Distinguishing differences between authentic artifacts and replicas is a significant challenge in the field of cultural heritage. In this study, we explore the application of neutron grating interferometry and tomography techniques to identify Korean copper coins in the nineteenth century of Joseon period by investigating structural differences between genuine objects and replicas. Neutron grating interferometry provides the microstructural information of coins, including features such as pores and precipitates, through a dark field image derived from small-angle neutron scattering. Additionally, neutron transmission tomography examines the three-dimensional internal structures and potentially hidden features of coins. Both neutron imaging techniques highlight regions that contain lead precipitates in the copper alloy, showing consistent agreement with optical imaging and with the quantitative lead content measured by energy dispersive X-ray spectroscopy. The distinct corrosion patterns observed in the authentic coin and replica provide empirical explanations for the general corrosion mechanism of copper alloy. This interpretation finds support in the moderate contribution of dark field contrast from cuprite, which underlies the signal of lead precipitates.

Two types of anion exchange ionomers, powder and dispersion, are studied in this work. The gas diffusion electrode with the dispersion-type ionomer exhibits strong hydrophobicity, thus not enabling sufficient ionic exchange during the potassium hydroxide exchange process, which in turn exhibits very poor performance. Hence gas diffusion electrode prepared with the powder-type ionomer is used to study the sensitivity and effect of reactant concentration and operating conditions on anion exchange membrane fuel cell performance. The results indicate that the cell performance is most sensitive to relative humidity followed by hydrogen concentration. In contrast, oxygen is not a major performance limiting factor validated by oxygen reactant sensitivity analysis. Results from neutron imaging experiments demonstrate that active water transport from cathode to anode through electro-osmotic drag is very active, which results in flooding on the anode side, causing significant reduction of cell performance. The combined experimental and neutron results provide valuable insight into the water management strategies to improve the stability of fuel cell performance, which has a significant impact towards the development of anion exchange membrane fuel cell.

Heterogeneity in component morphology and distribution, inherent in modern electrochemical devices, frequently limits device performance and durability. However, accurately characterizing heterogeneity is challenging as it requires high-contrast detection of evolving multi-material components and associated interfaces, and this often bottlenecks rational design. In this study, new insights into spatio-operational heterogeneity are quantitatively revealed within multi-component electrochemical systems using simultaneous neutron and X-ray tomography (NeXT). In operando fuel cells, this technique uniquely offers independent yet simultaneous and correlated characterization of material distribution and morphology. This enables accurate contextualization of liquid water within all key component interfaces in sufficient detail to resolve previously unidentified 4D heterogeneity. First, 4D heterogeneity in membrane thickness and water content is found to depend strongly upon location and operating conditions, with membrane thickness variations up to 80 mu m and membrane water content variation from dry to hydrated at 21 . Second, a direct experimental link is established between anisotropic humidification and local anisotropic swelling of the membrane. The observations lend unique insights into degradation mechanisms of the membrane and have notable implications on the practical durability of fuel cells. The proposed methodology is highly relevant to advancing multi-material electrochemical devices (with evidence of applicability to batteries provided).

Neutron interferometry uniquely combines neutron imaging and scattering methods to enable characterization of multiple length scales from 1 nm to 10 µm. However, building, operating, and using such neutron imaging instruments poses constraints on the acquisition time and on the number of measured images per sample. Experiment time-constraints yield small quantities of measured images that are insufficient for automating image analyses using supervised artificial intelligence (AI) models. One approach alleviates this problem by supplementing annotated measured images with synthetic images. To this end, we create a data-driven simulation framework that supplements training data beyond typical data-driven augmentations by leveraging statistical intensity models, such as the Johnson family of probability density functions (PDFs). We follow the simulation framework steps for an image segmentation task including Estimate PDFs → Validate PDFs → Design Image Masks → Generate Intensities → Train AI Model for Segmentation. Our goal is to minimize the manual labor needed to execute the steps and maximize our confidence in simulations and segmentation accuracy. We report results for a set of nine known materials (calibration phantoms) that were imaged using a neutron interferometer acquiring four-dimensional images and segmented by AI models trained with synthetic and measured images and their masks.

