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Electronic structure of aqueous nitrite and nitrate ions from resonant inelastic X ray scattering
Get PDFIn a comparative synchrotron X ray absorption, non resonant X ray emission and resonant inelastic X ray scattering investigation of aqueous nitrite and nitrate ions, we access both their unoccupied and occupied valence electronic structures. Complementary information is gained through the sensitivity to specific orbitals at the nitrogen and the oxygen 1s absorption edges. In particular, scattering through the pronounced 1s gt; pi resonances in combination with the scattering anisotropy and symmetry selection rules allow for an unambiguous assignment of molecular orbitals to their detected spectroscopic fingerprints. The nuclear dynamics in the 1s core excited states are discussed in the context of the vibrational substructure of the detected spectral lines and signatures of core excited state symmetry breaking are characterized through an analysis of the excitation energy detuning dependent spectra in combination with the involved potentials. A comparison between TD DFT based spectrum simulations for isolated molecules and sampled structures from a QM MM simulation reveals signatures of symmetry breaking induced by the solute solvent interactions and a different response of spectral signatures of in and out of plane orbitals to the solution environmen
Clicking [Mo CO 3 triphos ] to an azide terminated alkylthiol SAM structural, spectroscopic and electrochemical investigations
No full textThe synthesis and characterization of a new, linear triphos type pincer ligand furnished with an ethynyl moiety in the ligand backbone etPPPhTMSP and the derived tricarbonyl complex [Mo CO 3 etPPPhTMSP ] are described. Deprotection of the latter leads to [Mo CO 3 etPPPhHP ] which in turn is clicked onto an N3 terminated Au surface. The resulting monolayer is characterized by XPS, IRRAS and cyclic voltammetry, providing information on its chemical composition, the degree of surface coverage and the orientation of the headgroup. On the basis of these results, a protocol for the functionalization of surfaces with redox active transition metal complexes for applications in, e.g., electrocatalysis is develope
Affinity and Selectivity of Protein Ligand Recognition A Minor Chemical Modification Changes Carbonic Anhydrase Binding Profile
No full textDiscovery of small molecule drugs relies on their strong binding affinity compared to nontarget proteins, thus possessing selectivity. Minor chemical structure changes usually exhibit little change in the compound efficacy, with rare exceptions. We developed a series of nearly 50 ortho substituted benzenesulfonamides and experimentally measured their interactions with the 12 catalytically active human carbonic anhydrase CA isozymes. Inhibitors were designed using seven different substituent groups, including 4 sulfanyl substituted 3 sulfamoyl benzoates and benzamides, 4 sulfinyl substituted 3 sulfamoyl benzoates and benzamides, 4 sulfonyl substituted 3 sulfamoyl benzoates and benzamides, and 4 amino substituted benzamides. The oxidation state of sulfur at the ortho position significantly influenced the compound s affinity for CAIX, a target for anticancer drugs, demonstrating affinities hundreds of thousands of times stronger than related compounds. Coupled with X ray crystal structures and molecular docking, the relationship between structure and thermodynamics offers insights into how small changes in the structure lead to significant changes in affinity for drug desig
Ba Ni Ge Clathrate Transformation Maximizes Active Site Utilization of Nickel for Enhanced Oxygen Evolution Performance
Get PDFDiscovering novel oxygen evolution reaction OER pre catalysts with exceptional catalytic activity and long term stability is pivotal for advancing decarbonization technologies. In this study, we present the ternary Ba8Ni6Ge40 phase with an open clathrate structure exhibiting remarkable performance in alkaline OER. When integrated into an alkaline water electrolyzer, this clathrate precatalyst achieves high stability under a sustained current density of amp; 8764;550 mA cm amp; 8722;2 for 10 days. By combining in situ Raman spectroscopy, quasi in situ X ray absorption spectroscopy, and micro structural characterizations, we elucidate the complete electrochemical transformation of Ba8Ni6Ge40 90 weight leaching forming ultrathin nanosheets composed of a porous and defective NiOOH nanostructure with maximized accessible active site exposure. Notably, a reversible phase transition mainly between Ni OH 2 and NiOOH has also been established in the electrochemical redox process. Meanwhile, the successful application of the model Ba8Ni6Ge40 precatalyst represents a promising new class of functional inorganic materials for water electrolysi
