Many materials used for energy conversion have a complex structure and chemical composition, knowledge of which is important for both understanding the function of materials and energy conversion ...systems and for their further development. Synchrotron radiation and neutrons can make an important contribution to understanding the function of such systems. Taking examples from the fields of fuel cells, gas separation membranes, batteries, solar cells, and catalysts, the use of radiography, tomography, diffraction, scattering, and absorption edge spectroscopy is demonstrated. The strength of such methods is the in situ characterization of processes and compositions, and so the focus is on these aspects.
Fuel cells, gas separation membranes, batteries, solar cells, and catalysts were investigated with synchrotron X‐rays and neutrons to explore the process of synthesis, their internal structure, and function. The aspect of in situ characterization is emphasized.
The neutron imaging instrument CONRAD was operated as a part of the user program of the research reactor BER-II at Helmholtz-Zentrum Berlin (HZB) from 2005 to 2020. The instrument was designed to use ...the neutron flux from the cold source of the reactor, transported by a curved neutron guide. The pure cold neutron spectrum provided a great advantage in the use of different neutron optical components such as focusing lenses and guides, solid-state polarizers, monochromators and phase gratings. The flexible setup of the instrument allowed for implementation of new methods including wavelength-selective, dark-field, phase-contrast and imaging with polarized neutrons. In summary, these developments helped to attract a large number of scientists and industrial customers, who were introduced to neutron imaging and subsequently contributed to the expansion of the neutron imaging community.
Abstract
Silicon (Si) is proposed to be one of the most promising anode materials for next‐generation lithium‐ion batteries, but unsatisfactory discharge capacity and inevitable performance ...deterioration prevent their commercialisation. In situ synchrotron X‐ray tomography is applied to a Si‐composite electrode‐based battery in its pristine and first discharged state and the degradation of the electron‐ and/or ion‐conducting network, as well as degradation of Si particles, is quantitatively investigated. Thus, this study is complementary to previous X‐ray tomographic studies focusing on Si particles only. On the electrode level, the Si particles located in the central part of the electrode primarily experience crack formation; on the particle level, lithiation behaviour is heterogeneous and cavities are formed during electrode preparation and battery operation. The correlation between the electrochemical activities of Si particles and their individual contact with the conducting network is investigated and quantified: Si particles will experience lithiation only under the condition that at least 40 % of their surface is electrically and ionically connected.
A possible method to improve membrane humidity conditions in polymer electrolyte membrane fuel cells and, therefore, the cell performance is the optimization of microporous layer (MPL) structures. In ...this work, water transport in modified MPL materials in polymer electrolyte membrane fuel cells (PEMFCs) was investigated by in operando synchrotron X‐ray tomography. Three different types of MPLs are compared: A reference standard MPL material, an MPL material with a special wavy structure, and an MPL with randomly distributed holes. We found a strong impact of the modified MPL structure on the water distribution at operating temperatures of 40 and 55 °C and an increase of cell performance up to 14 % compared to the reference cell. We assume the water distribution at the membrane to be responsible for the performance increase and provide a detailed discussion.
Structural impacts: Three different types of modified microporous layer (MPL) materials are compared: A reference MPL material, an MPL with wavy structure, and an MPL with randomly distributed holes. There is a strong impact of the modified MPL structure on the water distribution at temperatures of 40 and 55 °C and an increase of cell performance compared to the reference cell.
Synchrotron X-ray absorption edge imaging was used to investigate the ruthenium distribution in both fresh and aged Pt/Ru-based membrane electrode assemblies (MEA) of direct methanol fuel cells. MEAs ...aged in different ways were analyzed: artificially aged by MeOH depletion and aged for 1700
h in an operating fuel cell stack. An element sensitive tomographic technique – differential X-ray absorption edge tomography – was applied allowing for a 3D-visualization of the ruthenium distribution within the MEA. We found a markedly changed Ru distribution after aging which is correlated to the GDL structure, the flow field geometry, and CO2 transport in the methanol solution.
► Catalyst aging was studied using a novel element selective method. ► Differential synchrotron X-ray k-edge tomography revealed 3D ruthenium distribution. ► Upon aging a significant redistribution of Ru in the MEAs of DMFCs was found. ► Ru redistribution strongly depends on the aging procedure applied.
