Operando Cell Research Articles

The AUREX cell: a versatile operando electrochemical cell for studying catalytic materials using X-ray diffraction, total scattering and X-ray absorption spectroscopy under working conditions.

Understanding the structure-property relationship in electrocatalysts under working conditions is crucial for the rational design of novel and improved catalytic materials. This paper presents the Aarhus University reactor for electrochemical studies using X-rays (AUREX) operando electrocatalytic flow cell, designed as an easy-to-use versatile setup with a minimal background contribution and a uniform flow field to limit concentration polarization and handle gas formation. The cell has been employed to measure operando total scattering, diffraction and absorption spectroscopy as well as simultaneous combinations thereof on a commercial silver electrocatalyst for proof of concept. This combination of operando techniques allows for monitoring of the short-, medium- and long-range structure under working conditions, including an applied potential, liquid electrolyte and local reaction environment. The structural transformations of the Ag electrocatalyst are monitored with non-negative matrix factorization, linear combination analysis, the Pearson correlation coefficient matrix, and refinements in both real and reciprocal space. Upon application of an oxidative potential in an Ar-saturated aqueous 0.1 M KHCO3/K2CO3 electrolyte, the face-centered cubic (f.c.c.) Ag gradually transforms first to a trigonal Ag2CO3 phase, followed by the formation of a monoclinic Ag2CO3 phase. A reducing potential immediately reverts the structure to the Ag (f.c.c.) phase. Following the electrochemical-reaction-induced phase transitions is of fundamental interest and necessary for understanding and improving the stability of electrocatalysts, and the operando cell proves a versatile setup for probing this. In addition, it is demonstrated that, when studying electrochemical reactions, a high energy or short exposure time is needed to circumvent beam-induced effects.

Understanding Organic Components of Solid Electrolyte Interphase on the Lithium Metal Anode

Lithium ion batteries have become the dominant form of energy storage used in consumer electronics and, recently, electric vehicles. However, high costs have prevented widespread deployment of lithium ion batteries for applications other than portable electronics, and the safety issues associated with liquid organic electrolytes remain to be addressed. In order to enable the greater utilization of electric vehicles, allow for grid scale energy storage, and meet the demands of new electronic applications, new materials for high energy density batteries must be developed. High capacity electrode materials like lithium metal have the potential to facilitate these technologies, but lithium metal electrodes are presently limited by significant side reactions, poor quality deposition, and the potential to form hazardous dendrites. Therefore, it is important to develop a clear understanding of the surface reactivity and growth behavior of the lithium metal at the interface with the electrolyte in order to enable stable long-term cycling.The products that form as a result of electrolyte decomposition reactions at the electrode interface are known to be extremely important in determining the final cell performance, yet characterizing the organic components of the solid electrolyte interphase (SEI) proves to be challenging with typical techniques. In this presentation we will discuss a combination of in operando and ex situ techniques developed in efforts to more comprehensively characterize the reaction intermediates and organic SEI products of electrolyte reduction reactions. Specifically, we employ electron paramagnetic resonance (EPR) spectroscopy to identify radical intermediates and clarify electrolyte reduction mechanisms. Furthermore, SEI product formation with respect to electrochemical potential and time will be described using data obtained from in operando ATR-FTIR. ATR-FTIR is a powerful method for characterizing organic species, but typical materials such as Ge, Si, and ZnSe react with lithium metal during deposition. In this talk, the development of a diamond based operando cell and its application to the characterization of organosulfur and fluorinated electrolytes will be discussed. With the understanding developed from these two techniques we provide new insights into the formation and chemical nature of SEI components that promote stable cycling of lithium metal electrodes.

Measuring the Electrolyte Distribution in Silver Gas Diffusion Electrodes during CO2 Electroreduction Using Operando Synchrotron Tomography

Electrochemical CO2 reduction (eCO2R) has emerged as a promising technology to support the shift away from fossil fuels in the chemical industry. When coupled with renewable energies it allows for an overall carbon-negative process, while enabling CO2 as a carbon source for the production of commodity chemicals. Efficient eCO2R requires gas diffusion electrodes (GDEs) that provide a large wetted surface area inside the porous system, while also preserving gaseous diffusion pathways for CO2 mass transport through their hydrophobicity. Under the high cathodic overpotential in eCO2R, electrowetting diminishes the hydrophobicity of the GDE and can lead to excessive flooding of the porous system [1]. This severely hinders the CO2 mass transport and thus gives rise to the competing hydrogen evolution reaction (HER), lowering the Faradaic efficiency of the process. Therefore, understanding the flooding behavior of GDEs is of major interest for further development of the process.Mathematic models can be applied here to describe the flooding state under the influence of electrowetting and elucidate its influence on the gas transport through the GDE. The validation of such models requires direct experimental measurements of the electrolyte saturation during eCO2R, which can be accomplished with the use of synchrotron radiation [2].In this work, experimental results for the direct measurement of the electrolyte saturation during eCO2R in sprayed silver GDEs are presented. In a first, these measurements were obtained in operando synchrotron tomography experiments, utilizing a high beam energy to penetrate through the 3 mm diameter GDE in the in-plane direction. The results indicate a higher beam absorption towards the gas side of the GDE, as well as higher absorption at increased current density. Key to the interpretation of these results is the disentanglement of the effects of concentration increase due to migration in the electric field and the actual increase in electrolyte saturation. The experimental results are used to validate a continuum model for a sprayed silver GDE in eCO2R which includes the effect of electrowetting on flooding behavior by introducing capillary pressure – saturation and contact angle – potential correlations [3]. A good agreement between model and tomography results is reached, showing an interplay between concentration increase and flooding effects.[1] Bienen, F., Paulisch, M. C., Mager, T., Osiewacz, J., Nazari, M., Osenberg, M., Ellendorff, B., Turek, T., Nieken, U., Manke, I., & Friedrich, K. A., Investigating the electrowetting of silver‐based gas‐diffusion electrodes during oxygen reduction reaction with electrochemical and optical methods. Electrochemical Science Advances (2022) e2100158.[2] Hoffmann, H., Paulisch, M. C., Gebhard, M., Osiewacz, J., Kutter, M., Hilger, A., Arlt, T., Kardjilov, N., Ellendorff, B., Beckmann, F., Markötter, H., Luik, M., Turek, T., Manke, I., & Roth, C., Development of a Modular Operando Cell for X-ray Imaging of Strongly Absorbing Silver-Based Gas Diffusion Electrodes. Journal of The Electrochemical Society 169 (2022) 044508.[3] Osiewacz, J., Löffelholz, M., Turek, T., Modeling the Influence of Electrolyte Distribution in Silver Gas Diffusion Electrodes for CO2 Electroreduction. ECS Meeting s 01 (2023) 1727. Figure 1

