In situ soft X-ray dynamic microscopy of electrochemical processes

We report a pilot study in in situ electrochemical X-ray dynamic microscopy, based on a model system: the anodic and cathodic behaviour of Ag in neutral NaCl and (NH₄)₂SO₄ aqueous solutions. In situ X-ray imaging highlighted mesoscopic features related to corrosion processes, yielding soluble (NH₄⁺ solution) and insoluble (Cl⁻ solution) corrosion products, as well as cathodic growth morphologies. X-ray absorption and phase contrast images were collected, confirming the feasibility of soft X-ray microscopic measurements with lateral resolution down to a few tens of nm in electrochemical cells for operation in a high vacuum environment in presence of liquid electrolytes.     

A new concept for corrosion inhibition of magnesium: Suppression of iron re-deposition

In our recent work (Höche et al. 2016) we proposed that non-faradaic dissolution of Fe impurities and/or iron containing phases with subsequent re-deposition of thin film of pure (“in statu nascendi”) iron enlarges cathodically active sites at the surface of corroding magnesium. The effect drastically accelerates corrosion of impurity containing Mg. In the present work we assume that if Fe re-deposition is prevented, the area of cathodic sites can be drastically decreased and hence corrosion of Mg can be suppressed. In this proof of concept work we use strong Fe^3 + complexing agents in order to remove dissolved iron cations from corrosion sites and prevent iron re-deposition. All used iron complexing agents efficiently lowered the corrosion rate of Mg. Direct correlation of complex stability with its inhibiting efficiency was established. It was shown that cyanide, salicylate, oxalate, methylsalicylate and thiocyanate efficiently reduce hydrogen evolution and suppress critical dark area formation.     

Ferricyanide Armed Anodes Enable Stable Water Oxidation in Saturated Saline Water at 2 A/cm2

The direct seawater electrolysis at high current density and low overpotential affords an effective strategy toward clean and renewable hydrogen fuel production. However, the severe corrosion of anode as a result of the saturation of Cl⁻ upon continuous seawater feeding seriously hamper the electrolytic process. Herein, cobalt ferricyanide / cobalt phosphide (CoFePBA/Co₂P) anodes with Cap/Pin structure are synthesized, which stably catalyze alkaline saturated saline water oxidation at 200–2000 mA cm⁻² over hundreds of hours without corrosion. Together with the experimental findings, the molecular dynamics simulations reveal that PO₄³⁻ and Fe(CN)₆³⁻ generated by the electrode play synergistic role in repelling Cl⁻ via electrostatic repulsion and dense coverage, which reduced Cl⁻ adsorption by nearly 5-fold. The novel anionic synergy endow superior corrosion protection for the electrode, and is expected to promote the practical application of saline water electrolysis.     

Investigation of coating delamination on steels by surface topography and Volta potential difference

Corrosion-induced delamination of an epoxy coating on the AISI/SAE 1045 carbon steel was studied under a humid atmospheric condition (temperature of 25 °C, one standard atmospheric pressure, and relative humidity of 90 %) by the technique of scanning Kelvin probe force microscopy (SKPFM). Surface-polished 1045 samples were first cold coated with the epoxy and then subject to the atmospheric corrosion under the humid atmospheric condition. At specified time intervals, surface Volta potential of the samples was measured using the SKPFM over the dry surface of epoxy coating. The map of Volta potentials demonstrated high contrasts among three characteristic zones: intact steel-epoxy interface, delaminated interface, and interface with active corrosion, which based on a rigorous calibration procedure were then linked to the actual corrosion potential of the steel (measured using a potentiostat w.r.t. a saturated calomel electrode). The SKPFM was found to be able to provide a mean of direct and nondestructive detection of early active corrosion and coating delamination of steels at a submicroscopic resolution, which outperformed the conventional electrochemical techniques for such purposes.     

