Christian Prehal

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Prehal

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Christian

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0000-0003-0654-0940

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Publications 1 - 10 of 13

Operando Scanning Small-/Wide-Angle X-ray Scattering for Polymer Electrolyte Fuel Cells: Investigation of Catalyst Layer Saturation and Membrane Hydration– Capabilities and Challenges
Aliyah, Kinanti Hantiyana; Appel, Christian; Lazaridis, Timon; et al. (2024)
ACS Applied Materials & Interfaces
Polymer electrolyte fuel cells are an essential technology for future local emission-free mobility. One of the critical challenges for thriving commercialization is water management in the cells. We propose small- and wide-angle X-ray scattering as a suitable diagnostic tool to quantify the liquid saturation in the catalyst layer and determine the hydration of the ion-conducting membrane in real operating conditions. The challenges that may occur in operando data collection are described in detail-separation of the anode and cathode, cell alignment to the beam, X-ray radiation damage, and the possibility of membrane swelling. A synergistic development of experimental setup, data acquisition, and data interpretation circumvents the major challenges and leads to practical and reliable insights.
Quantification of PEFC Catalyst Layer Saturation via In Silico, Ex Situ, and In Situ Small-Angle X-ray Scattering
Aliyah, Kinanti; Prehal, Christian; Diercks, Justus S.; et al. (2023)
ACS Applied Materials & Interfaces
The complex natureof liquid water saturation of polymerelectrolytefuel cell (PEFC) catalyst layers (CLs) greatly affects the deviceperformance. To investigate this problem, we present a method to quantifythe presence of liquid water in a PEFC CL using small-angle X-rayscattering (SAXS). This method leverages the differences in electrondensities between the solid catalyst matrix and the liquid water filledpores of the CL under both dry and wet conditions. This approach isvalidated using ex situ wetting experiments, which aid the study ofthe transient saturation of a CL in a flow cell configuration in situ.The azimuthally integrated scattering data are fitted using 3D morphologymodels of the CL under dry conditions. Different wetting scenariosare realized in silico, and the corresponding SAXS data are numericallysimulated by a direct 3D Fourier transformation. The simulated SAXSprofiles of the different wetting scenarios are used to interpretthe measured SAXS data which allows the derivation of the most probablewetting mechanism within a flow cell electrode.
On the nanoscale structural evolution of solid discharge products in lithium-sulfur batteries using operando scattering
Prehal, Christian; von Mentlen, Jean-Marc; Drvarič Talian, Sara; et al. (2022)
Nature Communications
The inadequate understanding of the mechanisms that reversibly convert molecular sulfur (S) into lithium sulfide (Li2S) via soluble polysulfides (PSs) formation impedes the development of high-performance lithium-sulfur (Li-S) batteries with non-aqueous electrolyte solutions. Here, we use operando small and wide angle X-ray scattering and operando small angle neutron scattering (SANS) measurements to track the nucleation, growth and dissolution of solid deposits from atomic to sub-micron scales during real-time Li-S cell operation. In particular, stochastic modelling based on the SANS data allows quantifying the nanoscale phase evolution during battery cycling. We show that next to nano-crystalline Li2S the deposit comprises solid short-chain PSs particles. The analysis of the experimental data suggests that initially, Li2S2 precipitates from the solution and then is partially converted via solid-state electroreduction to Li2S. We further demonstrate that mass transport, rather than electron transport through a thin passivating film, limits the discharge capacity and rate performance in Li-S cells.
Unraveling Multiphase Conversion Pathways in Lithium-Sulfur Batteries through Cryo Transmission Electron Microscopy and Machine Learning-Assisted Operando Neutron Scattering
von Mentlen, Jean-Marc; Senol Güngör, Ayca; Demuth, Thomas; et al. (2025)
ACS Nano
