We present a quantitative analysis of the influence of artificial ageing of gas diffusion layers (GDL) on the water distribution and transport in polymer electrolyte membrane fuel cells (PEMFCs) ...during cell operation. Water droplet size distributions are measured by means of in-operando neutron radiography. We find a strong correlation between droplet size distribution and GDL ageing time: With increasing GDL ageing, water droplet sizes in the flow field channels strongly decrease, indicating an ineffective water transport that leads to a reduced cell performance. This effect can be assigned to water accumulations on the GDL surface that block the gas supply towards the catalyst layer.
•Water droplet size distribution measured by means of neutron imaging.•Artificial GDL ageing applied to study effects on water distribution and transport.•Droplet sizes in flow field channels decrease with increasing GDL ageing.•Water on the GDL surface favourable blocks the gas supply with increasing GDL ageing.
In this study, synchrotron X-ray imaging is used to investigate the water transport inside newly developed GDM (gas diffusion medium) in polymer electrolyte membrane fuel cells. Two different ...measurement techniques, namely in-situ radiography and quasi-in-situ tomography were combined to reveal the relationship between the structure of the MPL (microporous layer), the operation temperature and the water flow. The newly developed MPL is equipped with randomly arranged holes. It was found that these holes strongly influence the overall water transport in the whole adjacent GDM. The holes act as nuclei for water transport paths through the GDM. In the future, such tailored GDMs could be used to optimize the efficiency and operating conditions of polymer electrolyte membrane fuel cells.
•Water distribution measured by means of synchrotron X-ray imaging.•The holes act as nuclei for water transport paths through the GDM.•At higher temperatures the effect of the holes is negligible.
We herein report on using a compact and low cost scintillator-camera based neutron detection system for quantitative time-of-flight imaging applications. While powerful pulsed neutron sources emerge ...and enable unprecedented scientific achievements, one bottleneck is the availability of suitable detectors that provide high count- and high frame- rate capabilities. For imaging applications the achievable spatial resolution/pixel size is obviously another key characteristic. While major effort was so far directed towards the development of neutron counting type imaging detectors, this work demonstrates that a camera based detector system as commonly employed at steady state sources can also be used if a suitable camera is utilized. This is demonstrated at the ESS test beamline (V20) at Helmholtz-Zentrum Berlin by recording the time-of-flight transmission spectrum of steel samples using a CMOS camera at 1 kHz frame rate, revealing the characteristic Bragg edge pattern. This 'simple' setup in the current state presents a useful option of neutron detection and has the potential to overcome many of the existing limitations and could provide a reliable alternative for neutron detector technology in general, given that the camera and scintillator technology keep up the current development speed.
Display omitted
•A radiography cell for in operando X-ray radiography was designed and built.•A self-assembled CR2032 coin cell was built for in operando neutron radiography.•In operando X-ray and ...neuron radiography were conducted by using Si electrode half cells.
Complementary in operando X-ray radiography and neutron radiography measurements were conducted to investigate and visualize the initial lithiation in silicon-electrode lithium-ion batteries. By means of X-ray radiography, a significant volume expansion of Si particles and the Si electrode during the first discharge was observed. In addition, many Si particles were found that never undergo electrochemical reactions. These findings were confirmed by neutron radiography, which, for the first time, showed the process of Li alloying with the Si electrode during initial lithiation. These results demonstrate that complementary X-ray and neutron radiography is a powerful tool to investigate the lithiation mechanisms inside Si-electrode based lithium-ion batteries.
The Cover Feature shows the vital importance of water management in polymer electrolyte membrane fuel cells (PEMFCs): inadequate hydration leads to reduced proton conductivity whereas excess water ...hinders the access of reactant gases to the catalytic active sites. Structural properties of fuel cell materials, in particular porosity, strongly affect the liquid water content and distribution within the cells as illustrated by three schematics of porous materials. Operando high‐resolution neutron imaging was utilized to visualize the liquid water in PEMFCs. The curves represent the profile of water distribution within the cells. More information can be found in the Communication by A. Mohseninia et al. on page 2931 in Issue 11, 2020 (DOI: 10.1002/cssc.202000542).
