Analysis Of Relaxation Times Research Articles

Investigating Cell Wall Diffusion in Wood Modified with Phenol Urea Formaldehyde Resin in Different Length Scales.

Wood modification using low molecular weight thermosetting resins improves the biological durability and dimensional stability of wood while avoiding increasingly regulated biocides. During the modification process, resin monomers diffuse from the cell lumen to the cell wall, occupying micropore spaces before in situ curing at 150 °C. This study investigated the mechanism of cell wall diffusion at multiple scales, comparing two test groups where diffusion was either facilitated or restricted. Antiswelling efficiency tests demonstrated improved dimensional stability when diffusion was facilitated. Differential scanning calorimetry showed that bound water was excluded more effectively from the cell wall if cell wall diffusion was enabled. Solid-state NMR spectroscopy (1H MAS and 13C MAS) with relaxation time analysis indicated that resin migrated to distinct locations within the cell wall, influenced by diffusion and drying conditions. These findings highlight how optimizing cell wall diffusion can significantly improve the performance of wood modification processes using thermosetting resins.

Temperature Dependence of Intermolecular Dynamics and Liquid Properties of Deep Eutectic Solvent, Reline.

We investigated the temperature dependence of the intermolecular dynamics, including intermolecular vibrations and collective orientational relaxation, of one of the most typical deep eutectic solvents, reline, using femtosecond Raman-induced Kerr effect spectroscopy (fs-RIKES), subpicosecond optical Kerr effect spectroscopy (ps-OKES), and molecular dynamics (MD) simulations. According to fs-RIKES results, the temperature-dependent intermolecular vibrational band peak at ∼90 cm-1 exhibited a redshift with increasing temperature. The density-of-state (DOS) spectrum of reline by MD simulations reproduced this fs-RIKES spectral feature. The decomposition analysis of the DOS spectra showed that all constituent components, including urea, cholinium cation, and chloride anion, also exhibited similar magnitudes of redshifts upon heating, indicating that the three species intermolecularly interact one another. The temperature sensitivity of the intermolecular vibrational frequency was high compared to that of ionic liquids. According to ps-OKES results, the slow orientational relaxation rate increased with increasing temperature; however, this phenomenon was not well explained by the Stokes-Einstein-Debye hydrodynamic model. Analysis of the orientational relaxation time based on the Stokes-Einstein-Debye model indicates that the decoupling between the orientational relaxation time and viscosity occurs at temperatures below ∼330 K. Quantum chemistry calculations of urea and the cholinium cation based on the MP2/6-311++G(d,p) level of theory confirmed that the contribution of intramolecular vibrational bands to low-frequency bands below 200 cm-1 was minimal. The densities, viscosities, electrical conductivities, and surface tensions of reline at various temperatures were also estimated and compared with the dynamics data.

A Comparative Study of the Oxygen Reduction Reaction on Pt and Ag in Alkaline Media

AbstractInvestigating the ORR under practical conditions is vital for optimizing metal–air batteries and alkaline fuel cells. Herein, we characterized Pt and Ag gas diffusion electrodes (GDE) in a GDE half‐cell in high alkaline concentrations at elevated temperatures by polarization curves and electrochemical impedance spectroscopy (EIS) combined with the distribution of relaxation times (DRT) analysis. The Pt catalyst's polarization curve displays substantial losses below 0.82 V vs. RHE. The DRT analysis reveals significantly increased charge transfer resistance and a decelerated ORR at that potential. RRDE measurements attributed the polarization loss observed for Pt catalysts to increased peroxide formation in this potential region triggered by the desorption of oxygenated species. Therefore, the ORR activity of Ag exceeds some of the here‐used Pt catalysts at high current densities. This work combines the benefits of the RRDE and the GDE half‐cell to study catalysts and identify the reaction mechanisms under conditions relevant to practical fuel cells and batteries. Moreover, the DRT analysis is introduced as an analytical tool to determine the charge transfer resistance contribution and the corresponding frequency of the ORR.

Synergistic analysis of oxygen transport resistance in polymer electrolyte membrane fuel cells

The oxygen transport resistance of polymer electrolyte membrane fuel cells operated under various conditions (e.g., temperature and relative humidity) was separated into molecular diffusion, Knudsen diffusion, and ionomer film (IF) resistances using the catalyst agglomerate model, dissection of oxygen transport resistance, and distribution of relaxation time analysis. Simultaneously, an analysis of resistance, including charge transfer, proton transfer, and high-frequency resistances, was performed. The Knudsen diffusion resistance of the catalyst layer was calculated by assessing the effects of relative humidity on porosity and pore size. Oxygen transport resistance was analyzed to establish a correlation between temperature, relative humidity, and IF resistance. Water negligibly impacted performance at low oxygen levels at all examined current densities. The fractional contributions of molecular diffusion, Knudsen diffusion, and IF resistances obtained using oxygen transport analysis could be effectively applied to mass transport resistance in the distribution of relaxation time analysis. The IF resistance in the catalyst layer was up to eight times higher than the Knudsen diffusion resistance and 150 times higher than the proton transfer resistance across all current densities, thus most strongly contributing to the catalyst layer resistance. In the gas diffusion layer, the molecular diffusion resistance was up to four times higher than the Knudsen diffusion resistance. Thus, we examined the relationship between the mass transport resistances of individual elements and IF behavior under different operating conditions, revealing that the design of the IF in the catalyst should be considered alongside the relationship between the gas diffusion layer and membrane for optimal performance.

Interface Degradation of LaCl3-Based Solid Electrolytes Coupled with Ultrahigh-Nickel Cathodes.