WBE联合EIS技术研究缺陷涂层下金属腐蚀

用电化学阻抗谱(EIS)结合丝束电极(WBE)技术研究了缺陷涂层浸泡在3.5%(质量分数)NaCl溶液中的劣化过程.从浸泡开始到完好涂层鼓泡失效,缺陷涂层丝束电极阻抗响应一直是缺陷区电极腐蚀反应过程特征,而完好涂层的劣化过程和涂层下的腐蚀反应过程特征被"平均掉".根据电极表面的电流分布,结合阻抗谱技术实现了对表面任意局部阴极和阳极区阻抗测试.研究发现,浸泡开始时,缺陷涂层阴极电流和阳极电流均出现在缺陷区,随着腐蚀过程的发展,阳极电流仍然保持在缺陷区,但阴极电流逐渐向完好涂层下扩展.根据实验结果,对缺陷处和涂层下金属腐蚀反应发生发展的机理进行了深入讨论.     

Delamination of organic coating on carbon steel studied by scanning Kelvin probe force microscopy

Corrosion‐induced delamination of an epoxy coating on the AISI/SAE 1045 carbon steel was studied under a humid atmospheric condition (temperature of 25 °C, 1 standard atmospheric pressure, relative humidity of 90%) by the technique of scanning Kelvin probe force microscopy (SKPFM). Surface‐polished 1045 samples were first cold‐coated with the epoxy and then subject to the atmospheric corrosion under the specified condition. At predetermined time intervals, surface Volta potential differences of the samples were measured using the SKPFM over the dry surface of epoxy coating. The map of Volta potential differences demonstrated high contrasts among three characteristic zones: intact steel‐epoxy interface, delaminated interface, and interface with active corrosion, which was then linked to the actual corrosion potential of the steel (measured using a potentiostat with respect to a saturated calomel electrode) based on a rigorous calibration procedure. It was found that the SKPFM was able to provide direct and nondestructive detection of early active corrosion and coating delamination on steels at a submicroscopic resolution, which outperformed the conventional electrochemical techniques for the same purposes. Copyright © 2012 John Wiley & Sons, Ltd.     

Superelectrophilic Behavior of an Anion Demonstrated by the Spontaneous Binding of Noble Gases to [B12Cl11]−

It is common and chemically intuitive to assign cations electrophilic and anions nucleophilic reactivity, respectively. Herein, we demonstrate a striking violation of this concept: The anion [B₁₂Cl₁₁]⁻ spontaneously binds to the noble gases (Ngs) xenon and krypton at room temperature in a reaction that is typical of “superelectrophilic” dications. [B₁₂Cl₁₁Ng]⁻ adducts, with Ng binding energies of 80 to 100 kJ mol⁻¹, contain B−Ng bonds with a substantial degree of covalent interaction. The electrophilic nature of the [B₁₂Cl₁₁]⁻ anion is confirmed spectroscopically by the observation of a blue shift of the CO stretching mode in the IR spectrum of [B₁₂Cl₁₁CO]⁻ and theoretically by investigation of its electronic structure. The orientation of the electric field at the reactive site of [B₁₂Cl₁₁]⁻ results in an energy barrier for the approach of polar molecules and facilitates the formation of Ng adducts that are not detected with reactive cations such as [C₆H₅]⁺. This introduces the new chemical concept of “dipole-discriminating electrophilic anions.”     

l‐Methioninium chloride and l‐seleno­methioninium chloride at 103 K

The crystal structures of the title compounds, (S)‐1‐carboxy‐3‐(methyl­sulfanyl)­propanaminium chloride, C₅H₁₂NO₂S⁺·Cl⁻, and (S)‐1‐carboxy‐3‐(methyl­selanyl)­propanaminium chloride, C₅H₁₂NO₂Se⁺·Cl⁻, are isomorphous. The proton­ated l ‐methionine and l ‐seleno­methionine mol­ecules have almost identical conformations and create very similar contacts with the Cl⁻ anions in the crystal structures of both compounds. The amino acid cations and the Cl⁻ anions are linked viaN—H⋯Cl⁻ and O—H⋯Cl⁻ hydrogen bonds.     

