Operando Techniques Research Articles

Advanced Characterization by Using Coupled Operando Mass Spectrometry and Operando Dilatometry

Mechanical modifications or harmful side reactions are undesirable ageing effects that can occur during cycling. These phenomena have a negative impact on cell performance and consequently limit cycle life. The focus here is on investigations of ageing processes such as volume changes and electrolyte decomposition during cycling.Combined thickness measurements and gas analytical studies of Li-Graphite half cells with a carbonate-based electrolyte are presented. In addition, the same measurements on Li-O2 cells with an ether-based electrolyte are introduced. The electrolytes consist of 1M LiPF6 in EC:DMC (1:1, wt) and 1M LiTFSI in DEGDME, respectively. All measurements were carried out using specially developed multifunctional test setups and accordingly modified test cells. The different cell specifications were examined by operando mass spectrometry (MS) and operando dilatometry. In addition, post-mortem gas chromatography-mass spectrometry (GC-MS) was conducted.Application-oriented analysis such as gas analysis, thickness measurements or both combined are suitable methods to define operating parameter, to benchmark and to identify decomposition reactions. Operando electrochemical dilatometry was conducted to check whether an irreversible increase in thickness occurred. On the corresponding cell configurations, the dilatation was recorded over the entire electrode stack as well as of the separate working electrode only. Furthermore, operando MS can be used to detect gaseous substances produced by (electro)chemical processes as a function of the state of charge. With the GC-MS, a post-mortem analysis was performed to identify the individual substances qualitatively.Results of the different cell specifications are shown and can be compared with each other. A detailed relationship can be demonstrated between the change in thickness and the potential profile. Moreover, the cyclic formation of several degradation products is detected. Possible correlations between gas evolution and thickness changes can be shown. In conclusion, these analytical studies provide a new important contribution to get a more detailed insight into ageing processes that take place. The possible coupling of two operando techniques enables an even more holistic examination to analyze cell performance.Parts of the presented work are supported by the Fraunhofer and Max-Planck cooperation program in the project “Clusterbatt” together with Fraunhofer IWS, Dresden and MPIKG, Potsdam. Parts of the presented work are funded by the German Federal Ministry of Education and Research (BMBF) in the joint German-Japanese project “OsabanPlus” (03XP0469C) together with Justus-Liebig-University Giessen, TU Braunschweig and University of Kyoto. Figure 1

Combining electrochemical, molecular simulation and operando techniques to investigate the stability of electrodes and organic electrolytes used in EDLCs

A comprehensive study involving Electrochemical, Mass Spectrometry, Raman & FT-IR operando analyses, and Molecular Dynamics Simulations is present to evaluate the stability of electrodes and electrolytes used in organic-based EDLCs. In this sense, we present some directions to correctly determine the maximum stable cell voltage, specific capacitance, energy, and power, as well as the equivalent series resistance. Multi-walled carbon nanotubes and activated carbon electrodes are contrasting in symmetric devices filled with 1.0 M LiTFSI and TEABF4 salts dissolved in AN, PC, and EC:DMC electrolyte. We observed anomalous transport caused by adsorption effects in the electrical double-layer in all electrochemical studies due to the defective nature of the ionic channels in the presence of displacement of finite-sized charge carriers. This behavior is unequivocally verified from the impedance analysis using a double-channel transmission line model representing the macrohomogenous behavior of the electrochemical system. The residual gas analysis suggested a maximum stable voltage of 3 V to avoid electrolyte degradation. The carbon-based electrodes remain stable in all cases, as evidenced by the Raman & FT-IR operando studies. We verified that the AC/TEABF4-PC/AC system is auspicious for further studies aiming to develop EDLC prototypes with high specific capacitance, energy, and power characteristics. The derivative analysis method involving the galvanostatic findings permitted us to verify the different dynamics regarding the charge-storage process in macro and microporous structures as a function of the applied current. Computational simulations indicated that [TEA]+ has a high affinity for the carbon electrodes, which is related to the higher electrochemical stability of TEABF4-PC.

