Synchrotron X-ray Radiography Research Articles

Elastic wave velocity measurements of sodium aluminosilicate glass and melt at high pressure and temperature

The combination of ultrasonic technique with synchrotron X-ray diffraction and radiography in a multi-anvil apparatus was utilized to measure the elastic wave velocities of sodium aluminosilicate glass and melt with the partially depolymerized composition of Na3AlSi3O9 (NAS). The measurements were conducted at pressure and temperature of up to 7.3 GPa and at ambient temperature for glass and up to 4.3 GPa and 2120 K for melt, respectively. The compressional wave velocity (VP) of the NAS glass remained mostly constant up to 4 GPa; subsequently, it increased with increasing pressure. Additionally, the NAS glass exhibited a minimum shear wave velocity (VS) at 4–5 GPa. Alternatively, the VP of the NAS melt was smaller than that of the NAS glass, showing a velocity minimum at ∼2 GPa. The negative pressure dependence of VP of the NAS melt is completely different from the depolymerized diopside (Di) melt, which shows a monotonic increase in VP with pressure. The contrasting behavior of the NAS and Di melts is caused by the difference in their structure, characterized by their degree of polymerization. Natural magma found in the interior of the Earth, such as basalt, has a partially depolymerized composition. This study indicates that the magma can exhibit elastic properties with negative pressure dependence, similar to the NAS melt.

Quantification of melt pool dynamics and microstructure during simulated additive manufacturing

The dynamics of laser spot melting and metallic alloy solidification are investigated through synchrotron x-ray radiography, 3D electron backscatter diffraction data, and computational fluid dynamics (CFD) simulations on a model NiMoAl alloy. Solidification velocities are measured from in-situ images to validate a CFD model of the spot melt. TriBeam tomography is used to reconstruct the melt pool in 3D, characterize the microstructure, and validate the CFD model melt pool dimensions. 3D geometrically necessary dislocation (GND) density calculations reveal extensive deformation at the sample surface. GND calculations integrated with the CFD model reveal that the halo of small, equiaxed grains adjacent to the fusion line is a result of recrystallization that occurred in the heat affected zone. By combining in-situ and ex-situ data modalities across a variety of temporal and spatial length scales, the microstructure formation mechanisms and their relationship to melt pool solidification are quantified.

Observation of Damage Initiation for Trans-laminar Fracture Using in situ Fast Synchrotron X-ray Radiography and ex situ X-ray Computed Tomography

AbstractTrans-laminar fracture is an important topic for engineering composites. In this study, trans-laminar fracture initiation in quasi-isotropic carbon/epoxy laminates made of non-crimp fabrics was examined using in situ fast synchrotron X-ray radiography and ex situ X-ray computed tomography. The maximum split lengths were measured by in situ radiography and were compared with the predicted values in a detailed FE model using cohesive elements. Ex situ computed tomography scans were also conducted to confirm that no fibre breakage occurs before the final load drop in the experiments. In situ and ex situ observations are complementary for the understanding of damage initiation.

Improving Water Management and Reactant Distribution in PEM Fuel Cells Via Flow Fields with Biomimetic Auxiliary Channels