Deciphering the Impact of Current, Composition, and Potential on the Lithiation Behavior of Graphite in Silicon-Graphite Anodes

Graphite is the most used anode material for current-generation lithium-ion batteries due to its beneficial cycle life, availability and reasonable rate capability. Still, the modest capacity of 372 mAhg-1 represents a bottleneck in the pursuit of high-energy density anodes. Enabling much higher theoretical capacities of 3600 mAhg-1 [1], silicon represents a promising candidate as anode material for next generation batteries. However, the alloying-based lithiation mechanism of silicon is accompanied by a large volumetric change of up to 300% upon cycling, leading to fast degradation due to electrode pulverization, continuous SEI formation and extensive electrolyte consumption. Even though shallow cycling of silicon anodes has been demonstrated in laboratory scale cells [2], the mixing of silicon with graphite is considered the most viable approach to lift energy density while maintaining appropriate cycle life.Due to the fundamentally different kinetics and potentials of Li insertion and extraction of both materials, the development of silicon-graphite composite electrodes is not straightforward. One of the key questions for optimization is how the incorporation of silicon impacts the (de)lithiation behavior of graphite as a function of the silicon:graphite mass ratio, operating current and electrode potential. While lithiation of graphite in composite electrodes of 15 wt% silicon has been shown to occur in a similar manner as pure graphite, higher fractions of silicon are expected to exert more stress on the graphite and represent kinetic barriers for Li diffusion. This study presents results from in-situ X-ray diffraction experiments (XRD) of silicon-graphite/Li half cells conducted at the European Synchrotron Radiation Facility (ESRF). Serving as a reference, the current-dependent (de)lithiation behavior of a pure graphite/Li half cell has been thoroughly investigated and systematically compared to the (de)lithiation behavior of two selected silicon-graphite composite anodes (silicon:graphite ratio of 30:70 and 70:30, respectively) exposed to the same formation cycle and C-rate protocol. An optimized and novel measurement setup was used, based on a perforated current collector of the anode, providing a complete picture of the graphite in-plane and interplanar structural changes as well as the evolution of semicrystalline silicon peaks which would usually be obscured by the current collector signal.By correlating the electrochemical features (voltage curve and differential capacity plot) with the in-situ diffraction data, it was possible to identify and assign the occurrence and absence of dilute-stage and ordered graphite intercalation compounds (GICs) for the respective electrodes, yielding an in-depth insight into the graphite state of charge upon (de)lithiation and how it is influenced by the silicon content and applied C-rate.As expected, the silicon is (de)lithiated within the entire potential range, whereas graphite is most electrochemically active at potentials lower than 260 mV. In both composite electrodes, graphite attains a lower lithiation degree compared to pure graphite. This is because the high theoretical capacity of silicon results in high specific currents, ultimately challenging the rate capability of graphite. Moreover, the high delithiation overpotential encountered in the composite electrodes results in a highly asymmetrical lithiation/delithiation behavior of graphite. Also, graphite lithiation is less uniform in the composite anodes, indicated by the coexistence of dilute GICs upon (de)lithiation, compared to pure graphite where dilute phases are fully consumed (formed) as (de)lithiation progresses. Surprisingly, the in-situ XRD studies did not reveal signs of structural degradation and strain of graphite as a result of mechanical interaction with silicon. Instead, the volume change of graphite is well correlated with the amorphization of crystalline, unreacted silicon and the volume evolution of silicon crystallites upon charge-discharge.To mitigate the observed effects, the work suggests nanostructuring and advanced electrode architectures towards higher utilization and more homogeneous lithiation of graphite. Overall, the study provides a demonstration of a suitable operando cell for studies of anodes for Li-based systems, and aids the rational design of silicon-graphite composite anodes.

Multi-Scale Correlative Characterization of Battery Aging Effects via XRM and SEM and In Operando Cell Experiments

Multi-Scale Correlative Characterization of Battery Aging Effects via XRM and SEM and In Operando Cell Experiments

Operando Spectroscopy to Understand Dynamic Structural Changes of Solid Catalysts.

