloys) has been performed. The investigations were done for periodic bulk models. The data at the atomic scale were extrapolated by using the Universal Binding Energy Relationships (UBERs) model in order to estimate the mechanical behavior of a 10 μm thick oxide scale. The calculated stress values are in good agreement with experiments. Tensile stress for the bulk chromia was observed. The effects of temperature and structural defects on cracking were investigated. The possibility of cracking intensifies at high temperature compared to 0 K investigations. Higher susceptibility to cracking was observed in presence of defects compared to nondefective oxide, in agreement with experimental observation. [ABSTRACT FROM AUTHOR]

Hydrous Cr 2 O 3 and Fe 2 O 3 surfaces without and with substitutional molybdenum were simulated by DFT modelling to investigate at the atomic scale the role of Mo in improving the corrosion resistance of passive films on stainless steels. The surface structures most energetically favoured were determined in the conditions of interest. For surfaces with a high degree of hydroxylation, the preferential location of substitutional Mo is just under the hydroxyl groups, in agreement with the experimental observations. The substitution by Mo is exothermic and Mo preferentially substitutes in Fe- than in Cr-rich zone of the inner barrier layer of passive films. • DFT modelling of (0001) hydrous Cr 2 O 3 and Fe 2 O 3 surfaces to study passivity. • Determination of energetically favoured terminations in the conditions of interest. • Exothermic substitution by Mo more favoured on Fe 2 O 3 than on Cr 2 O 3 surfaces. • Preferential location of Mo on the surface after highly hydroxylation. [ABSTRACT FROM AUTHOR]

[Display omitted] • Interfacial passivation mechanisms studied on Cr- and Mo-containing alloy surfaces. • D 2 O labelling applied to study the growth of nanometer-thick passive oxide film. • D-labelled species mostly detected in outer hydroxide layer of passive film. • Minor inward hydroxyl diffusion from electrolyte during anodic passivation. • Key role of hydroxyls initially in native oxide in forming Cr hydroxide. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) combined with deuterium labelling (D 2 O), 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 Cr 15 Fe 10 Co 5 Ni 60 Mo 10 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 D 2 O, 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. [ABSTRACT FROM AUTHOR]

• Formation of bi-layered films with physisorbed outer and chemisorbed inner layers. • 2-MBI bonding by N to metallic and oxidized Cu, S also involved on metallic Cu. • Formation of Cu(I)−2-MBI complex promoted by cathodic conversion of native Cu oxide. • Increased complex formation owing to Cu(I) ions generated by anodic oxidation. • Cu dissolution inhibited depending on pre-treatment used for interface formation. The interfacial bonding and the layered structure of 2-mercaptobenzimidazole (2-MBI) organic films adsorbed on electrochemically controlled copper surfaces and their corrosion inhibition effects in acidic chloride aqueous solution were investigated using an integrated approach of electrochemical methods and advanced surface analyses by X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry. It is shown that organic films formed on the copper surfaces are bi-layered with a chemisorbed inner layer and a physisorbed outer layer. In the chemisorbed inner layer, 2-MBI is bonded primarily by its nitrogen atoms with metallic and oxidized copper surfaces. Sulphur atoms are also involved in the bonding mechanism when metallic copper is directly accessible to the 2-MBI molecules. The initial presence of native copper oxides at the interface promotes the formation of Cu(I)-2-MBI metal-organic complexes in the chemisorbed inner layer using cathodic reduction to dissociate the oxide. Metal-organic complexes also form upon anodic polarisation due to Cu(I) ions generated by oxidation of the copper metal. 2-MBI effectively inhibits copper anodic dissolution in varying degrees, between 84% and 93%, depending on the pre-treatment used for the formation of the organic bi-layers. An enhanced protection of the substrate is obtained by adsorbing the 2-MBI inhibitor on an initially oxide-free surface, which is achieved by cathodic pre-treatment in absence of the inhibitor followed by 1 hour exposure to the inhibitor. [ABSTRACT FROM AUTHOR]

2,6-pyridinedicarboxylate (2,6-PDC) was studied as corrosion inhibitor for pure magnesium. The surface was prepared either by polishing or polishing followed by treatment with 1 M NaOH solution. The results show that 2,6-PDC promotes the formation of a denser protective oxide/hydroxide layer poor in PDC. The mechanism proposed includes forming weak PDC-Mg complexes that lower the free Mg2+ concentration available for the formation of Mg(OH) 2. This leads to growth of smaller Mg(OH) 2 platelets that are more densely packed and hence form a more protective layer. The highest inhibition efficiency of 2,6-PDC was achieved for samples with surface hydroxylated by NaOH treatment. • 2,6-PDC could effectively inhibit the corrosion of pure magnesium. • 2,6-PDC promotes the dissolution of pure magnesium during the initial phase of immersion. • 2,6-PDC promotes the formation of a denser Mg(OH) 2 /MgO on CP Mg samples. • The corrosion inhibition effect of 2,6-PDC is slightly improved by NaOH treatment on pure magnesium. [ABSTRACT FROM AUTHOR]