The bipolar plate, a component of the polymer electrolyte membrane (PEM) fuel cell is responsible for reactant delivery, product removal, and mechanical stability of PEM fuel cell stacks. Bipolar plates also account for 70-90% of the weight and volume, and 18-28% of the production cost of stacks (1). Improving the function of the flow fields embedded in the bipolar plates can significantly impact the energy density of PEM fuel cells by improving liquid water management and reactant distribution. Previous works show that water preferentially accumulates under the lands of flow fields in the gas diffusion layer (GDL) for various GDL materials, creating a heterogeneous distribution of water and reactants, thereby increasing cathode mass transport overpotential(2–4). Biomimetic channel architectures have been shown to enhance preferential water flow; however, these designs have not been tailored to control water accumulation for improved reactant distribution (5,6). Targeting areas of known water accumulation such as the under-land regions of GDLs, could have a profound impact on reducing mass transport losses and improving reactant homogeneity, thereby improving the power density and efficiency of the PEM fuel cell.In this work, biomimetic auxiliary channels were laser-cut into the lands of a parallel PEM fuel cell flow field to enhance the liquid water removal and reactant distribution in the under-land region of the GDL. Constant-current electrochemical testing and electrochemical impedance spectroscopy revealed a 29% increase in peak power density resulting from a 54% decrease in oxygen mass transport overpotential using the biomimetic flow field (BFF) compared to a baseline trapezoidal flow field (TFF). Operando synchrotron X-ray radiography revealed reduced GDL water accumulation when using the BFF compared to the TFF. Water accumulation under the BFF flow fields was more homogenous especially near the catalyst layer (CL) – GDL interface, indicating enhanced reactant distribution near the CL reaction sites. Therefore, the reduced mass transport overpotential and corresponding power density increase were attributed to enhanced liquid water removal and reactant distribution due to the biomimetic auxiliary channels. These results demonstrate that significant performance enhancements can be realized by embedding alternate pathways for air and water in the lands of flow field components. Ultimately, this work can be used to further optimize the design of bipolar plates for more efficient stacks and accelerate the commercialization of PEM fuel cells. Y. Wang, D. F. Ruiz Diaz, K. S. Chen, Z. Wang, and X. C. Adroher, Materials Today, 32, 178–203 (2020).N. Ge et al., Electrochim Acta, 328, 135001 (2019).D. Muirhead et al., Int J Hydrogen Energy, 42, 29472–29483 (2017).S. Chevalier et al., J Electrochem Soc, 164, F107–F114 (2017)N. Guo, M. C. Leu, and U. O. Koylu, Int J Hydrogen Energy, 39, 21185–21195 (2014).S. Feng et al., Science, 373, 1344–1348 (2021).

All-Solid-State Battery Safety Investigation in Calorimeter Coupled with Fast X-Ray Radiography

All-solid-state battery (ASSB) are expected to be a solution to increase energy density in Li-ion technology. However, high-energy storage capacities make the safety a crucial issue. The main reactions leading to thermal runaway in conventional LiB are anode/electrolyte at 110 °C, electrolyte decomposition at 150 °C and cathode/electrolyte at 300 °C. Therefore, without liquid electrolyte, it can be expected that ASSB are less likely to have a thermal runaway.To assess safety of such non-fully mature battery technologies, a new methodology is proposed and a closed calorimeter was designed to perform operando experiments in abuse conditions with high-speed synchrotron X-ray radiography and measurement of temperature, pressure and energy. The data and image of thermal runaway of all-solid-state batteries are presented and compared to the result of Li-ion batteries with liquid electrolyte. An 11 % decrease of heat release was measured for cell with solid electrolyte. Gas volume, amount of matter that reacts in the cell and reaction kinetics have also been compared.Such a methodology allows deepening hypotheses on associated material degradation and that can assist in development of new battery technologies, by evaluating battery safety from the start of the design from battery composition to cell shape.

(Invited) Pulsed Neutron and Synchrotron X-Ray Imaging of Liquid Water Formation and Transport in Polymer Electrolyte Fuel Cells