The continued advancement of complex materials often requires a deeper understanding of the structure-function relationship across many length scales, which quickly becomes an arduous task when multiple measurements are required to characterize hierarchical and inherently heterogeneous materials. Therefore, there are benefits in the simultaneous characterization of multiple length scales. At the National Institute of Standards and Technology, a new neutron far-field interferometer is under development that aims to enable a multi-scale measurement combining the best of small-angle neutron scattering (SANS) and neutron imaging and tomography. Spatially resolved structural information on the same length scales as SANS (0.001-1 mu m) and ultra-small-angle neutron scattering (USANS, 0.1-10 mu m) will be collected via dark-field imaging simultaneously with regular attenuation radiography (>10 mu m). The dark field is analogous to the polarization loss measured in spin-echo SANS (SESANS) and is related to isotropic SANS through a Hankel transform. Therefore, we use this close relationship and analyze results from SANS, USANS, SESANS and dark-field imaging of monodisperse spheres as a validation metric for the interferometry measurements. The results also highlight the strengths and weaknesses of these neutron techniques for both steady-state and pulsed neutron sources. Finally, we present an example of the value added by the spatial resolution enabled by dark-field imaging in the study of more complex heterogeneous materials. This information would otherwise be lost in other small-angle scattering measurements averaged over the sample.

Neutron radiography has been a powerful tool for measuring water content within operating fuel cells. The resolution for neutron imaging has been steadily improving and has demonstrated the ability to measure water content in industrially relevant catalyst layers. The difficulty in measuring catalyst layer or interfacial water content with neutron radiography is that the method assumes that the layers of the MEA are flat and uniform with no variation which is a poor assumption. To combat this assumption, it is necessary to move to neutron tomography that resolves the fuel cell in three dimensions. Combining neutron tomography with simultaneous X-ray tomography improves layer and interface identification which facilitates better water saturation measurements. In addition to capturing the “waviness” of the MEA, this method can be applied to tracking water distribution in structured 3D electrodes. This talk will demonstrate current developments in fast simultaneous neutron and X-ray tomography, methods to improve saturation calculations within the various porous layers, and showcase new hardware developments available to the NIST user community.

This work presents a novel porous transport layer (PTL), the hydrochannel PTL, that enables improved water management and record high round trip efficiency in unitized reversible fuel cells (URFCs). URFCs require rapid transport of O 2 and H 2 O to provide high performance in both fuel cell and water electrolyzer operation, but cell design is complicated by conflicting water management requirements: electrolyzers perform best with high liquid water saturation, whereas fuel cells perform best when liquid water saturation is as low as possible while still maintaining effective ionomer hydration. The hydrochannel PTL circumvents this obstacle by providing hydrophilic channels for water transport through an otherwise hydrophobic PTL, enabling optimal performance in both fuel cell and water electrolyzer modes. Neutron radiography measurements of water content in both operating modes confirm that the hydrochannel PTL enables high performance due to its improved water management capabilities.

Electrolysis is a critical component to realizing a true green hydrogen economy. The performance and efficiency of an electrolyzer is directly tied to the multiphase transport that occurs within the porous transport layer (PTL). The PTLs must allow sufficient water transport to the catalyst layer to maintain the reaction while removing the product gases. PTLs are typically created from titanium foams or sintered from titanium powders or fibers. The resultant structure is heterogenous and requires 3D imaging to properly capture the pore structure and transport pathways. The use of titanium for the PTL can make it difficult to track the multiphase flow using X-rays alone as the X-ray energy required to penetrate 1 cm or more reduces the contrast between water and oxygen without the use of contrast agents that could affect the reaction. Neutrons provide a penetrating probe capable of imaging through titanium while having extreme sensitivity to water. Combing neutrons and high energy X-rays provides an easy way to identify all components in the PTL, i.e., the solid structure, oxygen, and water. The National Institute of Standards and Technology provides the Neutron Imaging Facility to the larger research community through the Center for Neutron Research facility user program. This instrument provides the ability to perform simultaneous neutron and X-ray tomography. Moving from 2D radiography to 3D tomography is critical to fully understand the influence of the PTL pore structure on the multiphase transport. This talk will give an overview of the instrument capabilities, showcase past success for neutron imaging of electrolyzers, and provide current progress on development of hardware and data reduction methods for simultaneous neutron and X-ray tomography of electrolyzers.