Abstract: A new Ce, Zr and Nb-based conversion coating was designed for AZ91 and AM50 magnesium alloys. The corrosion protection provided by this coating was evaluated by electrochemical measurements (polarization curves, electrochemical impedance spectroscopy) in Na2SO4 electrolyte, and accelerated atmospheric corrosion tests (humid, SO2 polluted air, and salt spray). Its chemical composition was characterized by X-ray photoelectron spectroscopy (XPS). Electrochemical measurements showed that Mg alloys treated during 24h in the Ce–Zr–Nb conversion bath exhibit: (i) increased corrosion potential, (ii) decreased corrosion and anodic dissolution current densities, and (iii) increased polarization and charge transfer resistances. The accelerated corrosion tests revealed excellent atmospheric corrosion resistance for all Ce–Zr–Nb-treated samples, with or without an additional layer of epoxy–polyamide resin lacquer or paint. XPS analysis showed that the coating includes CeO2, Ce2O3, ZrO2, Nb2O5, MgO, and MgF2 as main components. No significant modification of the chemical composition was observed after cathodic and anodic polarization in Na2SO4. This new coating provides improved corrosion resistance, and excellent paint adhesion. It offers an alternative to the chromate conversion coating for magnesium alloys. [Copyright &y& Elsevier]

Abstract: STM, STS, LEED and XPS data for crystalline θ-Al2O3 and non-crystalline Al2O3 ultra-thin films grown on NiAl(001) at 1025K and exposed to water vapour at low pressure (1×10−7–1×10−5 mbar) and room temperature are reported. Water dissociation is observed at low pressure. This reactivity is assigned to the presence of a high density of coordinatively unsaturated cationic sites at the surface of the oxide film. The hydroxyl/hydroxide groups cannot be directly identify by their XPS binding energy, which is interpreted as resulting from the high BE positions of the oxide anions (O1s signal at 532.5–532.8eV). However the XPS intensities give evidence of an uptake of oxygen accompanied by an increase of the surface coverage by Al3+ cations, and a decrease of the concentration in metallic Al at the alloy interface. A value of ∼2 for the oxygen to aluminium ions surface concentration ratio indicates the formation of an oxy-hydroxide (AlO x OH y with x + y ∼2) hydroxylation product. STM and LEED show the amorphisation and roughening of the oxide film. At P(H2O)=1×10−7 mbar, only the surface of the oxide film is modified, with formation of nodules of ∼2nm lateral size covering homogeneously the surface. STS shows that essentially the valence band is modified with an increase of the density of states at the band edge. With increasing pressure, hydroxylation is amplified, leading to an increased coverage of the alloy by oxy-hydroxide products and to the formation of larger nodules (∼7nm) of amorphous oxy-hydroxide. Roughening and loss of the nanostructure indicate a propagation of the reaction that modifies the bulk structure of the oxide film. Amorphisation can be reverted to crystallization by annealing under UHV at 1025K when the surface of the oxide film has been modified, but not when the bulk structure has been modified. [Copyright &y& Elsevier]

The initial stages of growth of ordered layers of Al[sub 2]O[sub 3] on NiAl(001) single-crystal surfaces at 1025 K and 10[sup -7] mbar (10[sup -5]Pa) in O[sub 2] have been studied using scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). The STM results evidence the formation of elongated strips (26 Å wide and 11 Å high) of Al[sub 2]O[sub 3] oriented along the [100] and [010] directions of the substrate. With longer oxidation, the substrate is increasingly covered by rectangular and striped islands resulting from the vicinal and parallel growth of the strips. On the ultrathin oxide film formed after 500 L (1 L = 10[sup -6] torr-s (∼1.33 × 10[sup -4] Pa·s)) of exposure, STM atomic resolution images have been obtained for the first time. They evidence the [001] orientation of the oxygen sublattice in Bain epitaxy on the substrate. The observation of one-dimensional atomic trenches together with the strips observed on the nanometer scale is consistent with the growth of θ-Al[sub 2]O[sub 3]. The STS local measurements evidence the insulating behavior of the oxide layer formed with a gap value ranging from 7 and 8 eV for amorphous and ordered domains, respectively. [ABSTRACT FROM AUTHOR]

Advanced surface analytical techniques were used to study 2-mercaptobenzothiazole (2-MBT) adsorption and interfacial oxide effects on copper, and cyclic voltammetry was used to characterize corrosion inhibition in NaCl solution. 2-MBT adsorbs on metallic copper by its sulphur atoms along with a small fraction of nitrogen atoms. The 2-MBT film formed is thicker when the interfacial oxide is less. Upon anodic polarisation, a direct correlation between the thickness of 2-MBT layer and protection against corrosion initiation is observed. The metal-organic complexes, formed by an interaction between 2-MBT and Cu(I) ions, do not offer additional protection to the substrate. • 2-MBT inhibition of copper initial corrosion in NaCl studied by surface analysis. • 2-MBT adsorption mostly by sulphur atoms and partially by nitrogen atoms. • Thickness of 2-MBT layer dependent on quantity of interfacial oxides present. • Superior protection against corrosion offered by thicker 2-MBT barrier layer. • Metal-organic Cu-2-MBT complexes do not aid in corrosion protection of substrate. [ABSTRACT FROM AUTHOR]

Substitution of a metal cation by Mo and its effects on vacancy formation on (0001)-oriented chromia and hematite surfaces were studied using DFT calculations to provide atomistic insights on the experimentally observed Mo-enhanced passivity. The substitution is favoured energetically, resulting in Mo more enriched in the Fe-rich than in the Cr-rich oxide zones in passive oxide films. The presence of substitutional Mo disfavours the formation of O vacancies and favours metal vacancies, more significantly in Fe 2 O 3 than in Cr 2 O 3 , suggesting a prevention of passivity breakdown in chloride-rich environment and a cure of the Fe-rich weak sites of passivity by Mo. • Mo-enhanced passivity studied by DFT calculated (0001) Cr 2 O 3 and Fe 2 O 3 surfaces. • Substitution by Mo always exothermic, more favoured in Fe 2 O 3 than in Cr 2 O 3. • Formation of O vacancies disfavoured (and metal vacancies favoured) by Mo. • Mo effect on vacancy formation more significant on Fe 2 O 3 than on Cr 2 O 3 surfaces. • Beneficial effects for the resistance to localised corrosion of stainless steels and other alloys are discussed [ABSTRACT FROM AUTHOR]