Understanding the lithiation intermediates of a silicon-based alloying anode by using operando diffraction and Raman spectroscopic techniques

In the present study, the effect of lithiation on a chalcopyrite phase, cadmium silicon phosphide (CdSiP2) anode is studied. This silicon-based phosphide anode helps in overcoming certain challenges encountered towards the application of elemental silicon anode for lithium-ion battery. Despite of having a fairly high band gap, this material represents outstanding cycling stability for lithium storage. Half-cell configuration results in a capacity of 970 mAh g−1 towards the end of 500 cycles at an applicable rate of 300 mA g−1, whereas a capacity of 645 mAh g−1 is obtained at a rate of 5000 mA g−1 for about 1800 cycles. The rate capability studies suggest highly reversible storage processes when switching from extremely high current rates such as 30 A g−1. Full-cell studies indicate highly stable charge-discharge voltage profiles with an appreciable capacity of around 400 mAh g−1 towards the end of 1400 cycles. Further, in-situ X-ray diffraction (XRD) analysis indicates conversion processes and confirms the formation of phases such as Li3P, LiCdP, Li5SiP3, Li13Si4, Li22Si5 and CdLi at various stages of charge-discharge cycling.

In-situ monitoring of multiple signals evolution behaviour for commercial lithium-ion batteries during internal short circuit

Internal short circuit in lithium-ion batteries is a crucial hazard threatening. It is accurately difficult to monitor the internal signals in time of the lithium-ion batteries during the process of internal short circuit. Herein, a novel method is developed to monitor multiple signal evolution behaviour using a sealed tank and sensors. The internal signals of LFP batteries and NMC batteries exhibit different evolution behaviours, especially in the response sequence of pressure and gas. Battery capacity has an impact on ISC signal response sequence and time for LFP batteries, showing identical sequence and shorter time with the increase of capacity. The voltage and temperature are considered as sensitive signals for both LFP and NMC811 batteries that sensitive signals are defined based on their response speed. This operando technique provides a suitable platform for understanding the side reaction mechanism during thermal runaway in commercial LIBs.

Toward Operando Characterization of Interphases in Batteries.

Electrode/electrolyte interfaces are the most important and least understood components of Li-ion and next-generation batteries. An improved understanding of interphases in batteries will undoubtedly lead to breakthroughs in the field. Traditionally, evaluating those interphases involves using ex situ surface sensitive and/or imaging techniques. Due to their very dynamic and reactive nature, ex situ sample manipulation is undesirable. From this point of view, operando surface sensitive techniques represent a major opportunity to push boundaries in battery development. While numerous bulk spectroscopic, scattering, and imaging techniques are well established and widely used, surface sensitive operando techniques remain challenging and, to a larger extent, restricted to the model systems. Here, we give a perspective on techniques with the potential to characterize solid/liquid interfaces in both model and realistic battery configurations. The focus is on techniques that provide chemical and structural information at length and time scales relevant for the solid electrolyte interphase (SEI) formation and evolution, while also probing representative electrode areas. We highlight the following techniques: vibrational spectroscopy, X-ray photoelectron spectroscopy (XPS), neutron and X-ray reflectometry, and grazing incidence scattering techniques. Comprehensive overviews, as well as promises and challenges, of these techniques when used operando on battery interphases are discussed in detail.

Scanning tunneling microscopy under chemical reaction at solid–liquid and solid–gas interfaces

The task of bridging the pressure gap between ideal ultrahigh vacuum conditions and more realistic reaction conditions involving gas and liquid phases is crucial in surface and interfacial chemistry. Scanning tunneling microscopy (STM) has played a key role in addressing this challenge by enabling atomic-scale probing of the interface. STM enabled us to study surface structure, electronic structure, atomic manipulation, dynamics of molecules and atoms, and chemical properties of the surface at the atomic scale. Over the past four decades, the field of STM has undergone explosive growth. This review article focuses on recent advances in operando STM, specifically in the study of solid–liquid and solid–gas interfaces. It highlights the latest works in ambient-pressure STM, which has enabled the observation of atomic features under various gas and reaction conditions. This information sheds light on the surface mobility of adsorbates and atomic structures of reaction intermediates. The review also addresses research on electrochemical STM, which investigates the evolution of surface morphology under electrochemical processes and provides insights into atomic-scale reaction mechanisms. Finally, the article outlines future challenges and perspectives for operando STM techniques.