Fuel-cell electric vehicles (FCEVs) powered by hydrogen are expected to be the ultimate eco-friendly cars, and so developing low-cost, high-performance, and highly reliable FCEVs is strongly demanded. Polymer electrolyte fuel cells (PEFCs) consist of an electrolyte membrane sandwiched between an anode and a cathode, where both the anode and cathode have laminated structures composed of a catalyst-coated membrane (CCM) and gas channels in contact with a gas diffusion layer (GDL). The GDL consists of a microporous layer (MPL) and a substrate. One problem with PEFCs is that liquid water generated as a by-product of the electrochemical reaction at the catalyst accumulates in the GDL, and prevents oxygen from being transported through the gas channels to the catalyst. Therefore, to achieve a high power density, it is necessary to develop new materials and optimize the design of the gas channel to discharge water from the cathode to the exterior of the cell. We are currently constructing a multiscale analysis methodology that combines quantum beam analysis using X-rays and neutrons to clarify water behavior in a PEFC [1-9].In this presentation, we introduce three topics related to water behavior on scales ranging from several micrometers (pores in GDLs) to hundreds of millimeters (automotive fuel cells). The first topic concerns imaging the liquid water distribution in an MPL [2, 6]. The imaging analysis was performed using time-resolved synchrotron X-ray computed tomography while water vapor was supplied to the MPL side of the GDL. With increasing exposure to water vapor, the average volume of wet domains in the MPL initially increased, whereas the overall number of such domains decreased. This implies that wet domains expand by absorbing water vapor and combining with each other. As the exposure to water vapor was further increased, the volume fraction of wet domains in the MPL reached a steady state, indicating that liquid water was discharged to the outer surface of the MPL and to the substrate side. The second topic is obtaining mechanistic insights into water behavior in a subscale PEFC [8]. Time-resolved operando synchrotron X-ray radiography to determine the effects of temperature and relative humidity on the condensation and transport of water in PEFCs. The results show that condensation and transport to the channel can be classified into four categories: 1) concurrent liquid and vapor transport, 2) mainly liquid transport, 3) vapor transport, and 4) accumulation near the ribs. X-ray imaging experiments were conducted at the TOYOTA Beamline (BL33XU) at the SPring-8 facility. The third topic is operando neutron imaging of the water distribution and identifying water/ice phases in large automotive PEFCs during a cold start. We developed an experimental system using a pulsed spallation neutron beam at the RADEN instrument at BL22 of the Materials and Life Science Experimental Facility (MLF) in the Japan Proton Accelerator Research Complex (J-PARC). The results showed direct evidence of stepwise freezing inside the PEFC. The water initially accumulated in the center of the PEFC and began to freeze, and this was followed by PEFC shutdown as freezing progressed. We defined the time interval between the beginning of freezing and shutdown as the “extended time”. This is expected to be useful as an indicator for optimizing the cold-start protocol, cell design, and choice of material.Reference1) Y. Nagai, J. Eller, T. Hatanaka, S. Yamaguchi, S. Kato, A. Kato, F. Marone, H. Xu and F. N. Büchi, J. Power Sources, 435 (2019) 226809.2) S. Kato, S. Yamaguchi, W. Yoshimune, Y. Matsuoka, A. Kato, Y. Nagai and T. Suzuki, Electrochem. Commun., 111 (2020) 106644.3) S. Yamaguchi, S. Kato, A. Kato, Y. Matsuoka, Y. Nagai and T. Suzuki, Electrochem. Commun., 128 (2021) 107059.4) Y. Higuchi, D. Setoyama, K. Isegawa, Y. Tsuchikawa, Y. Matsumoto, J. D. Parker, T. Shinohara and Y. Nagai, Phys. Chem. Chem. Phys., 23 (2021) 1062-10715) S. Yamaguchi, S. Kato, W. Yoshimune, D. Setoyama, A. Kato, Y. Nagai, T. Suzuki, A. Takeuchi and K. Uesugi, J. Synchrotron Radiat., 29 (2022) 1258-1264.6) S. Kato, S. Yamaguchi, Y. Matsuoka, A. Kato, T. Suzuki and Y. Nagai, InterPore2022, Book of s, p139.7) K. Isegawa, D. Setoyama, Y. Higuchi, Y. Matsumoto, Y. Nagai and T. Shinohara, Nucl. Instrum. Methods Phys. Res. A 1040, 167260 (2022).8) A. Kato, S. Kato, S. Yamaguchi, T. Suzuki and Y. Nagai, J. Power Sources, 521 (2022), 230951.9) Y. Higuchi, W. Yoshimune, S. Kato, S. Hibi, D. Setoyama, K. Isegawa, Y. Matsumoto, H. Hayashida, H. Nozaki, M. Harada, N. Fukaya, T. Suzuki, T. Shinohara and Y. Nagai, to be submitted.

Synchrotron X-ray operando study and multiphysics modelling of the solidification dynamics of intermetallic phases under electromagnetic pulses