Despite competitive compatibility with high-nickel cathodes, chloride solid electrolytes (SEs) still experience inevitable side reactions at the cathode/SE interface, causing capacity decay in all-solid-state lithium batteries (ASSLBs) during cycling. Herein, a three-electrode ASSLB testing device is developed to comprehensively reveal the interface failure mechanisms of the ultrahigh-nickel LiNi0.92Co0.05Mn0.03O2 (NCM92) cathode paired with LaCl3-based chloride SE Li0.447La0.475Zr0.059Ta0.179Cl3 (LLZTC). Distribution of relaxation time (DRT) analysis clearly shows the ASSLB degradation accompanied by a significant NCM92/LLZTC interface impedance increase, which becomes more pronounced at the higher cutoff charging voltage of 4.8 V vs Li+/Li. Furthermore, time-of-flight secondary ion mass spectrometry (ToF-SIMS) and focused ion beam scanning electron microscopy (FIB-SEM) analysis also confirm the deterioration arising from active lattice oxygen and loss of physical contact at the NCM92/LLZTC interface. These findings reveal both electrochemical degradation and physical contact failure at the cathode/SE interface as key causes of the ASSLBs' capacity decay.

Deciphering Anion Exchange Membrane Water Electrolysis: A Distribution of Relaxation Times Approach

Anion exchange membrane water electrolysis (AEM-WE) stands out as a promising method for hydrogen production from renewable energy sources. Unlike proton exchange membrane water electrolysis (PEM-WE), AEM-WE offers the advantage of nonprecious metal catalysts due to mild alkaline conditions, while still enabling a compact cell design and operation under differential pressure. Remarkable performances of AEM-electrolysis cells have been demonstrated in literature, achieving current densities of up to 7.68 A·cm−2 [1], surpassing the record current density of PEM-WE at 6 A·cm−2 [2], both measured at 80 °C and 2 V. However, challenges related to efficiency and stability persist and demand effective solutions to unlock the full potential of AEM-WE. In order to achieve this, cell components, particularly the membrane, catalysts, and electrode structure have to be improved and advanced measurement techniques have to be applied.Different measurement tools serve to characterize, separate, and quantify the dynamic processes inherent in AEM-WE. Electrochemical impedance spectroscopy (EIS) serves as a valuable non-destructive, in-situ diagnostic tool for electrochemical cells, enabling the differentiation of various phenomena based on their respective relaxation times. Moreover, EIS enables the quantification of loss mechanisms thereby facilitating a targeted optimization of electrolysis components and the identification of weaknesses limiting long-time stability.Despite its utility, the broad use of EIS is hindered by its complex interpretation. The widely applied approach of fitting equivalent circuit models (ECMs) aims to extract quantitative data from the semi-circular shapes observed in Nyquist plots. However, the assumption of a physico-chemical meaningful ECM is challenging without prior knowledge of the number, size, and time constants of appearing loss mechanisms. Furthermore, the potential for multiple ECMs to fit one and the same experimental result introduces ambiguity, leading to potential misinterpretations of data.An alternative approach to analyse EIS spectra involves converting the measured data into the time (τ) domain and characterize the different mechanisms based on their characteristic relaxation times. The distribution of relaxation times (DRT) analysis has already been applied across diverse electrochemical systems, spanning from solid oxide fuel cells (SO-FC) and PEM fuel cells (PEM-FC) to PEM water electrolysis and AEM fuel cells (AEM-FC). However, to the best of the authors’ knowledge, DRT analysis of AEM-WE is still absent in literature.In this study we present a thorough investigation of an AEM-WE single-cell, employing a combination of electrochemical impedance spectroscopy (EIS) and the equivalent circuit model (ECM). Notably, we demonstrate the distribution of relaxation times (DRT) analysis at AEM-WE cells for the first time, utilizing a reversible hydrogen electrode (RHE) as a reference. Through half-cell EIS measurements and subsequent DRT spectra analysis, anodic and cathodic half-cell reactions are clearly identified and quantified. The DRT analysis differentiates five loss mechanisms within the AEM-WE system, encompassing the hydrogen evolution reaction, the oxygen evolution reaction, and ionic transport losses within the catalyst layers. By systematically varying operating parameters, we successfully attribute DRT peaks to their respective physicochemical origins. These findings provide valuable insights into the electrochemical processes within the AEM-WE single-cell, significantly advancing our understanding of underlying mechanisms.In fig. 1, we investigate the degradation of AEM-WE single cells through long-term experiments. Periodic EIS measurements enable an in-operando analysis of catalyst degradation. The impedance data is analysed using ECM and DRT. Ohmic contributions resulting from electric and ionic charge transport are distinguished from polarisation resistances arising from electrochemical reactions. A catalyst degradation is observable in fig 1b & c, where the low frequency resistance (LFR) in the Nyquist plot and the DRT peak area increases over time. However, fig. 1b also reveals the reduction of the high frequency resistance (HFR) resulting in an overall performance increase and voltage decrease.[1] N. Chen, S. Y. Paek, J. Y. Lee, J. H. Park, S. Y. Lee, Y. M. Lee, High-performance anion exchange membrane water electrolyzers with a current density of 7.68 a cm −2 and a durability of 1000 hours, Energy & Environmental Science 14 (12) (2021) 6338–6348. doi:10.1039/D1EE02642A.[2] M. Braig, R. Zeis, Distribution of relaxation times analysis of electrochemical hydrogen pump impedance spectra, Journal of Power Sources 576 (2023) 233203. doi:10.1016/j.jpowsour.2023.233203. Figure 1

Unraveling the Sequential Effect of Dual-Layered Hybrid Graphite Anodes on Electrode Utilization during Fast-Charging Li-Ion Batteries