Synthesis, Molecular Structure, and Water Electrolysis Performance of TiO2 Supported Raney IrOx Nanoparticles for the Acidic Oxygen Evolution Reaction
No full textDeveloping low cost, highly active, and stable catalysts for the acidic oxygen evolution reaction OER at the proton exchange membrane PEM water electrolyzer anodes remains a scientific priority. Reducing the iridium loading while increasing the intrinsic activity of the catalysts is essential for cost effective hydrogen production. Here, we address a family of TiO2 supported Raney IrOx catalysts with low iridium loading and high activity in single cell PEM water electrolyzer anode environments. A controlled Raney type Ni leaching process of pristine, supported IrNi alloy phases forms crystalline IrOx nanoparticles NPs featuring metallic Ir rich cores surrounded by more amorphous IrOx surfaces. This structure is shown to be conducive to catalytic activity and the suppression of membrane poisoning due to Ni degradation. The trace amounts of Ni remaining after leaching in the IrOx NPs result in heterogeneous crystal structure and induce local lattice strain. Further, we synthetically strike a balance between conductivity and activity and succeed to narrow down the notorious large performance gap between liquid electrolyte rotating disk electrodes RDEs and single cell membrane electrode assembly MEA electrolyzer measurements. OER stability numbers S numbers of the identified Raney IrOx anode catalysts surpass commercial IrO2 catalysts, confirming the stability of these catalysts. The PEM electrolyzer tests reveal that Raney IrOx anodes achieve 3 A cm 2 at 1.8 V with a low geometric Ir loading of ca. 0.3 mgIr cm 2, meeting the technically important power specific Ir utilization target of 0.05 gIr k
Unravelling the mechanistic complexity of the oxygen evolution reaction and Ir dissolution in highly dimensional amorphous hydrous iridium oxides
Get PDFUnderstanding the oxygen evolution reaction OER and Ir dissolution mechanisms in amorphous, hydrous iridium oxides am hydr IrOx is hindered by the reliance on crystalline iridium oxide theoretical models to interpret its behaviour. This study presents a comprehensive investigation of hydrous iridium oxide thin films HIROFs as a model for am hydr IrOx to elucidate electronic and structural transformations under OER conditions of proton exchange membrane water electrolyzers PEM WE . Employing in situ and operando Ir L3 edge X ray absorption spectroscopy supported by density functional theory calculations, we introduce a novel surface H terminated nanosheet model that better characterizes the short range structure of am hydr IrOx compared to previous crystalline models, which exhibits elongated Ir O bond lengths compared to rutile IrO2. This atomic model unveils the electronic and structural transformations of am hydr IrOx, progressing from H terminated nanosheets to structures with multiple Ir vacancies and shorter bond lengths at OER potentials. Notably, Ir dissolution emerges as a spontaneous, thermodynamically driven process, initiated at potentials lower than OER activation, which requires a parallel mechanistic framework describing Ir dissolution by Ir defect formation. Moreover, our results provide mechanistic insights into the activity stability relationship of am hydr IrOx by systematically screening the DFT calculated OER activity of diverse Ir and O chemical environments. This work challenges conventional perceptions of iridium dissolution and OER mechanisms in am hydr IrOx, providing an alternative perspective within a dual mechanistic framewor
Active harmonic EU cavity Commissioning and operation with beam
Get PDFALBA is a 3rd generation synchrotron light source located in Spain, in operation since 2012. In preparation for its upgrade to a 4th generation facility, which requires addressing the significantly reduced Touschek lifetime, ALBA has designed and constructed a higher order mode HOM damped active 3rd harmonic RF cavity. This cavity is designed to longitudinally lengthen the electron bunches, thereby reducing their density and enhancing the beam lifetime. The design is based on the EU HOM damped cavity currently employed in ALBA s main radio frequency RF system. The cavity prototype was installed in the BESSY II ring under a collaborative agreement between ALBA, HZB, and DESY, institutions that operate at the same main RF frequency, 500 MHz. This paper presents the first commissioning results, including bead pull measurements, high power conditioning and initial beam tests in both single and multi bunch operation modes. The results confirm that the cavity parameters are consistent with the design specifications, the HOMs are effectively mitigated, and the anticipated beam lifetime enhancement is achieved, demonstrating the feasibility of the designed cavit