We discuss instrumentation and analysis efforts at NIST to develop neutron dark-field imaging, simultaneous neutron/X-ray tomography and the Wolter optics neutron microscope. Progress will be highlighted through applications in electrochemistry, advanced manufacturing, concrete, and geology.

This study aims to determine an acquisitional and computational workflow that yields the highest quality spatio-spectral reconstructions in four-dimensional neutron tomography studies. The properties of neutrons enable unique image contrast modes, but accessing these modes requires defining the energy of the neutron beam, resulting in long acquisition times. We seek sparse angular tomography approaches to collect of order 100 tomograms at different neutron wavelengths using the minimum number of input projection images. In these computational image workflows, we identified and evaluated the main factors affecting the quality of the tomographic reconstruction such as the projection number, the reconstruction method, and the post-processing method and we report relationships between 3D reconstruction quality metrics and acquisition time. Based on these relationships, the performance of seeded simultaneous iterative reconstruction-based techniques (SIRT and SIRT with total variation regularization) yielded improved image quality and more accurate estimates of the reconstructed attenuation values compared to other methods, which included convolutional neural networks. The methods were then applied to a dose-reduced monochromatic dataset and characterized via signal-to-noise ratio (SNR) and single-voxel resolution.

Dark-field imaging probes the projected autocorrelation function at the autocorrelation length of the grating interferometer and quantitatively accesses the parameters of a microstructure model. The National Institute of Standards and Technology has developed a novel far-field grating interferometer to study hierarchical materials in various fields such as polymer science, geology, additive manufacturing under the INFER project. In this work, we detail the simulation of dark-field imaging which is one of the goals of INFER.

The performance of electrochemical energy devices, such as fuel cells and batteries, is dictated by intricate physiochemical processes within. To better understand and rationally engineer these processes, we need robust operando characterization tools that detect and distinguish multiple interacting components/interfaces in high contrast. Here, we uniquely combine dual-modality tomography (simultaneous neutron and x-ray tomography) and advanced image processing (iterative reconstruction and metal artifact reduction) for high-contrast multimaterial imaging, with signal and contrast enhancements of up to 10 and 48 times, respectively, compared to conventional single-modality imaging. Targeted development and application of these methods to electrochemical devices allow us to resolve operando distributions of six interacting fuel cell components (including void space) with the highest reported pairwise contrast for simultaneous yet decoupled spatiotemporal characterization of component morphology and hydration. Such high-contrast tomography ushers in key gold standards for operando electrochemical characterization, with broader applicability to numerous multimaterial systems.

Stereolithography of ceramics remains one of the most powerful additive manufacturing routes for the creation of intricate ceramic parts. Despite its utility as a forming tool, ceramic stereolithography requires a challenging debinding stage due to the requisite high polymeric loading. Earlier research has identified both the polymeric resin composition and debinding atmosphere to be crucial factors in improving debinding performance. Here, we use a combination of thermogravimetric analysis and neutron imaging to examine samples of different compositions printed using the same processing and exposure parameters. We quantify the influence of both polyethylene glycol addition and the use of different debinding atmospheres (argon and vacuum) on the debinding behavior of ceramic pellets. Specifically, we demonstrate a method for examining the concentration gradients that develop during thermal debinding with the aid of neutron tomography. We find that at a constant heating rate of 1 degrees C/min up to 500 degrees C, vacuum atmosphere appears to result in a greater number of cracks as compared to the use of argon. The vacuum atmosphere led to the development of lower concentration gradients in the samples on average. The greatest improvement resulted with the addition of polyethylene glycol to the samples. This addition led to significantly less cracking and much lower concentration gradients in samples during debinding. These results prompt us to conclude that while keeping printing and exposure parameters constant, composition modification has a more significant effect on the debinding improvement than heating atmosphere.