The efficient and fast recharging of Li-ion batteries without compromising capacity or safety is paramount in advancing energy storage technologies. This study addresses this challenge by developing a novel electrode design known as dual-layer electrode (DLE) technology, achieved via a carefully orchestrated sequential coating process involving two distinct anode materials. The primary objective is to minimize cell polarization, a critical factor impacting charging efficiency and battery longevity, particularly at higher charging currents.The research employs advanced electrochemical techniques such as electrochemical impedance spectroscopy (EIS) and distribution of relaxation times (DRT) analysis to delve into the dynamic evolution of electrode impedances. Notably, synthetic graphite (SG) exhibits varying impedance characteristics with changes in the state of charge (SOC), contrasting with the relatively stable impedance observed in natural graphite (NG) across SOC variations. This fundamental difference is a critical determinant in arranging NG and SG layers within the DLE, strategically considering the temporal SOC gradient encountered during fast charging cycles.The study leverages simulation models alongside experimental validation to ascertain the optimal positioning of NG and SG layers within the DLE structure. The results demonstrate that placing NG atop SG in the DLE configuration significantly reduces overall resistance, leading to remarkable performance gains. Specifically, the DLE exhibits a remarkable 61.0% capacity retention over 200 cycles when charged at a 4 C rate (equivalent to a 15-minute charging duration). This performance surpasses counterparts with reversed sequential coating and even outperforms single-layer electrodes utilizing either NG or NG/SG mixed electrodes.Furthermore, this research contributes valuable insights into the combinatorial sequence for multi-layer coating of various active materials, particularly in thick-electrode designs. The findings hold significant implications for advancing the development of high-performance Li-ion batteries tailored for fast-charging applications across diverse sectors by achieving lower resistivity and enhanced charging efficiency.

(Invited) Bi-Functional Oxygen Electrodes for Reversible Solid Oxide Cells

Solid oxide electrochemical cells operated reversibly in fuel cell and electrolysis modes (rSOCs), can enable the incorporation and integration of far greater amounts of solar and wind energy into our power grid. When deployed as islanded systems, they can also function as distributed generation systems thereby decreasing our reliance on the power grid. In this talk, we present results on rSOCs based on rare earth nickelate – rare-earth doped ceria composite oxygen electrodes that exhibit excellent reversible behavior when switched cyclically between solid oxide fuel cell (SOFC) and solid oxide electrochemical cell (SOEC) modes of operation. The cyclic mode-switching operation mitigates against cell degradation when compared to operating in single mode operation in electrolysis mode. Further, we have used distribution of relaxation times (DRT) analysis of impedance spectra obtained from single-mode (electrolysis) operated cells, and cells operated in switched-modes, to obtain clues into cell degradation mechanisms.

Interphase-Controlled Composite Electrolyte Based on LLZTO-Ionic Liquid for All Solid-State Battery

Solid-state electrolytes (SSEs) are promising alternatives to conventional liquid organic electrolytes in lithium-ion batteries (LIBs), primarily due to their non-flammability and potential to reduce battery size. SSEs are categorized into three types: solid polymer electrolytes (SPEs), inorganic ceramic electrolytes (ICEs), and composite solid electrolytes (CSEs). Solid polymer electrolytes (SPEs) offer good interface contact with electrodes but suffer from low ionic conductivity and poor mechanical stability. In contrast, inorganic ceramic electrolytes (ICEs) exhibit high ionic conductivity and excellent mechanical stability but have weak electrode contact due to stiffness. Composite solid electrolytes (CSEs) aim to combine the advantages of both SPEs and ICEs, utilizing inorganic filler and polymer host to enhance conductivity, mechanical stability, and electrode contact. Understanding the mechanisms behind the enhanced ionic conductivity of CSEs is important to getting the key. Previous studies have investigated various factors, including the type and morphology of fillers, with active fillers showing promise in improving conductivity by facilitating extra Li-ion transport and maintaining the amorphous phase of the polymer. However, the exact cause of enhanced conductivity remains unclear.This study proposes the use of ionic liquids to exclude the amorphous effect of polymers and compares the ionic conductivity with active fillers. Additionally, nanoparticles are introduced to form a solid phase without additional solvents, enhancing filler-polymer contact and promoting thixotropy in the electrolyte, which improves safety and stability. To investigate the interphase effect between filler and matrix, our study focuses on controlling the vacancy concentration on the filler surface using garnet-type oxide as the filler material. X-ray photoelectron spectroscopy (XPS) analysis reveals a difference in oxygen vacancy (O-v) concentration between raw material and filled powder, indicating the influence of surface vacancies on ionic conductivity. Experimental results show that the addition of fillers increases the ionic conductivity of electrolytes, with lower oxygen vacancy concentrations leading to higher ionic conductivity. Distribution of relaxation time (DRT) analysis indicates low resistance in the electrolyte at most timescales, especially showing low diffusion resistance, suggesting improved ion transport properties. COMSOL Multiphysics simulations prove consistent electrolyte current density from the whole electrolyte, inducing uniform ion flux to electrodes. Laser-induced breakdown spectroscopy (LIBS) and XPS depth profiles confirm thin and uniform growth of the solid electrolyte interphase (SEI) layer, contributing to cycle stability.Overall, our study provides insights into the role of surface-controlled fillers in enhancing electrochemical properties and understanding ion-conduction mechanisms in composite solid electrolytes (CSEs). We explore the interphase effect between filler and matrix using Li conductive oxide. Vacancies on the filler surface impact electrolyte properties; fewer vacancies correlate with improved ionic conductivity and stability. Results show enhanced conductivity in surface-controlled electrolytes compared to host or composite electrolytes. Oxygen-filled electrolytes demonstrate superior thermal and electrochemical stability, promoting uniform SEI layer formation and enhancing specific capacity and cycle stability in Li metal half-cells. These findings contribute to developing safer, more efficient solid-state batteries for various applications. Figure 1