The future ahead gas sensing with two-dimensional materials

The state of the art of the literature on two-dimensional (2D) materials currently used in conductometric and transistor-type gas sensing devices is here illustrated, followed by a survey of the potential research avenues opened by emerging 2D materials such as 2D oxides, 2D magnetic materials, and 2.5D hetero-structured and texturized materials. This Perspective also illustrates recent developments in experimental operando technique and computational methodologies that can be relevant in the field. Issues related to key performance parameters of 2D gas sensors are discussed from a perspective view against the performance of present state-of-the-art metal oxides-based gas sensing devices.

Nanoscale Engineering of P‐Block Metal‐Based Catalysts Toward Industrial‐Scale Electrochemical Reduction of CO2

AbstractThe efficient conversion of CO2 to value‐added products represents one of the most attractive solutions to mitigate climate change and tackle the associated environmental issues. In particular, electrochemical CO2 reduction to fuels and chemicals has garnered tremendous interest over the last decades. Among all products from CO2 reduction, formic acid is considered one of the most economically vital CO2 reduction products. P‐block metals (especially Bi, Sn, In, and Pb) have been extensively investigated and recognized as the most efficient catalytic materials for the CO2 electroreduction to formate. Despite remarkable progress, the future implementation of this technology at the industrial‐scale hinges on the ability to solve remaining roadblocks. In this review, the current research status, challenges, and prospects of p‐block metal‐based catalysts primarily for CO2 electroreduction to formate are comprehensively reviewed. The rational design and nanostructure engineering of these p‐block metal catalysts for the optimization of their electrochemical performances are discussed in detail. Subsequently, the recent progress in the development of state‐of‐the‐art operando characterization techniques together with the design of advanced electrochemical cells to uncover the intrinsic catalysis mechanism is discussed. Lastly, a perspective on future directions including tackling critical challenges to realize its early industrial implementation is presented.

Review on the Degradation Mechanisms of Metal-N-C Catalysts for the Oxygen Reduction Reaction in Acid Electrolyte: Current Understanding and Mitigation Approaches.

One bottleneck hampering the widespread use of fuel cell vehicles, in particular of proton exchange membrane fuel cells (PEMFCs), is the high cost of the cathode where the oxygen reduction reaction (ORR) occurs, due to the current need of precious metals to catalyze this reaction. Electrochemists tackle this issue in the short/medium term by developing catalysts with improved utilization or efficiency of platinum, and in the longer term, by developing catalysts based on Earth-abundant elements. Considerable progress has been achieved in the initial performance of Metal-nitrogen-carbon (Metal-N-C) catalysts for the ORR, especially with Fe-N-C materials. However, until now, this high performance cannot be maintained for a sufficiently long time in an operating PEMFC. The identification and mitigation of the degradation mechanisms of Metal-N-C electrocatalysts in the acidic environment of PEMFCs has therefore become an important research topic. Here, we review recent advances in the understanding of the degradation mechanisms of Metal-N-C electrocatalysts, including the recently identified importance of combined oxygen and electrochemical potential. Results obtained in a liquid electrolyte and a PEMFC device are discussed, as well as insights gained from in situ and operando techniques. We also review the mitigation approaches that the scientific community has hitherto investigated to overcome the durability issues of Metal-N-C electrocatalysts.

Highly Reversible Chevrel Phase Mo6Se8 Cathode with Low Voltage Hysteresis for Rechargeable Aluminum Batteries.

