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Solar_rev_2022

Thin-Film Oxynitride Photocatalysts for Solar Hydrogen Generation: Separating Surface and Bulk Effects Using Synchrotron X-Ray and Neutron-Based Techniques

The conversion of solar light into hydrogen by photoelectrochemical water splitting is one of the potential strategies that can allow the development of a carbon-neutral energy cycle. Oxynitride semiconductors are promising materials for this application, although important limitations must still to be addressed. One of the most important issues is physicochemical degradation of the semiconductor, at the interface with water, where the electrochemical reactions occur. In this regard, thin films, with well-defined and atomically flat surfaces, are invaluable tools for characterizing material properties and degradation mechanisms, while identifying strategies to mitigate detrimental effects. Thin oxynitride films may allow the use of complementary characterizations, not applicable to conventional powder samples. In particular, the study of the solid–liquid interface can benefit enormously from the use of thin films for synchrotron-based surface-sensitive X-Ray scattering methods and neutron reflectometry. These investigation approaches promise to speed up the design and discovery of new materials for the production of solar fuels, while paving the way for similar applications in other research fields. This work aims at reviewing the literature contributions on oxynitride thin films for solar water splitting summarizing what is learnt so far and suggesting experimental strategies to unveil what is still not clear.

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tensor_tomography

Macroscopic mapping of microscale fibers in freeform injection molded fiber-reinforced composites using X-ray scattering tensor tomography

Prediction of the mechanical properties dictated by the local microfiber orientation is essential for the performance characterization of fiber-reinforced composites. Typically, tomographic imaging methods that provide fine spatial resolution are employed to investigate various materials' local micro- and nano-architecture in a non-destructive manner. However, conventional imaging techniques are limited by a substantial trade-off between the structure size of interest and the accessible field of view (FOV). Researchers from the TOMCAT beamline at Paul Scherrer Institut, Xnovo Technology ApS, and the Technical University of Denmark have demonstrated the potential of X-ray scattering tensor tomography for industrial applications by characterizing the microstructure of a centimeter-sized industrially relevant freeform injection molding fiber-reinforced composite sample. This emerging technique provides unprecedented access to microstructural information over centimeter-sized sample volumes paving the way towards its potential integration as an invaluable tool, for instance, in the fiber-reinforced-composite (FRC) industry. The obtained fiber orientation and anisotropy information over statistically relevant large volumes can be used to predict the mechanical properties of final products, optimize production parameters, and improve fiber injection molding simulation frameworks. The work is published in Composites Part B: Engineering on 15 March 2022.

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