• Thermal stability of the passive film on 316 L stainless steel is investigated in situ by ToF-SIMS. • A step by step heating in ultra-high vacuum is applied. • The modifications of thickness, composition and layered structure on the passive film during stepwise heating are studied. • The changes in the passive film in the temperature range 25–300 °C are discussed. The modifications of the passive film formed on 316 L stainless steel surface during stepwise heating in ultra-high vacuum up to 300 °C have been studied in situ by ToF-SIMS. The pre-formed passive film (in 0.05 M H 2 SO 4) has a bilayer structure, comprising Fe-rich, Mo-rich (outer) and Cr-rich (inner) layers. Below 100 °C, the passive film is stable. At 100 °C–250 °C, dehydroxylation and dehydration is observed. Above 250 °C, the main modification in the film is formation of chromium oxide at the expense of oxidized iron. At higher temperature, thicker Cr-rich inner layer with sharper inner/outer oxide interface is formed. [ABSTRACT FROM AUTHOR]

The durability of passivable metals and alloys is often limited by the stability of the surface oxide film, the passive film, providing self-protection against corrosion in aggressive environments. Improving this stability requires to develop a deeper understanding of the surface structure and initial surface reactivity at the nanometric or atomic scale. In this work we applied scanning tunneling microscopy to unravel the surface structure of a model stainless steel surface in the metallic state and its local modifications induced by initial reaction in dioxygen gas. The results show a rich and complex structure of the oxide-free surface with reconstructed atomic lattice and self-organized lines of surface vacancies at equilibrium. New insight is brought into the mechanisms of initial oxidation at steps and vacancy injection on terraces leading to Cr-rich oxide nuclei and locally Cr-depleted terraces, impacting the subsequent mechanism of chromium enrichment essential to the stability of the surface oxide. Unlabelled Image • Surface atomic structure unraveled on oxide-free model austenitic stainless steel • Terraces terminated by reconstructed atomic lattice and self-organized vacancies • Cr oxide nucleation at defect sites of reduced atomic coordination (step edges) • Cr vacancy injection on terraces leading to Cr depletion on terraces [ABSTRACT FROM AUTHOR]

N‐Heterocyclic carbene (NHC)‐stabilized copper nanoparticles (NPs) were synthesized from an NHC–borane adduct and mesitylcopper(I) under thermal conditions (refluxing toluene for 2.5 h). NPs with a size distribution of 11.6±1.8 nm were obtained. The interaction between Cu NPs and NHC ligands was probed by X‐ray photoelectron spectroscopy, which showed covalent binding of the NHC to the surface of the NPs. Mechanistic studies suggested that NHC–borane plays two roles: contributing to the reduction of [CuMes]2 to release Cu0 species and providing NHC ligands to stabilize the copper NPs. [ABSTRACT FROM AUTHOR]

An approach for the identification of the origin of iron sulfides formation on iron surfaces using Time-of-Flight Secondary Ions Mass Spectrometry (ToF-SIMS) is reported here in. Two different sulfidation processes of iron surfaces are presented (both at room temperature): the first abiotic procedure was carried out using chronoamperometry (E = −0.8 V/SCE) of pure iron in 10 mM of Na 2 S,9H 2 O (pH = 11) while the second biotic procedure was accomplished by immersing a pure iron sample in a medium containing HS− ions produced by a sulfate-reducing bacterium (SRB) of the genus Desulfovibrio at an open circuit potential (OCP). A surface analytical method using Time-of-Flight Secondary Ions Mass Spectrometry (ToF-SIMS) coupled with ToF-SIMS spectra peak-fitting and data processing was developed to calculate an accurate sulfur isotopic fractionation δ34S V-CDT on iron sulfide layers formed on iron surfaces, thus allowing to discriminate between abiotically versus biotically generated sulfides. This approach contributes to a better understanding of iron surface interactions with sulfur containing environmental species of abiotic or biotic origin. • ToF-SIMS is used to study abiotically and biotically (from SRB) generated iron sulfide layers formed on iron surfaces. • A peak-fitting method and data processing was developed and applied on ToF-SIMS spectra. • Different sulfur isotopic fractionations δ34S (-0.23 ‰ and -13.69 ‰) were obtained for abiotic and biotic iron sulfide layers. • The ToF-SIMS approach presented allows the identification of bacterial contribution in sulfur corrosion products. • The ToF-SIMS approach allows a better understanding of biocorrosion to sulfur originated from abiotic and biotic sources in aqueous medium. [ABSTRACT FROM AUTHOR]

The mechanisms of initial oxide growth on the equiatomic CoCrFeMnNi high entropy alloy were studied in situ by X-ray photoelectron spectroscopy on clean, oxide-free surfaces exposed stepwise to low-pressure gaseous oxygen. Cr(III), Mn(III), Fe(III), Co(II) but no Ni(II) oxides were formed at 100 °C, and Mn(II) at 200 °C. Data quantification revealed a transition mechanism from selective initial oxidation to 3D kinetically-controlled growth, leading to stratification of the oxide film. Formation of the Co-rich outer layer above the Cr-rich inner layer first formed implies predominant cationic outward oxide growth supported by the overall stoichiometry of the film. • Initial oxide growth studied in situ starting from clean, oxide free surface. • Valence of oxides formed on CoCrFeMnNi HEA at 100 and 200 °C characterized. • Transition from selective initial oxidation to kinetically-controlled oxide growth revealed. • Stratification mechanism during early build-up of the surface oxide unravelled. • Predominant cationic outward oxide growth supported by overall stoichiometry. [ABSTRACT FROM AUTHOR]