Wolter optics present the opportunity to realize a practical neutron lens, which would convert a neutron imaging instrument from a pinhole camera to a microscope. This conversion would result in significant increases in neutron flux (up to 10,000 gain over the pinhole geometry) while maintaining high spatial resolution (about 3 μm). The Wolter optic system is currently being fabricated, and the first mirrors are expected to arrive in SEP 2023. As such, we focus this presentation on image simulation efforts. A ray tracing code has been developed that is able to simulate full three-dimensional imaging of extended objects placed in the Wolter optics neutron microscope. To simulate a fuel cell, we employ tomography measurements based on X-ray tomography and CAD-model derived volumes. The reason the Wolter optics system realizes such a large gain in flux is by focusing much of the flux from an extended neutron guide onto a small spot. Thus, conventional radiography of an extended object will not be possible, as the beam is similar to a cone beam which emanates from a small spot. We derive a tomography algorithm for this spot and will show its effectiveness on reconstructing simulated images. We also report on expected performance of the fabricated optical system in the current instrument configuration. Figure 1

Heterogeneity within electrochemical devices, such as fuel cells, influences their performance and durability in ways that are not fully understood. 4-dimensional (4-D; 3 spatial dimensions and time) operando visualization techniques such as X-ray (1-2) and neutron (3) tomography are powerful tools to probe heterogeneity within operating electrochemical devices in high spatiotemporal resolution. Combining neutron and X-ray tomography (NeXT) (3-4) simultaneously offers unique advantages over single-modality methods, especially in terms of enhanced contrast between materials. There is a significant opportunity to utilize NeXT to characterize and quantify heterogeneity within electrochemical devices during cell operation. In this study, we utilize quantitative NeXT to identify spatiotemporal heterogeneity in the morphology of the membrane electrode assembly (MEA) and water distribution within the porous layers and the membrane. A custom interfacial tracking algorithm is utilized to accurately characterize 4-D morphology and boundaries of cell components. Heterogeneity is found to depend upon location with respect to cell components and operating conditions (such as current density and inlet relative humidity). Variations in the MEA morphology is dominated by variations in membrane morphology, whereby variations of up to 80 μm is observed in membrane thickness for N117 membranes (Chemours, USA). We find that the interface between the gas diffusion layer and the enclosing gasket is a high porosity region that accumulates liquid water during cell operation, and this liquid accumulation leads to high membrane hydration and membrane swelling near the interface. With this study, we demonstrate the viability of quantitative NeXT to characterize operando heterogeneity within multi-component electrochemical devices, taking us a step closer towards rational control and design of inherent heterogeneity within these devices. References 1. Y. Singh, R. T. White, M. Najm, T. Haddow, V. Pan, F. P. Orfino, M. Dutta, and E. Kjeang, J. Power Sources., 412 (2019): 224-237. 2. Xu, Hong, Minna Bührer, Federica Marone, Thomas J. Schmidt, Felix N. Büchi, and Jens Eller, J. Electrochem. Soc., 168, no. 7 (2021): 074505. 3. J. M. LaManna, Y. Yue, T. A. Trabold, J. D. Fairweather, D. S. Hussey, E. Baltic and D. L. Jacobson, Meet. Abstr. - Electrochem. Soc., 32 (2017). 4. Shrestha, Pranay, Jacob Michael LaManna, Kieran Fahy, Junseob Kim, ChungHyuk Lee, Keonhag Keonhag Lee, Eli Baltic, David Jacobson, Daniel Hussey, and Aimy Bazylak, Meet. Abstr. - Electrochem. Soc. 242, no. 39, pp. 1451-1451 (2022).

