Synchrotron X-ray Radiography Research Articles

Synchrotron X-ray Radiography as a Highly Precise and Accurate Method for Measuring the Spatial Distribution of Liquid Water in Operating Polymer Electrolyte Membrane Fuel Cells

For the first time, the precision and the accuracy of liquid water content measurements in operating polymer electrolyte membrane (PEM) fuel cells from synchrotron X-ray radiographic imaging are determined. We define the precision of X-ray radiographic-based water measurements by combining two types of uncertainties. In the uncertainty of type A, the standard deviation of the average through-plane water thickness distribution is determined as a function of time and space. In the uncertainty of type B, the effects of the instrumentation (camera readout noise and X-ray energy level) in the Beer-Lambert law are considered. The volume of liquid water in the gas diffusion layer (GDL) is quantified with the greatest precision (plus or minus 5%) when using a beam energy of 24 keV and a low camera readout noise. The accuracy of our synchrotron X-ray-based liquid water measurements is determined from the direct comparison to neutron radiography measurements reported by Kotaka et al. (Electrochim. Acta. 146, 2014). The GDL through-plane distributions and volumes of liquid water measured by two techniques are in excellent agreement. From this work, synchrotron X-ray radiography is shown to be a powerful technique that is both precise and accurate for measuring the spatial distribution of liquid water in miniature operating PEM fuel cells.

Non-isothermal two-phase transport in a polymer electrolyte membrane fuel cell with crack-free microporous layers

Liquid water breakthrough events were observed in crack-free microporous layers (MPLs) of operating polymer electrolyte membrane (PEM) fuel cells through in situ synchrotron X-ray radiography. The measured water thicknesses were used as inputs into a one-dimensional (1D) heat and mass transport model. This 1D model was developed to describe the coupled relationship between liquid and vapour transport through the cathode GDL and the temperature distributions in the fuel cell that accompany the in operando measurements. The current density was increased from 1.4 to 2.4Acm−2, during which MPL breakthrough was observed. Immediately following MPL breakthrough events, the fraction of vapour-phase transport of the total water flux in the MPL increased by up to 5%. Post MPL breakthrough, further increases in current density resulted in increased thermal and water vapour concentration gradients in the MPL, and vapour transport was further enhanced. A temperature gradient at the cathode catalyst layer (CL)–MPL interface resulted in decreased threshold capillary pressures, and as a result higher liquid water saturations were observed near this interface. These findings suggest that the temperature gradient should be considered in two-phase flow modeling and pore network modeling due to its impact on liquid water distributions.

The spatial and temporal distribution of dendrite fragmentation in solidifying Al-Cu alloys under different conditions

The directional columnar solidification of Al-Cu alloy dendrites was studied in-situ by synchrotron X-ray radiography to investigate the spatial and temporal distribution of dendrite fragmentation, without and with an applied pulsed electromagnetic field (PEMF) and in different solidification directions. The differing arrangements had a strong and reproducible influence on fragmentation behaviour that was rationalised using a model of solute-driven re-melting of dendrite arms in microstructural regions of high vulnerability. Although absolute rates of fragmentation varied, all the fragmentation distributions had a characteristic peak in fragmentation rate at a distance of 500–800 μm into the mushy zone. Consistent with the need for solute-rich liquid flow for dendrite root re-melting, this peak was explained to occur under conditions where there was both comparatively steep liquid solute concentration gradients, measured directly from the radiographs, and relatively high permeability of the dendrite network to liquid flow.

Roles of Photon Scattering in Synchrotron X-ray Radiography of In Operando Visualizations of the Polymer Electrolyte Membrane Fuel Cell