• Surface oxide layers formed on 2304 duplex stainless steel are investigated. • The native surface and the passivated surface are compared. • An innovative coupling of XPS and ToF-SIMS is used. • The oxide layers formed on austenite and ferrite phases are locally characterized. • The effect of passivation on the surface oxide layer is discussed. This work reports an innovative methodology based on the coupling of XPS and ToF-SIMS in order to study the surface oxide layer formed on austenite and ferrite phases of duplex stainless steels. The native oxide film obtained after mechanical polishing and the passive film obtained after electrochemical passivation in 0.05 M H 2 SO 4 were investigated. Chromium and molybdenum contents were found to be higher in the oxide layer formed on ferrite phase. Nickel and nitrogen enrichments were found to be more pronounced under the oxide layer formed on austenite phase. The effect of passivation on the surface oxide layer is discussed. [ABSTRACT FROM AUTHOR]

Low corrosion protection performances of Trivalent Chromium Process (TCP) coatings with reference to Chromium Conversion Coatings (CCC) deposited on aluminium alloys can be overcome by application of post-treatment processes. This work shows the effect of post-treatment bath (containing hydrogen peroxide and lanthanum salt) on the chemical composition, structure and the corrosion performances of TCP coating deposited on AA 2024-T3 aluminium alloy. Different times of post-treatment bath were applied on the TCP coating and the samples were analyzed by Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS), X-ray Photoelectron Spectroscopy (XPS) and Glow Discharge-Optical Emission Spectrometry (GD-OES). The ToF-SIMS and GD-OES depth profiles show that the post-treatment time has no influence on the thickness of the TCP coating and on its bi-layered structure. It is composed of an outer layer, rich in zirconium and chromium oxides and an inner layer rich in aluminium oxides and oxy-fluorides. 3D ToF-SIMS images reveal an enrichment of Cr and Zr-like species over the surface of intermetallic particles with reference to alloy matrix, whereas a homogenous distribution of La is observed. The analysis of in-depth distribution shows that La is present principally in the outer part of the TCP coating. The La concentration increases with increasing post-treatment time. The effect of post-treatment time on protection was evaluated by Electrochemical Impedance Spectroscopy (EIS) and Linear Sweep Voltammetry (LSV) in a 0.001 M NaCl + 0.1 M Na 2 SO 4 electrolyte. The increased post-treatment time enhances the cathodic inhibition against oxygen reduction. The post-treatment provides improved coating homogeneity and sealing properties. • No thickness and structure modification of TCP coating induced by post-treatment • Significant inhibition of the cathodic oxygen reduction induced by post-treatment • Increase of La and decrease of Cr in TCP with higher post-treatment time • Homogenous surface distribution of La responsible for sealing coating defects [ABSTRACT FROM AUTHOR]

Abstract In situ Electro-Chemical Scanning Tunneling Microscopy (ECSTM) and Electron Back-Scatter Diffraction analysis of the same local microstructural region were combined to study the relationships between grain boundary (GB) type and structure and passivation on microcrystalline copper in 0.1 M NaOH aqueous solution. The results show that, for high angle random boundaries, passivation in the Cu(I) oxidation range is characterized by a decrease of the depth of GB edge region due to the formation of a passive film locally thicker than on the adjacent grains and thus to anodic oxidation being locally less efficient since it consumes more copper at the grain boundaries. For Σ3 CSL boundaries, the Cu(I) passivation efficiency was observed to be dependent on the local structure of the boundaries. A transition from more to less efficient passivation was observed for a deviation angle of 0.4–0.5° of the {111} GB plane with respect to the perfect geometry of an ideal coherent twin boundary. This transition would result from the effect on the local anodic oxidation properties of an increased density of misfit dislocations accommodating the increased deviation of the boundary plane from the exact CSL plane. Graphical abstract Image 1 Highlights • Local passivation at surface termination of grain boundaries studied in situ on copper. • Microstructure characterized by coupled ECSTM and EBSD local analysis. • Cu(I) passivation less efficient at random grain boundaries than on grains. • Cu(I) passivation efficiency dependent on local structure for Σ3 CSL boundaries. [ABSTRACT FROM AUTHOR]

Highlights • Duplex stainless steel and corresponding single phase alloys are compared. • The native oxide films formed after mechanical polishing are studied. • A coupling of XPS and ToF-SIMS is used. • The thickness, composition and chemical states of the oxide layer are investigated. • The link between the chemical compositions of the bulk and the surface is discussed. Abstract The surface oxide films formed after mechanical polishing on duplex stainless steel and corresponding single phase alloys were characterized by XPS and ToF-SIMS. The native oxide films are mixtures of oxides and hydroxides composed of Fe(III), Mo(IV) and Mo(VI) in the outer region and Cr(III) in the inner region. Nickel, molybdenum and nitrogen are enriched in the underlying metal while chromium and molybdenum are enriched in the oxide layer. The contents of alloying elements in the oxide layer and/or in the underlying metal are found to be directly related to their content in the bulk of the alloys. [ABSTRACT FROM AUTHOR]

