Jeffrey J. Lombardo

Zone-doubled Fresnel zone plates for high-resolution hard X-ray full-field transmission microscopy

The use of zone-doubled Fresnel zone plates for sub-20 nm spatial resolution in full-field transmission X-ray microscopy and tomography at the hard X-ray regime (8–10 keV) is demonstrated.

Quantitative x-ray phase imaging at the nanoscale by multilayer Laue lenses

For scanning x-ray microscopy, many attempts have been made to image the phase contrast based on a concept of the beam being deflected by a specimen, the so-called differential phase contrast imaging (DPC). Despite the successful demonstration in a number of representative cases at moderate spatial resolutions, these methods suffer from various limitations that preclude applications of DPC for ultra-high spatial resolution imaging, where the emerging wave field from the focusing optic tends to be significantly more complicated. In this work, we propose a highly robust and generic approach based on a Fourier-shift fitting process and demonstrate quantitative phase imaging of a solid oxide fuel cell (SOFC) anode by multilayer Laue lenses (MLLs). The high sensitivity of the phase to structural and compositional variations makes our technique extremely powerful in correlating the electrode performance with its buried nanoscale interfacial structures that may be invisible to the absorption and fluorescence contrasts.

Focused ion beam preparation of samples for X-ray nanotomography.

The preparation of hard material samples with the necessary size and shape is critical to successful material analysis. X-ray nanotomography requires that samples are sufficiently thin for X-rays to pass through the sample during rotation for tomography. One method for producing samples that fit the criteria for X-ray nanotomography is focused ion beam/scanning electron microscopy (FIB/SEM) which uses a focused beam of ions to selectively mill around a region of interest and then utilizes a micromanipulator to remove the milled-out sample from the bulk material and mount it on a sample holder. In this article the process for preparing X-ray nanotomography samples in multiple shapes and sizes is discussed. Additionally, solid-oxide fuel cell anode samples prepared through the FIB/SEM technique underwent volume-independence studies for multiple properties such as volume fraction, average particle size, tortuosity and contiguity to observe the characteristics of FIB/SEM samples in X-ray nanotomography.

Oxidation States Study of Nickel in Solid Oxide Fuel Cell Anode Using X-ray Full-field Spectroscopic Nano-tomography

Identifying the chemical state and coupling with morphological information in three dimensions are of great interest in energy storage materials, which typically involve reduction-oxidation cycling and structural evolution. Here, we apply x-ray nano-tomography with multiple x-ray energies to study oxidation states of nickel (Ni) and nickel oxide phases in Ni-yttria-stabilized zirconia (YSZ), a typical anode material of solid oxide fuel cells (SOFC). We present a method to quantitatively identify the nickel-based oxides from Ni-YSZ anode composite, and obtain chemical mapping as well as associated microstructures at nanometer scale in three dimensions. NiO particles manually placed on a Ni-YSZ composite anode were used for validation of the method, while no nickel oxides were found to be present within the electrode structure as remnants of the cell fabrication process. The application of the method can be widely applied to energy storage materials including SOFCs, Li-ion batteries, and supercapacitors, as...

Three-Dimensional Microstructural Imaging of Sulfur Poisoning-Induced Degradation in a Ni-YSZ Anode of Solid Oxide Fuel Cells

Following exposure to ppm-level hydrogen sulfide at elevated temperatures, a section of a solid oxide fuel cell (SOFC) Ni-YSZ anode was examined using a combination of synchrotron-based x-ray nanotomography and x-ray fluorescence techniques. While fluorescence measurements provided elemental identification and coarse spatial mapping, x-ray nanotomography was used to map the detailed 3-D spatial distribution of Ni, YSZ, and a nickel-sulfur poisoning phase. The nickel-sulfur layer was found to form a scale covering most of the exposed nickel surface, blocking most fuel reformation and hydrogen oxidation reaction sites. Although the exposure conditions precluded the ability to develop a detailed kinetic description of the nickel-sulfur phase formation, the results provide strong evidence of the detrimental effects of 100 ppm hydrogen sulfide on typical Ni-YSZ anode materials.

Comparison of X-ray Nanotomography and FIB-SEM in Quantifying the Composite LSM/YSZ SOFC Cathode Microstructure

Department of Mechanical Engineering, University of Connecticut, Storrs, CT, USA Electrochemical Engineering Group (GGEC), Centre for Interdisciplinary Electron Microscopy, Industrial Energy Systems Laboratory École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland Stanford Synchrotron Radiation Lightsource, Stanford Linear Accelerator Center Menlo Park, CA 94025, USA National Synchrotron Light Source II, Brookhaven National Laboratory Upton, NY 11973, USA

Analysis of Solid Oxide Fuel Cell LSM-YSZ Composite Cathodes With Varying Starting Powder Sizes

Solid oxide fuel cell cathodes have been examined using non-destructive x-ray nanotomography. The cathodes examined were a composite of strontium-doped lanthanum manganite (LSM) and yttria-stabilized zirconia (YSZ), with three different starting powder sizes of 0.3 μm, 0.5 μm, and 1 μm. Differential absorption contrast imaging was performed over the manganese K-edge (6539 eV) for the identification of the LSM, YSZ, and pore phases. The three phases were each segmented from reconstruction of the tomography data. Three dimensional volumes of the segmented phases were used to calculate structural characterization parameters of the sample including porosity, pore size distributions, and mean phase sizes. These parameters are reported and some correlations are drawn to the starting powder size.Copyright

The Role of Sulfur in the Porous Cermet Solid Oxide Fuel Cell Anode Microstructure

Sulfur poisoning can deactivate nickel catalysts in solid oxide fuel cells (SOFCs), resulting in a significant drop in fuel cell performance. In this paper, a Ni/YSZ SOFC anode exposed to 100 ppm H2S was examined using x-ray absorption contrast imaging for its microstructure and x-ray fluorescence (XRF) spectroscopy to probe and map Ni, S, and YSZ phases. It was observed that S was frequently found to be collocated with Ni, with higher concentrations being located on or near the surface of the Ni particles exposed to gas, while little S was found near the YSZ phase.Copyright

Numerical Simulation of Multiwalled Carbon Nanotube Growth in a Tube Flow Chemical Vapor Deposition Reactor

The deposition rate of carbon nanotubes in a tube flow CVD reactor was studied over different temperatures and inlet gas concentrations with a focus on particle size and the number nanotube walls per particle. It was found that larger particles and higher numbers of walls increased the use of carbon and required a higher concentration of the carbon feedstock gas, methane. These results show that optimizing reactor conditions will require tailoring the feedstock gas concentrations according to the particle size and expected number of walls per nanotube in order to ensure that there is enough carbon to facilitate nanotube forming reactions.© 2010 ASME

Reactor Scale Model of Multiwalled Carbon Nanotube Growth in a Tube Flow Chemical Vapor Deposition Reactor

Even though a large number of applications for multiwalled carbon nanotubes have been proposed, there is relatively limited knowledge about the optimal conditions in which to create multiwalled carbon nanotubes (MWNTs). Computational models have been shown to be a promising tool to determine the best carbon nanotube growth conditions. In this paper the growth of MWNTs in a tube flow CVD reactor was studied through the use of the commercial software package COMSOL, where details steps have been described to reformulate an existing single walled carbon nanotube (SWNT) growth model to accommodate MWNTs followed by validation and growth rate prediction. Higher growth rates were predicted for MWNTs than SWNTs which is a result of the increase in pathways for carbon to form carbon nanotubes based on the additional walls. Results indicate that selecting the correct number of walls can be important to the results of the model.© 2009 ASME