In this paper, we used synchrotron X-ray radiography and tomography to study systematically and in operando conditions the growth dynamics of the primary Al3Ni intermetallic phases in an Al-15wt%Ni alloy in the solidification process with magnetic pulses of up to 1.5 T. The real-time observations clearly revealed the growth dynamics of the intermetallics in time scale from millisecond to minutes, including phase growth instability, side branching, fragmentation and orientation alignment under different magnetic pulse fluxes. A multiphysics numerical model was also developed to calculate the alternating and cyclic Lorentz forces and stresses acting on the Al3Ni phases and the nearby melt due to the applied pulses. Combining the results of the operando experiments and modelling, for the first time, the differential forces between the growing Al3Ni phases and the nearby melt were quantified. The forces can create slip dislocations at the growing crystal front which can further develop into nm and µm crystal steps for initiating phase branching. Furthermore, the magnitudes of the shear stresses are strongly related to the size, morphological and geometric features of the growing Al3Ni phases. Dependent on the magnitude of the shear stresses, phase fragmentation could occur in a single pulse period or in multiple pulse periods via fatigue mechanism. This systematic research work elucidate some of the long-time debated hypotheses concerning intermetallic phases growth instability and phase fragmentation in pulse magnetic fields. The research establishes a robust theoretical framework for quantitative understanding of the intermetallic phase growth dynamics in solidification under pulse magnetic fields.

Synchrotron X-ray diffraction and radiography - Lattice strain characterization in thin-walled carbon fibre channel structures subjected to buckling

Carbon fibre composites are widely used in low specific stiffness and high strength structures such as airframes. Compressive loading of these assemblies can lead to buckling and localised deformation around defects and imperfections that can hinder performance and lead to overengineering via excessive safety factors. Synchrotron X-Ray Diffraction (SXRD) has recently been shown to be capable of performing lattice strain mapping within carbon fibre composites at the microscale, a previously unprecedented resolution. In this study SXRD and radiography was performed on carbon fibre composite columns produced via two different methods (standard lamination and half square) at a range of different load states: unbuckled, one-third of the buckling load and post buckling. The results provide quantitative insights into the impact of these different production methods on lattice strain and fibre orientation, as well as the influence these factors have on reducing buckling load (by up to 22%). As well as being the first use of SXRD on industrially representative full-size carbon fibre samples, these insights provide invaluable detail into the factors which limit performance and the origins of column failure; crucial factors required to optimise structural design, production and loading capability.

Dependence of vapor and liquid water removal on cross-flow in polymer electrolyte fuel cell investigated by operando synchrotron X-ray radiography

Excessive liquid water in the gas diffusion layer (GDL) of a polymer electrolyte fuel cell is known to degrade the performance. Cross-flow through the GDL is applied to reduce the liquid water in the GDL. However, cross-flow has a disadvantage with a high pressure drop and is difficult in practical use. Controlled cross-flow has the possibility to reduce the liquid water, while the pressure drop remains acceptable for application. This study experimentally quantifies the amount of liquid water in the GDL by operando synchrotron X-ray radiography and the cross-flow rate with different GDL thicknesses. The relationship between the cross-flow rate and the amount of liquid water indicates that liquid water could be reduced by a smaller pressure drop with a thicker GDL. In addition, vapor removal by cross-flow is evaluated, and the relative humidity of cross-flow does not increase to 100% after flowing through the GDL containing liquid water.

The mechanism of Fe-rich intermetallic compound formation and growth on inoculants revealed by electron backscattered diffraction and X-ray imaging

Fe-rich intermetallics affect critically the mechanical properties and recyclability of aluminium alloys. Increasing effort has been spent on the inoculation of these intermetallics, hoping to promote a finer distribution. Recently Al-5Ti-1B (wt.%), originally developed to refine α-Al, has been shown to refine Al13Fe4, an intermetallic phase present in a variety of Al alloys. However, mechanisms of the formation and growth of the intermetallics on the inoculants are unclear. In this paper, Ti is added to Fe-containing Al alloys to produce a large number of potent Al3Ti particles, the active inoculant in Al-5Ti-1B. We use a combination of electron backscattered diffraction, in situ synchrotron X-ray radiography and post-solidification X-ray computed tomography to investigate the formation and growth of primary Al13Fe4 on Al3Ti inoculants, first in a model Al-Fe alloy, with key insights then confirmed in a high Fe-containing, recycled 6xxx alloy. Crystallographic orientation relationships between Al13Fe4 and Al3Ti are analysed comprehensively, and the formation and growth dynamics of Al13Fe4 on Al3Ti is also unveiled. A strong link is revealed between the formation of Al13Fe4 on Al3Ti and a twinning-related pseudo-symmetry of Al13Fe4. Finally, a potential strategy to refine both intermetallics and α-Al in recycled alloys with elevated Fe concentration is proposed.