The oxidation behaviours of polycrystalline and monocrystalline Ni-base alloys (Ni-16Cr-8Fe (wt%)) were investigated in situ by Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS). The oxide layer formed is duplex: an inner chromium-rich layer and an outer layer which is rich in nickel and iron. Time evolution of the composition of inner layer from pure Cr 2 O 3 towards spinel (NiCr 2 O 4 ) was observed. The oxidation kinetics was accelerated by alloy grain boundaries, which can favour the diffusion of chromium. Both the parabolic and volatilization constants increased with increasing temperature, with k p varying from 1.9×10 −3 to 1.6×10 −2 nm 2 .s −1 , and k v from 1.0×10 −3 to 2.9×10 −3 nm.s −1 . [ABSTRACT FROM AUTHOR]

In situ X-ray photoelectron spectroscopy real-time measurements and angular-dependent high resolution core level analysis were used for the first time to investigate the Cr enrichment and oxide growth mechanisms on a model 304 austenitic stainless steel surface in the very initial stages of oxidation leading to pre-passivation. The oxidation kinetics was followed for increasing oxygen exposure and temperature, revealing an early nucleation regime (for exposure <10 L) leading to the formation of a strongly Cr-enriched Cr 3+ /Fe 3+ mixed layer followed by an oxide growth regime where preferential iron oxidation takes over and mitigate the initial chromium enrichment. [ABSTRACT FROM AUTHOR]

The depth profiling of hydrogen and deuterium in polycrystalline and monocrystalline Nickel-base alloys (Ni-16Cr-8Fe, wt%) was performed by Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS) and Elastic Recoil Detection Analysis (ERDA) after oxidation in simulated primary medium conditions containing 9 at.% D 2 O. The use of deuterium isotopic tracer in ToF-SIMS has demonstrated the presence of deuterium in the oxide layer for oxidation times of 300 min and 100 h. The quantities of deuterium were determined by ERDA using a 2 MeV 4 He ion beam. Finally, the penetration coefficient α was calculated, and ranged from 0.01 to 0.04. [ABSTRACT FROM AUTHOR]

• Investigation of native and passive surface films formed on Ni-20 at.% Cr alloy surfaces. • Surface analysis by in situ electrochemical measurements combined with advanced ex situ surface analysis. • Mechanistic understanding of the effects of high-temperature hydrogen annealing pretreatment. • Enhanced corrosion resistance of electrochemically passivated surface by high-temperature hydrogen annealing pretreatment. • Increase in Cr enrichment of initially weakly protected sites of the inner barrier layer. The effect of high-temperature annealing under hydrogen gas (H 2) surface preparation on a binary polycrystalline Ni-20 at.% Cr alloy was investigated in comparison with conventional mechanical grinding surface preparation. Duplex surface films with inner Cr(III) oxide and outer Ni(II) and Cr(III) hydroxide layers natively formed before and after H 2 annealing were characterized by X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectroscopy. A thinner and less homogeneous inner barrier layer formed after H 2 annealing caused an oxidation peak at the active/passive transition in the linear sweep voltammetry measurement in a 0.5 M H 2 SO 4 solution. Despite this high oxidation peak, passivation of the H 2 annealed surface resulted in the formation of a more corrosion resistant inner layer than on the mechanically ground surface, as demonstrated by electrochemical impedance spectroscopy. The corrosion resistant passive film formation of the H 2 annealed surface is attributed to the increased Cr enrichment of the inner layer caused by the selective Ni dissolution providing corrosion resistance to the initially weakly protected sites of the natively formed surface film. [ABSTRACT FROM AUTHOR]

The role of the SiC substrate surface on the resistance to the local initiation of tarnishing of thin-layered silver stacks for demanding space mirror applications was studied by combined surface and interface analysis on model stack samples deposited by cathodic magnetron sputtering and submitted to accelerated aging in gaseous H 2 S. It is shown that suppressing the surface pores resulting from the bulk SiC material production process by surface pretreatment eliminates the high aspect ratio surface sites that are imperfectly protected by the SiO 2 overcoat after the deposition of silver. The formation of channels connecting the silver layer to its environment through the failing protection layer at the surface pores and locally enabling H 2 S entry and Ag 2 S growth as columns until emergence at the stack surface is suppressed, which markedly delays tarnishing initiation and thereby preserves the optical performance. The results revealed that residual tarnishing initiation proceeds by a mechanism essentially identical in nature but involving different pathways short circuiting the protection layer and enabling H 2 S ingress until the silver layer. These permeation pathways are suggested to be of microstructural origin and could correspond to the incompletely coalesced intergranular boundaries of the SiO 2 layer. [ABSTRACT FROM AUTHOR]

In this work, we addressed the local degradation mechanisms limiting the prelaunch environmental durability of thin-layered silver stacks for demanding space mirror applications. Local initiation and propagation of tarnishing were studied by combined surface and interface analysis on model stack samples consisting of thin silver layers supported on lightweight SiC substrates and protected by thin SiO2 overcoats, deposited by cathodic magnetron sputtering and submitted to accelerated aging in gaseous H2S. The results show that tarnishing is locally initiated by the formation of Ag2S columns erupting above the stack surface. Ag2S growth is promoted at high aspect ratio defects (surface pores) of the SiC substrate as a result of an imperfect protection by the SiO2 overcoat. Channels most likely connect the silver layer to its environment through the protection layer, which enables local H2S entry and Ag2S growth. The silver sulfide columns grow in number and size eventually leading to coalescence with increasing H2S exposure. In more advanced stages, tarnishing slows down owing to saturation of all pre-existing imperfectly protected sites of preferential sulfidation. However, it progresses radially at the basis of the Ag2S columns underneath the protection layer, consuming the metallic silver layer and deteriorating the protecting overcoat. [ABSTRACT FROM AUTHOR]

