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Swelling of Steel Film by Hydrogen Absorption at Cathodic Potential in Electrolyte
No full textAn ≈4 nm FeCrNi film, deposited on a Ru/BC multilayer (ML), is used to study cathodic hydrogen charging in electrolyte. A thin film on a ML allows obtaining precise quantitative information on surface metal composition and oxidation state using the X‐ray standing wave technique combined with near‐edge X‐ray absorption spectroscopy. The metal composition is found being close to the composition of stainless steel (SS) 304, and, as for bulk steel, the outer 2 nm passive layer, consisting of oxidized iron and chromium, is depleted of nickel. Overall, it is found that the film represented a useful replica of the surface of bulk steel. Following exposure to 0.1 KCl electrolyte at −0.6 V versus Ag/AgCl, 11.3 (±3)% swelling of the film by hydrogen absorption is observed. The estimated absorbed amount is exceeding reported bulk absorption under similar conditions by more than an order of magnitude. Strong hydrogen absorption appears to be enabled by the 2D character of the thin film, i.e., a significantly lower associated strain energy compared with bulk absorption. The strong surface swelling is suggested to be related to the lowering of the pitting corrosion resistance of SS surfaces reported following hydrogen exposure
High Capacity and High‐Rate NASICON‐ Cathode for Na‐Ion Batteries via Modulating Electronic and Crystal Structures
No full textPotential-Induced Pitting Corrosion of an Model Electrode under Oxygen Evolution Reaction Conditions
No full textSophisticated -based model electrodes are prepared by deposition of a 10 nm thick single-crystalline layer supported on a structure-directing template, exposing a regular array of mesoscopic rooflike structures. With this model electrode together with the dedicated in situ synchrotron based techniques (SXRD, XRR) and ex situ characterization techniques (SEM, ToF-SIMS, XPS), the corrosion process of in an acidic environment (pH 0.4) is studied on different length scales. Potential-induced pitting corrosion starts at 1.48 V vs SHE and is initiated at so-called surface grain boundaries, where three rotational domains of meet. The most surprising result is, however, that even when the electrode potential is increased to 1.94 V vs SHE 60–70% of the film still stays intact down to the mesoscale and atomic scale and no uniform thinning of the layer is encountered. Neither flat terraces nor single steps are attacked. Ultrathin single-crystalline layers seem to be much more stable to anodic corrosion than hitherto expected
Pure Molecular Beam of Water Dimer
No full textSpatial separation of water dimer from water monomer and larger water-clusters through the electric deflector is presented. A beam of water dimer with purity and a rotational temperature of K was obtained. Following strong-field ionization using a fs laser pulse with a wavelength centered around nm and a peak intensity of we observed proton transfer and of the ionized water dimer broke apart into a hydronium ion and OH
Magneto-optical Kerr effect and nuclear resonant scattering study of uni-directional anisotropy in hard-soft magnetic bilayers
No full textThe present work reports the unconventional exchange bias (EB) phenomena in an exchange-coupled hard and soft magnetic bilayer system and the tunability of EB. The EB phenomena, i.e., shifting of the hysteresis loop of the soft (Fe) layer is observed when the hard magnetic (L1 FePt) layer is under the remanent state indicating the development of unidirectional anisotropy. The nuclear resonant scattering measurements clearly reveal the development of unidirectional anisotropy in the soft magnetic (Fe) layer, when the hard magnetic layer is under the remanent state. The magnetization reversal process is investigated by measuring two in-plane orthogonal components of magnetization, i.e., parallel (M and perpendicular (M) to the applied field using the magneto-optical Kerr effect (MOKE). When the magnetic field is applied parallel (antiparallel) to the biasing field direction, (H) magnetization reversal is nonuniform, and on the other hand, the rotation of magnetization is observed when the magnetic field is applied away from the HSAT direction. In addition, the sign inversion of the M component is observed when the magnetic field is applied at the same angle on either side of the H direction, which clearly imply the change in handedness of the chirality of spin structure during the magnetization reversal of the soft layer. Further, it is observed that the EB decreases with the increase of soft magnetic (Fe) layer thickness, demonstrating the tunable nature of EB phenomena even in these unconventional systems