Acyclic Schiff base salts derived from 1,3‐diaminopropane and 1,3‐diamino‐2‐hydroxypropane

Two salts of acyclic Schiff base cationic ligands, namely N,N′‐bis(2‐nitrobenzyl)propane‐1,3‐diammonium dichloride monohydrate, C₁₇H₂₂N₄O₄²⁺·2Cl⁻·H₂O, (I), and 2‐hydroxy‐N,N′‐bis(2‐nitrobenzyl)propane‐1,3‐diammonium dichloride, C₁₇H₂₂N₄O₅²⁺·2Cl⁻, (II), were synthesized as precursors in order to obtain new acyclic and macrocyclic multidentate ligands and complexes. The cation conformations in compounds (I) and (II) are different in the solid state, although the cations are closely related chemically. Similarly, the hydrogen‐bonding networks involving ammonium cations, hydroxyl groups and chloride anions are also different. In the cation of compound (II), the hydroxyl group is disordered over two sets of sites, with occupancies of 0.785 (8) and 0.215 (8).     

Low‐dimensional compounds containing bioactive ligands. IV. Unusual ionic forms of 5‐chloroquinolin‐8‐ol

Bis(5‐chloro‐8‐hydroxyquinolinium) tetrachloridopalladate(II), (C₉H₇ClNO)₂[PdCl₄], (I), catena‐poly[dimethylammonium [[dichloridopalladate(II)]‐μ‐chlorido]], {(C₂H₈N)[PdCl₃]}_n, (II), ethylenediammonium bis(5‐chloroquinolin‐8‐olate), C₂H₁₀N₂²⁺·2C₉H₅ClNO⁻, (III), and 5‐chloro‐8‐hydroxyquinolinium chloride, C₉H₇ClNO⁺·Cl⁻, (IV), were synthesized with the aim of preparing biologically active complexes of Pd^II and Ni^II with 5‐chloroquinolin‐8‐ol (ClQ). Compounds (I) and (II) contain Pd^II atoms which are coordinated in a square‐planar manner by four chloride ligands. In the structure of (I), there is an isolated [PdCl₄]²⁻ anion, while in the structure of (II) the anion consists of Pd^II atoms, lying on centres of inversion, bonded to a combination of two terminal and two bridging Cl⁻ ligands, lying on twofold rotation axes, forming an infinite [–μ₂‐Cl–PdCl₂–]_n chain. The negative charges of these anions are balanced by two crystallographically independent protonated HClQ⁺ cations in (I) and by dimethylammonium cations in (II), with the N atoms lying on twofold rotation axes. The structure of (III) consists of ClQ⁻ anions, with the hydroxy groups deprotonated, and centrosymmetric ethylenediammonium cations. On the other hand, the structure of (IV) consists of a protonated HClQ⁺ cation with the positive charge balanced by a chloride anion. All four structures are stabilized by systems of hydrogen bonds which occur between the anions and cations. π–π interactions were observed between the HClQ⁺ cations in the structures of (I) and (IV).     