Solid materials like heterogeneous catalysts are highly dynamic and continuously tend to change when exposed to the reaction environment. To understand the catalyst system under true reaction conditions,operando spectroscopy is the key to unravel small changes, which can ultimately lead to a significant difference in catalytic activity and selectivity. This was also the topic of the 7th International Congress on Operando Spectroscopy in Switzerland in 2023. In this article, we discuss various examples to introduce and demonstrate the importance of this area, including examples from emission control for clean air (e.g. CO oxidation), oxidation catalysis in the chemical industry (e.g. oxidation of isobutene), future power-to-X processes (electrocatalysis, CO2 hydrogenation to methanol), and non-oxidative conversion of methane. All of these processes are equally relevant to the chemical industry. Complementary operando techniques such as X-ray absorption spectroscopy (XAS), X-ray diffraction (XRD), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and Raman spectroscopy were utilized to derive the ultimate structure of the catalyst. The variety of conditions requires distinctly different operando cells that can reach a temperature range of 400-1000 °C and pressures up to 40 bar. The best compromise for both the spectroscopy and the catalytic reaction is needed. As an outlook, we highlight emerging methods such as modulation-excitation spectroscopy (MES) or quick-extended X-ray absorption fine structure (QEXAFS) and X-ray photon in/out techniques, which can provide better sensitivity or extend X-ray based operando studies.

Shedding Light on Electrocatalysts: Practical Considerations for Operando Studies with High‐Energy X‐Rays

AbstractOperando studies using high‐energy X‐rays from synchrotron sources are essential for unraveling the complex material transformation that electrocatalysts undergo under operating conditions. This article explores key considerations to perform these experiments and the insights gained from such studies on nanostructured electrocatalysts. Critical factors include optimizing electrochemical performance while obtaining high‐quality X‐ray signals, which often require compromises. The electrochemical operando cell design is crucial, and several different cells are discussed here. Working electrode geometries parallel to the X‐ray beam, probed with a microfocused beam, are emerging as promising solutions for realistic electrochemical performance in operando cells. Careful attention must also be paid to the electrochemical measuring conditions, electrode loading, and beam damage to ensure reliable experiments. When carefully performed and by combining multiple characterization techniques, operando studies with high‐energy X‐rays offer the unique possibility to fully understand the structure of the active electrocatalyst.

(Invited) Considerations in Sample Environment and Data Processing for Operando Cell Studies by Neutron Depth Profiling

Neutron depth profiling (NDP) is a nominally non-destructive analytical technique used to measure select isotopes (6Li, 14N, 10B, etc...) in a diversity of materials. NDP can be conducted on operating Li-ion cells and be used to provide researchers real-time information about cell formation, conductance, and resilience. The increased use of NDP for electrochemical studies within the past decade has inspired the development of new sample preparation and data reduction strategies. Select topics that have been studied in the U.S. have included issues of neutron attenuation and scattering due to the addition of a protective capping layer over a cell, the possible need for matrix matched standards for complex materials, and the streamlining of the NDP data reduction procedure. Several challenges remain, however, including improving NDP data acquisition and reduction methods for detectable, low-Z isotopes such as 14N and 35Cl and improving upon the NDP data reduction and processing procedures so that they are more accessible to non-instrument specialists. All these topics will be discussed in this presentation.

Operando Surface X-Ray Diffraction Studies of Co Oxide Catalyst Films for Electrochemical Water Splitting

The need for environmental friendly and sustainable energy conversion has triggered renewed interest into the electrochemical and photoelectrochemical splitting of water. A key challenge in this field is the development of economically viable electrocatalyst materials for the oxygen evolution reaction (OER). Transition-metal oxide catalysts, in particular the cobalt (hydr)oxide materials, have been found as promising candidates, since they are earth-abundant, efficient and scalable over a wide range of electrochemical conditions [1]. They present good catalytic properties and stability in alkaline solution under ambient conditions. Although a wide variety of different catalysts with rather diverse nanoscale morphologies have been synthesized and studied, the atomic scale surface structure usually is still unknown or poorly defined. This makes it difficult to compare their electrocatalytic activity and correlate it with ab initio theoretical studies, which hinders the development of clear structure-reactivity relationships and unambiguous determination of the OER reaction mechanism.We presentsystematic comparative studiesof structurally well-defined, 18-35nm thick Co3O4 films, prepared by electrodeposition or physical vapor deposition (PVD) on Au(111), Au(100) and Ir(100) single crystals. In all cases a well ordered epitaxial Co3O4(111) arrangement results, but the film morphology differs substantially, as shown by AFM and surface X-ray diffraction (SXRD). In order to elucidate the quantitative relationship between the catalyst surface structure and the OER reactivity, synchrotron-based operando SXRD and electrochemical measurements were performed simultaneously under reaction conditions, using a dedicated operando cell which allows massive gas evolution and current densities of up to 150 mA/cm2 [2,3].We find that the Co3O4(111) layers prepared by PVD on Ir(100) stay perfectly stable in the pre-OER and OER potential regime, whereas all electrodeposited films exhibit reversible changes in the oxide structure and oxidation state, in agreement with a previous study of Co3O4 catalysts [2]. Specifically, we observe the reverse formation of an ultrathin X-ray-amorphous CoOx(OH)y skin layer above 1 V vs. RHE and the gradual buildup of tensile lattice strain in the underneath, remaining Co3O4 layer with increasing potential. These structural changes occur for all electrodeposited samples, albeit to a different extent, depending on the film morphology [3]. Studying the relationship between the effective thickness of this skin layer and the OER reactivity, we found clear evidence that the entire skin layer is a three dimensional OER zone, which strongly exceeds one monolayer.Our results suggest that even subtle changes of the surface morphology have large influence on the OER activity of the Co3O4 catalyst, which may be expected also for other spinel-type transition metal oxides. On the one hand, this reveals that great care as to be taken in comparing the OER activity of differently prepared catalysts. On the other hand, these observations may provide a base for targeted preparation of highly reactive oxide catalysts.[1] C. C. L. McCrory et al., Journal of the American Chemical Society 2015, 137, 4347.[2] F. Reikowski, et al., ACS Catalysis, 2019, 9, 3811.[3] T. Wiegmann, et al., ACS Catalysis, 2022, 12, 256.