In situ X-ray imaging of hot cracking and porosity during LPBF of Al-2139 with TiB2 additions and varied process parameters

Laser powder bed fusion (LPBF) additive manufacturing of 2XXX series Al alloys could be used for low volume specialist aerospace components, however, such alloys exhibit hot cracking susceptibility that can lead to component failure. In this study, we show two approaches to suppress the formation of hot cracks by controlling solidification behaviour using: (1) TiB2 additions; and (2) optimisation of LPBF process parameters. Using high-speed synchrotron X-ray radiography, we monitored LPBF of Al-2139 in situ, with and without TiB2 under a range of process conditions. In situ X-ray radiography results captured the crack growth over 1.0 ms at a rate of ca. 110 mm s−1, as well as pore evolution, wetting behaviour and build height. High-resolution synchrotron X-ray computed tomography (sCT) was used to measure the volume fraction of defects, e.g. hydrogen pores and microcracks, in the as-built LPBF samples. Our results show adding TiB2 in Al-2139 reduces the volume of cracks by up to 79 % under a volume energy density of 1000 to 5000 J mm−3, as well as reducing the average length, breadth, and surface area of cracks.

Measurement of liquid water distribution in GDL under cross-flow-inducing parallel flow field using operando synchrotron X-ray radiography

Baffles in flow field channels for air in a polymer electrolyte fuel cell are known to enhance the performance by inducing convective flow through the gas diffusion layer (GDL) with smaller pressure loss than interdigitated flow fields. This work experimentally correlates performance enhancement with the amount of liquid water in a GDL. A parallel flow field (PFF) that has different inlet and outlet opening sizes is applied to induce cross-flow in the GDL under the rib between adjacent air channels. Operando synchrotron X-ray radiography experiments are conducted to compare the amount of water in the GDL with that for a PFF having the same inlet and outlet sizes. The performance enhancement by application of different opening sizes increases with decreasing relative humidity and increasing air flow rate. A significant performance enhancement is observed when the amount of water in the GDL substrate under the rib becomes almost zero. No performance enhancement is observed under over-humidified conditions, although a decrease in the amount of water in the GDL is still observed, which suggests that the performance becomes insensitive to the difference in the liquid water saturation as the saturation increases.

Solidification sequence of CrMnFeCoCu dual-FCC multicomponent alloy

Multicomponent and multi-phase alloys derived from the CrMnFeCoNi alloy are receiving increasing interest in the field of structural materials. Such materials have large degrees of freedom compared with conventional alloys, therefore, their solidification sequence can be more complex. Herein, the solidification sequence of the CrMnFeCoCu alloy, where Ni in the CrMnFeCoNi alloy is substituted with Cu, was investigated using synchrotron X-ray radiography and X-ray diffraction. This study demonstrated that the microstructure composed of two phases with face-centered-cubic (FCC) structures was not simply formed through the conventional multiphase solidification manner. The uniform liquid phase first splits into two liquid phases, and they individually solidify into the two FCC solid phases. The massive-like body-centered-cubic (BCC) to FCC transformation for one of the solid phases was also confirmed. Understanding the liquid-liquid phase separation and the solid-phase transformation identified in this study can be useful for controlling the microstructure of multicomponent and multi-phase alloys.

Coupling in-situ synchrotron X-ray radiography and FT-IR spectroscopy reveal thermally-induced subsurface microstructure evolution of solid propellants

Coupling in-situ synchrotron X-ray radiography and FT-IR spectroscopy reveal thermally-induced subsurface microstructure evolution of solid propellants

Characterization of local mechanical properties of Al/Cu Magnetic Pulse Welded joints under high strain rates using synchrotron X-ray imaging

Magnetic Pulse Welding (MPW) is a method of growing interest allowing the joining of dissimilar materials such as aluminum and copper. The global mechanical properties of the joint are often evaluated with conventional tests, using the fully welded joint. However, these cannot elucidate the local mechanical properties of the joint or its interface when subjected to high strain rates loads. Cubic samples of Al/Cu have been designed and extracted from MPW joints, in order to locally characterize the mechanical properties. Samples were exposed to high strain-rate loading using the Split-Hopkinson Pressure Bar (SHPB) coupled to ultra-fast synchrotron X-ray radiography in order to investigate related failure processes in-situ. The measurements of the interface evolution were related to the macroscopic applied load. In addition, synchrotron microtomography was performed on the samples before mechanical deformation. Aside from the feasibility proof, this work provides, for the first time, the correlation of the interfacial opening evolution and the influence of pre-existing cracks of the weld. It is observed that, the pre-existing cracks at the interface correspond to the initiation sites of interfacial separation between the two dissimilar metals.

