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A multi analytical study on 20 synthetic ultramarine blue and cobalt blue oil paint samples from tubes belonging to Edvard Munch s studio
No full textRobustness of the pyrochlore structure in rare earth A2Ir2O7 iridates and pressure induced structural transformation in IrO2
No full textA comprehensive study of the structural properties of the heavily investigated rare earth A2Ir2O7 iridate series under extreme conditions is presented. From Pr2Ir2O7 to Lu2Ir2O7, the series is sufficiently covered by iridates with A Pr, Sm, Dy, Ho, Er, Tm, Yb, and Lu; general trends and systematics within the series, including the understudied heavy rare earth members, are dependably followed. Temperature and pressure dependent synchrotron X ray powder diffraction experiments reveal robustness of the pyrochlore structure throughout the series, down to 4 K and up to 20 GPa. The thermal expansivity of the pyrochlore lattice is determined, all falling in the Debye temperature range of amp; 952;D 360 420 K. The pressure compressibility shows a systematic increase of the bulk modulus with the rare earth atomic number from K 180 210 GPa. Combining the results of thermal measurements Debye temperature and pressure measurements bulk modulus enables us to determine the Grüneisen parameter of selected members and compare it to previous studies. Temperature and pressure evolution of the fractional coordinate of oxygen at 48f Wyckoff position, the sole free fractional coordinate in the crystal structure, is investigated and discussed regarding the antiferromagnetic ordering of the Ir magnetic moments. In addition to results on A2Ir2O7 iridates, the temperature and pressure evolution of the crystal structure of an IrO2 minority phase is followed. The tetragonal rutile type structure is stable down to the lowest temperature. However, an application of pressure of approximately 15 GPa induces a structural transition The tetragonal structure is orthorhombically distorted. The orthorhombic structure is still not fully stabilised at 20 GPa, and further distortion of the lattice or subsequent structural transformations is expected with increasing external pressur
Adsorbate Configurations in Ni Single Atom Catalysts during CO2 Electrocatalytic Reduction Unveiled by Operando XAS, XES, and Machine Learning
No full textNickel and nitrogen co doped carbon Ni N C catalysts are attracting attention due to their exceptionally high performance in the electrocatalytic reduction of CO2 amp; 8290; CO2 amp; 8290;RR to CO. However, the direct experimental insight into the working mechanism of these catalysts is missing, hindering our fundamental understanding and their further improvement. This work sheds light on the nature of adsorbates forming under CO2 amp; 8290;RR at singly dispersed Ni sites. In particular, operando high energy resolution fluorescence detected x ray absorption near edge structure HERFD XANES at the Ni amp; 119870; edge together with valence to core x ray emission spectroscopy vtc XES and x ray absorption XAS at the Ni amp; 119871;3 edge were employed to unveil the structure and electronic properties of the reaction intermediates. These techniques, coupled with unsupervised and supervised machine learning methodologies and density functional theory, enabled a comprehensive characterization of the local atomistic and electronic structure of the working Ni N C catalysts. Specifically, we were able to distinguish between the structural and electronic changes of the Ni sites associated with the CO2 amp; 8290;RR functionality from the effect of radiation induced damage, providing direct insight into the bond formation between the Ni centers and CO2 amp; 8290;RR intermediates such as CO adsorbate
Effect of the synthesis route and Co Coverage on Co Ti3C2Tx materials for the oxygen evolution reaction
Get PDFGreen hydrogen resulting from water electrolysis is a key component for the transition to a renewable energy economy. However, it s success highly depends on active and stable electrocatalysts for the oxygen evolution reaction OER which is the bottleneck reaction of water electrolysis. Herein we assess the OER performance of non noble metal based electrocatalysts comprising Co oxide hydroxide and delaminated 2D transition metal carbide sheets, Ti3C2Tx MXene. The catalytically active sites are provided by Co oxide hydroxide, while the MXene contributes exceptional electrical conductivity. Our comprehensive electrochemical evaluation of their OER performance reveals that the chemical functionalization of Co on MXene sheets outperforms the pure Co or MXene alone, as well as physically mixed materials, across all tested performance metrics. From the materials characterisation, the chemical functionalized Co OH 2 Ti3C2Tx materials exhibit increased formation of layered double hydroxide LDH Co OH 2 structures compared to the pure Co OH 2 and physically mixed materials which may result in the improved OER activity observed for these materials. These findings emphasize the potential of anchoring transition metal oxides hydroxides on MXene as a superior OER electrocatalyst for advancing sustainable green hydrogen productio