Electrochemical exsolution of metal nanoparticles from perovskite oxide upon electrolysis

This study presents a comprehensive investigation into the electrochemical reduction of LSCF perovskite during electrolysis, aiming to understand the exsolution of metal nanoparticles. The exsolution of metal nanoparticles from perovskite electrodes can significantly enhance their electrochemical performance in electrolysis. By applying cathodic polarization to the perovskite oxide electrode, the exsolution process was shown to be electrochemically induced within a few minutes. Additionally, a user-designed X-ray absorption spectroscopy operando cell was employed to analyze the edge energy change of the B-site atoms during electrolysis. The electrochemical reduction of perovskite and the subsequent exsolution of the B-site metal nanoparticles were investigated by scanning the cell voltage, providing an understanding of the electrochemical behavior during electrolysis. The electrochemical switching point, characterized by a decrease in the incremental area-specific resistance, was identified. This study offers valuable insights into the electrochemical exsolution process of metal nanoparticles from perovskite oxide electrodes.

Development of the Ni-Rich Li1+XNi0.905Co0.043Al0.052O2 High-Energy-Density Cathode Materials for Li-Ion Cells: Operando XRD Studies, Surface Modification, and Electrochemical Properties

With an increasing pressure to address major energy and environmental issues associated with consumption of the fossil fuels, the public is more and more aware of the need for electrification of the transportation sector. However, the rapid development of electric vehicles (EV) industry has put forward much higher and strict requirements for the energy storage density and safety of the applied batteries. Obviously, the accessible to the driving range per charge, depend on the characteristics of the EV batteries, which in turn depend mainly on the reversible capacity of the cathode and anode materials. To meet the demand of more than 500 kilometers driving range, development of high-energy-density cathode materials is required. Currently, the Ni-rich layered oxides (LiNiO2-type) are considered as primary candidates for a significant boosting of the properties, due to the very high reversible discharge capacity (>200 mAh g-1), high operating voltage (~3.7 V vs. Li/Li+), and relatively low costs. Nevertheless, such oxides still suffer from severe issues, such as surface sensitivity, poor structure with Li/Ni mixing effect, and insufficient thermal stability, which hinder their practical application. In particular, presence of LiOH/Li2CO3 lithium residuals in the active material, which originate from the synthesis process, has deleterious effect on the rate performance and may affect cycling stability of the cells.In this work, a simple vibratory dry mixing method was adopted to synthesize high-Ni-content Li1+xNi0.905Co0.043Al0.052O2 (NCA90) cathode materials with varying lithium excess used during the preparation route. The Ni-rich [Ni0.905Co0.043Al0.052](OH)2 precursor was used in the synthesis. The obtained samples maintained the desired ball-like morphology of the precursor, as well as layered R-3m crystal structure. To quantify the lattice volume changes during charge and discharge, operando XRD experiments were also conducted. A custom-made cell, having a Be window was used for the measurements. Two cycles were measured, with the first one up to 4.3 V, and the second up to 4.5 V. The registered charge/discharge curves, obtained using the operando cell, were nearly the same as those obtained using the normal 2032 coin-type half cells. Analysis of the XRD operando data showed that the a lattice parameter decreases monotonically as the charging proceeds, whereas the c parameter initially increases, and then begins to contract, for voltages higher than ca. 4.0 V. Above ca. 4.2 V, the c parameter abruptly decreases, which can be related to the so called H2 → H3 phase transition. It is worth noting that this transition is responsible for the capacity fading. During charge and discharge, the observed behavior of the 003 reflection was reversible, but showing small changes in the recorded intensity and position of the peak. Overall, the generated profiles of the structural changes of the Ni90 cathode materials are almost symmetrical, with only small asymmetric behavior, especially visible during the first cycle. The results indicate that the operando XRD tests are important for realizing the real-time monitoring and provide on-site information of the structural evolution and phase transitions occurring for the cathode materials. Also, the electrochemical performance of the NCA90 cathodes was characterized using 2032 coin-type half cells with a Li metal anode and 1 M LiPF6 in EC:DEC 1:1 vol. ratio electrolyte. The cycling tests were performed between 2.7 V and 4.3-4.5 V at different current densities. One of the best performing Li1.05Ni0.905Co0.043Al0.052O2 cathode delivered an initial discharge capacity of 234.5 mAh g-1 at 0.05 C, with a capacity retention of 70.7% after 100 cycles. Finally, an attempt was done to introduce surface coating of the obtained cathode materials, in order to enhance the capacity retention.