Synchrotron X-ray radiography has been proven to be a powerful tool for visualizing and quantifying the in operando liquid water distributions in polymer electrolyte membrane (PEM) fuel cells. Water thickness, the accumulated water content at an image pixel, was calculated by normalizing the images collected to isolate the presence of liquid water. Images containing liquid water are called wet images, and are evaluated with respect to a reference image in the absence of liquid water, called the dry image. This normalization process is based on the Beer-Lambert law, and the attenuation coefficient of liquid water (at the applied photon energy level) is vital for this calculation. The attenuation coefficient for monoenergetic X-ray photons, provided by the National Institute of Standards and Technology (NIST), describes the probability that a photon will interact with the particles in a material as it travels a unit distance in the direction of the beam. Hence, the liquid water thickness calculation is highly dependent on the correct use of the attenuation coefficient. The incorrect use of a monoenergetic attenuation coefficient in synchrotron X-ray image analysis may lead to significant inaccuracies attributed to the neglect of scattering effects and higher harmonics contamination, which may be present at a synchrotron beamline. In our previous work (1), a calibration experiment was developed to experimentally obtain the water attenuation coefficient based from six known thicknesses of liquid water. The calibrated attenuation coefficient was 18.9% lower than the value for the monoenergetic photons at 20 keV. This deficit implied that at least one of the two prescribed phenomena (scattering and higher harmonics) contributed to the measured intensity in the obtained images. The purpose of this study is to determine the ratios of produced X-ray intensities that arise due to the scattering effect and higher harmonics, respectively. From this work, a correction method for calculating the water thickness can be proposed based on the scattering ratio. This correction method is vital for increasing the accuracy of water quantification. The calibration experiments were performed with a range of photon energy levels and filters at the Canadian Light Source. It was observed that the scattered signal increased as a function of water thickness, and this trend was more significant for lower experimental energy levels. The results suggested that the calibration experiment should be conducted with customized devices that contain liquid water with comparable quantities to that which one would find in the PEM fuel cell, in order to accurately simulate the in operando scattering effect. The existence of the higher harmonics was verified at the experimental energy level of 20 keV, and the water attenuation coefficient was experimentally measured to be 0.258 cm-1, which is in agreement with the value reported by NIST at 40 keV (0.268 cm-1). From the results obtained at 20 keV with the high-transmission filter, the ratio of higher harmonics was determined to be 0.9%–1.4% of the incident beam intensity. From this work, the authors urge that caution should be exercised when using selecting energy levels that could contain higher harmonic photons.

Accelerated Degradation of Polymer Electrolyte Membrane Fuel Cell Gas Diffusion Layers: Performance Degradation and Steady State Liquid Water Distributions with in Operando Synchrotron X-ray Radiography

The polymer electrolyte membrane (PEM) fuel cell is a promising alternative power source for electric vehicles, forklifts, and stationary backup power due to its high power density, low operating temperature, and clean emissions. The gas diffusion layer (GDL) facilitates the transport of heat, reactant gases, water vapor, and liquid water in the PEM fuel cell. The GDL is a highly porous material composed of dense arrays of carbon fibers, resins, and polytetrafluoroethylene (PTFE). Additionally, it is typically coated with a micro porous layer (MPL), which results in the reduction of contact resistance at the catalyst layer interface and the overall improvement in water management. Effective water management must be achieved within the GDL over the entire operating lifetime in order to improve the commercial success of PEM fuel cells. Investigations into the effects of ageing on water management within the GDLs can be useful tools to guide this success. Water is required to maintain polymer electrolyte membrane hydration and ionic conductivity; however, excess water tends to accumulate in the catalyst layer, GDL, and flow channels. This accumulation limits mass transport and leads to performance losses. Therefore, effective water management in the GDLs is essential for improving cell performance, durability, and stability. Most GDL research has been focused on the impact of GDL materials and microstructure design on overall performance, rather than durability. Decreased GDL hydrophobicity has been found after only a few hundred hours of operation (1, 2). Therefore, a clear understanding of the influence of GDL degradation on the liquid water behavior is essential. As a tool to visualize this behaviour, synchrotron X-ray radiography is a powerful technique for visualizing liquid water transport behavior within an operating PEM fuel cell. High intensity X-rays generated at the BMIT-BM beamline of the Canadian Light Source were used for identifying liquid water inside the GDLs and capturing the multiphase flow behavior in an operating PEM fuel cell. Figure 1 is an example synchrotron X-ray radiograph of the fuel cell in operando, illustrating the spatial distribution of liquid water. The observed pixel brightness was correlated to the presence of liquid water, and the saturation profile across the GDL thickness was obtained. In this study, as-received fresh GDLs were immersed in a 35wt % solution of H2O2 at 90o C for 12 hours in order to perform an accelerated artificial ageing process. As-received fresh and artificially aged GDLs were then used to assemble specialized fuel cells for synchrotron imaging. Both the electrochemical performance and liquid water transport behavior were observed for a range of current densities. Additionally, the effect of changes in relative humidity on performance was compared to investigate the effect of artificial ageing. Notable differences in cell performance and liquid water transport behavior were observed at steady state operating conditions. The cell with aged GDLs showed lower cell voltage and higher quantities of liquid water than those of as-received fresh GDLs. The impacts of aging on the liquid water distributions within the GDL and on cell performance will be presented in this work. The objective of current work is to highlight the potential degrading effect on liquid water management in long term fuel cell operation.