Transfer learning for molecular property predictions from small datasets
Get PDFMachine learning has emerged as a new tool in chemistry to bypass expensive experiments or quantum chemical calculations, for example, in high throughput screening applications. However, many machine learning studies rely on small datasets, making it difficult to efficiently implement powerful deep learning architectures such as message passing neural networks. In this study, we benchmark common machine learning models for the prediction of molecular properties on two small datasets, for which the best results are obtained with the message passing neural network PaiNN as well as SOAP molecular descriptors concatenated to a set of simple molecular descriptors tailored to gradient boosting with regression trees. To further improve the predictive capabilities of PaiNN, we present a transfer learning strategy that uses large datasets to pre train the respective models and allows us to obtain more accurate models after fine tuning on the original datasets. The pre training labels are obtained from computationally cheap ab initio or semi empirical models, and both datasets are normalized to mean zero and standard deviation one to align the labels distributions. This study covers two small chemistry datasets, the Harvard Organic Photovoltaics dataset HOPV, HOMO LUMO gaps , for which excellent results are obtained, and the FreeSolv dataset solvation energies , where this method is less successful, probably due to a complex underlying learning task and the dissimilar methods used to obtain pre training and fine tuning labels. Finally, we find that for the HOPV dataset, the final training results do not improve monotonically with the size of the pre training dataset, but pre training with fewer data points can lead to more biased pre trained models and higher accuracy after fine tunin
Photo excited charge transfer from adamantane to electronic bound states in water
Get PDFAqueous nanodiamonds illuminated by UV light produce free solvated electrons, which may drive high energy reduction reactions in water. However, the influence of water conformations on the excited state electron transfer mechanism are still under debate. In this work, we offer a theoretical study of charge transfer states in adamantane water structures obtained by linear response time dependent density functional theory. Small water clusters with broken hydrogen bonds are found to efficiently bind the electron from adamantane. A distinction is made with respect to the nature of the water clusters some bind the electron in a water cavity, others along a strong permanent total dipole. These two types of bound states are more strongly binding, the higher their electron affinity and their positive electrostatic potential, the latter being dominated by the energy of the lowest unoccupied molecular orbital of the isolated water clusters. Structural sampling in a thermal equilibrium at room temperature via molecular dynamics snapshots confirms under which conditions the underlying waters clusters can occur and verifies that broken hydrogen bonds in the water network close to adamantane can create traps for the solvated electro
POxylated stereocomplexes from PEtOx b PLA diblock copolymers
Get PDFAn omega hydroxyl terminated poly 2 ethyl 2 oxazoline PEtOx was obtained by termination of the cationic ringopening polymerization of 2 ethyl 2 oxazoline with acetate and subsequent transesterification with methanol. The resulting PEtOx OH featuring a degree of polymerization DP of 18 was used as a macroinitiator for the ring opening polymerization of L lactide as well as D lactide. The resulting PEtOx b PLA block copolymers featured DP values of 25, 50, 100, and 150, respectively, and were characterized by means of size exclusion chromatography, 1H NMR spectroscopy as well as matrix assisted laser desorption ionization mass spectrometry. Differential scanning calorimetry, wide angle x ray scattering and polarized light microscopy indicated the formation of stereocomplexes in racemic blends of PEtOx b PLA with opposing chirality. Thereby, the amorphous PEtOx block did not affect the modification of the stereocomplex crystallites, as shown by comparison with data obtained from PLA homopolymer stereocomplexes. Similar to those, the degree of crystallinity and melting temperature decreased with increasing molar mass of the PLA in the stereocomplexes formed from PEtOx b PLA block copolymer