Structural Heterogeneity in Single Particle Imaging Using X-ray Lasers
No full textOne of the challenges facing single particle imaging with ultrafast X-ray pulses is the structural heterogeneity of the sample to be imaged. For the method to succeed with weakly scattering samples, the diffracted images from a large number of individual proteins need to be averaged. The more the individual proteins differ in structure, the lower the achievable resolution in the final reconstructed image. We use molecular dynamics to simulate two globular proteins in vacuum, fully desolvated as well as with two different solvation layers, at various temperatures. We calculate the diffraction patterns based on the simulations and evaluate the noise in the averaged patterns arising from the structural differences and the surrounding water. Our simulations show that the presence of a minimal water coverage with an average 3 Å thickness will stabilize the protein, reducing the noise associated with structural heterogeneity, whereas additional water will generate more background noise
Dewetting-Alloying of Nicu Bilayers on Surfaces for Noble Metal-Free Photocatalytic Evolution
No full textWe present an approach to fabricate an efficient noble metal-free photocatalytic platform for H2 evolution and provide evidences that the photocatalyst active state forms via a photo-induced redox process in organic-water mixtures.To fabricate the photocatalytic platform, NiCu bilayers (thickness in the range of a few nm) are deposited by Ar-plasma sputtering on anodic TiO2 nanocavity arrays.[1] A subsequent thermal treatment triggers solid-state dewetting[2,3] of the metal bilayer, i.e. owing to surface diffusion, the Ni and Cu films agglomerate and inter-mix forming NiCu bimetallic nanoparticles at the TiO2 surface.[4] This approach allows for a full control over key features of the NiCu nanoparticles, e.g. size, loading, composition and co-catalytic H2 generation ability. We found that dewetted-alloyed NiCu nanoparticles not only are significantly more reactive than their pure Ni or Cu counterparts, but also lead to H2 generation rates that approach those of noble metal (Pt) modified TiO2 nanocavities.Characterization results (EDS-TEM, XPS and XRD) of the as-formed photocatalyst suggest the co-catalyst nanoparticles to feature a NiCu bimetallic core and an oxide (or hydroxide) shell – the latter presumably forms by surface oxidation under ambient conditions.To identify the chemical state of the NiCu nanoparticles during photocatalysis, we carried out XAS operando experiments[5,6] (beam line P65 at DESY – Petra III, Hamburg, Germany) at the Cu K and Ni K edges, in fluorescence mode, under UV light illumination in degassed ethanol-water solutions.Our results demonstrate that under operando conditions the co-catalyst is subjected to changes of the Ni and Cu chemical state:[7–9] we observe that surface Ni and Cu oxide species are reduced (by TiO2 conduction band electrons) in the early stage of illumination – this converts the co-catalyst nanoparticles into the active metallic NiCu phase.[1] J. E. Yoo, K. Lee, M. Altomare, E. Selli, P. Schmuki, Angew. Chemie Int. Ed. 2013, 52, 7514–7517.[2] C. V. Thompson, Annu. Rev. Mater. Res. 2012, 42, 399–434.[3] M. Altomare, N. T. Nguyen, P. Schmuki, Chem. Sci. 2016, 7, 6865–6886.[4] D. Spanu, S. Recchia, S. Mohajernia, O. Tomanec, Š. Kment, R. Zboril, P. Schmuki, M. Altomare, ACS Catal. 2018, 8, 5298–5305.[5] M. Fracchia, P. Ghigna, A. Vertova, S. Rondinini, A. Minguzzi, Surfaces 2018, 1, 138–150.[6] A. Minguzzi, O. Lugaresi, C. Locatelli, S. Rondinini, F. D'Acapito, E. Achilli, P. Ghigna, Anal. Chem. 2013, 85, 7009–7013.[7] J. S. Schubert, J. Popovic, G. M. Haselmann, S. P. Nandan, J. Wang, A. Giesriegl, A. S. Cherevan, D. Eder, J. Mater. Chem. A 2019, 7, 18568–18579.[8] B. Mei, K. Han, G. Mul, ACS Catal. 2018, 8, 9154–9164.[9] M. J. Muñoz-Batista, D. Motta Meira, G. Colón, A. Kubacka, M. Fernández-García, Angew. Chemie Int. Ed. 2018, 57, 1199–1203