Modeling the Influence of Electrolyte Distribution in Silver Gas Diffusion Electrodes for CO2 Electroreduction

The chemical industry has been increasingly focusing on reducing CO2 emissions in recent years. One promising way to do this is via CO2 electroreduction, a technology that does not only reduce CO2 emissions but also allows CO2 to be used as a source of carbon for making commodity chemicals. A key to efficient CO2 electroreduction is the electrolyte management inside the porous system of gas diffusion electrodes (GDEs). Flooding of electrodes can severely hinder mass transfer and thereby prevent CO2 reduction, giving rise to the parasitic hydrogen evolution reaction [1]. Although the measurement of electrolyte saturation is possible through methods like synchrotron radiography, these measurements are highly expensive, and thus not always readily available [2]. Modeling can help here to better understand the influence of electrolyte saturation, and predict possible measures for improving the process.In most CO2 electrolysis models in literature, the electrolyte saturation is a fixed parameter [3,4]. This assumption does not always hold true, as effects like electro-wetting change the wetting behavior of the GDE for different operating conditions. In this new modeling approach, correlations between capillary pressure and saturation, as well as between contact angle and potential are introduced, making the description of these changes possible. These correlations are gained from pore network simulations of the electrode material reconstructed from FIB-SEM measurements. The correlations are implemented in a one dimensional continuum model that includes discretized balance spaces for liquid and gas phase inside the porous system of the GDE, ideally mixed gas and electrolyte bulk spaces on the respective sides of the electrode, as well as boundary layers between bulk and electrode. Homogeneous reactions of the carbonate buffer system in the liquid phase and electrochemical reactions inside the GDE are considered. Transport of species is calculated using Maxwell-Stefan diffusion, migration in the potential field resulting from the Nernst-Planck equation, and flow through the porous electrode according to Darcy’s law. Additionally phase transfer processes like gas dissolution and evaporation of water are considered. The GDE model is validated with experimental data for CO2 electrolysis, enabling insights into the processes in the GDE and elucidating the influence of electrolyte saturation on the CO2 mass transfer.[1] Bienen, F., Paulisch, M. C., Mager, T., Osiewacz, J., Nazari, M., Osenberg, M., Ellendorff, B., Turek, T., Nieken, U., Manke, I., & Friedrich, K. A., Investigating the electrowetting of silver‐based gas‐diffusion electrodes during oxygen reduction reaction with electrochemical and optical methods. Electrochemical Science Advances (2022) e2100158.[2] Hoffmann, H., Paulisch, M. C., Gebhard, M., Osiewacz, J., Kutter, M., Hilger, A., Arlt, T., Kardjilov, N., Ellendorff, B., Beckmann, F., Markötter, H., Luik, M., Turek, T., Manke, I., & Roth, C., Development of a Modular Operando Cell for X-ray Imaging of Strongly Absorbing Silver-Based Gas Diffusion Electrodes. Journal of The Electrochemical Society 169 (2022) 044508.[3] Löffelholz, M., Osiewacz, J., Lüken, A., Perrey, K., Bulan, A., & Turek, T., Modeling electrochemical CO2 reduction at silver gas diffusion electrodes using a TFFA approach. Chemical Engineering Journal 435 (2022) 134920.[4] Weng, L.-C., Bell, A. T., & Weber, A. Z., Modeling gas-diffusion electrodes for CO2 reduction. Physical Chemistry Chemical Physics 25 (2018) 16973–16984. Figure 1

Applying DRIFT Spectroscopy for High Temperature Electrochemical Cells-Lessons from SMOX Based Gas Sensors