In-situ synchrotron X-ray radiography study of primary Fe-rich phases growth in Al-Fe( Cu) alloys

Plate-like iron-rich intermetallic phases (Fe-rich phases) greatly decrease the elongation and fatigue strength of recycled Al alloys. The alloy composition and the manufacturing process parameters influence the type, and shape of Fe-rich phases. In this study, the influence of the cooling rate (0.1, 0.5, and 1.0 °C/s) on the nucleation and growth of primary Fe-rich phases during solidification of Al-Fe(Cu) alloy has been quantified by synchrotron X-ray radiography. The Kikuchi patterns and deep-etched methods showed that rod-shape and plate-like primary Al3Fe phases are present in the studied alloy. The in-situ experimental results indicate that the total number and number density of primary Fe-rich phases in AlFe alloys is very similar at cooling rates of 0.1 °C/s and 1.0 °C/s but increases a 300 % at cooling rate of 0.5 °C/s. The nucleation rate of Al3Fe in AlFe alloys at three cooling rates (0.1, 0.5, and 1.0 °C/s) are 15.5, 44.0, 25.0 No./s, respectively. These decrements are due to alloy compositions are very closed to the eutectic composition (about 1.8% Fe), the less time for them to form primary Fe-rich phases at high cooling rate of 1.0 °C/s. The variation trend of total number, number density, and nucleation rate of primary Al3Fe phases in Al-Cu-Fe alloys is similar to those of in AlFe alloys. The maximum length of typical Al3Fe phases in AlFe alloys decrease from 845 μm to 222 μm as the cooling rate increased. This is because that higher cooling rate resulting in less diffusion time for limiting Fe atoms diffusion, also inhibiting them grow into large plates. The combined Cu addition and higher cooling rate resulting in the constitutional undercooling, and finally promote the formation of refined primary Al3Fe particles.

Determining Substrate Oxygen Transport Resistance at Limiting Current Using Pore Network Modelling

The polymer electrolyte membrane (PEM) fuel is a promising technology to supplant traditional, greenhouse gas emitting energy conversion devices. However, widespread commercial adoption of the PEM fuel cell is hindered by the high cost of the precious metals required for its catalyst (1). The amount of catalyst required in a PEM fuel cell can be reduced if the reactant (oxygen) is delivered more efficiently to the catalyst. Therefore, previous studies have sought to characterize the mechanisms affecting oxygen transport in PEM fuel cells (2)(3)(4)(5). In past studies, the oxygen transport resistance of a PEM fuel cell was measured at limiting current, and this value was further decomposed into contributions from individual PEM fuel components using empirical modelling. By resolving each PEM fuel cell component’s contribution to oxygen transport resistance, an informed approach can be undertaken to design next generation components with enhanced oxygen transport capabilities.In this study, we employed pore network modelling to quantify the oxygen transport resistance arising from the presence of liquid water within the substrate region of the gas diffusion layer (GDL). First, we captured the operando liquid water distribution within a PEM fuel cell operating at limiting current using synchrotron X-ray radiography. Next, we used a combination of invasion percolation and an in-house water invasion inlet selection algorithm to partially saturate the representative pore network of the substrate and to reproduce the mean water saturation. Finally, we obtained substrate oxygen transport resistance values by performing transport simulations on the partially saturated pore network and compare our findings with the experimental observations. References X. X. Wang, M. T. Swihart, and G. Wu, Nature catalysis, 2, 7 (2019).D. R. Baker, D. A. Caulk, K. C. Neyerlin, and M. W. Murphy, J. Electrochem. Soc., 156, B991 (2009).T. Reshtenko, J. St-Pierre, J. Electrochem. Soc., 161, F1089 (2014)D. Muirhead, R. Banerjee, M. G. George, N. Ge, P. Shrestha, H. Liu, J. Lee, A. Bazylak, Electrochimica Acta, 274 (2018).N. Ge, P. Shrestha, M. Balakrishnan, D. Ouellette, A. K. C. Wong, H. Liu, C. H. Lee, J. K. Lee, A. Bazylak, Electrochimica acta, 328 (2019).