Water management in a fuel cell is an essential prerequisite for achieving high cell performance, where sufficient water is required for membrane hydration while excess liquid water leads to undesired mass transport losses. Existing heterogeneity within the fuel cell, such as those created by flow-field lands and channels create three-dimensional (3-D) heterogeneity in water distribution within the fuel cell components, which may have long term effect on the durability of fuel cell components, such as the membrane (1). 3-D visualization techniques such as X-ray (1-4) and neutron (5) tomography are powerful in revealing the effect of the existing heterogeneity on water distributions in 3-D. However, there is an opportunity to combine neutron and X-ray tomography (6) to probe into the details of these heterogenous water distributions even further and clarify their impacts on 3-D membrane hydration. In this study, we investigate the effect of heterogeneity in fuel cells (primarily land-channel heterogeneity) on 3-D membrane hydration and membrane morphology changes during fuel cell operation using simultaneous neutron and X-ray tomography (NeXT). The fuel cell is tested at varying gas humidity conditions in a serpentine flow-field configuration. A simultaneous coupling of neutron and X-ray imaging provides high contrast across various components of the fuel cell. Specifically, neutrons are highly attenuated by hydrogen atoms; hence neutron imaging is used to accurately locate and quantify operando water distribution. X-rays are sensitive to metals; hence simultaneous X-rays imaging is used to track metal-containing components (metal flow-field) and interfaces (such as interface between Pt-containing catalyst layer and membrane). This study demonstrates how heterogeneity in fuel cells plays a role in 3-D membrane hydration and needs to be tailored to enhance cell performance. References Y. Singh, R. T. White, M. Najm, T. Haddow, V. Pan, F. P. Orfino, M. Dutta, and E. Kjeang, J. Power Sources., 412 (2019): 224-237. Y. Nagai, J. Eller, T. Hatanaka, S. Yamaguchi, S. Kato, A. Kato, F. Marone, H. Xu and F. N. Büchi, J. Power Sources. , 435 (2019). S. J. Normile, D. C. Sabarirajan, O. Calzada, V. De Andrade, X. Xiao, P. Mandal, D. Y. Parkinson, A. Serov, P. Atanassov and I. V. Zenyuk, Meter. Today Energy. , 9 (2018). S. S. Alrwashdeh, I. Manke, H. Markötter, M. Klages, M. Göbel, J. Haußmann, J. Scholta and J. Banhart, ACS Nano. , 11, 6 (2017). J. M. LaManna, Y. Yue, T. A. Trabold, J. D. Fairweather, D. S. Hussey, E. Baltic and D. L. Jacobson, Meet. Abstr. - Electrochem. Soc. , 32 (2017). J. M. LaManna, D. S. Hussey, E. Baltic and D. L. Jacobson, Rev. Sci. Instrum. , 88, 11 (2017).

An abstract is not available for this content so a preview has been provided. As you have access to this content, a full PDF is available via the ‘Save PDF’ action button.