In operando diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, the metal oxide sample is illuminated by the infrared beam, and the scattered (rather than transmitted) light is collected with appropriate optics for analysis. In addition to being better suited for operando methods, DRIFT spectroscopy has also been found to be more surface sensitive than other IR techniques suitable for powder samples, such as TIRS, ATR-IRS, and PM-IRRAS.(Roedel et al., 2008) DRIFT spectroscopy has allowed for significant gains in understanding the surface chemistry of semiconducting metal oxide (SMOX) based sensors to be made.Despite the potential usefulness in unravelling different surface mechanisms, ranging from the influence of humidity on the oxygen reduction reaction in fuel cell cathodes to insights about the anodic coking mechanisms when using hydrocarbon fuels, the use of DRIFTs for metal oxide electrochemical cells is still in its infancy, with only a handful of near operando studies being reported. (Cumming et al., 2015; Hauser et al., 2020; Tezel et al., 2022) One critical consideration is the potentially problematic intrinsic IR radiation of samples and the limited stability of cell materials at the high relevant operation temperatures. Nonetheless, using clever cooling systems that prevent the windows from overheating and intricate cell designs to allow for separate oxygen and fuel supply, Cumming et al. and more recently Hauser et al. were able to measure DRIFT spectra at elevated temperatures on cells. (Cumming et al., 2015; Hauser et al., 2020) In both cases, DRIFT spectra were depicted up to 600 ˚C without reports of significant errors due to radiation stemming from the sample. As a result, it is promising that through further optimization, DRIFT spectroscopy could become a useful tool for studying metal oxide based electrochemical systems.For the further optimization, lessons learned during the development of operando cells for SMOX based gases sensors are pertinent. Here a way forward for the optimization will be presented. Starting with practical aspects of DRIFT spectroscopy, e.g. need for precisely controlled room environments in non-evacuated systems or increased signal intensity through window optimization. Common artefacts will be shown, and avoidance strategies will be shown, e.g. ice bands that can be removed through detector evacuation. Additional considerations that are relevant specifically when working with metals oxides will be reviewed and the advantages of selecting the referencing method of Olinger and Griffiths over the traditionally used Kubelka-Munk will be elaborated.(Cumming et al., 2015; Jill M Olinger & Peter R Griffiths, 1988) The usefulness of using isotopically labelled gases to differentiate surface species, e.g. separate metal-oxygen groups from metal-hydroxides, will be discussed. Finally, the potential pitfalls of comparing different samples quantitatively will be highlighted. Overall, this presentation will provide a useful guideline for the future design of an operando DRIFT chamber for oxide based electrochemical cells.BibliographyCumming, D. J., Tumilson, C., Taylor, S. F. R., Chansai, S., Call, A. v., Jacquemin, J., Hardacre, C., & Elder, R. H. (2015). Development of a diffuse reflectance infrared fourier transform spectroscopy (DRIFTS) cell for the in situ analysis of co-electrolysis in a solid oxide cell. Faraday Discussions, 182, 97–111. https://doi.org/10.1039/c5fd00030kHauser, D., Nenning, A., Opitz, A. K., Klötzer, B., & Penner, S. (2020). Spectro-electrochemical setup for in situ and operando mechanistic studies on metal oxide electrode surfaces. Review of Scientific Instruments, 91(8). https://doi.org/10.1063/5.0007435Jill M Olinger, & Peter R Griffiths. (1988). Quantitative effects of an Absorbing Matrix on Near-Infrared Diffuse Reflectance Spectra. Anal. Chem., 60(21), 2427–2435.Roedel, E., Urakawa, A., Kureti, S., & Baiker, A. (2008). On the local sensitivity of different IR techniques: Ba species relevant in NOx storage-reduction. Physical Chemistry Chemical Physics, 10(40), 6190–6198. https://doi.org/10.1039/b808529cTezel, E., Guo, D., Whitten, A., Yarema, G., Freire, M., Denecke, R., McEwen, J.-S., & Nikolla, E. (2022). Elucidating the Role of B-Site Cations toward CO2 Reduction in Perovskite-Based Solid Oxide Electrolysis Cells . Journal of The Electrochemical Society, 169(3), 034532. https://doi.org/10.1149/1945-7111/ac5e9b

(Invited) Understanding Oxygen Transport in Polymer Electrolyte Membrane Water Electrolyzers Using X-Ray Computed Tomography

This study aims to understand the fundamental processes that affect catalyst utilization and gas transport through the porous media in polymer electrolyte water electrolyzers (PEWEs) to optimize porous transport layers (PTLs) and flow-fields. We designed a novel operando x-ray computed tomography (CT) cell that can resolve oxygen transport along a 10 cm x 1 cm membrane electrode assembly (MEA) active area. The flow field with two straight channels was designed for this operando cell. X-ray CT with the field of view (FOV) of about 3 mm x 2 mm and resolution of 0.7 um allowed visualizing MEA and flow channels of operando PEWEs. The cell features three observation windows that are transparent to x-rays. These are located near the inlet, in the middle of the flow-channels and at the outlet. In addition, thermocouples are embedded in various locations in the cell to measure temperature profiles of the cell. Oxygen content in the flow-channels was observed for various current densities using 2D radiography technique, with 5 ms time resolution step size. The cell morphology and steady-state oxygen distribution in the PTL were observed using stained water (stained with NaI). The results show significant oxygen enrichment in the channels near the outlet, as well as higher oxygen presence in the PTLs near the outlet. This new cell design can enable simultaneous heat and mass transport measurements along the flow channels. Inlet-outlet variations in oxygen content at scale of 10 cm is of relevant to single cell testing in the laboratory.

High-sensitivity IR to UV broadband ellipsometry and transmission characterization of high-purity glasses

Glasses are widely used as transparent substrates in thin-film and optical applications, but also as window materials in devices and operando cells. Determining the dielectric properties of the glass over a wide spectral range is often the crucial first step for the subsequent quantitative spectroscopic analysis, design and application of layer stacks and complex sample systems. Reflection-based ellipsometry—the method of choice for this task—is challenging for thick transparent substrates because of backside reflections that influence the optical response. Here, we extend the methodological treatment of backside reflections in ellipsometry by accounting for the spatial overlap—and its dependence on incidence angle, thickness and refractive index—between the light beams’ cross-sections and the detector aperture. We thereby demonstrate the incorporation of backside reflections in high-sensitivity multi-instrument, multi-angle ellipsometry and transmission for both measurement and quantitative modeling of glasses. Consolidating data from three instruments, we determine the dielectric function of two high-purity fused silica (Suprasil1) and quartz (Herasil102) glasses from the deep-ultraviolet to the mid-infrared (200–25000nm), with a sensitivity to absorption features as small as 10–7. Our non-destructive approach obviates the need for sample modifications like backside roughening, thus laying the foundation for future detailed ellipsometry studies on lower-purity glasses such as soda–lime- and borosilicate-based substrates for thin-film applications.