Rechargeable aluminum (Al) batteries have attracted considerable interest as potential large-scale energy storage technologies due to the abundance, high theoretical capacity, and high safety of Al. We report here a highly reversible Al-Mo6Se8 prototype cell with low discharge-charge hysteresis (approximately 50 mV under 30 mA g-1 at 50 °C), ultra-flat discharge plateau, and exceptional cycle stability: the reversible capacity retaining at a steady 77 mA h g-1 after more than 1800 cycles. The Al intercalation-extraction mechanism is probed with ex situ and operando XRD techniques, revealing the reversible intercalation reaction from Mo6Se8 to Al4/3Mo6Se8. The stable electrochemical performance and unambiguous intercalation mechanism of the Al-Mo6Se8 system provide an alternative for beyond-lithium battery technologies.

Unraveling the Electronic Structure and Dynamics of the Atomically Dispersed Iron Sites in Electrochemical CO2 Reduction.

Single-atom catalysts with a well-defined metal center open unique opportunities for exploring the catalytically active site and reaction mechanism of chemical reactions. However, understanding of the electronic and structural dynamics of single-atom catalytic centers under reaction conditions is still limited due to the challenge of combining operando techniques that are sensitive to such sites and model single-atom systems. Herein, supported by state-of-the-art operando techniques, we provide an in-depth study of the dynamic structural and electronic evolution during the electrochemical CO2 reduction reaction (CO2RR) of a model catalyst comprising iron only as a high-spin (HS) Fe(III)N4 center in its resting state. Operando 57Fe Mössbauer and X-ray absorption spectroscopies clearly evidence the change from a HS Fe(III)N4 to a HS Fe(II)N4 center with decreasing potential, CO2- or Ar-saturation of the electrolyte, leading to different adsorbates and stability of the HS Fe(II)N4 center. With operando Raman spectroscopy and cyclic voltammetry, we identify that the phthalocyanine (Pc) ligand coordinating the iron cation center undergoes a redox process from Fe(II)Pc to Fe(II)Pc-. Altogether, the HS Fe(II)Pc- species is identified as the catalytic intermediate for CO2RR. Furthermore, theoretical calculations reveal that the electroreduction of the Pc ligand modifies the d-band center of the in situ generated HS Fe(II)Pc- species, resulting in an optimal binding strength to CO2 and thus boosting the catalytic performance of CO2RR. This work provides both experimental and theoretical evidence toward the electronic structural and dynamics of reactive sites in single-Fe-atom materials and shall guide the design of novel efficient catalysts for CO2RR.

In Situ and Operando Characterization Techniques in Stability Study of Perovskite-Based Devices

Metal halide perovskite materials have demonstrated significant potential in various optoelectronic applications, such as photovoltaics, light emitting diodes, photodetectors, and lasers. However, the stability issues of perovskite materials continue to impede their widespread use. Many studies have attempted to understand the complex degradation mechanism and dynamics of these materials. Among them, in situ and/or operando approaches have provided remarkable insights into the degradation process by enabling precise control of degradation parameters and real-time monitoring. In this review, we focus on these studies utilizing in situ and operando approaches and demonstrate how these techniques have contributed to reveal degradation details, including structural, compositional, morphological, and other changes. We explore why these two approaches are necessary in the study of perovskite degradation and how they can be achieved by upgrading the corresponding ex situ techniques. With recent stability improvements of halide perovskite using various methods (compositional engineering, surface engineering, and structural engineering), the degradation of halide perovskite materials is greatly retarded. However, these improvements may turn into new challenges during the investigation into the retarded degradation process. Therefore, we also highlight the importance of enhancing the sensitivity and probing range of current in situ and operando approaches to address this issue. Finally, we identify the challenges and future directions of in situ and operando approaches in the stability research of halide perovskites. We believe that the advancement of in situ and operando techniques will be crucial in supporting the journey toward enhanced perovskite stability.

The Entanglement of Li Capping and Deposition: An Operando Optical Microscopy Study.

