Distribution Of Relaxation Times Research Articles

P2-Na0.67Mn0.7Ni0.2Co0.1O2 stabilized by optimal active facets for sodium-ion batteries.

Considering factors such as crustal reserves, atomic mass, redox potential and energy density, sodium-ion batteries (SIBs) are regarded as the most promising alternative to lithium-ion batteries (LIBs). Transition metal-based layered oxides, especially typical NaxMnO2, stand out among cathode materials due to their low cost and high energy density. However, NaxMnO2 cathodes face several challenges, including Jahn-Teller distortion, manganese dissolution, structural collapse, irreversible phase transition and significant capacity loss. In addition, the significant changes in lattice parameters can lead to the formation of cracks and nanovoids. It has been reported that optimizing the assembly of surface facets can be beneficial to electrochemical properties. In this work, Na0.67MnO2 (NMO) with a multilayered structure featuring (distinct {010} active facets and Na0.67Mn0.7Ni0.2Co0.1O2 (NMNCO) with a homogeneous polyhedra structure featuring distinct {001} active facets were synthesized. The initial charge capacity of NMNCO reached 110.1mA h g-1 at a current density of 10mA g-1. After 100 cycles at 100mA g-1, it displayed a good cycling retention rate of 82.1%. The distribution of relaxation times (DRT) reveals the facile transfer of Na+ ions in the NMNCO cathode. In addition, the effects of Ni and Co are revealed, and the mechanism underlying the relationship between distinct surface facet and crack formation is studied.

Investigation of Distribution of Relaxation Times Responding to Valve-Regulated Lead Acid Batteries Degradation Process

Investigation of Distribution of Relaxation Times Responding to Valve-Regulated Lead Acid Batteries Degradation Process

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.

Effect of Confinement on the Translational Diffusivity of Small Dye Molecules in Thin Polystyrene Films and Its Connection to Tg-Confinement and Fragility-Confinement Effects.

Using fluorescence, we study the impact of nanoscale confinement on the translational diffusivity (D) of trace levels of a small-molecule dye, 9,10-bis(phenylethynyl)anthracene (BPEA), in supported polystyrene (PS) films via Förster resonance energy transfer (FRET). Reductions in BPEA diffusivity are observed in films thinner than ∼200 nm, with D decreasing by 80-90% in 100 nm-thick films compared to bulk. The activation energy of BPEA diffusivity increases from ∼210 kJ/mol in bulk films to ∼370 kJ/mol in 130 nm-thick films. BPEA exhibits a greater diffusivity-confinement effect than a larger dye, decacyclene, in terms of the length scale at which the effects of confinement become evident and the percentage reduction in diffusivity. For both BPEA and decacyclene, the diffusivity-confinement effect in supported PS films occurs at a length scale much larger than that for the glass transition temperature (Tg)-confinement effect and somewhat larger than that for the fragility-confinement effect. This difference in confinement-effect length scales can be rationalized as follows: small-molecule dye diffusivity relates predominantly to short times in the α-relaxation distribution, whereas Tg relates to long times in the α-relaxation distribution, and fragility reflects the overall breadth of this relaxation time distribution. If confinement results in a narrower relaxation time distribution in PS films with the short-time relaxations being shifted to longer times and the longest-time relaxation regimes being shifted to shorter times, then Tg, diffusivity, and fragility all decrease at sufficient levels of confinement. If the narrowing with confinement begins with the shortest relaxation time regimes, then fragility and small-molecule dye diffusivity are influenced by confinement at larger length scales than Tg.

Correlation between Electrochemical Relaxations and Morphologies of Conducting Polymer Dendrites

Conducting Polymer Dendrites (CPD) can engrave sophisticated patterns of electrical interconnects in their morphology with low-voltage spikes and few resources: they may unlock in operando manufacturing functionalities for electronics using metamorphism conjointly with electron transport as part of the information processing. The relationship between structure and information transport remains unclear and hinders the exploitation of the versatility of their morphologies to store and process electrodynamic information. This study details the evolution of CPD's circuit parameters with their growth and shape. Through electrochemical impedance spectroscopy, multiple distributions of relaxation times are evidenced and evolve specifically upon growth. Correlations are established between dispersive capacitances of dendritic morphologies and growth duration, independently from exogenous physical variables: distance, evaporation or aging. Deviation of the anomalous capacitance from the conventional Debye dielectric relaxation can be programmed, as the growth controls the dispersion coefficient of the dendrite's constant-phase elements relaxation. These results suggest that the fading-memory time window of pseudo-capacitive interconnects can practically be conditioned using CPD morphogenesis as an in materio learning mechanism. This study confirms the perspective of using electrochemistry for unconventional electronics, engraving information in the physics of conducting polymer objects, and storing information in their morphology, accessible by impedance spectral analysis.

