Evolution of electrochemical interfaces in solid oxide fuel cells (SOFC): a Ni and Zr resonant anomalous ultra-small-angle X-ray scattering study with elemental and spatial resolution across the cell assembly
TL;DR: In this article, anomalous ultra-small-angle X-ray scattering (anomalous USAXS) measurements were used to quantify the component phase interfacial surface areas as a function of position within the electrodes and electrolyte of a SOFC assembly.
Abstract: Electrochemical interfaces are key to the direct conversion of fuels to electrical energy and lend energy converters like solid oxide fuel cells (SOFC) their functionality. Over extended operation at high temperatures, the microstructure of the underlying component materials in the cathodes, anodes and electrolytes evolve to an extent that these interfaces become affected and ultimately impaired, giving rise to performance degradation. We present anomalous ultra-small-angle X-ray scattering (anomalous USAXS) measurements to quantify the component phase interfacial surface areas as a function of position within the electrodes and electrolyte of a SOFC assembly. Using USAXS at a 3rd generation X-ray synchrotron facility, the primary microstructural parameters obtained are the mean feature size, size distribution and surface area, determined over a contiguous length scale from nanometers to micrometers in a single measurement at a given position. Here, a spatial resolution of <20 μm has been achieved perpendicular to the SOFC electrode and electrolyte layers. Anomalous USAXS measurements at X-ray energies just below the Ni and Zr K-absorption edges have enabled the electrochemically-active solid components and their associated void morphologies to be distinguished from each other close to the electrode/electrolyte interfaces. The anomalous variation of the X-ray scattering contrast with X-ray energy has been exploited to distinguish Ni-rich or Zr-rich component microstructures from adjacent phases, and to determine the interfacial surface areas both between specific solid phases and between each phase and the void network. Such information provides improved insights for relating the morphology of the SOFC triple phase boundary (TPB, where the reactant gas, electron-conducting and ion-conducting phases coincide) to the various component interfaces in the adjacent microstructure. We demonstrate how such measurements determine the electrochemically-active interface response to SOFC service life, especially in the anode with and without sulfur present in the fuel. Our approach can be generalized to address degradation issues at a quantitative level in other electrochemical systems such as batteries and photo-electrochemical cells.
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TL;DR: The certification of a new NIST standard reference material for the calibration of small-angle X-ray scattering intensity is described, including the purpose, use and applicability of the SRM together with limitations and uncertainties in the intensity calibration provided.
Abstract: The certification of a new standard reference material for small-angle scattering [NIST Standard Reference Material (SRM) 3600: Absolute Intensity Calibration Standard for Small-Angle X-ray Scattering (SAXS)], based on glassy carbon, is presented. Creation of this SRM relies on the intrinsic primary calibration capabilities of the ultra-small-angle X-ray scattering technique. This article describes how the intensity calibration has been achieved and validated in the certified Q range, Q = 0.008–0.25 A−1, together with the purpose, use and availability of the SRM. The intensity calibration afforded by this robust and stable SRM should be applicable universally to all SAXS instruments that employ a transmission measurement geometry, working with a wide range of X-ray energies or wavelengths. The validation of the SRM SAXS intensity calibration using small-angle neutron scattering (SANS) is discussed, together with the prospects for including SANS in a future renewal certification.
49 citations
Cites methods from "Evolution of electrochemical interf..."
...Using this method, the X-ray energy calibration for USAXS measurements has been demonstrated to within a standard uncertainty of 1.5 eV (Allen et al., 2014)....
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12 Oct 2021
TL;DR: Small-angle scattering (SAS) as discussed by the authors is a technique that is able to probe the structural organization of matter and quantify its response to changes in external conditions, such as temperature, pressures, flows, shears or stresses.