Physicochemical Impedance Modelling of Porous Electrodes in All-Solid-State Electrochemical Devices

Fundamental knowledge about performance limiting processes in electrochemical devices like battery-, fuel- and electrolyzer-cells is mandatory for a model-aided development. The method of choice to analyze these processes is electrochemical impedance spectroscopy, enabling a separation of electrochemical processes differing in their relaxation frequencies. In order to improve the deconvolution of these processes in the impedance spectrum, the distribution of relaxation times (DRT) analysis is a well-established method [1].In case of porous, multiphase electrodes, the DRT usually doesn’t enable a simple correlation of a peak in the DRT with a single polarization process in an electrode. The complex coupling of electronic and ionic charge transport via charge transfer reactions, often described by a transmission line model (TLM) [2-4], induces a number of peaks in the DRT. TLM parametrization just by operating and/or electrode parameter variations is often insufficient. Since different parameter sets can result in identical spectra [3], a straightforward CNLS-fit is insufficient and a pre-parameterization by determining at least a few model parameters independently is required.In this study, impedance spectra of two all-solid-state electrochemical devices, an all-solid-state battery and a solid oxide cell, are analyzed by the distribution of relaxation times. Physicochemically motivated impedance models based on the TLM-approach were derived, pre-parameterized and applied to quantify different loss processes in the cells. The pre-parameterization included microstructural parameters obtained by focus ion beam tomography and conductivity data. The model development and areas of application will be discussed in detail within this contribution, focusing on the differences between the two investigated all-solid-state electrochemical devices.

Study on Catalyst and Binder Degradation Analysis during Electrode Degradation Using EIS in PEMFC

Research is underway to reduce the cost of PEMFCs by decreasing the loading amount of Pt catalyst, which necessitates research on catalyst structures and binders to compensate for the resulting decrease in performance and durability. Recent studies have focused on improving performance using binders such as high oxygen permeation ionomer (HOPI), but research on the durability of such binders is lacking. The primary challenge in studying binder durability lies in the difficulty of binder degradation analysis. Since the binder in the catalyst layer exists in small quantities within the catalyst layer, and degradation is difficult to distinguish from membrane degradation, it is crucial to develop analysis methods to identify binder degradation. Distribution relaxation time (DRT) analysis is a method that utilizes Electrochemical Impedance Spectroscopy (EIS) to analyze resistance in detail by representing it as distribution relaxation time peaks. By using DRT analysis, the resistance in EIS can be subdivided into ORR charge transfer resistance, oxygen transfer resistance, and proton transfer resistance and changes in the ion transfer resistance of the catalyst layer can be analyzed in situ to observe binder degradation. In this study, we aim to analyze the degradation of catalyst and binder ionomer during electrode degradation using EIS in situ. In addition, we compare the electrochemical analysis results and post-analysis results with the EIS analysis results to examine the suitability for EIS analysis. Electrode degradation was carried out using the DOE catalyst degradation protocol. Characterization during electrode degradation included I-V, EIS, mass activity, CV, LSV, while post-degradation analysis involved AFM, XRD, XRF analysis to analyze electrode catalyst and binder degradation. As catalyst degradation progressed, the cell's performance decreased, leading to increased charge transfer resistance (CTR), decreased electrochemical surface area (ECSA), and decreased mass activity. Catalyst degradation was observed through changes in ORR charge transfer resistance in DRT analysis, while binder degradation was confirmed through changes in proton transfer resistance in DRT results and Warburg-like response impedance. The results obtained from the postmortem of degraded MEAs matched well with the results obtained from DRT analysis.

Kinetic Investigation of Electrode Reaction Processes on Ni-GDC Cermet Fuel Electrodes for Reversible Solid Oxide Cells

Introduction Reversible solid oxide cells (r-SOCs) are electrochemical energy devices that can reversibly switch between power generation by fuel cell operation (SOFC mode) and hydrogen production by steam electrolysis (SOEC mode). R-SOCs can adjust the demand and supply in renewable energy utilization. In order to design high performance and durable r-SOC electrodes for practical usage, it is essential to systematically understand the electrode reaction processes and electrode degradation factors in both SOFC and SOEC modes. Such fundamental information is also necessary for the analysis of electrode performance and the development of performance simulation models. The dependence of polarization resistance on electrode fabrication conditions and operating conditions has been investigated using steady-state polarization and impedance measurements for electrode materials used in either SOFCs or SOECs, and rate-determining reactions have also been discussed [1-5]. However, it is necessary to evaluate the electrode reaction mechanisms of electrode materials suitable for r-SOC operation in an integrated and detailed manner. Therefore, this study aims to systematically evaluate the similarities and differences in the fuel electrode reaction processes in both SOFC and SOEC modes from the viewpoint of dependence on operating conditions by using the distribution of relaxation times (DRT) analysis. Experimental As shown in Figure 1 (a), Ni-GDC cermet, a composite of Ni and mixed-conducting Gd0.9Ce0.1O2 (GDC), was used as the fuel electrode material, ScSZ as the electrolyte, and (La0.6Sr0.4)(Co0.2Fe0.8)O3 (LSCF) as the air electrode. GDC layer was inserted between the air electrode and the electrolyte plate as a buffer layer. Electrochemical impedance measurements were performed by supplying H2-H2O gas mixture to the fuel electrode of the fabricated cell, and varying operating temperature, H2-H2O ratio, and current density. Measurements were carried out in both SOFC and SOEC modes. The obtained impedance data were subjected to the DRT analysis to separate the polarization resistance components of the fuel electrode in the relaxation time domain of the electrode response. The area of each DRT peak corresponds to the resistance of each electrode process from which each peak originates. In this study, the dependence of the resistance of each DRT peak on the operating conditions was quantitatively investigated. As shown in Figure 1 (b), the microstructure of the electrodes was observed using FIB-SEM, confirming a porous electrode structure. Results and Discussion Figure 1 (c) shows the operating temperature dependence of the typical DRT peaks of the Ni-GDC cermet fuel electrode, in SOFC mode. In the range of 10-1 to 106 Hz where the frequency response was measured, three main DRT peaks appeared, P1: 10-1 to 100 Hz, P2: 100 to 102 Hz, and P3: 102 to 103 Hz, all DRT peak areas decreased with increasing operating temperature. In the presentation, the dependence of each DRT peak on operating parameters and the related electrode reaction processes will be discussed.

