This article demonstrates spatial mapping of the local and nanoscale structure of thin film objects using spatially resolved pair distribution function (PDF) analysis of synchrotron X-ray diffraction data. This is exemplified in a lab-on-chip combinatorial array of sample spots containing catalytically interesting nanoparticles deposited from liquid precursors using an ink-jet liquid-handling system. A software implementation is presented of the whole protocol, including an approach for automated data acquisition and analysis using the atomic PDF method. The protocol software can handle semi-automated data reduction, normalization and modeling, with user-defined recipes generating a comprehensive collection of metadata and analysis results. By slicing the collection using included functions, it is possible to build images of different contrast features chosen by the user, giving insights into different aspects of the local structure.

Pr2NiO4 (PNO) is a known active oxygen electrode for solid oxide cells but undergoes phase transformation at high temperatures. An in-situ synchrotron study on PNO electrodes show that phase transformation reaches nearly 100% in a long-term operation. Such significant phase transformation is expected to play a detrimental role on the cell performance. However, PNO retains the activity in an enduring operation. The origin for this dichotomy has remained obscure. The aim of this article is to investigate the origin for retained activity and performance stability in PNO electrode. High-resolution transmission electron microcopy analysis shows the presence of a large number of nanoclusters (similar to 5 nm) through the entire electrode bulk, which are localized in the 20-60 nm region. In-situ synchrotron studies show that those nanoclusters are nickelates that account for the retained activity during phase transformation.

Praseodymium nickelates are promising materials to be used as an oxygen electrode in solid oxide cells. Phase transformation in these materials, however, is a major challenge, which may cause durability issues in a fuel cell or electrolyzer. There is a need to develop a strategy that allows researchers to construct an in situ phase-stable and active cathode material. The aim of this study is to complement our previous publications on the electrochemical properties of the (Pr1-xNdx)(2)Ni1-yCuyO4+delta series, which has shown an increased performance stability by 2 orders of magnitude when compared to bare Pr2NiO4+delta. Systematic structural studies on a wide range of compositions were conducted in situ via long-term thermal annealing tests on powders. The structure-property relationship has been investigated using X-ray total scattering and atomic pair distribution function at a synchrotron source. In this work, we provide an attempt to identify a potential origin of structural stability and phase transition in praseodymium nickelates. A high temperature structure can be "frozen" preventing changes in M-O bond lengths, consequently leading to a stabilized structure. Results indicate that the two layers, associated with both Pr and Ni sites, are involved simultaneously in fully stabilizing the parent phase. Furthermore, it was found that Cu-doping on the Ni-site (in Pr2NiO4 structure) alone is not sufficient in stabilizing the parent phase. The structure and stability of the system were then investigated via density functional theory calculations, and computations of the density of states were undertaken for the Cu-doped and baseline compositions. It was found that p-d interactions, i.e., oxygen-metal orbital interactions, were enhanced as Cu was used to dope the PNNO, thus increasing the structural stability of the material.

The use of the non-negative matrix factorization (NMF) technique is validated for automatically extracting physically relevant components from atomic pair distribution function (PDF) data from time-series data such as in situ experiments. The use of two matrix-factorization techniques, principal component analysis and NMF, on PDF data is compared in the context of a chemical synthesis reaction taking place in a synchrotron beam, applying the approach to synthetic data where the correct composition is known and on measured PDFs from previously published experimental data. The NMF approach yields mathematical components that are very close to the PDFs of the chemical components of the system and a time evolution of the weights that closely follows the ground truth. Finally, it is discussed how this would appear in a streaming context if the analysis were being carried out at the beamline as the experiment progressed.

Here, we present an automated and rapid method for nondestructive mapping of crystal grains in a rod-shaped sample. The approach was designed for application to in situ float-zone crystal growth experiments at an X-ray synchrotron source but could be useful in other applications. The methods have been tested on a TiO2 boule grown in an optical float-zone furnace. The approach applies a statistical filter to polycrystalline diffraction patterns on two-dimensional (2D) detectors to rapidly determine the degree of powder quality of the signal. When larger crystals emerge in the growth, their position, size, and shape can be tracked using an automated blob-tracking algorithm that follows individual Bragg peaks as a function of position in a grid scan, even when multiple crystals are contributing spots to diffraction images. This method is found to be robust as the same crystal shape can be independently reconstructed using different sets of Bragg reflections. Image segmentation methods are then used to map out the polycrystalline grains. We also note that other information about crystal quality, such as mosaicity or strain state, may be inferred and mapped from the intensity variation of the Bragg peaks at different locations within the sample.