Biomimetic Microchannels for the Passive Management of Water in PEM Fuel Cells

In polymer electrolyte membrane (PEM) fuel cells, the bipolar plates (BPPs) are responsible for the transport of reactants (via embedded flow fields), heat, and electrons, and account for 18-28% of the cost of fuel cell systems1. Thus, there is a great opportunity to improve the energy density of PEM fuel cells by improving the functions of BPPs, such as providing liquid water management, which affects reactant delivery and heat distribution. Previous work has shown that mass transport losses due to liquid water accumulation under the lands and channels of PEM fuel cell flow fields limit the power density of fuel cells2. Previous work has demonstrated that water will preferentially flow in a desired direction by implementing biomimetic wicking structures3; however, such wicking structures have not been previously implemented into a fuel cell. Furthermore, the design of BPPs has not been tailored to target areas of water accumulation.In this work, biomimetic geometries that promote passive unidirectional water wicking were implemented in a PEM fuel cell flow field to enhance liquid water removal and the distribution of reactant gases. The BPPs were characterized via constant current electrochemical testing and electrochemical impendence spectroscopy (EIS) to elucidate the dominant losses observed during operation. Operando synchrotron X-ray radiography was performed during the electrochemical testing in order to quantify the liquid water accumulation on the cathode side of the PEM fuel cell. The spatial distribution of liquid water was combined with EIS characterizations to explain the performance of the designs at high current densities, where mass transport losses typically dominate. The results from this work can be used to further optimize the design of PEM fuel cell bipolar plates in order to produce more efficient fuel cell stacks and drive PEM fuel cells into the global energy market. References Y. Wang, D. F. Ruiz Diaz, K. S. Chen, Z. Wang, and X. C. Adroher, Materials Today, 32, 178–203 (2020).N. Ge et al., Electrochimica Acta, 328, 135001 (2019).J. Feng and J. P. Rothstein, Journal of Colloid and Interface Science, 404, 169–178 (2013).

Effect of B addition on the formation of Fe-rich phases in Al-Si-Fe alloys

Boron (B) is an effective grain refiner in Al-Si alloys, but the mechanism responsible for the effect of B on the formation and growth of Fe-rich phases is still in debate. In this paper, we used in-situ synchrotron X-ray radiography, combined with optical microscopy, scanning electron microscopy, thermodynamics and first-principles calculations, to study the influence of B on the nucleation and growth of Fe-rich phases in Al-7Si-xFe (x = 1.2–3.0) alloys. The results showed that B had an excellent influence on the grain refinement of Al-7Si-1.2Fe alloys, but it had no obvious effect on the morphology and distribution of Fe-rich phases due to the eutectic reaction to form Al-AlB2. B had a certain refining effect on primary Fe-rich phases in Al-Si-Fe alloys with high Fe content (≥2.36 wt. %), but it cannot completely inhibit the formation of these plate-like Fe-rich phases. The in-situ synchrotron X-ray radiography results showed that the addition of B significantly reduced the formation temperature of primary Fe-rich phases. First-principles calculations showed that the adsorption energy of B on the nucleation sites , e.g., α-Al2O3 (0001), was significantly higher than that of Fe, which inhibited the nucleation of the primary Fe-rich phase above the Al-AlB2 eutectic temperature and promoted its undercooling of nucleation. Furthermore, many α-Al nuclei formed during the transition to the Al-AlB2 eutectic; their subsequent growth hindered the development of the primary Fe-rich phase. The results of this study provide insights for designing new recycled Al-Si alloys and fundamental knowledge of Fe-rich phase modification by B addition.

Safety Evaluation of All-Solid-State Batteries: An Innovative Methodology Using In Situ Synchrotron X-ray Radiography

Safety Evaluation of All-Solid-State Batteries: An Innovative Methodology Using In Situ Synchrotron X-ray Radiography