Functionalization of monolithic MOF thin films with hydrocarbon chains to achieve superhydrophobic surfaces with tunable water adhesion strength
No full textWhile the accessible pores render an enormous variety of functionalities to the bulk of metal organic frameworks MOFs , the outer surfaces exposed by these crystalline materials also offer unique characteristics not available when using conventional substrates. By grafting hydrocarbon chains to well defined MOF thin films SURMOFs prepared using layer by layer methods, we were able to fabricate superhydrophobic substrates with static water contact angles over 160 . A detailed theoretical modelling of the hydrocarbon chains grafted on the outer SURMOF surface with well defined spacing between anchoring points reveals that the grafted hydrocarbon chains behave similarly to polymer brushes during wetting, where conformational entropy is traded with mixing entropy. The chains are coiled and can access many different conformations, as evidenced directly by infrared spectroscopy. The entropic contributions from the coiled state lead to a pronounced reduction of the surface free energy, rendering superhydrophobic properties to the functionalized SURMOFs. On the other side, the water adhesion strength could be decreased by increasing the surface roughness on the nanometer scal
Room Temperature Dehydrogenation of Gaseous Methanol over Polycrystalline Gold Triggered and Traced by Oxygen Kedge Xrays
Get PDFThe room temperature conversion of gaseous methanol to carbon monoxide and hydrogen on a polycrystalline Au film at ambient pressure has been triggered and characterized by oxygen K edge excitation and vibrationally resolved resonant inelastic X ray scattering. The rate limiting first methanol dehydrogenation step is driven by ultrafast O H dissociation and deprotonation of O K edge excited CH3OH. The Au surface further dehydrogenates the CH3O photoradical created by X rays via electron transfer from the Au surface. With vibrationally resolved resonant inelastic X ray scattering, we trace the CO molecular potential energy surface along the C O coordinate. The CO bond softens, and the C O stretch frequency changes from 2250 to 2065 cm 1 at a CO chemisorption energy of 38 58 kJ mol. This constitutes weak chemisorption as compared to the transition metals but also stronger bonding than the physisorbed CO species on single crystal Au surfaces. In liquid methanol, the recombination of the CH3O photoradical created by X rays with protons quenches this conversio
High order multilayer coated blazed grating for a high transmission and high resolution tender X ray monochromator spectrometer
Get PDFGrating optics lie in the heart of X ray spectroscopy instruments. The low efficiency and angular dispersion of conventional single layer coated gratings significantly limit the transmission and energy resolution of monochromators and spectrometers, particularly in the tender X ray region E 1 5keV . Multilayer coated blazed gratings MLBGs operating at high diffraction orders offer the advantage of achieving both high efficiency and high dispersion simultaneously. Tender X ray monochromators and spectrometers using different high order MLBGs have been designed, all demonstrating one to two orders of magnitude higher transmission compared to conventional systems. By employing a 2400 l mm MLBG at the 4th or 8th diffraction order, the theoretical energy resolution of the instrument is improved by two to three times at 2.5 keV. Two MLBGs operating at the 2nd and 4th orders have been fabricated, showcasing remarkable efficiencies of 34 12 at 2.5 keV, surpassing that of single layer coated gratings by an order of magnitude. Further optimization of manufacturing accuracy can yield even higher efficiencies. The measured angular dispersion agrees well with theoretical predictions, supporting the potential for high resolution. High order MLBG optics pave the way for a new generation of tender X ray monochromators spectrometers that offer both high transmission and high resolutio