(Digital Presentation) In-Situ Quantification of Individual Electrode Polarization and Depth Validation of the Distribution of Relaxation Times Methods Feasibility in PEM Fuel Cell

The article titled "Dynamics of anion exchange membrane electrolysis: Unravelling loss mechanisms with electrochemical impedance spectroscopy, reference electrodes and distribution of relaxation times" explores the challenges and mechanisms in anion exchange membrane water electrolysis (AEM-WE). The study by Matthias Ranz and colleagues employs electrochemical impedance spectroscopy (EIS), half-cell measurements using a reversible hydrogen electrode (RHE), and distribution of relaxation times (DRT) analysis to delve into the dynamics of AEM-WE cells.AEM-WE is gaining attention as a promising technology for hydrogen production due to its potential cost benefits over conventional electrolysis systems. However, its adoption faces obstacles such as efficiency issues and high degradation rates. To address these challenges, the research employs detailed electrochemical characterization techniques, providing new insights into the operational dynamics of AEM-WE cells.The study reveals five major loss mechanisms within AEM-WE systems: hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and ion transport losses, among others, occurring mostly within the catalyst layers. The findings also discuss the influence of various operating parameters on these loss mechanisms and how they can be systematically tracked and analyzed through EIS.A significant aspect of the research is the application of DRT analysis, a method not previously used in AEM-WE studies. This analysis method helps in identifying and quantifying the different electrochemical phenomena contributing to cell losses. By correlating these phenomena with their physicochemical origins, the study enhances understanding of the underlying processes within AEM-WE cells.Moreover, the use of equivalent circuit models in conjunction with EIS data provides a deeper understanding of the electrochemical behavior of the system. This combined approach allows for a more precise characterization of the impedance features and the differentiation of processes such as ion transport and electrochemical reactions.Ultimately, the research highlights the complexity of the AEM-WE process and emphasizes the need for advanced diagnostic tools to optimize performance and stability. By pinpointing the specific causes of efficiency losses and identifying opportunities for material and process improvements, the study contributes significantly to the development of more robust and efficient AEM-WE systems.In conclusion, the research not only elucidates the various loss mechanisms in AEM-WE but also showcases the potential of advanced electrochemical techniques like EIS and DRT in enhancing the understanding and optimization of this promising hydrogen production technology. This work sets a foundation for future studies aimed at overcoming the limitations of AEM-WE and advancing towards its commercial viability.

Composition and Conductivity Evaluation of Cathode Active Materials/Solid Electrolytes for Lithium-Ion Batteries

Solid-state batteries have attracted considerable attention as innovative secondary batteries for future electric energy societies due to their high safety and energy density. In particular, sulphide-based solid electrolytes are positioned as promising materials for solid-state batteries due to their excellent ion conductivity properties. However, a challenge exists with sulfide-based solid electrolytes, as high lithium-ion conductivity resistance occurs upon contact with the positive electrode active material due to the formation of a lithium-ion deficiency layer. Previous studies have shown that reducing interface resistance can be reduced by coating the active material with lithium-ion conductors such as LiNbO3. It is believed that by structuring the active material and solid electrolyte to conduct ions through a buffer layer, the lithium ion deficiency can be reduced, and the electrical potential barrier of lithium ions near the interface can be suppressed. However, the ion conduction mechanism at the interface between the active material and solid electrolyte formed by uniformly coating of the active material has not been sufficiently elucidated.This study aims to elucidate the ion conduction mechanism at the interface between the positive electrode active material crystal and the solid electrolyte by achieving uniform coating of a buffering layer. We aim to achieve uniform coating driven by the evaporation of a mixed solution of LiTaO3 dispersed in water and LiCoO2 crystals. Furthermore, by preparing electrodes using only binders without the use of conductive agents via a paste method, we aim to reduce factors related to resistance and elucidate the ion conduction mechanism at specific interfaces.For the coating of the buffer layer on the active material crystal, a LiTaO3 water solution obtained from an external source was prepared, and a LiCoO2 crystal dispersion solution was prepared, and the influence on coating under different conditions of LiTaO3 concentration and heat treatment temperature for LiCoO2 crystals was investigated.Scanning electron microscope (SEM) observations showed no change in the coating morphology under temperature conditions of 300 to 500°C. Additionally, X-ray photoelectron spectroscopy (XPS) showed no change in the dependence of the Ta bonding state on temperature conditions. However, it was confirmed that the weight ratio of Ta coated on the surface increased with the increasing concentration of LiTaO3. Subsequently, electrodes were prepared using slurry from synthesized active material/buffering layer composites, and ion conduction resistance was measured using impedance measurements. Ion conduction resistance dependent on the amount of coating was observed in composites synthesized at 400°C and 500°C. In composites synthesized at 300°C, a tendency for higher ion conduction resistance with less coating and an overall high resistance value were observed. Moreover, differential relaxation time (DRT) analysis revealed that the relaxation frequency of the main resistance component changed with increasing heat treatment temperature. However, no shift in relaxation frequency of resistance components was observed with coating amount.From these results, it was revealed that coating crystal morphology changes depending on the temperature conditions and coating amount changes depending on the concentration. Furthermore, synthesis of composites at high temperatures reduced Li-ion conduction resistance. This is believed to be due to atomic diffusion occurring at high temperatures during heat treatment, resulting in Ta bonding to the CoO2 structure on the surface of LiCoO2, continuously joining the interfaces. Additionally, it is believed that the reduction in grain boundary resistance occurred due to particle densification. In the future, solid-state batteries using sulfide-based solid electrolytes will be fabricated to investigate the suppression of lithium-ion conduction resistance and its conduction mechanism.AcknowledgementThis work was supported in part by Grant-in-Aid for Scientific Research (22H01847), Aichi Priority Research Program, the Strategic Innovation Program (SIP) of the Cabinet Office and by joint researches with industries.