Sr,Ba and Cd arsenates with the apatite‐type structure

X‐ray diffraction analysis of single crystals of three new arsenates adopting apatite‐type structures yielded formula Sr₅(AsO₄)₃F for strontium arsenate fluoride, (I), (Sr_1.66Ba_0.34)(Ba_2.61Sr_0.39)(AsO₄)₃Cl for strontium barium arsenate chloride, (II), and Cd₅(AsO₄)₃Cl_0.58(OH)_0.42 for cadmium arsenate hydroxide chloride, (III). All three structures are built up of isolated slightly distorted AsO₄ tetrahedra that are bridged by Sr²⁺ in (I), by Sr²⁺/Ba²⁺ in (II) and by Cd²⁺ in (III). Compounds (I) and (II) represent typical fluorapatites and chlorapatites, respectively, with F⁻ at the 2a (0, 0, ) site and Cl⁻ at the 2b (0, 0, 0) site of P6₃/m. In contrast, in (III), due to the requirement that the smaller Cd²⁺ cation is positioned closer to the channel Cl⁻ anion (partially substituted by OH⁻), the anion occupies the unusual 2a (0, 0, ) site. Therefore, Cl⁻ is similar to F⁻ in (I), coordinated by three A2 cations, unlike the octahedrally coordinated Cl⁻ in (II) and other ordinary chlorapatites. Furthermore, in (III), using FT–IR studies, we have inferred the existence of H⁺ outside the channel in oxyhydroxyapatites and provided possible atomic coordinates for a H atom in HAsO₄²⁻, leading to a proposed formulation of the compound as Cd₅(AsO₄)_3−x(HAsO₄)_xCl_0.58(OH)_{0.42−x−(y/2)}O_x+(y/2)□_y/2.     

4-(Phenyldiazenyl)naphthalen-1-amine and its hydrochloride

The crystal structures of 4-(phenyl­diazenyl)­naphthalen-1-amine, C₁₆H₁₃N₃, (I), and its hydro­chloride, (4-amino­naph­thal­en-1-yl)­phenyl­diazenium chloride, C₁₆H₁₄­N₃⁺·­Cl⁻, (II), have been determined from X-ray single-crystal and powder data, respectively. The effect of the crystal environment on the molecular electronic structure was analysed on the AM1 level. One of the two symmetry-independent mol­ecules in (I) is involved in intermolecular hydrogen bonding, so that its dipole moment is twice as large as that of the other mol­ecule. The cations in (II) form stacks along [100], with the Cl⁻ anions forming hydrogen bonds to all three H atoms attached to N atoms.     

Hydrogen‐bonded network in the trichloroacetate salts of 2‐amino‐5‐chloropyridinium and 2‐methyl‐5‐nitroanilinium monohydrate

In the crystal structures of 2‐amino‐5‐chloropyridinium trichloroacetate, C₅H₆ClN₂⁺·C₂Cl₃O₂⁻, (I), and 2‐methyl‐5‐nitroanilinium trichloroacetate monohydrate, C₇H₉N₂O₂⁺·C₂Cl₃O₂⁻·H₂O, (II), the protonated planar 2‐amino‐5‐chloropyridinium [in (I)] and 2‐methyl‐5‐nitroanilinium [in (II)] cations interact with the oppositely charged trichloroacetate anions to form hydrogen‐bonded one‐dimensional chains in (I) and, together with water molecules, a three‐dimensional network in (II). The crystals of (I) exhibit nonlinear optical properties. The second harmonic generation efficiency in relation to potassium dihydrogen phosphate is 0.77. This work demonstrates the usefulness of trichloroacetic acid in crystal engineering for obtaining new materials for nonlinear optics.     

Proton‐bifurcated C—H⋯(O,O) hydrogen bonds in 2,3‐dichloro‐6‐nitro­benzyl­aminium chloride

In the crystal structure of the title salt, C₇H₇Cl₂N₂O₂⁺·Cl⁻, the chloride anions participate in extensive hydrogen bonding with the aminium cations and indirectly link the mol­ecules through multiple N⁺—H⋯Cl⁻ salt bridges. There are two independent mol­ecules in the asymmetric unit, related by a pseudo‐inversion center. The direct inter­molecular coupling is established by C—H⋯O, C—H⋯Cl and C—Cl⋯Cl⁻ inter­actions. A rare three‐center (donor bifurcated) C—H⋯(O,O) hydrogen bond is observed between the methyl­ene and nitro groups, with a side‐on intra­molecular component of closed‐ring type and a head‐on inter­molecular component.     