Facile design of alloy-based hybrid layer to stabilize lithium metal anode

Lithium (Li) metal has been considered a promising anode candidate for next-generation energy-storage applications due to its ultrahigh capacity. However, the uncontrolled dendrite growth and continuous side reactions challenge the cycle life and practical application. Herein, by a facile and mild solution method, we build a compact LiZn alloy-based hybrid layer on the Li-metal surface. This hybrid layer exhibits favorable chemical stability, excellent wettability to electrolyte, and enhanced thermodynamic affinity to Li. As a result, the hybrid layer modified lihtium metal anode (HL-Li) enables accelerated Li-ion diffusion kinetics and dense Li deposition. Through the operando cell evaluation, moreover, we demonstrate that the hybrid layer restricts the Li dendrite growth of Li metal anodes effectively by reducing the volume expansion to half. Endowed with both thermodynamic and kinetic superiority, HL-Li exhibits low overpotential and prolonged cycles in both symmetric cells and full cells. Our work confirms the lithiophilic hybrid layer obtained by a facile solution process to enable dendrite-free deposition, providing a guidance for the synthesis of high-performance Li metal anode materials.

Operando Neutron Radiography Measurements of a Zero-Gap Alkaline Electrolysis Cell

Low temperature alkaline water electrolysis is a well-known technology for hydrogen production and advantageous because less noble metals are needed compared to Proton Exchange Membrane (PEM) electrolysis. However, the two-phase flow behavior and especially the gas bubble distribution and flow during the operation in a zero-gap alkaline electrolysis cell have not been investigated in sufficient detail. Previous studies used e.g. transparent model electrolysis cells or focused on single flow phenomena e.g. gas bubble nucleation, growth or detachment.Recent publications show evidence that the ohmic resistance of zero-gap alkaline electrolysis cells is greater than the ohmic resistance of the used diaphragm, which has been believed the only term contributing to the ohmic resistance in zero-gap cells [1]. This suggests that the evolving gas bubbles might have a relation to the total ohmic resistance of the cell. As possible reasons nano bubbles in the pores of the diaphragm and a possible finite gap between electrodes and diaphragm is mentioned [2]. Haverkort et al. assume that the frontal area of the electrodes might be inactive [3].To prove the hypothesis and to deepen the general understanding of the two-phase flow inside an alkaline electrolysis cell we conducted operando cell measurements and visualized the electrolyte-gas bubble flow in an alkaline electrolysis cell by using neutron radiography. Thanks to the powerful neutron source at Institute Laue-Langevin in Grenoble, it was possible to observe the whole flow field with all flow channels at once with a sufficient temporal resolution to observe the movement of single gas bubbles, from nucleation to the moment of exiting the channel. The temporal resolution was 50 fps, which makes these measurement, to the best authors’ knowledge, the first to show the transient effects inside of a zero gap alkaline electrolysis cell. For the measurements, the NeXT (Neutron and X-Ray Tomograph) instrument was used which is the imaging station with one of the highest neutron fluxes of the world (1.4 E10 n/cm²/s at the end of the guide) [4]. The neutron beam was used to carry out through-plane measurements of the electrolysis cell.The measurements were conducted at a variety of operation conditions, varying the current density, the electrolyte volume flow and the operation temperature. At different operation conditions Electrical Impedance Spectroscopy (EIS) measurements have been conducted to measure the ohmic resistance of the cell. The used cell is an alkaline single cell out of a Nickel alloy with vertical parallel flow channel and a pocket milled to the backside of the cell in order to increase the transmission through the cell material.From the results of the measurements we observe a relation between current density (forming gas amount) and the ohmic resistance and thus establish a relation to the gas bubble behavior inside the electrolysis cell. Furthermore, we analyzed the velocity of the gas bubbles inside the channel depending on the different operation conditions, as well as the agglomeration behavior of the bubbles and their flow regime.[1] Phillips et al.,Minimising the ohmic resistance of an alkaline electrolysis cell through effective cell design, 2017[2] de Groot et al., Ohmic resistance in zero gap alkaline electrolysis with a Zirfon diaphragm,2021[3] Haverkort et al., Voltage losses in zero-gap alkaline water electrolysis,2021[4] Tengattini et al., NeXT-Grenoble, the Neutron and X-ray tomograph in Grenoble, 2020 Figure 1

Battery Degradation and Lifetime – Studies within the Faraday Institution on NMC811/Graphite Full Cells