(Invited) Study on the Effect of Additive in High Nickel NMC – Graphite Libs for HF- Scavenging and Stabilization of Cei Layer

Lithium ion batteries have been marked by steady progress over the past few decades owing to their high volumetric and gravimetric energy storage densities. The advent of LIBs resulted in the consistent shift of automotive industry towards hybrid EV's and BEV's. The Nissan Leaf, introduced in December 2010, became the first modern all-electric, zero tailpipe emission five door family hatchback to be produced for the mass market from a major manufacturer. Nissan has made constant efforts in improving the existing LIBs.With the advent of new high nickel cathode materials there has been an improvement in the energy density of LIBs and the ability to internalize the material supply chain. However, these cathode materials induce additional challenges due to instability of cathode electrolyte interface and dissolution of transition metals in the systems.[1-4]In the current work, electrolyte additive has been explored for stabilizing the cathode surface by stabilizing the cathode electrolyte interface in NMC811 and Graphite system in carbonate electrolyte system. The cycling data was analyzed with different capacity vs voltage and/current to identify the effect of additive and cycling degradation on the reaction kinetics and potentials. A methodology involving Distribution of Relaxation time (DRT) analysis, equivalent circuit design and electrochemical impedance fitting was developed to identify the different electrochemical components of the cell and their contribution towards the increase in internal resistance. The analysis was conducted during formation cycles and at different checkpoints for long cycling scenarios. The contribution of cathode and anode resistances were deconvoluted for the mixed impedance signal. Furthermore, XPS and TEM analysis were used to verify different features of the cathode and anode wherever applicable and feasible, to study the effect of the additive. Cui, Z., & Manthiram, A. (2023). Thermal Stability and Outgassing Behaviors of High‐nickel Cathodes in Lithium‐ion Batteries. Angewandte Chemie International Edition, 62(43), e202307243.Yu Wu, Xiang Liu, Li Wang, Xuning Feng, Dongsheng Ren, Yan Li, Xinyu Rui, Yan Wang, Xuebing Han, Gui-Liang Xu, Hewu Wang, Languang Lu, Xiangming He, Khalil Amine, Minggao Ouyang, Development of cathode-electrolyte-interphase for safer lithium batteries, Energy Storage Materials, Volume 37, 2021, Pages 77-86, ISSN 2405-8297.Hou, J., Lu, L., Wang, L. et al. Thermal runaway of Lithium-ion batteries employing LiN(SO2F)2-based concentrated electrolytes. Nat Commun 11, 5100 (2020).Yu Wang, Xuning Feng, Yong Peng, Fukui Zhang, Dongsheng Ren, Xiang Liu, Languang Lu, Yoshiaki Nitta, Li Wang, Minggao Ouyang, Reductive gas manipulation at early self-heating stage enables controllable battery thermal failure, Joule, Volume 6, Issue 12, 2022, Pages 2810-2820,ISSN 2542-4351.

Quantifying Individual Electrode Polarization and Elucidating Interactive Phenomena in PEM Fuel Cells

Fuel cells (FCs) that utilize hydrogen as fuel represent a clean and advanced energy conversion technology[1]. In the past two decades, FCs have achieved significant breakthroughs through the development of key materials and components. Nevertheless, quantifying the polarization and dynamics of individual electrodes and components under operating conditions remains a challenge for FC systems, which involve multiple physical and electrochemical processes. Electrochemical impedance spectroscopy (EIS), a widely used non-invasive technique, provides extensive information about the charge transport and reaction kinetics in the frequency domain[2]. The distribution of relaxation times (DRT) method further increases the resolution of the impedance in the relaxation domain[3]. In general, various physical and electrochemical processes occurring on the two electrodes manifest as peaks in the DRT plot. The areas corresponding to these peaks quantify the resistance contributed by each respective process. However, the DRT peaks are still highly convoluted, and additional efforts are required to assign the peak contributions and further separate the resistances of cathode processes and anode processes. In this work, we designed a Pt-wire (Au-wire) micro-reference electrode/ probe (MRE), which is laminated between two PEMs (Nafion® 212), and positioned centrally within the active area. The artifact-free impedance spectra of the cathode and anode under operating conditions were recorded by utilizing the pseudo-reference electrode. The DRT functions of the cathode and anode can add up to the total DRT function of the cell. Under these conditions, The ion conduction resistance, capacitance of the electrode, and contact resistance at the electrode∣∣MRE interface can be quantified. Multiple operation conditions including relative humidity of both electrodes, back pressures, and gas compositions are studied to verify the reliability of the DRT method in PEMFC research. Hence, this study offers a novel approach to guiding the development of high-performance PEMFC by quantifying the resistance associated with various processes in PEMFC components. Reference: [1] F. Xiao, T. Chen, Y. Peng, R. Zhang, Fault diagnosis method for proton exchange membrane fuel cells based on EIS measurement optimization, Fuel Cells, 22 (2022) 140-152.[2] J. Kwon, P. Choi, S. Jo, H. Oh, K.-Y. Cho, Y.-K. Lee, S. Kim, K. Eom, Identification of electrode degradation by carbon corrosion in polymer electrolyte membrane fuel cells using the distribution of relaxation time analysis, Electrochim. Acta, 414 (2022).[3] Y. Wang, N. Xu, X.-D. Zhou, Quantifying individual electrode polarization and unraveling the interactive phenomenon in solid oxide fuel cells, Next Energy, 1 (2023).