Dendrite growth and low Coulombic efficiency impede the practical application of Li-metal batteries. As such, monitoring Li deposition and stripping in real-time is crucial to understanding the fundamental lithium growth kinetics. This work presents an operando optical microscopic technique that enables precise current density control and quantification of Li layer properties (i.e., thickness and porosity) to study Li growth in various electrolytes. We discover the robustness and porosity of the remaining capping layer after the Li stripping process as the critical features governing the subsequent dendrite propagation behavior, resulting in distinct capping and stacking phenomena that affect Li growth upon cycling. While dendrite propagation quickly occurs through the fracture of the fragile Li capping layer, uniform Li plating/stripping can be facilitated by the compact and robust capping layer even at high current densities. This technique can be extended to evaluate dendrite suppression treatments in various metal batteries, providing in-depth information on metal growth mechanisms.

Structure Dynamics of Carbon-Supported Platinum-Neodymium Nanoalloys during the Oxygen Reduction Reaction

Platinum-rare earth nanoalloys have been predicted to be promising proton exchange membrane fuel cell (PEMFC) electrocatalysts for the cathodic oxygen reduction reaction (ORR). However, their implementation in PEMFCs is limited by the challenge of their preparation as carbon-supported nanostructures. Consequently, the practical structure–activity–stability trends for this class of nanoalloys remain largely unexplored. Herein, carbon-supported Pt–Nd nanoalloys as ORR electrocatalysts are described. The physical chemistry of selected electrocatalysts was extensively investigated by means of combined ex situ and operando techniques, which reveal the unique structural dynamics of Pt–Nd nanoalloys in a simulated PEMFC cathode environment. The experimental observations, supported by theoretical calculations, indicate that after initial significant structural modification in the early stage of operation, the ORR activity is mediated in the longer term by surface compressive strain rather than charge transfer between Pt and Nd. Such key operando structure–activity–stability relations underpin further optimization of carbon-supported Pt-rare earth nanoalloys as fuel cell cathode catalysts.

Revealing active Cu nanograins for electrocatalytic CO2 reduction through operando studies

AbstractCopper (Cu) has been regarded as a highly efficient electrocatalyst for the conversion of CO2 into a multicarbon product. However, the catalytic mechanism and the active sites of Cu catalysts under operating conditions still remain elusive. Yang's team applied systematic operando characterization techniques to provide a quantitative analysis of the valence states and the chemical environment of Cu nanocatalysts under electrochemical reaction conditions, which clearly reveal the evolution of Cu nanocatalysts before and after the entire electrochemical CO2 reduction.

In Situ/Operando Methods for Understanding Electrocatalytic Nitrate Reduction Reaction.

With the development of industrial and agricultural, a large amount of nitrate is produced, which not only disrupts the natural nitrogen cycle, but also endangers public health. Among the commonly used nitrate treatment techniques, the electrochemical nitrate reduction reaction (eNRR) has attracted extensive attention due to its mild conditions, pollution-free nature, and other advantages. An in-depth understanding of the eNRR mechanism is the prerequisite for designing highly efficient electrocatalysts. However, some traditional characterization tools cannot comprehensively and deeply study the reaction process. It is necessary to develop in situ and operando techniques to reveal the reaction mechanism at the time-resolved and atomic level. This review discusses the eNRR mechanism and summarizes the possible in situ techniques used in eNRR. A detailed introduction of various in situ techniques and their help in understanding the reaction mechanism is provided. Finally, the current challenges and future opportunities in this research area are discussed and highlighted.