Lithium-ion batteries (LIBs) find use in a wide range of applications, each of which has its own design specifications and practical requirements. With regards to the role of LIBs in mitigating carbon emissions, and therefore climate change, it is desirable to support the rapidly growing adoption of electric vehicles and renewable grid-storage systems via development of higher energy density, lower cost, and improved rate capability. However, the design of energy-dense, low-cobalt, and/or high-rate cell chemistries is impeded by inherent trade-offs with cycling and calendar lifetimes. A key goal for the automotive and utilities industries is therefore to predict battery lifetime for new cell designs and chemistries at a very high level of confidence, for example through improved understanding of the physical and chemical processes that determine the state of health of battery systems.As part of the Faraday Institution, the UK’s independent institute for electrochemical energy storage technology, the Battery Degradation Project has built new understanding of the underlying physical and chemical processes that can lead to degradation in energy-dense NMC811/graphite lithium-ion cells as a model system. Led by the University of Cambridge (Clare Grey PI) in collaboration with eight UK universities, the research consortium is working closely with industry partners to create a new hub for lithium-ion battery research and to address key challenges and opportunities in the field. This presentation will give an overview of the research consortium’s diverse membership, key milestones, and technical progress.To date, the consortium has been applying a variety of analytical techniques to study degradation processes in NMC811/graphite cells. For example, electrochemical testing and operando solid-state 7Li nuclear magnetic resonance spectroscopy (NMR) were combined to monitor processes in both electrodes individually, including Li-ion mobility and its changes with temperature.1 The method is now being applied to understand how the dynamics are affected by long-term structural damage to the NMC811 material. A series of differential voltage analysis experiments have been paired with operando X-ray diffraction measurements to propose the mechanism behind a critical ‘turning point’ in NMC811/graphite cells, following which degradation accelerates significantly.2 New operando cell designs have been developed to measure changes in cell pressure,3 which are being paired with solution NMR spectroscopy,4 and differential electrochemical mass spectrometry to quantify electrolyte oxidation. The role and rate of transition-metal dissolution in cells under stressed cycling conditions, namely cycling at high temperature (60 °C) and high upper cut-off voltages (4.4, 4.6 V), has been investigated.5 Scanning transmission electron microscopy-energy dispersive X-ray spectroscopy (STEM-EDX) measurements were coupled with time-of-flight secondary-ion mass spectrometry (Tof-SIMS) to observe the Al-containing phases at NMC811 surfaces and grain boundaries.7 New spectroscopic methods are also being developed, including Kerr-gated Raman, which allows sensitive measurements of electrode materials and electrolytes with lower background signal than conventional Raman spectroscopy.6 Finally, X-ray computed tomography methods have been developed that enable operando imaging and spectroscopic mapping of heterogeneities at a sub-particle length scale and across large areas of electrodes, which are being applied to study the origins of microstructural defects, cracking, and redox activity during charging, cycling, or storage.8,9 Reference s: K. Märker, C. Xu, and C. P. Grey, J. Am. Chem. Soc., 142, 17447–17456 (2020). W. M. Dose, C. Xu, C. P. Grey, and M. F. L. De Volder, Cell Rep. Phys. Sci., 1, 100253 (2020). N. Ryall and N. Garcia-Araez, J. Electrochem. Soc., 167, 110511 (2020). B. L. D. Rinkel, D. S. Hall, I. Temprano, and C. P. Grey, J. Am. Chem. Soc., 142, 15058–15074 (2020). Z. Ruff, C. Xu, and C. P. Grey, J. Electrochem. Soc., 168, 060518 (2021). L. Cabo-Fernandez, A. R. Neale, F. Braga, I. V. Sazanovich, R. Kostecki, and L. J. Hardwick, Phys. Chem. Chem. Phys., 21, 23833–23842 (2019). J. Lee, H. Amari, M. Bahri, Z. Shen, C. Xu, Z. Ruff, C. P. Grey, O. Ersen, A. Aguadero, N. D. Browning, and B. L. Mehdi, Batter. Supercaps, 4, 1813–1820 (2021). T. M. M. Heenan, A. Wade, C. Tan, J. E. Parker, D. Matras, A. S. Leach, J. B. Robinson, A. Llewellyn, A. Dimitrijevic, R. Jervis, P. D. Quinn, D. J. L. Brett, and P. R. Shearing, Adv. Energy Mater., 10, 2002655 (2020). C. Tan, A. S. Leach, T. M. M. Heenan, H. Parks, R. Jervis, J. N. Weker, D. J. L. Brett, and P. R. Shearing, Cell Rep. Phys. Sci., 100647 (2021).

Development of a Modular Operando Cell for X-ray Imaging of Strongly Absorbing Silver-Based Gas Diffusion Electrodes

Metal-based gas diffusion electrodes are utilized in chlor-alkali electrolysis or electrochemical reduction of carbon dioxide, allowing the reaction to proceed at high current densities. In contrast to planar electrodes and predominantly 2D designs, the industrially required high current densities can be achieved by intense contact between the gas and liquid phase with the catalytically active surfaces. An essential asset for the knowledge-based design of tailored electrodes is therefore in-depth information on electrolyte distribution and intrusion into the electrode’s porous structure. Lab-based and synchrotron radiography allow for monitoring this process operando. Herein, we describe the development of a cell design that can be modularly adapted and successfully used to monitor both the oxygen reduction reaction and the electrochemical reduction of CO2 as exemplary and currently very relevant examples of gas-liquid reactions by only minor modifications to the cell set-up. With the reported cell design, we were able to observe the electrolyte distribution within the gas diffusion electrode during cell operation in realistic conditions.

Operando Photo-Electrochemical Catalysts Synchrotron Studies.

The attempts to develop efficient methods of solar energy conversion into chemical fuel are ongoing amid climate changes associated with global warming. Photo-electrocatalytic (PEC) water splitting and CO2 reduction reactions show high potential to tackle this challenge. However, the development of economically feasible solutions of PEC solar energy conversion requires novel efficient and stable earth-abundant nanostructured materials. The latter are hardly available without detailed understanding of the local atomic and electronic structure dynamics and mechanisms of the processes occurring during chemical reactions on the catalyst–electrolyte interface. This review considers recent efforts to study photo-electrocatalytic reactions using in situ and operando synchrotron spectroscopies. Particular attention is paid to the operando reaction mechanisms, which were established using X-ray Absorption (XAS) and X-ray Photoelectron (XPS) Spectroscopies. Operando cells that are needed to perform such experiments on synchrotron are covered. Classical and modern theoretical approaches to extract structural information from X-ray Absorption Near-Edge Structure (XANES) spectra are discussed.