Understanding the complex physicochemical processes in conversion-type batteries requires investigations across multiple length scales. Here, we present a methodological approach to examine Li-S batteries on the nanoscale by combining cryogenic transmission electron microscopy (cryoTEM) with operando small-angle neutron scattering (SANS). CryoTEM revealed discharge products with a biphasic structure consisting of nanocrystalline Li2S within an amorphous Li2S x matrix. Data analysis of complementary operando SANS measurements was accelerated by a convolutional neural network trained to predict scattering curves based on plurigaussian random fields, enabling comprehensive parameter space exploration for model fitting. Our findings are in line with disproportionation-driven deposition of Li2S2 particles that agglomerate and partially reduce to Li2S via solid-state conversion. This challenges the conventional view of direct, stepwise electroreduction of polysulfides at the electrode-electrolyte interface. Overall, our multitechnique approach demonstrates the value of combining localized high-resolution imaging with time-resolved operando scattering measurements to understand complex electrochemical conversion pathways in next-generation energy storage systems.
Exclusive Solution Discharge in Li–O2 Batteries?
Prehal, Christian; Mondal, Soumyadip; Lovicar, Ludek; et al. (2022)
ACS Energy Letters
Capacity, rate performance, and cycle life of aprotic Li-O2 batteries critically depend on reversible electrodeposition of Li2O2. Current understanding states surface-adsorbed versus solvated LiO2 controls Li2O2 growth as surface film or as large particles. Herein, we show that Li2O2 forms across a wide range of electrolytes, carbons, and current densities as particles via solution-mediated LiO2 disproportionation, bringing into question the prevalence of any surface growth under practical conditions. We describe a unified O2 reduction mechanism, which can explain all found capacity relations and Li2O2 morphologies with exclusive solution discharge. Determining particle morphology and achievable capacities are species mobilities, true areal rate, and the degree of LiO2 association in solution. Capacity is conclusively limited by mass transport through the tortuous Li2O2 rather than electron transport through a passivating Li2O2 film. Provided that species mobilities and surface growth are high, high capacities are also achieved with weakly solvating electrolytes, which were previously considered prototypical for low capacity via surface growth.
Understanding Rate and Capacity Limitations in Li-S Batteries Based on Solid-State Sulfur Conversion in Confinement
Senol Güngör, Ayca; von Mentlen, Jean-Marc; Ruthes, Jean G.A.; et al. (2024)
ACS Applied Materials & Interfaces
Li-S batteries with an improved cycle life of over 1000 cycles have been achieved using cathodes of sulfur-infiltrated nanoporous carbon with carbonate-based electrolytes. In these cells, a protective cathode-electrolyte interphase (CEI) is formed, leading to solid-state conversion of S to Li2S in the nanopores. This prevents the dissolution of polysulfides and slows capacity fade. However, there is currently little understanding of what limits the capacity and rate performance of these Li-S batteries. Here, we aim to deepen our understanding of the capacity and rate limitation using a variety of structure-sensitive and electrochemical techniques, such as operando small-angle neutron scattering (SANS), operando X-ray diffraction (XRD), electrochemical impedance spectroscopy, and galvanostatic charge/discharge. Operando SANS and XRD data give direct evidence of CEI formation and solid-state sulfur conversion occurring inside the nanopores. Electrochemical measurements using two nanoporous carbons with different pore sizes suggest that charge transfer at the active material interfaces and the specific CEI/active material structure in the nanopores play the dominant role in defining capacity and rate performance. This work helps define strategies to increase the sulfur loading while maximizing sulfur usage, rate performance, and cycle life.
Are SAXS and SANS suitable to extract information on the role of water for electric-double-layer formation at the carbon-aqueous-electrolyte interface?
Seyffertitz, Malina; Stock, Sebastian; Rauscher, Max Valentin; et al. (2024)
Faraday Discussions
This study reports on the applicability of X-ray transmission (XRT), small- and wide-angle X-ray scattering (SAXS/WAXS) and small-angle neutron scattering (SANS) for investigating fundamental processes taking place in the working electrode of an electric double-layer capacitor with 1 M RbBr aqueous electrolyte at different applied potentials. XRT and incoherent neutron scattering are employed to determine global ion- and water-concentration changes and associated charge-balancing mechanisms. We showcase the suitability of SAXS and SANS, respectively, to get complementary information on local ion and solvent rearrangement in nanoconfinement, but also underscore the limitations of simple qualitative models, asking for more quantitative descriptions of water-water and ion-water interactions via detailed atomistic modelling approaches.
Current status and future perspectives of lithium metal batteries
Varzi, Alberto; Thanner, Katharina; Scipioni, Roberto; et al. (2020)
Journal of Power Sources