Interfacial Interaction in MeOx MWNTs Me Cu, Ni Nanostructures as Efficient Electrode Materials for High Performance Supercapacitors
Get PDFDue to their unique physical and chemical properties, complex nanostructures based on carbon nanotubes and transition metal oxides are considered promising electrode materials for the fabrication of high performance supercapacitors with a fast charge rate, high power density, and long cycle life. The crucial role in determining their efficiency is played by the properties of the interface in such nanostructures, among them, the type of chemical bonds between their components. The complementary theoretical and experimental methods, including dispersion corrected density functional theory DFT D3 within GGA PBE approximation, scanning electron microscopy SEM , X ray diffraction XRD , Raman, X ray photoelectron, and X ray absorption spectroscopies, were applied in the present work for the comprehensive investigation of surface morphology, structure, and electronic properties in CuOx MWCNTs and NiOx MWCNTs. As a result, the type of interfacial interaction and its correlation with electrochemical characteristics were determined. It was found that the presence of both Ni O C and Ni C bonds can increase the contact between NiO and MWCNTs, and, through this, promote electron transfer between NiO and MWCNTs. For NiOx MWCNTs, better electrochemical characteristics were observed than for CuOx MWCNTs, in which the interfacial interaction is determined only by bonding through Cu O C bonds. The electrochemical properties of CuOx MWCNTs and NiOx MWCNTs were studied to demonstrate the effect of interfacial interaction on their efficiency as electrode materials for supercapacitor application
Effect of Iron Doping in Ordered Nickel Oxide Thin Film Catalyst for the Oxygen Evolution Reaction
No full textWater splitting has emerged as a promising route for generating hydrogen as an alternative to conventional production methods. Finding affordable and scalable catalysts for the anodic half reaction, the oxygen evolution reaction OER , could help with its industrial widespread implementation. Iron containing Ni based catalysts have a competitive performance for the use in commercial alkaline electrolyzers. Due to the complexity of studying the catalysts at working conditions, the active phase and the role that iron exerts in conjunction with Ni are still a matter of investigation. Here, we study this topic with NiO 001 and Ni0.75Fe0.25Ox 001 thin film model electrocatalysts employing surface sensitive techniques. We show that iron constrains the growth of the oxyhydroxide phase formed on top of the Ni or NiFe oxide, which is considered the active phase for the OER. Besides, operando Raman and grazing incidence X ray absorption spectroscopy experiments reveal that the presence of iron affects both, the disorder level of the active phase and the oxidative charge around Ni during OER. The observed compositional, structural, and electronic properties of each system have been correlated with their electrochemical performanc
Revealing the degradation pathways of layered Li rich oxide cathodes
No full textLayered lithium rich transition metal oxides are promising cathode candidates for high energy density lithium batteries due to the redox contributions from transition metal cations and oxygen anions. However, their practical application is hindered by gradual capacity fading and voltage decay. Although oxygen loss and phase transformation are recognized as primary factors, the structural deterioration, chemical rearrangement, kinetic and thermodynamic effects remain unclear. Here we integrate analysis of morphological, structural and oxidation state evolution from individual atoms to secondary particles. By performing nanoscale to microscale characterizations, distinct structural change pathways associated with intraparticle heterogeneous reactions are identified. The high level of oxygen defects formed throughout the particle by slow electrochemical activation triggers progressive phase transformation and the formation of nanovoids. Ultrafast lithium de intercalation leads to oxygen distortion dominated lattice displacement, transition metal ion dissolution and lithium site variation. These inhomogeneous and irreversible structural changes are responsible for the low initial Coulombic efficiency, and ongoing particle cracking and expansion in the subsequent cycle