Fe-based air alkaline batteries are promising candidates for large scale energy storage due to their low cost, eco-friendliness and high energy density. In this work, pure iron was studied as negative electrode of Fe-air batteries with and without Na 2 S added to the KOH alkaline electrolyte in order to bring new insight on the mechanisms of inhibition of the hydrogen evolution reaction (HER) and improvement of the electrochemical performances of the Fe electrode. Electrochemical (CV, galvanostatic discharge), spectroscopic (XPS, ToF-SIMS) and microscopic (SEM) analysis were applied to characterize the effect of the sulfide additive (Na 2 S) on the electrochemical behavior of Fe electrodes and their chemical and morphological modifications. Surface analysis performed by XPS and ToF-SIMS revealed the formation of a markedly thicker oxide/hydroxide layer. The mechanism of formation of this thick oxide/hydroxide layer is initiated by the adsorption of sulfur (S ads ) at the oxide/metal interface that inhibits the HER during the first stages of electrochemical process and promotes subsequent anodic oxidation. With the Na 2 S electrolyte additive, Fe(0)/Fe(II) conversion/deconversion is suppressed and charge/discharge proceeds mostly by Fe(II)/Fe(III) conversion/deconversion with improved capacity owing to the porous morphology of the oxide/hydroxide layer. [ABSTRACT FROM AUTHOR]

Adsorption of Pb atoms on the Ni(111), Ni(100), Fe(110), and Cr(110) metallic surfaces was studied theoretically within an ab initio density functional theory approach (DFT). (√3 × √3)R30° super structures for Ni(111), and (2 × 2) for the other surfaces, corresponding to the saturation state, were considered. The preferred adsorption sites are found to be ternary sites for Ni(111), Fe(110), Cr(110) and quaternary sites for Ni(100). Adsorption on Fe and Cr is less exothermic than on Ni, by 0.16 and 0.33 eV/mol respectively. Adsorption on model surfaces of Ni based alloys was also investigated. It was found that the energy of adsorption depends mostly on the chemical composition of the ternary site, and can be described by a linear combination of the energies of adsorption on the pure metals. The nature of the second nearest neighbour of the adsorbed Pb atom has no significant influence on the adsorption energy. Average energies of adsorption were calculated in two cases: the limit of low coverage, and the saturation. The energies of adsorption of Pb at saturation on nickel base alloy surface representative of alloy 600 (Ni-15Cr-8Fe) and alloy 690 (Ni-30Cr-8Fe) were calculated to be 0.07 and 0.11 eV lower than on pure Ni respectively. [ABSTRACT FROM AUTHOR]

The effects of surface pretreatments (degreasing and pickling) on the characteristics of the Trivalent Chromium Process (TCP) coating on pure aluminum and on AA2024-T351 aluminum alloy were investigated here by means of surface sensitive techniques: X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The XPS and ToF-SIMS results evidence that the TCP coating homogeneity is strongly dependent on the pretreatment process used. The TCP coverage factor, calculated from XPS results, is significantly lower, on both pure aluminum and AA2024-T351 alloy surface, when a pickling step is applied. One of the main effects of pickling pretreatment is strong metallic copper enrichment at the surface of the 2024 alloy, associated with chemical dissolution of Al-Cu intermetallic particles. However, it is evidenced here, that the copper enrichment is not detrimental for the quality of the TCP coating. The coating failure, observed when the pickling step is applied, can be assigned to a faster kinetics of the coating growth leading to formation of thicker conversion coating more susceptible to cracking or to the localized presence of aluminum fluoride species leading to the appearance of coating defects or detachment. [ABSTRACT FROM AUTHOR]

Room temperature ionic liquids (RTILs) attract much attention as a new type of environmentally benign electrolytes for Li-ion batteries due to their numerous interesting physicochemical properties. Here, in this paper, Li intercalation/deintercalation in presence of the N -butyl- N -methylpyrrolidinium bis(trifluoromethanesulfonyl) imide (PYR 14 TFSI) and N -methyl- N -propylpyrrolidinium bis(fluorosulfonyl)imide (PYR 13 FSI) containing 0.3 M LiTFSI, was evaluated in a thin 100 nm layer of V 2 O 5 deposited on Al substrate by atomic layer deposition. Potentiodynamic tests performed in LiTFSI/Pyr 14 TFSI show a quasi-reversible Li intercalation during 10 cycles (between 2.4 and 5 V) with an average coulombic efficiency of 99%. The capacity, calculated from the 1st cycle, is found to be 182 mAh g −1 , about 19% (±2%) higher than the theoretical capacity reported for V 2 O 5 (147 mAh g −1 ). X-ray photoelectron spectroscopy analysis confirms that the intercalation of more than 1 mol of Li + per V 2 O 5 is achieved as also the possible presence of a solid permeable interface (SPI) layer on the V 2 O 5 surface. Likewise, the Li + in-depth distribution on the V 2 O 5 layer after intercalation in RTILs measured by time-of-flight secondary ion mass spectrometry ion depth profiles, show small irreversible electrode modifications with the presence of lithium through the entire V 2 O 5 layer with significant lithium trapping at the V 2 O 5 layer/Al substrate interface. [ABSTRACT FROM AUTHOR]

The oxidation of chromium at 300 °C was investigated in situ by ToF -SIMS for three different oxygen pressures ( $$P_{{{\text{O}}_{2} }} = 2.0 \times 10^{ - 7}$$ , 6.0 × 10 and 2.0 × 10 mbar). Sequential exposure to the O isotopic tracer was performed to reveal the governing transport mechanism in the oxide film. The evolution of the oxide thickness was monitored. Volatilization of CrO was evidenced. A model was used to describe the kinetics resulting from the measurements. Both the parabolic and volatilization constants showed a dependence on oxygen partial pressure like $$P_{{{\text{O}}_{2} }}^{ - 1/n}$$ , with n = 1.9 ± 0.1, indicating a defect structure mainly consisting of oxygen vacancies. The re-oxidation in O shows a growth of the oxide layer at the metal/oxide interface, demonstrating an oxidation process governed by anionic transport via oxygen vacancies. The diffusion coefficient of oxygen in the oxide was determined by fitting the ToF -SIMS depth profiles. It is 2.0 × 10 cm s. [ABSTRACT FROM AUTHOR]