We validate the use of matrix factorization for the automatic identification of relevant components from atomic pair distribution function (PDF) data. We also present a newly developed software infrastructure for analyzing the PDF data arriving in streaming manner. We then apply two matrix factorization techniques, Principal Component Analysis (PCA) and Non-negative Matrix Factorization (NMF), to study simulated and experiment datasets in the context of in situ experiment.

Journal Article Robust Nanostructure from High Throughput Powder Diffraction Data Get access Simon J L Billinge, Simon J L Billinge Department of Applied Physics and Applied Mathematics, Columbia University, New York, NY, USACondensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, NY, USA Search for other works by this author on: Oxford Academic Google Scholar Christopher J Wright, Christopher J Wright Department of Applied Physics and Applied Mathematics, Columbia University, New York, NY, USA Search for other works by this author on: Oxford Academic Google Scholar Chia-Hao Liu, Chia-Hao Liu Department of Applied Physics and Applied Mathematics, Columbia University, New York, NY, USA Search for other works by this author on: Oxford Academic Google Scholar Michael Waddell, Michael Waddell Department of Applied Physics and Applied Mathematics, Columbia University, New York, NY, USA Search for other works by this author on: Oxford Academic Google Scholar Pavol Juhas, Pavol Juhas Computational Science Initiative, Brookhaven National Laboratory, Upton, NY, USA Search for other works by this author on: Oxford Academic Google Scholar Eric Dooryhee, Eric Dooryhee National Synchrotron Light Source-II, Brookhaven National Laboratory, Upton, NY, USA Search for other works by this author on: Oxford Academic Google Scholar Sanjit Ghose, Sanjit Ghose National Synchrotron Light Source-II, Brookhaven National Laboratory, Upton, NY, USA Search for other works by this author on: Oxford Academic Google Scholar Milinda Abeykoon, Milinda Abeykoon National Synchrotron Light Source-II, Brookhaven National Laboratory, Upton, NY, USA Search for other works by this author on: Oxford Academic Google Scholar Arman Arkilic, Arman Arkilic National Synchrotron Light Source-II, Brookhaven National Laboratory, Upton, NY, USA Search for other works by this author on: Oxford Academic Google Scholar Daniel Allan, Daniel Allan National Synchrotron Light Source-II, Brookhaven National Laboratory, Upton, NY, USA Search for other works by this author on: Oxford Academic Google Scholar ... Show more Thomas Caswell Thomas Caswell National Synchrotron Light Source-II, Brookhaven National Laboratory, Upton, NY, USA Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 23, Issue S1, 1 July 2017, Pages 172–173, https://doi.org/10.1017/S1431927617001544 Published: 04 August 2017

Nickelate (e.g. Pr2NiO4) exhibits high activity towards the oxygen reduction reaction over a wide temperature range (600 - 900 oC), which makes it a promising candidate as an advanced cathode for solid oxide fuel cells. However, a phase transition occurs in Pr2NiO4 during cell operation, following: Pr2NiO4 à Pr6O11 + Pr3Ni2O7. As a result, the quantification of the degree of phase transformation becomes necessary to understand the structure-electrochemical property relationship. In this presentation, we report our recent work on (1) replacing the oxide current collector with a gold metal grid, which enables the cathode to expose to the x-ray beam. The x-ray analysis was performed at room temperature and (2) utilizing in situ capability to study the kinetics and mechanisms of phase evolution and establishing the relationship between high-temperature structures and the electrochemical performance. Finally, we will compare the XRD results acquired from room temperature with these in situ studies. This material is based upon work supported by the U.S. Department of Energy under Award Number DE-FE0023475.