The lithiation and delithiation mechanisms of multiple‐Sn particles in a customized flat radiography cell were investigated by in situ synchrotron radiography. For the first time, four (de)lithiation ...phenomena in a Sn‐electrode battery system are highlighted: 1) the (de)lithiation behavior varies between different Sn particles, 2) the time required to lithiate individual Sn particles is markedly different from the time needed to discharge the complete battery, 3) electrochemical deactivation of originally electrochemically active particles is reported, and 4) 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 LIBs.
Lithiation close up: A radiography cell is designed and manufactured for in situ investigation of the underlying (de)lithiation mechanisms in a Sn/C‐composite electrode. Four (de)lithiation phenomena are highlighted: 1) an inhomogeneous electrochemical (de)lithiation, 2) a varying individual lithiation time versus whole cell discharge time, 3) an electrochemical deactivation, and 4) a dynamic (de)lithiation pathway.
To conduct simulations of transport properties within fuel cell materials 3D-data are required as input. For a functional simulation of flow and thermal characteristics the morphological features of ...the gas diffusion layer (GDL) materials must be well-defined. In this regard, the distribution of the distinct substances in the GDL, each of which is represented by a different parameter set, plays a decisive role. By means of synchrotron X-Ray computed tomography a fuel cell equipped with SGL® 28BC GDL material is recorded in 3D. The segmentation of the solid structural components and the identification of water agglomerations in the components are fulfilled by image processing techniques. This step is often realized using a lot of simplifications, like the reduction to only one or two different materials or idealized structural characteristics. In the presented work 8 different phases are defined according to the cell materials, which are the catalyst layer, the carbon fibers, the Teflon (PTFE)-binder, the micro porous layer (MPL), the flow field ribs, the pore spaces as well as the water in pore spaces of the GDL substrate and in the MPL. The image processing steps used for the classification of each voxel into these phases are described in detail in this work. Benefiting from this classification methodology, the macroscopic properties of the GDL materials such as water saturation, diffusivity, thermal and electrical conductivity can be obtained in simulations.
•Operated PEMFC recorded by synchrotron X-Ray tomography.•Described 3D image processing allows for classification of eight different phases.•Classified 3D data highly suitable for simulations of water transport properties.
An important step in the analysis of liquid water distributions in high resolution tomographies of PEMFCs is the segmentation of water and cell materials. This is conducted via subtraction of the dry ...from the operated state of the cells. The morphology of the gas diffusion layer (GDL) slightly changes due to membrane swelling at high humidification that makes quantification of water amounts hardly possible and leads to artifacts and false water detection. Here we present a computational algorithm identifying the changes in GDL morphology via local shift detection of the tomographic data sets that allows for an optimal quantification of water amounts. We compare the technique with typical global alignment methods. The results reveal huge errors in water quantification of up to 50% for the global alignment method that can be mostly avoided by using the presented technique. The morphology correction algorithm can basically be applied to many research fields, where operando measurements are important. This applies for a wide variety of materials employed in most types of fuel cells, electrolyzer cells, batteries and hydrogen storage systems.
•Morphology correction of tomographic data for quantification of liquid water distribution.•Local shift detection via image correlation used for morphology correction.•Technique applicable to fuel cells, batteries and many more.
Display omitted
•New type of flow field channel design with barriers.•10% performance increase compared to reference PEM fuel cell.•Neutron imaging used to quantify water distribution in ...operando.•Water around barriers helps to increase catalyst gas supply.•Homogenous water distribution over the whole active area.
We present a study on a new type of flow field channel design for polymer electrolyte membrane fuel cells (PEMFCs). Small barriers have been implemented into the flow field channels that force the gas flow to move through the gas diffusion layers in order to improve the supply of the catalyst with reactant gases. We investigated the water distribution in the PEMFC with neutron imaging during operation and compared the results with a comparable reference cell without barriers. We found strong hints for an increased mechanical gas flow resistance by the barriers caused by additional liquid water agglomerations. Furthermore water distribution in the barrier flow field is much more homogenous compared to the reference cell. We assume that both effects, namely the gas flow through the GDL and the homogenous water distribution are responsible for the found performance increase of up to 10%.
PDF