Abstract: Small-angle scattering (SAS) is a technique that is able to probe the structural organization of matter and quantify its response to changes in external conditions. X-ray and neutron scattering profiles measured from bulk materials or materials deposited at surfaces arise from nanostructural inhomogeneities of electron or nuclear density. The analysis of SAS data from coherent scattering events provides information about the length scale distributions of material components. Samples for SAS studies may be prepared in situ or under near-native conditions and the measurements performed at various temperatures, pressures, flows, shears or stresses, and in a time-resolved fashion. In this Primer, we provide an overview of SAS, summarizing the types of instrument used, approaches for data collection and calibration, available data analysis methods, structural information that can be obtained using the method, and data depositories, standards and formats. Recent applications of SAS in structural biology and the soft-matter and hard-matter sciences are also discussed. Small-angle scattering can reveal the structural organization of bulk materials and materials at surfaces and quantify their response to changes in external conditions. This Primer provides an overview of small-angle scattering using both X-rays and neutrons, and includes instrumentation, data collection and the type of structural information gathered in various applications.
35 citations
19 citations
21 May 2020
TL;DR: In this paper, a series of Sr2MMoO6-δ double perovskite solid oxide fuel cell (SOFC) anode materials (where 0 ≤ δ ≤ 0.041 and M = Fe, Co, or Ni) were synthesized, and the changes in their morpholog...
Abstract: In this study, a series of Sr2MMoO6-δ double perovskite solid oxide fuel cell (SOFC) anode materials (where 0 ≤ δ ≤ 0.041 and M = Fe, Co, or Ni) were synthesized, and the changes in their morpholog...
6 citations
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TL;DR: In this paper, relativistic calculations of the photoelectric cross section have been made and the integral for the principal contribution to Δf′ has been evaluated numerically without approximation to the form of the cross section-vs-energy curve, as has been done in previous calculations.
Abstract: Anomalous scattering factors Δf′ and Δf″ have been calculated relativistically for Cr, Fe, Cu, Mo, and Ag Kα radiations for the atoms Li through Cf. An interpolation scheme for other wavelengths is included in a separate report. Relativistic calculations of the photoelectric cross section have been made and the integral for the principal contribution to Δf′ has been evaluated numerically without approximation to the form of the cross section‐vs‐energy curve, as has been done in previous calculations. Many of the results are significantly different from previous calculations. Where experimental values exist, agreement for Δf″ is improved. For the rare gases, except for xenon, agreement between Δf′ and experiment is improved. Because of the more rigorous evaluation of Δf′ from cross‐section information, it is presumed that the present Δf′ values are more accurate than previous calculated values. Calculated mass absorption coefficients for the elements are included as incidental information.
2,698 citations
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TL;DR: In this article, a review of the experimental measurements which are used to establish the wavelength of this line on an absolute angstrom basis is given, and the recommended wavelength values are listed in \AA{}* units together with probable errors; corresponding energies are given in keV.
Abstract: Inconsistencies in accepted values (in x units) of x-ray reference lines have recently been demonstrated, although all are supposedly based on "good" calcite crystals. Factors supporting the selection of the W $K{\ensuremath{\alpha}}_{1}$ line as the X-Ray Wavelength Standard are critically discussed. A review is given of the experimental measurements which are used to establish the wavelength of this line on an absolute angstrom basis. Its value is $\ensuremath{\lambda}$ W $K{\ensuremath{\alpha}}_{1}=(0.2090100\ifmmode\pm\else\textpm\fi{}5 \mathrm{ppm})$ \AA{}. This may be used to define a new unit, denoted by \AA{}*, such that the W $K{\ensuremath{\alpha}}_{1}$ wavelength is exactly 0.2090100 \AA{}*; hence 1\AA{}*=1\AA{}\ifmmode\pm\else\textpm\fi{}5 ppm. The wavelengths of the Ag $K{\ensuremath{\alpha}}_{1}$, Mo $K{\ensuremath{\alpha}}_{1}$, Cu $K{\ensuremath{\alpha}}_{1}$, and the Cr $K{\ensuremath{\alpha}}_{2}$ have been established as secondary standards with probable error of approximately one part per million. Sixty-one additional x-ray lines have been used as reference values in a comprehensive review and reevaluation of more than 2700 emission and absorption wavelengths. The recommended wavelength values are listed in \AA{}* units together with probable errors; corresponding energies are given in keV. A second table lists the wavelengths in numerical order, and likewise includes their energies in keV.