This study is to complement an early report (the manuscript is attached for review purpose) on the role of interlayer on activity and performance stability in praseodymium nickelates. The aforementioned report showed a remarkable 48% increase in power density while switching from common GDC interlayer to a new interlayer chemistry (PGCO). Furthermore, a stable long-term performance was linked with suppressed reaction between the cathode and PGCO interlayer. In this article, we report in situ studies of the phase evolution. The high energy XRD studies at a synchrotron source showed fully suppressed phase transition in praseodymium nickelates with PGCO interlayer, while the electrodes on the GDC interlayer undergo substantial phase transformation. Furthermore, in operando and post-test XRD analyses shown fully suppressed structural changes in electrodes operated in full cells at 750 degrees C and 0.80 V for 500 hours. SEM-EDS analysis showed that the formation of PrOx at the cathode-interlayer interface may play a role in a decrease of mechanical integrity of the interfaces, due to thermal expansion mismatch, leading to a local stress between the two phases. Consequently, phase evolution at a narrow interface may propagate toward the electrode bulk, leading to structural changes and performance degradation. (C) The Author(s) 2017. Published by ECS. All rights reserved.

We report selective electrocatalytic reduction of carbon dioxide to carbon monoxide on gold nanoparticles (NPs) in 0.5 M KHCO3 at 25 °C. Among monodisperse 4, 6, 8, and 10 nm NPs tested, the 8 nm Au NPs show the maximum Faradaic efficiency (FE) (up to 90% at -0.67 V vs reversible hydrogen electrode, RHE). Density functional theory calculations suggest that more edge sites (active for CO evolution) than corner sites (active for the competitive H2 evolution reaction) on the Au NP surface facilitates the stabilization of the reduction intermediates, such as COOH*, and the formation of CO. This mechanism is further supported by the fact that Au NPs embedded in a matrix of butyl-3-methylimidazolium hexafluorophosphate for more efficient COOH* stabilization exhibit even higher reaction activity (3 A/g mass activity) and selectivity (97% FE) at -0.52 V (vs RHE). The work demonstrates the great potentials of using monodisperse Au NPs to optimize the available reaction intermediate binding sites for efficient and selective electrocatalytic reduction of CO2 to CO.

The use of doped ceria as an interlayer in solid oxide fuel cells (SOFCs) is ubiquitous, which provides better thermal expansion match and prevents interaction between the cathode (e.g. LSCF) and electrolyte (e.g. YSZ). However, the role of ceria interlayer on the cathode phase durability and catalytic activity remains obscure. This is particularly true in nickelate cathodes (e.g. Pr2NiO4). Here, we report that traditional Gd-doped ceria (GDC) interlayer substantially accelerates the phase transition in Pr2NiO4. Two new interlayer designs were investigated in order to circuvent the phase evolution by using (1) a thin Pr6O11 film deposited on the surface of GDC, and (2) a Pr-doped ceria interlayer. The latter design not only suppresses the phase transition, but also results in a 48% increase in cathode performance; and more importantly, it leads to a zero degradation over long-term measurements. Systemetic in situ and post analyses were carried out to understand the mechanism, by which the interlayer affects the cathode durability and activity. This material is based upon work supported by the U.S. Department of Energy under Award Number DE-FE0023475.

Area detectors have become the predominant type of detector for the rapid acquisition of X-ray diffraction, small-angle scattering and total scattering. These detectors record the scattering for a large area, giving each shot good statistical significance to the resulting scattered intensity I(Q) pattern. However, many of these detectors have pixel level defects, which cause error in the resulting one-dimensional patterns. In this work, new software to automatically find and mask these dead pixels and other defects is presented. This algorithm is benchmarked with both ideal simulated and experimental datasets.

During operation Pr 2 NiO 4+δ cathode undergoes partial phase transitions which results in evolution of PrO x and higher order layered structure (Pr 3 Ni 2 O 7 ). Simultaneously, the elemental diffusion occurs where praseodymium migrates towards cathode/buffer interface and reacts with doped ceria deep within its bulk. It is speculated that the presence of ceria may promote the diffusion of Pr into the buffer layer due to a large solubility of Pr in ceria. Recently, we observed that the elemental substitution with Nd on the A-site in Pr 2 NiO 4+δ can slow the diffusion process. With increase in Nd content the formation of PrO x and higher order Pr 3 Ni 2 O 7 phase is suppressed. In this presentation, we will discuss (1) the role of buffer chemistry on the diffusion or Pr and (2) whether or not the absence of Pr in buffer layer further promotes the phase evolution in Pr 2 NiO 4 . Thermal annealing tests were performed at various temperatures and compared to electrochemical measurements in full cells. X-ray diffraction and scanning electron microscopy analyses were used to study the long term phase evolution and reaction with buffer layer.