A fundamental clarification of the electro‐chemo‐mechanical coupling at the solid–solid electrode|electrolyte interface in all‐solid‐state batteries (ASSBs) is of crucial significance but has proven ...challenging. Herein, (synchrotron) X‐ray tomography, electrochemical impedance spectroscopy (EIS), time‐of‐flight secondary‐ion mass spectrometry (TOF‐SIMS), and finite element analysis (FEA) modeling are jointly used to decouple the electro‐chemo‐mechanical coupling in Li10SnP2S12‐based ASSBs. Non‐destructive (synchrotron) X‐ray tomography results visually disclose unexpected mechanical deformation of the solid electrolyte and electrode as well as an unanticipated evolving behavior of the (electro)chemically generated interphase. The EIS and TOF‐SIMS probing results provide additional information that links the interphase/electrode properties to the overall battery performance. The modeling results complete the picture by providing the detailed distribution of the mechanical stress/strain and the potential/ionic flux within the electrolyte. Collectively, these results suggest that 1) the interfacial volume changes induced by the (electro)chemical reactions can trigger the mechanical deformation of the solid electrode and electrolyte; 2) the overall electrochemical process can accelerate the interfacial chemical reactions; 3) the reconfigured interfaces in turn influence the electric potential distribution as well as charge transportation within the SE. These fundamental discoveries that remain unreported until now significantly improve the understanding of the complicated electro‐chemo‐mechanical couplings in ASSBs.
The fundamental electro‐chemo‐mechanical coupling mechanisms in Li10SnP2S12‐based symmetrical all‐solid‐state‐batteries are studied and the obtained results suggest that 1) the interfacial volume changes induced by the (electro)chemical reactions can trigger mechanical deformation; 2) the overall electrochemical process can accelerate the interfacial chemical reactions; 3) the reconfigured interfaces in turn influence the electric potential distribution as well as charge transportation.
An experimental in situ study was performed to investigate the effects of the catalyst layer (CL) and cathode microporous layer (MPLc) perforation on the water management and performance of polymer ...electrolyte membrane fuel cells (PEMFCs). Polymeric pore formers were utilized to produce perforated CL and MPL structures. High‐resolution neutron tomography was employed to visualize the liquid water content and distribution within different components of the cell under channel and land regions. The results revealed that at humid conditions, the perforated layers enhanced the liquid water transport under the channel regions. Moreover, at high current densities, the performance was improved for the cells with perforated layers compared to a baseline cell with non‐perforated layers, owing to reduced mass transport losses.
The lay(er) of the land: The effect of the catalyst layer and microporous layer perforation on water management and performance of PEMFCs is studied. High‐resolution operando neutron tomography is used to visualize the liquid water content and distribution beneath the land and channel regions. The perforated layers enhance the performance of the cells at high current densities owing to more efficient water transport through larger pores.
In this study, ex-situ experiments performed with a point injection device are conducted to evaluate water distributions in gas diffusion layer (GDL) materials which serve as porous transport media ...in polymer electrolyte membrane fuel cells (PEMFCs). In this regard, GDL samples manufactured by SGL Group are placed into the point injection device and visualized by means of synchrotron X-ray radiographic and tomographic imaging. The resulting image data undergoes a coordinate transformation that ascertains water agglomerations in GDL pores with regard to their radial displacements from the injection point. In this way, water transport in two different GDL samples possessing the same structural characteristics, but with unique compression rates, are investigated in terms of in-plane water distribution. The radial displacement analysis indicated that the pore saturation of the compressed GDL is higher in both the micro porous layer (MPL) region and the carbon fiber substrate region than that of the uncompressed GDL. The water agglomerations in the uncompressed GDL are predominantly observed in the vicinity of the injection point, indicating a limited in-plane transport. Conversely, in the compressed case water accumulations are detected far from the injection point, even at the edge of the GDL, pointing out that compression promotes the in-plane transport. Prior to the ex-situ experiments, both GDL samples have undergone an ageing procedure to mimic realistic cell operating conditions.
•In-plane water transport in GDL is revealed by radial displacement analysis.•GDL compression increases in-plane water transport.•Gas-phase geometric tortuosity correlates with in-plane water transport.•Artificial accelerated degradation of GDL mimics realistic cell conditions.
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