X ray Compton Tomography

The potentials of incoherent X ray scattering Compton tomography are investigated. Imaging materials of very different density or atomic number at once is a perpetual challenge for X ray tomography or radiography, in general. In a basic laboratory set up for simultaneous perpendicular Compton scattering and direct beam attenuation tomographic scans are conducted by single channel photon counting. This results in asymmetric distortions of the projection profiles of the scattering CT data set. In a first approach corrections of Compton scattering data by taking advantage of rotational symmetry yield tomograms without major geometric artefacts. A cylindrical sample composed of PE, PA, PVC, glass and wood demonstrates similar Compton contrast for all the substances, while the conventional absorption tomogram only reveals the two high order materials. Comparison to neutron tomography reveals astonishing similarities except for the glass component without hydrogen . Therefore, Compton CT bears the potential to replace neutron tomography, which requires much more efforts

In situ radiographic investigation of de lithiation mechanisms in a tin electrode lithium ion battery.

The lithiation and delithiation mechanisms of multiple Sn particles in a customized flat radiography cell were investigated by in amp; 8197;situ synchrotron radiography. For the first time, four de lithiation phenomena in a Sn electrode battery system are highlighted 1 amp; 8197;the de lithiation behavior varies between different Sn particles, 2 amp; 8197;the time required to lithiate individual Sn particles is markedly different from the time needed to discharge the complete battery, 3 amp; 8197;electrochemical deactivation of originally electrochemically active particles is reported, and 4 amp; 8197;a change of electrochemical behavior of individual particles during cycling is found and explained by dynamic changes of de lithiation pathways amongst particles within the electrode. These unexpected findings fundamentaly expand the understanding of the underlying de lithiation mechanisms inside commercial lithium ion batteries LIBs and would open new design principles for high performance next generation LIB

Morphological evolution of electrochemically plated stripped lithium microstructures by synchrotron X ray phase contrast tomography

Due to its low redox potential and high theoretical specific capacity, Li metal has drawn worldwide research attention because of its potential use in next generation battery technologies such as Li S and Li O2. Unfortunately, uncontrollable growth of Li microstructures LmSs, e.g., dendrites, fibers during electrochemical Li stripping plating has prevented their practical commercialization. Despite various strategies proposed to mitigate LmS nucleation and or block its growth, a fundamental understanding of the underlying evolution mechanisms remains elusive. Herein, synchrotron in line phase contrast X ray tomography was employed to investigate the morphological evolution of electrochemically deposited dissolved LmSs nondestructively. We present a 3D characterization of electrochemically stripped Li electrodes with regard to electrochemically plated LmSs. We clarify fundamentally the origin of the porous lithium interface growing into Li electrodes. Moreover, cleavage of the separator caused by growing LmS was experimentally observed and visualized in 3D. Our systematic investigation provides fundamental insights into LmS evolution and enables us to understand the evolution mechanisms in Li electrodes more profoundl

Pore Network Modeling of Compressed Fuel Cell Components with OpenPNM

Pore network modeling is used to model water invasion and multiphase transport through compressed PEFC gas diffusion layers. Networks are created using a Delaunay tessellation of randomly placed base-points setting the pore locations and its compliment, the Voronoi diagram, is used to define the location of fibers and resultant pore and throat geometry. The model is validated in comparison to experimental capillary pressure curves obtained on compressed and uncompressed materials. Primary drainage is simulated with an invasion percolation algorithm that sequentially invades pores and throats separately with excellent agreement to experimental data, but required a slight modification to account for the higher aspect ratio of compressed pores. Compression is simulated by scaling the through-plane coordinates in a uniform manner representing a GDL wholly beneath the current-collector land. The relative permeability and diffusivity show some dependence on uniform compression. In-plane porosity variations introduced by land-channel compression are also investigated which have a marked effect on the limiting current. Saturation at breakthrough does not appear to be dependent on compression. However, a more important parameter, namely the peak saturation, is shown to influence the fuel cell performance and is dependent on the percolation inlet conditions

Impact of catalyst layer morphology on the operation of high temperature PEM fuel cells

Electrochemical impedance spectroscopy (EIS) is a well-established method to analyze a polymer electrolyte membrane fuel cell (PEMFC). However, without further data processing, the impedance spectrum yields only qualitative insight into the mechanism and individual contribution of transport, kinetics, and ohmic losses to the overall fuel cell limitations. The distribution of relaxation times (DRT) method allows quantifying each of these polarization losses and evaluates their contribution to a given electrocatalyst\u27s depreciated performances. We coupled this method with a detailed morphology study to investigate the impact of the 3D-structure on the processes occurring inside a high-temperature polymer electrolyte membrane fuel cell (HT-PEMFC). We tested a platinum catalyst (Pt/C), a platinum-cobalt alloy catalyst (Pt$_{3}$Co/C), and a platinum group metal-free iron-nitrogen-carbon (Fe–N–C) catalyst. We found that the hampered mass transport in the latter is mainly responsible for its low performance in the MEA (along with its decreased intrinsic performances for the ORR reaction). The better performance of the alloy catalyst can be explained by both improved mass transport and a lower ORR resistance. Furthermore, single-cell tests show that the catalyst layer morphology influences the distribution of phosphoric acid during conditioning

Visualization of water accumulation in micro porous layers in polymer electrolyte membrane fuel cells using synchrotron phase contrast tomography

Using phase contracted synchrotron X ray tomography, this study investigates the water distribution within the microporous layer MPL of polymer electrolyte membrane fuel cells PEMFCs . Synchrotron X ray tomography used to analyze the water distribution in the whole gas diffusion medium GDM , which comprises the microporous layer MPL and the gas diffusion layer GDL . The MPL has already been identified. In the future, the development of GDMs could be employed to enhance the performance and operating conditions of PEMFC