Single phase (Pr1-xNdx)2NiO4 powders (x=0, 0.25, 0.50, 0.75, 1) were synthesized via glycine-nitrate combustion process. Rietveld refinement shows that the unit cell volume decreases linearly with an increase of x. This volume contraction is mainly driven by a decrease in c parameter which follows Vegard’s Law. Reproducible performance was obtained for each cathode composition providing the wealth of data for quantitative studies. The overall cell performance decreases with an increase in Nd content between 650 and 850 °C, based on analysis of area specific resistance and i-E measurements. Performance stability was studied at 750 °C and 0.8 V. In comparison to the parent compound Pr2NiO4, the total polarization increases by 29% in (Pr0.5Nd0.5)2NiO4 and by twofold in (Pr0.25Nd0.75)2NiO4. Although exhibiting the highest peak performance, Pr2NiO4-based cells show 4% performance degradation within 500 hours, while the degradation is negligible in other compositions. Dynamic dependency of EIS spectra, as function of current density, is in agreement with dc measurements.

A new method to quantify the phase evolution in nickelates is developed using sintered metal grids as cathode current collectors. The metal grids not only enable us to carry out phase quantification studies in cathodes, but also retaining the cell’s performance and stability. Moreover, they are chemically compatible with the cathode and allow XRD analysis of the surface and bulk of the cathode after cell operation. Multiple cells were tested to study the reproducibility of measurements. High performance was observed in cells with metal grids, extending the application of this method to cathode durability studies in state-of-the-art SOFCs. Respective advantages and challenges of the method are discussed with an emphasis on phase quantification, and the effects of different noble metals in cells regarding their thermal, electrical, chemical, and mechanical stability. Au was found to be the most suitable current collector due to its low chemical reactivity with the cathode and mechanical compatibility at operating conditions.

Praseodymium nickelate (Pr2NiO4) is an active oxygen electrode for solid oxide fuel cells, but undergoes phase transition at elevated temperatures (e.g., 750°C). Quantification of this phase evolution in an operating single cell is challenging because of the overlap of X‐ray diffraction (XRD) peaks between the cathode and oxide current collector. In this work, we replace the oxide current collector with a gold metal grid, circumventing these challenges by allowing the exposure of the cathode to the X‐ray beam, while eliminating peak overlap. Quantification of the phase evolution was performed by a least‐squares fitting of the linear combination of XRD standards against the experimental patterns. Energy‐dispersive spectroscopy analysis on long‐term operated cells showed the absence of reactions between the gold grids and the cathodes. Additionally, the grids exhibited excellent mechanical stability under operating conditions and enabled similar cell performance as an oxide current collector.

The advantages of the electrochemical conversion of carbon dioxide to fuels using renewable energy sources are twofold: (1) it has the potential to accomplish a carbon-neutral energy cycle and (2) it can provide an approach to tackle the environmental challenges caused by anthropogenic carbon dioxide emissions. Although thermodynamically possible, the kinetics of carbon dioxide reduction to fuels remains challenging and therefore, an efficient and robust electrocatalyst is needed to promote the reaction. The ideal catalyst for the electrochemical CO2 reduction must be capable of mediating multiple proton-coupled electron transfer reactions at low overpotentials, suppressing the concurrent hydrogen evolution reaction, converting CO2 to desired chemicals with high selectivity, and achieving long-term stability. Extensive research has been carried out on metallic electrocatalysts during the past three decades; however, further studies are need to develop materials that are simultaneously efficient and stable for practical purposes. The focus of this presentation is to report the use of N-doped carbon nanostructures as the electrocatalysts, which are highly efficient, selective and more importantly, stable catalysts to achieve CO2 conversion to CO. The catalytic activity of N-doped carbon nanotubes (NCNTs) was further benchmarked against other metallic catalysts reported in literature. Compared to noble metals Ag & Au, these NCNTs exhibited a lower overpotential to achieve similar selectivity towards CO formation. The dependence of catalytic activity, i.e., the overpotential and selectivity for CO formation on the defect structures (pyridinic, graphitic, pyrrolic-N) inside NCNTs will be discussed. The presence of both pyridinic and graphitic-N was found to significantly decrease the absolute overpotential and increase the selectivity towards CO formation. In addition, the electrocatalytic activity of two-dimensional materials will be presented. Overall, pyridinic-N defects exhibited the highest catalytic activity; thereby suggesting the directions for developing carbon nanostructures as metal-free electrocatalysts for CO2 reduction.