Charge injection dynamics in oxygen-functionalized and heteroatom-doped reduced graphene oxide and their impact on supercapacitor performance: An experimental and DFT investigation

To elucidate the synergistic effects of oxygen functional groups (OFGs) and heteroatoms (HAs) on charge injection dynamics and the electrochemical performance of reduced graphene oxide (rGO), a combination of experimental techniques and density functional theory (DFT) analyses were employed. GO was synthesized using a modified Hummers method and the sample reduced hydrothermally at 150 °C demonstrated the highest areal capacitance of 817 mF/cm2. To understand the diffusion and charge transfer characteristics, the diffusion coefficient and distribution of relaxation time studied using the Electrochemical Impedance Spectroscopy data. Further the X-ray photoelectron spectroscopy (XPS) confirmed the incorporation of OFGs and HAs in the rGO. A partially oxygen-functionalized, nitrogen, and sulfur-doped graphene (NS-POG) model was constructed based on the XPS data and analyzed using DFT. The projected density of states analysis revealed a Fermi level shift, indicating the introduction of excess electrons due to incorporating OFGs and HAs in graphene, thereby improving the charge carrier concentration in the partially reduced or oxidized systems. The NS-POG system exhibited a quantum capacitance of 85.92 μF/cm2. Additionally, potassium ion (K+) adsorption studies indicated that the adsorption energy was highest near sulfur atoms, suggesting that electrolyte ions exhibit enhanced electrochemical activity in proximity to sulfur. These findings provide insight into the mechanisms by which OFGs and HAs enhance the performance of rGO and highlighting the potential of NS-rGO in supercapacitor applications.

Evaluation of the electrical behavior of tungsten trioxide and cobalt oxide nanoparticles filled poly (ɛ-caprolactone) composite for optoelectronic devices

This study obtains the electrical characterization of nanocomposites comprising Poly(ɛ-caprolactone) (PCL), tungsten trioxide (WO3), and cobalt oxide (Co3O4) nanoparticles. The fabrication of these nanocomposites through a casting method aimed to enhance their electrical conductivity and dielectric properties. The AC conductivity (σac) was analyzed across varying frequencies, revealing a notable increase with the addition of Co3O4 nanoparticles, particularly up to the high content of Co3O4 nanoparticles. This enhancement is attributed to the formation of ion transport pathways and the increased amorphous regions within the PCL matrix. Dielectric properties were assessed through ε′ and ε'') measurements, which exhibited a decrease with increasing frequency, indicating the dielectric relaxation processes of the composite. The complex electric modulus analysis demonstrated a significant relationship between the real and imaginary components, suggesting potential ionic conductivity in the nanocomposites. Additionally, the Argand plot revealed a depressed semicircle, indicating a distribution of relaxation times, which further confirmed the enhancement of conductivity with raising laser ablation time. Overall, the results indicate that the addition of WO3 and Co3O4 nanoparticles significantly improves the electrical properties of PCL, making these nanocomposites suitable for various electrical applications.

Abnormally enhanced Hall Lorenz number in the magnetic Weyl semimetal NdAlSi

In Landau’s celebrated Fermi liquid theory, electrons in a metal obey the Wiedemann–Franz law at the lowest temperatures. This law states that electron heat and charge transport are linked by a constant L0, i.e., the Sommerfeld value of the Lorenz number (L). Such relation can be violated at elevated temperatures where the abundant inelastic scattering leads to a reduction of the Lorenz number (L < L0). Here, we report a rare case of remarkably enhanced Lorenz number (L > L0) discovered in the magnetic topological semimetal NdAlSi. Measurements of the transverse electrical and thermal transport coefficients reveal that the Hall Lorenz number Lxy in NdAlSi starts to deviate from the canonical value far above its magnetic ordering temperature. Moreover, Lxy displays strong nonmonotonic temperature and field dependence, reaching its maximum value close to 2L0 in an intermediate parameter range. Further analysis excludes charge-neutral excitations as the origin of enhanced Lxy. Alternatively, we attribute it to the Kondo-type elastic scattering off localized 4f electrons, which creates a peculiar energy distribution of the quasiparticle relaxation time. Our results provide insights into the perplexing transport phenomena caused by the interplay between charge and spin degrees of freedom.

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.

Identifying electrochemical processes by distribution of relaxation times in proton exchange membrane electrolyzers

Distribution of relaxation time (DRT) is used to interpret electrochemical impedance spectroscopy (EIS) for proton exchange membrane (PEM) water electrolyzers, with an attempt to separate overlapped relaxation processes in Nyquist plots. By varying operating conditions and catalyst loadings, four main relaxation peaks arising from EIS can be identified and successfully separated from low to high frequencies as (P1) mass transport, (P2) oxygen evolution reaction kinetics, (P3) reaction kinetics (with faster time constant than P2), and (P4) ionic transport. The shape, height, and frequency of the DRT peaks change with different membrane electrode assembly (MEA) configurations. Electron microscopy reveals distinct features from the cross-sectioned MEAs which verify critical DRT results in that increasing the iridium (Ir)-anode loading from 0.2 mgIr/cm2 to 1.5 mgIr/cm2 reduces kinetic losses due to higher site-access; a thick and compacted anode, however, also triggers higher ohmic resistances from membrane/catalyst layer hydration and increases transport losses due to longer ionomer pathways. DRT provides higher resolution to EIS for deconvoluting processes with different relaxation times and the quantification of DRT peaks improves the accounting of total losses from each process.