• Corrosion inhibition and interfacial bonding of 2-MBT studied on copper. • Electrochemistry combined with advanced surface analysis by XPS and ToF-SIMS. • Inhibition enhanced by cathodic reduction of interface before 2-MBT adsorption. • 2-MBT bonded to metallic copper and copper oxide islands via the S atoms. • Exo- and endocyclic S atoms released by dissociation and bonded to metallic Cu. Electrochemistry along with advanced surface analyzes (X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry) were implemented to investigate copper corrosion inhibition by 2-mercaptobenzothiazole (2-MBT) in hydrochloric aqueous solution and the effects of electrochemical control on the formation of the inhibiting interface. It is shown that reducing the native surface oxide by cathodic reduction prior to exposure to the inhibitor drastically decreases the rate of anodic dissolution. Additionally, increasing the exposure time of the metal surface to the inhibitor results in even better protection against dissolution. 2-MBT adsorbs as multilayers and bonds to both metallic copper and residual copper oxide islands via its sulphur atoms. Partial dissociation of the molecule, releasing the exocyclic sulphur, which then bonds to metallic Cu, is observed. Further dissociation of the molecule, releasing the endocyclic sulphur, is induced by anodic polarization, forming defects in the organic layer and thus compromising the barrier properties of the organic layer. [ABSTRACT FROM AUTHOR]

ToF-SIMS and XPS are combined to study the adsorption of tetradecyl-benzyldimethyl-ammonium (BDA-C14) bromide corrosion inhibitor on carbon steel surface. BDA-C14 forms a protective layer with N-containing polar head group interacting with carbon steel surface. The adsorbed inhibitor surface coverage strongly depends on immersion time and inhibitor concentration. A maximum and uniform coverage is found for sufficiently long exposure times at a critical inhibitor concentration of about 25 ppm w. The uniform adsorbed inhibitor layer formed on the surface mitigates the formation of iron chloride/hydroxide intermediates and thus enhances the corrosion protection of carbon steel in aggressive environment. • The adsorption of BDA-C14 corrosion inhibitor on carbon steel surface was studied by ToF-SIMS and XPS. • The inhibitor forms a protective layer with N-containing polar head group interacting with carbon steel surface. • The adsorbed inhibitor surface coverage strongly depends on immersion time and inhibitor concentration. • The critical concentration for a maximum and uniformed inhibitor coverage on carbon steel is determined. • The uniform adsorbed inhibitor layer on carbon steel can mitigate the formation of iron chloride/hydroxide intermediates. [ABSTRACT FROM AUTHOR]

The high self-corrosion rate of Mg in aqueous electrolyte generates H 2 , which is the main impediment to restrict the utilization of Mg-air batteries. However, organic/inorganic hybrid electrolyte is prone to reduce the Mg degradation. Herein, the effect of different ethanol fractions in water with 0.6 M NaCl on corrosion behavior of Mg and battery discharge performances is demonstrated. The significant corrosion inhibition in a high content of ethanol (≥20 vol%) in electrolyte is attributed to the formation of a thinner, more corrosion protective layer enriched in magnesium oxide as demonstrated by scanning electron microscopy, X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry. Contrarily, in water-based electrolyte a thick, porous and rough layer principally composed of magnesium hydroxide is formed. By varying the ethanol to water fraction in the electrolyte in full battery cell, it is shown that even a small ethanol content (≤ 5 vol%), can greatly enhance the electrochemical performances of Mg anode. Within several ethanol content, 0.5 vol% demonstrates the best performances with a limited corrosion rate and greatly improves the discharge performance and the battery lifetime. It is demonstrated here that application of inorganic/organic dual electrolyte is a promising and easy way towards a well-controlled Mg anode reactivity and improved performances of Mg-air battery. [Display omitted] • Significant corrosion inhibition in high content of ethanol (≥ 20 vol%). • Formation of a thinner, more corrosion protective layer enriched in MgO in presence of ethanol. • Growth of a thick, porous and rough layer composed of Mg(OH) 2 in water-based electrolyte. • The best discharge performance and battery lifetime in 0.5 vol% ethanol content. [ABSTRACT FROM AUTHOR]

The ideal solid oxide fuel cells (SOFCs) can be powered by readily available hydrocarbon fuels containing impurities. While this is commonly recognized as a key advantage of SOFC, it also, together with the elevated operating temperature, becomes the main barrier impeding the in-situ or operando investigations of the anode surface chemistry. Here, using a well-designed quenching experiment, we managed to characterize the near-surface structure of La 0.4 Sr 0.6 TiO 3+δ (LST) anode in SOFCs fuelled by H 2 S-containing methane. This new method enabled us to clearly observe the surface amorphization and sulfidation of LST under simulated SOFC operating conditions. The ∼1 nm-thick two dimensional sulfur-adsorbed layer was on top of the disordered LST, containing –S, –SH and elemental sulfur species. In SOFC test, such “poisoned” anode showed increased performances: a ten-fold enhanced power density enhancement (up to 30 mW cm −2 ) and an improved open circuit voltage (from 0.69 V to 1.17 V). Moreover, its anodic polarization resistance in methane decreased to 21.53 Ω cm 2 , a difference of 95% compared with the sulfur-free anode. Control experiments confirmed that once the adsorbed sulfur species were removed electrochemically, methane conversion slowed down simultaneously till full stop. [ABSTRACT FROM AUTHOR]

