Abstracts sélectionnés 2020

2-mercaptobenzothiazole corrosion inhibitor deposited at ultra-low pressure on model copper surfaces.
X. Wu, F. Wiame, V. Maurice, P. Marcus, Corrosion Science 2020, 108464. https://doi.org/10.1016/j.corsci.2020.108464.

Adsorption of 2-mercaptobenzothiazole (2-MBT) at ultra-low pressure and room temperature on metallic and pre-oxidized Cu(111) surfaces and its thermal stability were investigated using X-ray photoelectron spectroscopy in order to better understand the interfacial corrosion inhibiting properties. 2-MBT is lying flat in the monolayer with two sulphur atoms bonded to Cu and decomposes partially yielding atomic sulphur when interacting with metallic copper prior to forming molecular multilayers. Decomposition is prevented by surface pre-oxidation with 2D oxide dissociation accelerating the 2-MBT initial adsorption kinetics. 2-MBT further decomposes and partially desorbs above 100 °C. A pre-adsorbed 2-MBT monolayer on metallic copper inhibits surface corrosion.

DFT study of n-alkyl carboxylic acids on oxidized aluminum surfaces: from standalone molecules to self-assembled-monolayers M. Poberžnik, F. Chiter, I. Milošev, P. Marcus, D. Costa, A Kokalj, Applied Surface Science 2020, accepted.

We report on a systematic DFT study of adsorption of n-alkyl
carboxylic acids (CA) on oxidized aluminum surfaces, where we address the roles of the adsorption mode, molecular coverage, tilt angle of alkyl
chain, and alkyl chain size on the stability of the formed CA monolayers.
Adsorption was modeled on two models of the hydroxylated ultrathin-oxide
film, supported on Al(111), which differ in OH coverage, types of
adsorption sites, and their lateral distribution. Two different
adsorption modes were considered: (i) plain adsorption mode and (ii)
acid-base condensation adsorption mode. While on the fully hydroxylated
surface we only identified monodentate bonded carboxylates, bidentates
are by about 1 eV more stable than monodentates near OH vacancies.
Molecular packing within the monolayer is driven by lateral interchain
interactions and the optimum tilt angle is achieved when the interchain
distances are similar to those in the polyethylene crystal. The
adsorption energy can be decomposed into the headgroup–surface and
lateral interchain components, the former being largely independent on
the chain size and the latter being proportional to the number of C atoms
in the chain. Consequently, the adsorption is stabilized by about 1
eV/molecule at full monolayer coverage as passing from CA-2 to CA-18.

Passivation Mechanisms and Pre-Oxidation Effects on Model Surfaces of FeCrNi Austenitic Stainless Steel.
Ma, L.; Pascalidou, E.-M.; Wiame, F.; Zanna, S.; Maurice, V.; Marcus, P. Corrosion Science 2020, 108483. https://doi.org/10.1016/j.corsci.2020.108483.

Passivation mechanisms were investigated on (100)-oriented Fe-18Cr-13Ni surfaces with direct transfer between surface preparation and analysis by X-ray photoelectron spectroscopy and scanning tunneling microscopy and electrochemical characterization. Starting from oxide-free surfaces, pre-oxidation at saturation under ultra-low pressure (ULP) oxygen markedly promotes the oxide film Cr(III) enrichment and hinders/delays subsequent iron oxidation in water-containing environment. Exposure to sulfuric acid at open circuit potential causes preferential dissolution of oxidized iron species. Anodic passivation forces oxide film re-growth, Cr(III) dehydroxylation and further enrichment. ULP pre-oxidation promotes Cr(III) hydroxide formation at open circuit potential, compactness of the nanogranular oxide film and corrosion protection.

High-Current-Density CO2-to-CO Electroreduction on Ag-Alloyed Zn Dendrites at Elevated Pressure.
Lamaison, S.; Wakerley, D.; Blanchard, J.; Montero, D.; Rousse, G.; Mercier, D.; Marcus, P.; Taverna, D.; Giaume, D.; Mougel, V.; et al. Joule 2020. https://doi.org/10.1016/j.joule.2019.11.014.