With the lithium-ion technology approaching its intrinsic limit with graphite-based anodes, Li metal is recently receiving renewed interest from the battery community as potential high capacity anode for next-generation rechargeable batteries. In this focus paper, we review the main advances in this field since the first attempts in the mid-1970s. Strategies for enabling reversible cycling and avoiding dendrite growth are thoroughly discussed, including specific applications in all-solid-state (inorganic and polymeric), Lithium–Sulfur (Li–S) and Lithium-O2 (air) batteries. A particular attention is paid to recent developments of these battery technologies and their current state with respect to the 2030 targets of the EU Integrated Strategic Energy Technology Plan (SET-Plan) Action 7. © 2020 Elsevier B.V.
Rational Design for Monodisperse Gallium Nanoparticles by In Situ Monitoring with Small-Angle X-ray Scattering
Schenk, Florian M.; Wintersteller, Simon; Clarysse, Jasper; et al. (2025)
Journal of the American Chemical Society
Colloidal chemistry is a well-known synthetic platform for producing size-uniform nanoparticles. However, the optimization of each material system still relies on a tedious trial-and-error approach in a multiparametric space, commonly referred to as design-of-experiments. This process is particularly laborious for emerging material classes for which only a handful of syntheses have been reported. Alternative approaches for the rational design of colloidal nanoparticles involve studying the reaction with in situ methods, thereby revealing the true underlying rules for the synthesis of monodisperse nanoparticles. Here, we focus on highly promising but little-studied colloidal gallium nanoparticles, using synchrotron-based small-angle X-ray scattering as a highly suitable in situ monitoring technique. We investigate the intertwined effects of process temperature, concentration of reactants, and the sterics of surface ligands during the hot-injection synthesis of gallium colloids. For quantitative comparison, we provide a description of gallium synthesis through the timestamps of partially overlapping reaction, nucleation, and growth stages. Our results reveal the key role of surface ligands in balancing the kinetics of nucleation and growth, as well as in enabling colloidal stability during the synthesis. Furthermore, we demonstrate that the large overlap between the nucleation and growth stages does not preclude the formation of monodisperse gallium nanoparticles. Our in situ experiments suggest several possible strategies for achieving size-uniform colloidal nanoparticles, thus enabling a rational design for the peculiar system of liquid metal nanodroplets and offering insights that can be extended to other monodisperse colloids prepared via hot-injection synthesis.
In situ small-angle X-ray scattering reveals solution phase discharge of Li–O2 batteries with weakly solvating electrolytes
Prehal, Christian; Samojlov, Aleksej; Nachtnebel, Manfred; et al. (2021)
Proceedings of the National Academy of Sciences of the United States of America
Electrodepositing insulating lithium peroxide (Li2O2) is the key process during discharge of aprotic Li–O2 batteries and determines rate, capacity, and reversibility. Current understanding states that the partition between surface adsorbed and dissolved lithium superoxide governs whether Li2O2 grows as a conformal surface film or larger particles, leading to low or high capacities, respectively. However, better understanding governing factors for Li2O2 packing density and capacity requires structural sensitive in situ metrologies. Here, we establish in situ small- and wide-angle X-ray scattering (SAXS/WAXS) as a suitable method to record the Li2O2 phase evolution with atomic to submicrometer resolution during cycling a custom-built in situ Li–O2 cell. Combined with sophisticated data analysis, SAXS allows retrieving rich quantitative structural information from complex multiphase systems. Surprisingly, we find that features are absent that would point at a Li2O2 surface film formed via two consecutive electron transfers, even in poorly solvating electrolytes thought to be prototypical for surface growth. All scattering data can be modeled by stacks of thin Li2O2 platelets potentially forming large toroidal particles. Li2O2 solution growth is further justified by rotating ring-disk electrode measurements and electron microscopy. Higher discharge overpotentials lead to smaller Li2O2 particles, but there is no transition to an electronically passivating, conformal Li2O2 coating. Hence, mass transport of reactive species rather than electronic transport through a Li2O2 film limits the discharge capacity. Provided that species mobilities and carbon surface areas are high, this allows for high discharge capacities even in weakly solvating electrolytes. The currently accepted Li–O2 reaction mechanism ought to be reconsidered.

Publications 1 - 10 of 13

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