Accelerated Degradation of Polymer Electrolyte Membrane Fuel Cell Gas Diffusion Layers: Mass Transport Resistance and Liquid Water Accumulation at Limiting Current Density with in operando Synchrotron X-ray Radiography

The polymer electrolyte membrane fuel cell (PEMFC) continues to develop as a viable alternative to the combustion engine in automotive applications. As this technology advances, it is critical that the PEMFC is capable of maintaining performance for long term operation. In an effort to understand the degradation of fuel cell performance over time, a study into the development of an accelerated gas diffusion layer degradation protocol was completed. As part of an effort to quantify the effects of this accelerated degradation, in situ synchrotron radiography imaging techniques were coupled with performance testing in order to quantify the effects of this degradation on water saturation profiles, transport resistance, and limiting current in an operating fuel cell. Gas diffusion layer samples of SGL 25 BC and SGL 29 BC were artificially aged in a concentrated solution of hydrogen peroxide (30% wt.) for a period of 12 hours at an elevated temperature of 90 degrees Celsius. Hydrogen peroxide facilitates chemical corrosion of the carbon material in the gas diffusion layer and was found to significantly affect the wettability of the degraded samples. Hydrogen peroxide was selected to facilitate the degradation mechanism due to the fact that it is a recognized chemical species found in operating fuel cells and produced at the catalyst layer (1, 2). The accelerated degradation procedure that was used in this study was found to primarily affect the wettability of the tested gas diffusion layers. Consequently, it was expected that the most significant impact of this degradation mechanism would be in the mass transport losses at high current densities. For this reason, a limiting current investigation was performed. Unlike other studies of limiting current in which the cathode oxygen concentration is varied (3), a limiting current study based on varying the relative humidity of reactant gases was performed. In this study, limiting current was measured for relative humidities of 0%, 50%, 80%, 90%, and 100% for several fuel cells with fresh and degraded GDLs. Simultaneous synchrotron imaging was used to quantify the distribution of liquid water in the anode and cathode of the operating cell during these limiting current studies. Trends with respect to reactant transport resistance, water saturation profiles, and limiting current were quantified as a function of relative humidity and degree of degradation. For all tested samples, as the relative humidity was reduced, the corresponding limiting current increased. It was also found that the limiting current liquid water saturation profile was independent of the reactant gas relative humidity. Additionally, artificial degradation led to increased liquid water saturation levels in the operating fuel cell. This work illustrates the potential impacts of long term fuel cell operation on the water management of PEMFC gas diffusion layers.

Impact of Liquid Water on Oxygen Transport Resistance in a PEMFC Cathode Via Limiting Current Methods and Concurrent Synchrotron X-Ray Radiography

The accumulation of liquid water formed by the electrochemical reaction of hydrogen and oxygen in a polymer electrolyte membrane (PEM) fuel cell causes a gas diffusion layer (GDL) to become effectively less porous and more tortuous. To achieve designs directed for water and gas transport in PEMFC diffusion media, a nuanced understanding of the nature and extent of GDL water as an impedance to oxygen flux is required. In this work, a limiting current approach was used to measure the mass transport resistance in a custom PEM fuel cell. Using a small active area at high stoichiometric ratios, it was assumed that the concentration of gases was constant along the length of the reactant flow channels, creating a uniform concentration gradient across the entire diffusion medium. If the fuel cells are then operated at the limiting current density, where cell potential approaches zero, it can also be assumed that all the reactants are being consumed and the concentration of reactants at the reaction site is effectively zero. Consequently, oxygen transport resistance in these conditions can be inferred directly from the limiting current density using the following equation, where RT is the transport resistance in s/cm, c0 is the oxygen concentration at the reactant channel and iL is the limiting current: RT = 4Fc0/iL Previously, through a thorough set of limiting current experiments at a range of operating conditions, Baker et al.1 showed that the carbon-fiber diffusion medium is the dominant contributor to oxygen transport resistance. Owejan et al.2 combined limiting current methods with in situ neutron radiography to demonstrate a strong qualitative correlation between GDL saturation and oxygen transport resistance. Synchrotron radiography has been established as a powerful tool for visualizing water distribution in PEMFC diffusion media3. In this work, synchrotron X-ray radiographs were obtained with a pixel size of 6.5 µm with a spatial resolution of 10 μm. GDL materials were imaged in operando at limiting current over a range of relative humidities (set in the inlet cathode gas stream). Figure 1 (a) is an example radiograph of a cell operating at limiting current density processed according to the Beer-Lambert law5,6. A distinct in-plane variation in liquid water distributions is visible between regions over ribs and regions over channels (Figure 1 (b)). This work exploits the high spatial resolution for capturing liquid water accumulation trends, information which is essential for building towards a direct, quantitative empirical relation between oxygen transport resistance and GDL saturation.