Scanning tunneling microscopy was used to study the reactivity of self-organized nanostructured O/Cu(110) surfaces towards H 2 S. We took advantage of the fast and easy nanostructuring process of the O/Cu(110) system to study in detail the reaction mechanisms on three structures having different width of CuO stripes. Detachment of Cu–O chains from CuO stripes occurred in all cases but the formation of S-c(2 ×2) islands was observed only on wider ( >10 nm) CuO stripes. At low exposure, structures were observed at the CuO stripe edge. Linear structures, aligned along the [ 1 1 ¯ 0 ] direction and showing 2 × periodicity, were also observed on copper stripes. The competition between detachment and c(2 × 2) island growth mechanism depends on the H 2 S adsorption rate. At higher pressure, it is shown that the sulfidation only proceeds by sulfur islands growth in wider CuO stripes. These results show that self-organized nanostructures on metal surfaces are powerful tools to study reactions at the nanometer scale and the relationship between local structure and reactivity. [ABSTRACT FROM AUTHOR]

We report on the stability of large sulfur islands, formed by exposing the nanostructured O/Cu(110) surface to H 2 S. We have found that these islands, composed of several hundreds of atoms, show a dynamic behavior at room temperature and undergo both Smoluchowski and Ostwald ripening. An additional decay mechanism has been observed at sub-saturation sulfur coverages. The island decay can be described by a classical power law. However, oscillatory deviations from the model have been observed and possible reasons for their occurrence are discussed. At saturation sulfur coverage, the islands are still mobile and undergo ripening, but no decay is observed. In these conditions, a new nanostructured S/Cu(110) surface is formed. [ABSTRACT FROM AUTHOR]

X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ions mass spectrometry (ToF-SIMS) analyses were performed to characterize the interaction of Cu with mercaptobenzothiazole (MBT) in aqueous solution for 1 h and 24 h in absence and presence of NaCl. The fingerprints of the molecules are identified with XPS (S, N and C signals). The analysis of the Cu 2p core level and Auger Cu peaks allow us to show that the Cu metal is covered by a Cu 2 O oxide layer whose thickness increases with exposure time in the absence of MBT. It is found that MBT forms multilayers on Cu oxide and inhibits the oxide layer growth. The XPS data are consistent with MBT adsorbed on oxide in multilayers, with a small fraction adsorbed on metallic Cu. These interactions are then further characterized using ToF-SIMS. The results suggest adsorption of the MBT molecules in a strongly bonded layer through both S atoms of the organic molecule oriented towards the surface, covered by a weakly bonded multilayer. Quantitative treatments of XPS intensities allows us to evaluate a layer thickness of 23 Å and 32 Å after 1 h and 24 h, respectively. Co-adsorbed water is also identified. The presence of water in the organic layer (ratio H 2 O/MBT = 0.28) may explain the orientation of the molecules with S directed towards the surface and N interacting through H bonds with water molecules, as suggested by complementary DFT calculations. The adsorption of MBT is similar in presence of NaCl and in pure water, and also inhibits the oxide growth. In addition, MBT adsorption inhibits the adsorption of Cl on the Cu surface. Inductively Coupled Plasma Optical Emission Spectrophotometry (ICP OES) experiments demonstrate that MBT adsorption inhibits Cu dissolution, even after 20 days immersion in NaCl. Thus, we demonstrated that MBT, by adsorbing and forming a full monolayer at the Cu surface, inhibits further oxide growth, Cl adsorption and copper dissolution in NaCl. [Display omitted] • MBT adsorbs on Cu immersed in water and forms multilayers with thicknesses of 2.3–3.2 nm. • Adsorbed MBT inhibits the copper oxide growth, Cl adsorption and copper dissolution in NaCl. • The first MBT layer close to the substrate is bonded to copper via the two S atoms oriented towards the surface. • Water is present in the organic film in a ratio H 2 O/MBT = 0.28. • Water in the organic film has a determinant role in molecule orientation, as shown by DFT calculations. • A fraction of MBT is adsorbed on metallic copper, healing some depassivated areas. [ABSTRACT FROM AUTHOR]

The adsorption of a model protein, the bovine serum albumin (BSA), on plasma-deposited silver nanocomposite thin films was investigated in situ by quartz crystal microbalance (QCM) and ex situ by X-ray photoelectron spectroscopy (XPS). For comparison, BSA adsorption was also studied on pure silver sample and on the polymeric matrix without silver nanoparticles. Both techniques showed that BSA adsorption systematically occurred, regardless of the chemical composition of the solid surface. BSA adsorption was found to be a fast and irreversible process. For the adsorbed BSA layer characterization, a general island model was considered. The height of the protein islands ( h ) and their surface coverage ( γ ) were estimated from combined QCM and XPS data. On the polymeric matrix, the surface coverage was low whereas on pure silver sample and on the nanocomposite film, it was significantly increased. From QCM measurements, mass loss at a constant rate, ascribed to the release and dissolution of Ag particles from the nanocomposite film into the surrounding solution, was observed before and after BSA adsorption, with two different associated rates. The decrease of the silver release rate after BSA adsorption is explained by silver particles coverage by protein islands. BSA molecules adsorbed on silver nanoparticles have a “blocking” effect, decreased the rate of silver nanoparticle release. However, silver dissolution as Ag + ions may still occur. [ABSTRACT FROM AUTHOR]