High-Performance Alkaline Seawater Electrolysis with Anomalous Chloride Promoted Oxygen Evolution Reaction

A highly selective and durable oxygen evolution reaction (OER) electrocatalyst is the bottleneck for direct seawater splitting because of side reactions primarily caused by chloride ions (Cl⁻). Most studies about OER catalysts in seawater focus on the repulsion of the Cl⁻ to reduce its negative effects. Herein, we demonstrate that the absorption of Cl⁻ on the specific site of a popular OER electrocatalyst, nickel-iron layered double hydroxide (NiFe LDH), does not have a significant negative impact; rather, it is beneficial for its activity and stability enhancement in natural seawater. A set of in situ characterization techniques reveals that the adsorption of Cl⁻ on the desired Fe site suppresses Fe leaching, and creates more OER-active Ni sites, improving the catalyst's long-term stability and activity simultaneously. Therefore, we achieve direct alkaline seawater electrolysis for the very first time on a commercial-scale alkaline electrolyser (AE, 120 cm² electrode area) using the NiFe LDH anode. The new alkaline seawater electrolyser exhibits a reduction in electricity consumption by 20.7 % compared to the alkaline purified water-based AE using commercial Ni catalyst, achieving excellent durability for 100 h at 200 mA cm⁻².     

Lamotrigine,an antiepileptic drug,and its chloride and nitrate salts

In lamotrigine [systematic name: 6‐(2,3‐dichlorophenyl)‐1,2,4‐triazine‐3,5‐diamine], C₉H₇Cl₂N₅, (I), the asymmetric unit contains one lamotrigine base molecule. In lamotriginium chloride [systematic name: 3,5‐diamino‐6‐(2,3‐dichlorophenyl)‐1,2,4‐triazin‐2‐ium chloride], C₉H₈Cl₂N₅⁺·Cl⁻, (II), the asymmetric unit contains one lamotriginium cation and one chloride anion, while in lamotriginium nitrate, C₉H₈Cl₂N₅⁺·NO₃⁻, (III), the asymmetric unit contains two crystallographically independent lamotriginium cations and two nitrate anions. In all three structures, N—H...N hydrogen bonds form an R₂²(8) dimer. In (I) and (II), hydrophilic layers are sandwiched between hydrophobic layers in the crystal packing. In all three structures, hydrogen bonds lead to the formation of a supramolecular hydrogen‐bonded network. The significance of this study lies in its illustration of the differences between the supramolecular aggregation in the lamotrigine base and in its chloride and nitrate salts.     

Determination of metallothionein in Daphnia magna by modified square wave cathodic stripping voltammetry

Metallothioneins (MTs) are widely used as biomarkers in environmental studies. However, eliminating interfering factors for MT determination in vivo by electrochemical detection is difficult. In this study, NO₃⁻ and Cl⁻ were found to negatively affect MT determination in Daphnia magna by square wave cathodic stripping voltammetry (SWCSV). The relevant mechanism was analyzed, and results were used to modify the original electrochemical testing parameters and environmental conditions. This modified SWCSV achieved accurate MT concentrations in D. magna, leading to detection limits as low as picomolar levels.     

Structural comparison of three N‐(4‐halogenophenyl)‐N′‐[1‐(2‐pyridyl)ethylidene]hydrazine hydrochlorides