Irreversible Electrochemical Reaction at High Voltage Induced by Distortion of Mn and V Structural Environments in Na4MnV(PO4)3

As the importance of developing low-cost and high-capacity materials is emerging, Mn-based Na4MnV(PO4)3 positive electrode materials that allow multiredox reactions are in the spotlight for Na-ion batteries. The structure that gives highly reversible electrochemical reactions, when two Na+ (out of four) are de-inserted, deteriorates rapidly when the third Na+ is extracted at high voltage, resulting in poor cyclability. In this work, using synchrotron-based operando techniques, we perform long-range and local structural analyses to determine the origins of the rapid structural decay of Na4MnV(PO4)3 when the third Na+ is extracted. Operando XRD shows a significant change in the crystal structure (c parameter increases rapidly) as the occupancy of the Na (1) site decreases at high voltage. The local environments of Mn and V, monitored by operando XAS, remain rather symmetrical up to the extraction of two Na+, while both Mn and V show drastic local distortions when the third Na+ is extracted. These structural degradations are found to further progress when cycling to high voltage. This study presents important aspects of how local and long-range structure modifications can affect the electrochemical performance in multiredox NASICON materials.

Experimental and Computational Aspects of Electrochemical Reflection Anisotropy Spectroscopy: A Review

AbstractElectrode/electrolyte interfaces play a crucial role in many electrochemical energy conversion and storage technologies. Hence, a deep understanding of the interfacial structure, energetic alignment and processes is of high relevance and has triggered the development of a number of in situ and operando techniques. One approach for gaining information about the change in surface chemistry and structure on an atomic scale is reflection anisotropy spectroscopy (RAS). This review presents and discusses the continuing effort to develop RAS as an in situ optical probe for solid‐liquid interfaces under applied potentials. Experimental and computational basic principles are presented and key challenges of electrochemical RAS are highlighted. Furthermore, we exemplarily demonstrate the potential of the method for spectroelectrochemistry, focusing on indium phosphide‐ and gold‐aqueous electrolyte interfaces as exemplary case studies, and outline research directions for battery systems.

Understanding the effect of MXene in a TMO/MXene hybrid catalyst for the oxygen evolution reaction

Very recently, it has been reported that mixed transition metal oxide (TMO)/MXene catalysts show improved performance over TMO only catalysts for the oxygen evolution reaction (OER). However, the reasoning behind this observation is unknown. In this work mixed Co(OH)2/Ti3C2Tx were prepared and characterized for the OER using ex situ and operando spectroscopy techniques in order to initiate the understanding of why mixed TMO/MXene materials show better performances compared to TMO only catalysts. This work shows that the improved electrocatalysis for the composite material compared to the TMO only catalyst is due to the presence of higher Co oxide oxidation states at lower OER overpotentials for the mixed TMO/MXene catalysts. Furthermore, the presence of the MXene allows for a more mechanically robust film during OER, making the film more stable. Finally, our results show that small amounts of MXene are more advantageous for the OER during long-term stability measurements, which is linked to the formation of TiO2. The sensitivity of MXene oxidation ultimately limits TMO/MXene composites under alkaline OER conditions, meaning mass fractions must be carefully considered when designing such a catalyst to minimize the residual TiO2 formed during its lifetime.

Novel <i>operando</i> observation technique based on combined optical coherence tomography–thermogravimetry for monitoring internal structural changes of drying ceramic slurries

In the wet forming of ceramics, it is critical to control the cracking and deformation of the ceramic slurry during the drying process. This necessitates a comprehensive understanding of the changes in the internal structure of the slurry during the drying process using a high-resolution technique that enables direct and high speed observation. In this study, a combined system of optical coherence tomography (OCT) and thermogravimetry (TG) was developed for the operando observation of the evolution of the internal structure of a drying SiO2 slurry. In the early stages of drying, the OCT signal intensity changed significantly owing to the Brownian motion of the SiO2 particles in the slurry. The slurry was found to shrink as it dried and then lose its fluidity, and the ceramic particles were found to agglomerate from the surface. In the final stages of drying, localized dry regions developed in the vicinity of the slurry surface and expanded with drying. Crack formation was also observed in a part of the localized dry regions. Therefore, crack formation was attributed to inhomogeneous drying-induced shrinkage and stress generated in the drying object during the progression of localized drying. The novel operando observation technique using combined OCT-TG is successfully demonstrated to be an effective approach for understanding the internal structural changes in opaque slurries during their drying.