The electrocatalytic conversion of CO2  into valuable chemical feedstocks is a highly sought-after route to recycle CO2 emissions. Among the expected products, CO is a valuable synthon for organic syntheses and fuel generation. Nevertheless, most current electrocatalytic systems do not generate CO at a sufficient rate or purity for its subsequent direct conversion. Herein, we report the rational design of novel and highly active Ag-alloyed Zn dendritic electrodes with remarkable CO2-to-CO selectivity. Through fine-tuning of the individual electrodeposition parameters, the Ag content, porosity, thickness, and surface area of the electrodes were optimized, leading to a CO2-to-CO selectivity as high as 91%, which could be sustained above an average of 90% over 40 h. Increase of the CO2 pressure (up to 9.5 bar) to enhance the CO2  concentration allowed CO partial current densities as high as –286 mA.cm−2 to be achieved, setting a new record for predominantly Zn-based electrodes operating in neutral pH.

Water Desorption Effects on the Surface Electrical Resistance of Air-Exposed Hydrogenated Diamond.
Flammini, R.; Satta, M.; Bellucci, A.; Girolami, M.; Wiame, F.; Trucchi, D. M. Applied Surface Science 2020, 512, 145491. https://doi.org/10.1016/j.apsusc.2020.145491.

The air-exposed hydrogenated diamond surface has been studied by carrier transport measurements and density functional theory. Our results have allowed us to understand the close relationship between the physisorbed water molecules and the electrical resistance. We have therefore been able to show that the evolution of the resistance over time and temperature can be related to the extent of the hole accumulation layer originating at the surface of the hydrogenated diamond. The method has allowed us to estimate the desorption energy of a single water molecule by means of resistance measurements alone.

Chloride-Induced Alterations of the Passive Film on 316L Stainless Steel and Blocking Effect of Pre-Passivation.
Wang, Z.; Seyeux, A.; Zanna, S.; Maurice, V.; Marcus, P. Electrochimica Acta 2020, 329, UNSP 135159. https://doi.org/10.1016/j.electacta.2019.135159.

Electrochemical polarization measurements were combined with surface analysis by Time of Flight Secondary Ion Mass Spectroscopy (ToF-SIMS), X-Ray Photoelectron Spectroscopy (XPS) and Atomic Force Microscopy (AFM) to study the alterations of the passive film on 316 L austenitic stainless steel induced by the presence of chlorides in sulfuric acid electrolyte. The work was performed at a stage of initiation of localized corrosion preceding metastable pitting at the micrometer scale as verified by current transient analysis and AFM. The results show that Cl− ions enter the bilayer structure of the surface oxide already formed in the native oxide-covered initial surface state at concentrations below the detection limit of XPS (<0.5 at%), mostly in the hydroxide outer layer where Fe(III) and Mo(IV,VI) species are concentrated but barely in the oxide inner layer enriched in Cr(III). Their main effect is to produce a less resistive passive state by poisoning dehydroxylation and further Cr(III) and Mo(IV,VI) enrichments obtained in the absence of chlorides. This detrimental effect can be suppressed by pre-passivation in a Cl−-free electrolyte, which blocks the entry of chlorides in the passive film, including in the outer exchange layer, and enables the beneficial aging-induced variations of the composition to take place despite the presence of chlorides in the environment.

Carbon-Nanotube-Supported Copper Polyphthalocyanine for Efficient and Selective Electrocatalytic CO2 Reduction to CO.
Karapinar, D.; Zitolo, A.; Huan, T. N.; Zanna, S.; Taverna, D.; Galvao Tizei, L. H.; Giaume, D.; Marcus, P.; Mougel, V.; Fontecave, M. Chemsuschem 2020, 13 (1), 173–179. https://doi.org/10.1002/cssc.201902859.

Electroreduction of CO2 to CO is one of the simplest ways to valorise CO2 as a source of carbon. Herein, a cheap, robust, Cu‐based hybrid catalyst consisting of a polymer of Cu phthalocyanine coated on carbon nanotubes, which proved to be selective for CO production (80 % faradaic yield) at relatively low overpotentials, was developed. Polymerisation of Cu phthalocyanine was shown to have a drastic effect on the selectivity of the reaction because molecular Cu phthalocyanine was instead selective for proton reduction under the same conditions. Although the material only showed isolated Cu sites in phthalocyanine‐like CuN4 coordination, in situ and operando X‐ray absorption spectroscopy showed that, under operating conditions, the Cu atoms were fully converted to Cu nanoparticles, which were likely the catalytically active species. Interestingly, this restructuring of the metal sites was reversible.