Accelerated Degradation of Polymer Electrolyte Membrane Fuel Cell Gas Diffusion Layers: Performance Degradation and Steady State Liquid Water Distributions with in Operando Synchrotron X-ray Radiography

As-received pristine gas diffusion layers (GDLs) were degraded through an accelerated artificial aging process by immersion into a 35% solution of H2O2 at 90°C for 12 hours. Polarization curves were obtained while synchrotron X-ray radiography was performed to investigate the effect of ageing on liquid water transport behavior. Peak output power density of the fuel cell composed of the aged GDL reached only 76% of that of the fuel cell composed of the pristine GDL. This performance degradation was attributed to an increase in mass transport resistance associated with liquid water accumulation at the aged GDL and flow field channel interface. The aged GDLs showed more liquid water accumulation at the microporous layer (MPL)/carbon substrate interface and carbon substrate regions than pristine GDLs at low current density operation. A fully developed water profile was established at lower current density for the aged GDLs compared to pristine GDLs.

Roles of Photon Scattering in Synchrotron X-ray Radiography of In Operando Visualizations of the Polymer Electrolyte Membrane Fuel Cell

A numerical model was developed to predict the attenuated component and the undesired scattered component in the measured X-ray intensity during water visualizations using synchrotron X-ray radiography. The scattering component was found to increase as a function of water thickness traversed by the X-ray beam, and this led to a decrease in the calibrated attenuation coefficient. Due to this relationship between the scattering component and the water thickness, a small water thickness range was demonstrated to produce highly representative attenuation coefficients that resulted in the improved accuracy of water quantifications. Therefore, it was recommended that the calibrated attenuation coefficient should be obtained based on a water thickness range that most appropriately matches the expected liquid water thickness in an operating polymer electrolyte membrane fuel cell.

Performance Benefits of Multiwall Carbon Nanotubes in the Polymer Electrolyte Membrane Fuel Cell Gas Diffusion Layer

A commercial gas diffusion layer (GDL) with a microporous layer (MPL) containing multiwall carbon nanotubes (MWCNT) exhibited better performance in a polymer electrolyte membrane (PEM) fuel cell than that with a conventional GDL. This performance benefit was attributed to improved oxygen mass transport in the cathode GDL. The operation of the fuel cell was visualized with synchrotron X-ray radiography to measure the liquid water saturation in the two GDLs. A higher liquid water saturation was measured in the operating fuel with the MWCNT-based MPL than with the conventional MPL. But, the MWCNTs induced higher effective porosity within the GDL, allowing for improved overall oxygen transport, and thus the cell performed better even with higher saturation of liquid water in the GDL.

Determining the Impact of Dynamic Load Conditions on Interfacial Liquid Water Accumulation in Polymer Electrolyte Membrane Fuel Cell Gas Diffusion Layers Using Synchrotron X-Ray Radiography

Automotive power demand is dynamic, so the transient multiphase transport behavior must be understood and considered in the design of next generation polymer electrolyte membrane (PEM) fuel cell materials. In-operando synchrotron X-ray radiography was used to measure the changes in liquid water saturation of the gas diffusion layer (GDL) during changes in operational current density. Through in-operando visualizations at high temporal and spatial resolutions, we observed that the liquid water saturation of the GDL increases with increasing current density, but a threshold saturation in the GDL is eventually reached, despite further increases in current density. A time lag between the change in current density and the onset of increasing GDL saturation was also observed.