On Three Fundamental Questions Concerning Activity and Stability in Solid Oxide Cells

The aim of this presentation is to address three fundamental questions related to solid oxide cells: Are the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) indeed the rate-limiting steps in the high-performance of solid oxide cells, and how can we accurately quantify the area specific resistance of the oxygen electrode?What causes the phenomenon known as “electrochemically driven phase transformation,” and how can our understanding of this process be applied to create electrodes that are both high-performing and durable?How can we develop reliable accelerated testing protocols for both solid oxide fuel cells and solid oxide electrolysis cells, and which physical processes are being accelerated through these tests? The accurate quantification of electrode polarization in fuel cells and electrolyzers holds critical importance but presents a significant challenge due to the extensive overlap in polarizations from both the anode and cathode, whether in DC or AC measurements. This overlap creates a notable gap in our understanding of electrode behavior and in the development of electrochemical devices that are both high-performing and durable. In this presentation, I will introduce a reliable method for measuring the polarization of individual electrodes within a solid oxide cell. This technique is versatile and can be easily adapted for use in various types of electrochemical cells. Additionally, we will explore the limitations associated with using the distribution of relaxation times analysis for determining the polarization of individual electrodes.We will then address the origin for the phase transformation observed in an oxygen electrode during operation, as opposed to what is seen with thermally annealed materials. By integrating electronic conduction at the interface layer, we can significantly reduce the occurrence of phase transformation. This understanding of “electrochemically driven phase change” is crucial for the development of reliable accelerated testing protocols. Such protocols are essential in solid oxide fuel cell research to speed up the investigation of durability issues, quickly identify potential failure mechanisms, and ultimately estimate the lifespan of electrochemical cells. In our study, we compared solid oxide fuel cells operated at constant current density with those subjected to accelerated testing methods, which involve intermittent current injections. We have formulated a general accelerated testing framework, which will be presented in detail.Finally, we will present a theoretical model that underlies those three questions and can be used to address stability and durability issues in solid oxide cells. Acknowledgements: The presenter would like to thank Prof. Anil Virkar, Dr. Emir Dogdibegovic, and Dr. Yudong Wang, for their invaluable contributions to the work presented. This work was made possible through the support of projects DE-FE0026097, DE-FE0031667, DE-AR0001346, and DE-FE0032110.

Method for Precise Oxygen Resistance Analysis in Polymer Electrolyte Membrane Fuel Cells Under Various Operating Conditions

The simultaneous changes occurring in the internal materials of Polymer Electrolyte Membrane Fuel Cells (PEMFCs) under dynamic operating conditions make characterizing the inherent resistance of each material under different operating conditions highly complex. Therefore, the isolation of the internal resistance of components and the identification of the resistance elements that significantly affect PEMFC performance are essential, but comprehensive studies analyzing the internal resistance under different operating conditions have been scarce.This study proposes a complex resistance analysis methodology capable of isolating the oxygen resistance of a PEMFC single cell under different operating conditions (relative humidity, temperature, supply gas). The Knudsen diffusion within the catalyst layer is calculated according to the operating conditions using a catalyst agglomerate model. This calculation is combined with the dissection of the oxygen transport resistance to distinguish between molecular diffusion, Knudsen diffusion and ionomer film resistance under limiting current density conditions. In addition, an equation has been developed that accurately predicts the ionomer film resistance as a function of changes in temperature and RH, proposing a new approach to mapping ionomer film resistance. Then, by inputting three forms of resistance from the dissection of the oxygen transport resistance analysis as percentages into the distribution of relaxation time analysis, the newly developed methodology gives insight into the contributions of seven different resistance elements at different current densities. This provides an indicator for determining ionomer resistance without the need for temperature and RH experiments. In addition, this research identifies the design of the ionomer within the catalyst layer as a key determinant of PEMFC cell performance, highlighting the significant impact that molecular or Knudsen diffusion can have depending on operating conditions. Consequently, through an in-depth analysis of oxygen stability under different operating conditions, this study will provide essential insights for future PEMFC cell design.