1,467 citations
TL;DR: In this article, the design and operation of Solid Oxide Fuel Cells (SOFCs) is discussed, noting the restrictions based on materials' requirements and fuel specifications and the advantages of SOFCs with respect to other fuel cell technologies.
Abstract: The generation of energy by clean, efficient and environmental-friendly means is now one of the major challenges for engineers and scientists Fuel cells convert chemical energy of a fuel gas directly into electrical work, and are efficient and environmentally clean, since no combustion is required Moreover, fuel cells have the potential for development to a sufficient size for applications for commercial electricity generation This paper outlines the acute global population growth and the growing need and use of energy and its consequent environmental impacts The existing or emerging fuel cells’ technologies are comprehensively discussed in this paper In particular, attention is given to the design and operation of Solid Oxide Fuel Cells (SOFCs), noting the restrictions based on materials’ requirements and fuel specifications Moreover, advantages of SOFCs with respect to the other fuel cell technologies are identified This paper also reviews the limitations and the benefits of SOFCs in relationship with energy, environment and sustainable development Few potential applications, as long-term potential actions for sustainable development, and the future of such devices are discussed
1,403 citations
TL;DR: Irena as mentioned in this paper is a tool suite for analysis of both X-ray and neutron small-angle scattering (SAS) data within the commercial Igor Pro application, bringing together a comprehensive suite of tools useful for investigations in materials science, physics, chemistry, polymer science and other fields.
Abstract: Irena, a tool suite for analysis of both X-ray and neutron small-angle scattering (SAS) data within the commercial Igor Pro application, brings together a comprehensive suite of tools useful for investigations in materials science, physics, chemistry, polymer science and other fields. In addition to Guinier and Porod fits, the suite combines a variety of advanced SAS data evaluation tools for the modeling of size distribution in the dilute limit using maximum entropy and other methods, dilute limit small-angle scattering from multiple non-interacting populations of scatterers, the pair-distance distribution function, a unified fit, the Debye–Bueche model, the reflectivity (X-ray and neutron) using Parratt's formalism, and small-angle diffraction. There are also a number of support tools, such as a data import/export tool supporting a broad sampling of common data formats, a data modification tool, a presentation-quality graphics tool optimized for small-angle scattering data, and a neutron and X-ray scattering contrast calculator. These tools are brought together into one suite with consistent interfaces and functionality. The suite allows robust automated note recording and saving of parameters during export.
1,225 citations
TL;DR: In this paper, the authors review the development of Cr-tolerant cathodes for intermediate temperature solid oxide fuel cells, and a possible mechanism of Cr deposition at cathodes are briefly reviewed as well.
Abstract: The composition and microstructure of cathode materials has a large impact on the performance of solid oxide fuel cells (SOFCs). Rational design of materials composition through controlled oxygen nonstoichiometry and defect aspects can enhance the ionic and electronic conductivities as well as the catalytic properties for oxygen reduction in the cathode. Cell performance can be further improved through microstructure optimization to extend the triple-phase boundaries. A major degradation mechanism in SOFCs is poisoning of the cathode by chromium species when chromium-containing alloys are used as the interconnect material. This article reviews recent developments in SOFC cathodes with a principal emphasis on the choice of materials. In addition, the reaction mechanism of oxygen reduction is also addressed. The development of Cr-tolerant cathodes for intermediate temperature solid oxide fuel cells, and a possible mechanism of Cr deposition at cathodes are briefly reviewed as well. Finally, this review will be concluded with some perspectives on the future of research directions in this area.
1,016 citations