Accelerated Degradation of Polymer Electrolyte Membrane Fuel Cell Gas Diffusion Layers: Mass Transport Resistance and Liquid Water Accumulation at Limiting Current Density with in operando Synchrotron X-ray Radiography

An SGL 29BC gas diffusion layer (GDL) was degraded (aged) in hydrogen peroxide. The impact of ageing was measured through deviations from pristine GDLs in terms of limiting current densities, oxygen mass transport resistances, and liquid water spatial distributions in the GDL. For dry and saturated cathode conditions (oxygen concentrations of 1% and 21%, respectively) the fuel cell containing the aged GDL reached limiting current densities that were up to 10.3% lower and experienced increases in oxygen mass transport resistance of up to 11.7% versus the pristine GDL. This performance reduction was attributed to a higher liquid water content (13% more at an oxygen concentration of 21%) in the aged GDL under the channel compared to the pristine GDL. In fuel cells built with aged and pristine GDLs, up to 200% more water was present in the GDL under the land compared to under the channel at limiting current operation.

Strength of orthoenstatite single crystals at mantle pressure and temperature and comparison with olivine

Oriented single crystals of orthopyroxenes (OPx) were deformed in axisymmetric compression in the D-DIA at pressure and temperature in excess of 3 GPa and 1040 °C. Two crystal orientations were tested with the compression axis parallel to either [101]c crystallographic direction, to investigate [001](100) dislocation slip-system strength, or [011]c direction to investigate [001](010) slip-system strength. These slip systems are the most active in orthopyroxenes. Applied differential stresses and specimen strain rates were measured in situ by synchrotron X-ray diffraction and radiography. We used these data and comparison with previously reported low-pressure flow laws for protoenstatite and orthoenstatite to determine the power law parameters for the deformation of orthoenstatite crystals, which characterize OPx dislocation slip-system strengths. Applying these laws at reasonable mantle stresses along oceanic and continental geotherms indicates that OPx [001](100) slip system is weaker than OPx [001](010) slip system to ∼260 km depth where the strengths converge. It also indicates that both OPx slip systems are significantly stronger than olivine slip systems throughout the upper mantle, except in the upper most mantle, in the lithosphere, were OPx [001](100) slip system may be as weak or even weaker than olivine [100](010) easy slip system.

Effect of traveling magnetic field on solute distribution and dendritic growth in unidirectionally solidifying Sn–50 wt%Pb alloy: An in situ observation

Synchrotron X-ray radiography was used to in situ study the solute distribution and the dendritic growth during the bottom-up solidification of Sn–50wt%Pb alloy under a traveling magnetic field (TMF) for the first time. The buoyance driven evolution and motion of the plumes containing Sn-rich melt are directly observed in the solidification front before the application of TMF. A forced melt flow from left to right is induced with the application of TMF, which results in the redistribution of the solute concentration (facilitate the solute transportation and reduce the local fluctuations considerably) and the change of the dendrite morphologies (promote/suppress the growth of the secondary arms, remelting and fragmentation of dendrites). Meanwhile, the concentration variations of Sn around the solidification front are quantitatively analyzed through the extraction of gray level from sequenced X-ray images.

In operando measurements of liquid water saturation distributions and effective diffusivities of polymer electrolyte membrane fuel cell gas diffusion layers

In this work, the in operando determinations of liquid water saturation and corresponding effective diffusivities were measured for polymer electrolyte membrane fuel cell gas diffusion layers (GDLs). Through-plane liquid water saturation profiles were obtained by combining liquid water thicknesses measured from in operando synchrotron X-ray radiography and the GDL porosity distributions from ex situ X-ray computed tomography. The effective diffusivity of these partially saturated GDLs were determined from electrochemical impedance spectroscopy (EIS) measurements combined with results from our one-dimensional fuel cell impedance model. The ratio of the effective diffusivity of the GDL to the oxygen bulk diffusivity was found to follow a power law relationship, (1−savg)2.80 which is in agreement with measurements typically reported in the literature from limiting current and three-dimensional mass transport models. The methodology presented in this paper provides a novel, in operando and complementary alternative technique for measuring the effective diffusivity of partially saturated GDLs.