Impact of Electrode Reversal Method on Electrode Degradation By High-Potential Environment in Polymer Electrolyte Membrane Fuel Cells

Polymer electrolyte membrane fuel cells (PEMFCs) are key energy conversion devices, that address global energy challenges and climate change and are prized for various applications due to their high efficiency, low operating temperature, fast startup, and low toxic emissions. Enhancing PEMFC durability is crucial for advancing commercialization. Thus, prioritizing research on Catalyst Layer (CL) degradation mechanisms of Membrane Electrode Assembly (MEA) and developing analytical methods to understand extreme degradation conditions are becoming imperative.In PEMFCs’ operational scenarios, various issues deteriorate the membrane electrode assembly (MEA) of PEMFCs, leading to irreversible performance declines. These include Pt dissolution, ionomer degradation, carbon corrosion [1], and occasional membrane mechanical issues. Of these, the electrochemical carbon oxidation reaction is particularly detrimental, causing a significant reduction in electrochemical double layer capacitance (EDLC), the formation of oxygen functional groups in carbon supports, and substantial deterioration in electrochemical surface area (ECSA) [2, 3], ultimately leading to degraded PEMFC performance.On the other hand, reversible performance degradation occurs during fuel cell operation, which specific operational recovery procedures can rectify. Mechanisms contributing to reversible voltage degradation include the platinum oxide formation, adsorption of impurity ions and contaminants on the catalyst surface, water flooding/dehydration, and oxidation of the carbon support surface to create hydrophilic oxygen-containing groups [4]. Understanding reversible degradation mechanisms and recovery strategies is important for efficient operation, improved durability, and prolonged cell lifespan. Typically, the "electrode reversal" method is practical and economical, allowing power output during recovery without additional equipment, thereby minimizing recovery operation runtime.In this study, we examine the impact of the electrode reversal method on PEMFC performance and the deterioration tendency of MEA during carbon corrosion of cathode CL (Figure 1). Accelerated stress tests (AST) were conducted at high potentials exceeding 1.0 V (vs. RHE), specifically investigating the relationship between electrode degradation behaviors, porous carbon structural properties including ionic resistance and EDLC, and overall PEMFC performance.Particularly noteworthy after the electrode reversal recovery method were the discernible variations in degradation behaviors and diverse rates of performance decline observed through electrochemical impedance spectroscopy (EIS) analysis. EIS can be used to isolate the contribution of many processes to performance loss, allowing investigation of the effect of carbon corrosion-induced catalyst layer changes on fuel cell performance [5]. The EIS data underwent evaluation via parametric fitting utilizing the transmission line model (TLM) applied to the EIS spectrum. Furthermore, relaxation time distribution (DRT) analysis was employed to directly analyze internal resistance factors as a diagnostic tool for assessing electrode degradation by enhancing the TLM-based impedance analysis results. During the ASTs, electrochemical measurements (i-V, CV, LSV, and EIS) were performed to estimate the degree of PEMFC degradation, we also conducted ex-situ surface analysis of MEA using SEM, TEM, and XPS to elucidate the specific degradation components. Fig. 1 Electrode Reversal Recovery method during Anode cycling AST of the PEMFC single cell (a) polarization curves (i-V curves); 10 A constant current test (b)-(d): (b) fresh MEA, (c) after 250 cycles, (d) after 500 cycles of Anode cycling AST References [1] Sorrentino, Antonio, Kai Sundmacher, and Tanja Vidakovic-Koch. "Polymer electrolyte fuel cell degradation mechanisms and their diagnosis by frequency response analysis methods: a review." Energies 13.21 (2020): 5825.[2] Macauley, Natalia, et al. "Carbon corrosion in PEM fuel cells and the development of accelerated stress tests." Journal of The Electrochemical Society 165.6 (2018): F3148.[3] Kwon, JunHwa, et al. "Identification of electrode degradation by carbon corrosion in polymer electrolyte membrane fuel cells using the distribution of relaxation time analysis." Electrochimica Acta (2022): 140219.[4] Yang, Wenbin, et al. "Investigation of an electrode reversal method and degradation recovery mechanisms of PEM fuel cell." Electrochimica Acta 449 (2023): 142181.[5] Kwon, JunHwa, et al. "A Comparison Study on the Carbon Corrosion Reaction under Saturated and Low Relative Humidity Conditions via Transmission Line Model-Based Electrochemical Impedance Analysis." Journal of The Electrochemical Society 168.6 (2021): 064515. Figure 1

Utilizing Distribution of Relaxation Times Analysis for Water Content Management in Anion Exchange Membrane Fuel Cells

Amid escalating concerns over air pollution and energy scarcity, Anion Exchange Membrane Fuel Cells (AEMFCs) are increasingly recognized as a viable solution for power generation, offering high efficiency, and zero emissions. Water plays a critical role within these systems as a reactant, consumed at the cathode and generated at the anode. This process can lead to disparities in water content, potentially compromising the cell's performance. Therefore, it is imperative to maintain optimal water distribution to facilitate effective charge transport and enhance electrochemical reaction kinetics. Consequently, devising a robust water management strategy is essential to ensuring the sustained operation and longevity of AEMFCs.Characterizing the water conditions at the anode and cathode under various operational states (normal, drying, or flooding) is a pivotal step underpinning effective water management strategies. Electrochemical Impedance Spectroscopy (EIS) provides a valuable tool for examining various resistances associated with kinetics, mass transport, and ohmic losses across different operational timescales, thereby facilitating a detailed assessment of water transport dynamics. Traditional analyses of EIS data often depend on equivalent circuit models, which require predefined assumptions and the selection of initial components. However, this study adopted the Distribution of Relaxation Times (DRT) methodology for its exceptional capability to disaggregate components, enabling a more nuanced analysis of the polarization processes. The DRT methodology was applied to scrutinize the patterns of loss and variation within each polarization process under varying water flooding and drying conditions at the anode and cathode. Moreover, to deepen our comprehension of how water content influences mass transport and electrochemical reaction kinetics, a three-dimensional multi-physics model for AEMFCs was developed. This model comprehensively integrates considerations of water phase transitions, heat and mass transfer, as well as the transport of liquid and dissolved water, alongside electrochemical reactions. These efforts collectively forge a comprehensive and systematic framework to advance the application of the distribution of relaxation times in optimizing fuel cell performance.