2‐{1‐[(4‐Chloroanilino)methylidene]ethyl}pyridinium chloride methanol solvate, C₁₃H₁₃ClN₃⁺·Cl⁻·CH₃OH, (I), crystallizes as discrete cations and anions, with one molecule of methanol as solvent in the asymmetric unit. The N—C—C—N torsion angle in the cation indicates a cis conformation. The cations are located parallel to the (02) plane and are connected through hydrogen bonds by a methanol solvent molecule and a chloride anion, forming zigzag chains in the direction of the b axis. The crystal structure of 2‐{1‐[(4‐fluoroanilino)methylidene]ethyl}pyridinium chloride, C₁₃H₁₃FN₃⁺·Cl⁻, (II), contains just one anion and one cation in the asymmetric unit but no solvent. In contrast with (I), the N—C—C—N torsion angle in the cation corresponds with a trans conformation. The cations are located parallel to the (100) plane and are connected by hydrogen bonds to the chloride anions, forming zigzag chains in the direction of the b axis. In addition, the crystal packing is stabilized by weak π–π interactions between the pyridinium and benzene rings. The crystal of (II) is a nonmerohedral monoclinic twin which emulates an orthorhombic diffraction pattern. Twinning occurs via a twofold rotation about the c axis and the fractional contribution of the minor twin component refined to 0.324 (3). 2‐{1‐[(4‐Fluoroanilino)methylidene]ethyl}pyridinium chloride methanol disolvate, C₁₃H₁₃FN₃⁺·Cl⁻·2CH₃OH, (III), is a pseudopolymorph of (II). It crystallizes with two anions, two cations and four molecules of methanol in the asymmetric unit. Two symmetry‐equivalent cations are connected by hydrogen bonds to a chloride anion and a methanol solvent molecule, forming a centrosymmetric dimer. A further methanol molecule is hydrogen bonded to each chloride anion. These aggregates are connected by C—H...O contacts to form infinite chains. It is remarkable that the geometric structures of two compounds having two different formula units in their asymmetric units are essentially the same.     

9‐(2,6‐Dichloro­phen­oxycarbonyl)‐10‐methyl­acridinium trifluoro­methane­sulfonate and its precursor 2,6‐dichloro­phenyl acridine‐9‐carboxyl­ate

The title compounds, C₂₁H₁₄Cl₂NO₂⁺·CF₃O₃S⁻, (I), and C₂₀H₁₁Cl₂NO₂, (II), form triclinic crystals. Adjacent cations of (I) are oriented either parallel or antiparallel; in the latter case, they are related by a centre of symmetry. Together with the CF₃SO₃⁻ anions, the antiparallel‐oriented cations of (I) form layers in which the mol­ecules are linked via a network of C—H·O and π–π inter­actions (between the benzene rings). These layers, in turn, are linked via a network of multidirectional π–π inter­actions between the acridine rings, and the whole lattice is stabilized by electrostatic inter­actions between ions. Adjacent mol­ecules of (II) are oriented either parallel or antiparallel; in the latter case, they are related by a centre of symmetry. Parallel‐oriented mol­ecules are arranged in chains stabilized via C—H·Cl inter­actions. These chains are oriented either parallel or antiparallel and are stabilized, in the latter case, via multidirectional π–π inter­actions and more generally via dispersive inter­actions. Acridine and independent benzene moieties lie parallel in the lattices of (I) and (II), and are mutually oriented at an angle of 33.4 (2)° in (I) and 9.3 (2)° in (II).     

Effects of anodic oxidation on corrosion properties of Al coating by arc spraying in seawater

A layer of Al coatings was prepared on the S355 steel by arc spraying, which was conducted by anodic oxidation treatment; the morphologies, chemical element compositions and phases of Al coating, and anodic oxide layer were analyzed with field emission scanning electron microscope (FESEM), energy dispersive spectrometer (EDS) and X‐ray diffraction (XRD), respectively. The corrosion protections of Al coating before and after anodic oxidation were discussed with a seawater immersion test; the corrosion resistance mechanisms of Al coating and anodic oxide layer in the seawater were also investigated. The results show that the thickness of Al coating is about 300 µm by arc spraying, the sample surfaces become loose after seawater immersion corrosion and Cl^? and O^2? penetrate into the substrate from the cracks, destroying the binding properties of coating–substrate, and the coating fails. After anodic oxidation, the oxide layer is formed in the surface of Al coating with the thickness of about 30 µm; the corrosion products are mainly composed of Al(OH)₃, which barraged the holes caused by seawater corrosion. The corrosion cracks are formed during the corrosion, while the number and depth of cracks decrease obviously after anodic oxidation treatment. The corrosion of Al coating becomes the local corrosion after anodic oxidation treatment, and the grains are smaller, which are easily nucleated to form a new corrosion resistance layer. Copyright © 2015 John Wiley & Sons, Ltd.