Study on the Formation and Precipitation Mechanism of Mn5Si3 Phase in the MBA-2 Brass Alloy

Mn5Si3 is an attractive dispersion in the special brass, owing to its high hardness and high wear resistance. In the present study, synchrotron X-ray radiography and rapid cooling were applied to investigate the formation mechanism of Mn5Si3 phase in the MBA-2 brass alloy. The primary Mn5Si3 phase is proved to exist stably in the alloy melt and nucleate from the melt at temperatures above 1373 K (1100 °C). In addition, the precipitation mechanism of Mn5Si3 phase is addressed systematically by the isothermal heat treatment. The Mn5Si3 particles are observed to precipitate from the matrix at temperatures above 1023 K (750 °C), and a crystallographic orientation relationship is found between the precipitated Mn5Si3 particle and β phase: \( (110)_{\beta } //(1\overline{1} 00)_{{{\text{Mn}}_{5} {\text{Si}}_{3} }} \) and \( [\overline{1} 11]_{\beta } //[11\overline{2} \overline{2} ]_{{{\text{Mn}}_{5} {\text{Si}}_{3} }} \). However, the precipitation of Mn5Si3 phase is thermodynamically inhibited at lower temperatures, which can be ascribed to the increase in the Gibbs free energy of formation of Mn5Si3 with decreasing the temperature.

Study on the Solidification of Sn-Pb Alloy under Direct Current Field by Synchrotron X-Ray Radiography

In this paper, synchrotron X-ray radiography was used to study the grain refining performance of direct current (DC) during the solidification of Sn-50 wt.% Pb alloy. Based on the radiographs, the variations of equiaxed grain number and dendrite growth rate with time were measured and analyzed. It is shown that DC mainly affects the microstructure formation through changing the nucleation behavior and the dendrite growth rate. When DC was applied during the whole process of solidification, the nucleation was enhanced and the dendrite growth was suppressed, which resulted in significant grain refinement.

Growth of Equiaxed Dendrite in Al-20wt.%Cu Alloy by Synchrotron X-Ray Radiography

Synchrotron X-ray radiography was used to in-situ study the growth of equiaxed dendrite during the solidification of Al-20 wt.% Cu alloy. Equiaxed dendrites with two different morphologies were formed in nearly isothermal conditions. The image processing was used to improve the image quality. The time evolution of the primary dendrite arm length and the corresponding growth rates were analyzed. The experimental results indicated that the solute interaction was the main factor to influence the equiaxed dendrites growth. Besides, the rotation and floating of the dendrites were also observed during the early growth phase.

Convection and solidification influenced by thermo-electric effect

We analyse the thermo-electric-magnetic (TEM) forces both on the liquid metal and immersed solid particles which mimics equiaxed grains. Firstly, we provide a summary of analytical works performed in a previous paper. Then, we present experimental works on in situ and real time visualization of the directional solidification of Al-10wt%Cu alloy by means of synchrotron X-ray radiography during directional solidification under a transverse 0.08 T permanent magnetic field. The experiments bring definite evidence of the existence of various phenomena which could be related to the thermoelectric effect acting directly on equiaxed grains. Comparisons between the predicted and observed horizontal deviations of the particles are in fairly good agreement.

Calibrating the X-ray attenuation of liquid water and correcting sample movement artefacts during in operando synchrotron X-ray radiographic imaging of polymer electrolyte membrane fuel cells.

Synchrotron X-ray radiography, due to its high temporal and spatial resolutions, provides a valuable means for understanding the in operando water transport behaviour in polymer electrolyte membrane fuel cells. The purpose of this study is to address the specific artefact of imaging sample movement, which poses a significant challenge to synchrotron-based imaging for fuel cell diagnostics. Specifically, the impact of the micrometer-scale movement of the sample was determined, and a correction methodology was developed. At a photon energy level of 20 keV, a maximum movement of 7.5 µm resulted in a false water thickness of 0.93 cm (9% higher than the maximum amount of water that the experimental apparatus could physically contain). This artefact was corrected by image translations based on the relationship between the false water thickness value and the distance moved by the sample. The implementation of this correction method led to a significant reduction in false water thickness (to ∼0.04 cm). Furthermore, to account for inaccuracies in pixel intensities due to the scattering effect and higher harmonics, a calibration technique was introduced for the liquid water X-ray attenuation coefficient, which was found to be 0.657 ± 0.023 cm(-1) at 20 keV. The work presented in this paper provides valuable tools for artefact compensation and accuracy improvements for dynamic synchrotron X-ray imaging of fuel cells.