Demand for high purity hydrogen production using renewable energy sources is growing to meet the clean energy demands. Polymer electrolyte membrane water electrolyzer (PEMWE) is one of the viable options for H 2 production, but its high capital cost and operational expenditures increase the cost of H 2 . Improving the interface between the catalyst layer (CL) and the porous transport layer (PTL) is critical to increasing the efficiency of PEMWEs and thereby lowering the cost of H 2 . Increased contact between the CL and PTL improves catalyst utilization, and the optimal structure of the PTL reduces the mass transport issues related to O 2 bubble removal.(1-3) Improved understanding of the PTL microstructure is necessary to improve the performance and efficiency of the PEMWE. This work presents a systematic study to elucidate the effect of PTL properties (morphology, thickness, and porosity) and their impact on PEMWE performance under different operating conditions. Polarization curves with different anode PTL (felt, sinter and pore graded hierarchical PTL) are presented in Figure 1a. The separation of mass transport resistance and the contract resistance for the different PTLs will be elucidated to show the impact of water management and interfacial contact. Mass transport in an operating electrolyzer is also studied by estimating the water content using neutron imaging. Figure 1b shows water thickness across a membrane electrode assembly (MEA) with a pore graded hierarchical PTL in anode at different current densities. Water content across the MEA with different PTL is also studied. The cells with these PTLs were evaluated in operando using micro x-ray computed tomography (CT) and x-ray radiography. The x-ray techniques revealed oxygen distribution within the PTLs on the pore-scale at varied current densities, complementing neutron imaging water thickness studies and providing micro-scale insight into transport. Acknowledgment This research is supported by the U.S. Department of Energy (DOE) Hydrogen and Fuel Cell Technologies Office, through the H2NEW consortium. References J. K. Lee, C. Lee, K. F. Fahy, B. Zhao, J. M. LaManna, E. Baltic, D. L. Jacobson, D. S. Hussey and A. Bazylak, Cell Reports Physical Science , 1 , 100147 (2020). T. Schuler, J. M. Ciccone, B. Krentscher, F. Marone, C. Peter, T. J. Schmidt and F. N. Büchi, Advanced Energy Materials , 10 , 1903216 (2020). P. Lettenmeier, S. Kolb, F. Burggraf, A. S. Gago and K. A. Friedrich, Journal of Power Sources , 311 , 153 (2016). Figure 1

Journal Article Simultaneous Neutron and X-ray Tomography for Materials Research Get access JM LaManna, JM LaManna National Institute of Standards and Technology, Gaithersburg, MD, USA Corresponding author: Jacob.LaManna@nist.gov Search for other works by this author on: Oxford Academic Google Scholar MC Daugherty, MC Daugherty National Institute of Standards and Technology, Gaithersburg, MD, USADepartment of Chemical & Biomolecular Engineering, University of Maryland, College Park, MD, USA Search for other works by this author on: Oxford Academic Google Scholar Y Kim, Y Kim National Institute of Standards and Technology, Gaithersburg, MD, USADepartment of Chemistry & Biochemistry, University of Maryland, College Park, MD, USA Search for other works by this author on: Oxford Academic Google Scholar DS Hussey, DS Hussey National Institute of Standards and Technology, Gaithersburg, MD, USA Search for other works by this author on: Oxford Academic Google Scholar E Baltic, E Baltic National Institute of Standards and Technology, Gaithersburg, MD, USA Search for other works by this author on: Oxford Academic Google Scholar DL Jacobson DL Jacobson National Institute of Standards and Technology, Gaithersburg, MD, USA Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 28, Issue S1, 1 August 2022, Pages 246–247, https://doi.org/10.1017/S1431927622001817 Published: 01 August 2022

Neutron imaging offers deep penetration through many high-Z materials while also having high sensitivity to certain low-Z isotopes such as 1H, 6Li, and 10B. This unique combination of properties has made neutron imaging an attractive tool for a wide range of material science and engineering applications. However, measurements made by neutron imaging or tomography are generally qualitative in nature due to the inability of detectors to discriminate between neutrons which have been transmitted through the sample and neutrons which are scattered by the sample or within the detector. Recent works have demonstrated that deploying a grid of small black bodies (BBs) in front of the sample can allow for the scattered neutrons to be measured at the BB locations and subsequently subtracted from the total measured intensity to yield a quantitative transmission measurement. While this method can be very effective, factors such as the scale and composition of the sample, the beam divergence, and the resolution and construction of the detector may require optimization of the grid design to remove all measurement biases within a given experimental setup. Therefore, it is desirable to have a method by which BB grids may be rapidly and inexpensively produced such that they can easily be tailored to specific applications. In this work, we present a method for fabricating BB patterns by thick film printing of Gd2O3 and evaluate the performance with variation in feature size and number of print layers with cold and thermal neutrons.