Experimental Evidence for the Incorporation of Two Metals at Equivalent Lattice Positions in Mixed‐Metal Metal–Organic Frameworks
No full textMetal–organic frameworks containing multiple metals distributed over crystallographically equivalent framework positions (mixed‐metal MOFs) represent an interesting class of materials, since the close vicinity of isolated metal centers often gives rise to synergistic effects. However, appropriate characterization techniques for detailed investigations of these mixed‐metal metal–organic framework materials, particularly addressing the distribution of metals within the lattice, are rarely available. The synthesis of mixed‐metal FeCuBTC materials in direct syntheses proved to be difficult and only a thorough characterization using various techniques, like powder X‐ray diffraction, X‐ray absorption spectroscopy and electron paramagnetic resonance spectroscopy, unambiguously evidenced the formation of a mixed‐metal FeCuBTC material with HKUST‐1 structure, which contained bimetallic Fe−Cu paddlewheels as well as monometallic Cu−Cu and Fe−Fe units under optimized synthesis conditions. The in‐depth characterization showed that other synthetic procedures led to impurities, which contained the majority of the applied iron and were impossible or difficult to identify using solely standard characterization techniques. Therefore, this study shows the necessity to characterize mixed‐metal MOFs extensively to unambiguously prove the incorporation of both metals at the desired positions. The controlled positioning of metal centers in mixed‐metal metal–organic framework materials and the thorough characterization thereof is particularly important to derive structure–property or structure–activity correlations
Structural Basis of Inhibition of Insulin-Regulated Aminopeptidase by a Macrocyclic Peptidic Inhibitor
No full textInsulin-regulated aminopeptidase (IRAP) is a transmembrane zinc metallopeptidase with many important biological functions and an emerging pharmacological target. Although previous structural studies have given insight on how IRAP recognizes linear peptides, how it recognizes its physiological cyclic ligands remains elusive. Here, we report the first crystal structure of IRAP with the macrocyclic peptide inhibitor HA08 that combines structural elements from angiotensin IV and the physiological substrates oxytocin and vasopressin. The compound is found in the catalytic site in a near canonical substrate-like configuration and inhibits by a competitive mechanism. Comparison with previously solved structures of IRAP along with small-angle X-ray scattering experiments suggests that IRAP is in an open conformation in solution but undergoes a closing conformational change upon inhibitor binding. Stabilization of the closed conformation in combination with catalytic water exclusion by the tightly juxtaposed GAMEN loop is proposed as a mechanism of inhibition
Identification of targets of AMPylating Fic enzymes by co-substrate-mediated covalent capture
No full textVarious pathogenic bacteria use post-translational modifications to manipulate the central components of host cell functions. Many of the enzymes released by these bacteria belong to the large Fic family, which modify targets with nucleotide monophosphates. The lack of a generic method for identifying the cellular targets of Fic family enzymes hinders investigation of their role and the effect of the post-translational modification. Here, we establish an approach that uses reactive co-substrate-linked enzymes for proteome profiling. We combine synthetic thiol-reactive nucleotide derivatives with recombinantly produced Fic enzymes containing strategically placed cysteines in their active sites to yield reactive binary probes for covalent substrate capture. The binary complexes capture their targets from cell lysates and permit subsequent identification. Furthermore, we determined the structures of low-affinity ternary enzyme–nucleotide–substrate complexes by applying a covalent-linking strategy. This approach thus allows target identification of the Fic enzymes from both bacteria and eukarya