Adsorption and Thermal Stability of 2-Mercaptobenzothiazole Corrosion Inhibitor on Metallic and Pre-Oxidized Cu(111) Model Surfaces.
Wu, X.; Wiame, F.; Maurice, V.; Marcus, P. Applied Surface Science 2020, 145132. https://doi.org/10.1016/j.apsusc.2019.145132.

2-mercaptobenzothiazole (2-MBT) is used for its corrosion inhibition properties. In this study, the adsorption of 2-MBT on metallic and pre-oxidized Cu(1 1 1) surfaces was investigated using Auger Electron Spectroscopy and Scanning Tunneling Microscopy. Growth and structure of molecular films adsorbed at ultra low pressure and room temperature on clean and pre-oxidized Cu(1 1 1) surfaces were characterized. On clean metallic Cu(1 1 1) surface, local triangular R19.1° structures are formed at low exposures (3–4 L), which are assigned to the adsorption of atomic S resulting from partial decomposition of 2-MBT. At 10 L, a full non-ordered monolayer of 2-MBT is formed, and further exposure leads to the formation of a non-ordered multilayer. The thickness of the outermost 2-MBT layer is 1.3 Å, which suggests that the outermost molecules of the multilayer are lying flat. Oxidation of the copper surface prior to exposure to 2-MBT results in more compact and homogeneous molecular films. The initial 2D oxide is dissociated and replaced by 2-MBT. Thermal stability at different temperatures was studied on clean and pre-oxidized copper surfaces saturated with 2-MBT. A R19.1° structure is observed in both cases for temperatures higher than C, indicating the decomposition of 2-MBT and a copper surface covered with atomic S.

Study of the Surface Oxides and Corrosion Behaviour of an Equiatomic CoCrFeMnNi High Entropy Alloy by XPS and ToF-SIMS.
Wang, L.; Mercier, D.; Zanna, S.; Seyeux, A.; Laurent-Brocq, M.; Perriere, L.; Guillot, I.; Marcus, P. Corrosion Science2020, 108507. https://doi.org/10.1016/j.corsci.2020.108507.

XPS and ToF-SIMS analysis have been combined with electrochemical measurements to determine the corrosion behavior of the equiatomic CoCrFeMnNi high entropy alloy. An XPS methodology based on analysis of the 3p core level spectra was developed to determine the composition and thickness of oxide films. Both native oxide (∼1.4 nm) and passive films (∼ 1.6 nm) formed in acidic medium are duplex, comprising Cr and Mn inner layer and Cr/Fe/Co mixture outer layer. No nickel is observed in the oxide layer. The effects of exposure of the native film to sulfuric acid and passivation under anodic polarization have been investigated.

Chromium Valence Change in Trivalent Chromium Conversion Coatings on Aluminium Deposited under Applied Potentials.
J. Qi, J. Światowska, P. Skeldon, P. Marcus, Corrosion Science 2020, 108482. https://doi.org/10.1016/j.corsci.2020.108482.

The electroassisted (EA) deposition of trivalent chromium conversion coatings on aluminium is investigated with a focus on the influence of applied potential on the chromium valence state, as determined by Raman spectroscopy. The morphology and compositions of the coatings were investigated by scanning electron microscopy and energy-dispersive spectroscopy. The EA coatings were formed in naturally-oxygenated SurTec 650 chromitAl solution at constant potentials of −1.5 and −0.5 VSCE. The coatings contained chromium and zirconium constituents. The potentials resulted in net cathodic and anodic current densities, respectively, during the coating growth. Comparisons were made with coating formation at the open-circuit potential (OCP). The coating thickness increased in order −0.5 VSCE < OCP < −1.5 VSCE, a result of increasing alkalinity from the cathodic reaction that facilitates deposition of the coating constituents. Fresh coatings formed at −1.5 VSCE revealed the presence of Cr6+ species. By contrast, Cr6+ species were not resolved in the coating formed at −0.5 VSCE. It is proposed that less H2O2 is generated at −0.5 VSCE to oxidize Cr3+ coating species.