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

The Distribution of Capacitive Times for the Analysis of Electrochemical Impedance Spectroscopy Data from Supercapacitors

Electrochemical impedance spectroscopy (EIS) is the experimental technique of choice for studying the properties of various electrochemical systems, including batteries, fuel cells, and supercapacitors [1]. In particular, EIS data collected from supercapacitors was successfully analyzed with the distribution of relaxation times (DRT) to elucidate charging and discharging mechanisms at the electrodes [2]. The DRT method is especially appealing as it represents a non-parametric alternative to the standard equivalent circuits and physical models [3].The DRT method relies on the assumption that a blip of current linearly results in a voltage that decays with a characteristic timescale [4]. Deconvolving the DRT from measured impedances allows the identification of these characteristic timescales to characterize and optimize the performance of supercapacitors. Nevertheless, due to diffusional and mass-transport-related phenomena, the imaginary part of the impedance of supercapacitors generally diverges at low frequencies, which renders the DRT method less accurate [5]. In fact, the impedance modelled with the DRT tends to a finite real value at low frequencies. In other words, the DRT method is less suitable to identify timescales larger than a few seconds. To overcome this limitation, the distribution of capacitive times (DCT) was proposed by Brug et al. [6]. The DCT method models the admittance, i.e., the inverse of the impedance, in a similar fashion as the DRT describes the impedance. Recently, our group derived the theory underlying the DCT method to facilitate its application and enrich the framework of non-parametric distributions for EIS data analysis [7]. We also used artificial and real battery data to showcase the potential of the DCT method.In this presentation, we will first summarize the main properties of the DCT, and in particular highlight the differences between the DCT and the DRT. Then, we will illustrate how to use the DCT to analyze real data from an electric double-layer supercapacitor with porous carbon electrodes. Moreover, we will explain how to recover the DCT from the experimental impedance, before showing how to compute physical parameters from the DCT spectrum. Overall, we envision that the DCT method will deepen the understanding of EIS data measured from supercapacitors.

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.

DRT Characterization of Lithium-Ion Batteries for eVTOL Applications

The demand for electric vehicles (EV) and electric vertical take-off and landing (eVTOL) aircraft is growing exponentially. The lithium-ion battery (LIB) is commonly selected for such applications due to its promising relatively high energy and power density. However, range limitations, capacity fade, and durability of Li-ion systems limit EVs. These questions become even more vital when discussing aerospace applications of eVTOL, which have more stringent requirements for safety, power, and durability. Additionally, cell-to-cell-variations (CtCv) play a major role in pack performance. To address the current needs, this work employs a characterization method combining the techniques of electrochemical impedance spectroscopy (EIS) and distribution of relaxation times (DRT), allowing for better characterization of cell performance and degradation at relevant high C-rates. In this work, cells are cycled at high-rate discharge (10C and 25C) at various temperatures to mimic eVTOL applications, with characterization tests being performed at beginning of life and every 50 cycles for a total of 500 cycles.By applying DRT to the EIS data, the electrochemical processes inside the cell can be deconvoluted and examined [1-3]. Gaussian peaks are fit to the DRT distribution function, and the resistance of each process can be predicted, thereby monitoring changes in HFR, interfacial particle-particle interactions, SEI/CEI interphase layers, and charge transfer/intercalation kinetics at various states of charge (SOC) and cycle number. Furthermore, diffusion related processes can also be identified and estimated from DC current-interrupt/application methods.Degradation tests were performed to simulate various thermal boundary conditions faced by eVTOLs ranging from 20°C to -20°C. The results reveal that, at high discharge rates operating at room temperature, cells reached up to 90°C and signatures of degradation in the SEI layer are seen in the DRT data. Other cells cycled at 0°C show evidence of lithium plating due to the cold environment. Active cooling at 20°C showed the least degradation as identified from the various internal processes. This method of testing provides an approach to comprehensively analyze individual internal degradation modes of a Li-ion battery.

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).

(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.

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.

Advancements in Analyzing Organic Additives in Electroplating Baths: A Focus on Electrochemical Impedance Spectroscopy (EIS) Coupled with Distribution of Relaxation Times (DRT)

Organic additives play a crucial role in upholding the quality of metallic coatings within commercial electroplating baths. However, their effectiveness diminishes over time due to degradation and drag-out. Continuous monitoring and precise dosing are imperative to uphold optimal concentration levels, preserving both technical integrity and aesthetic appeal. Traditional chromatographic techniques are impractical for routine industrial analysis due to the complex formulation and synergistic effects of various additives. Electrochemical methods, such as the Hull cell test and Cyclic Voltammetric Stripping (CVS) measurements, are commonly employed to adjust additive concentrations based on their impact on the electrodeposition process. Although widely utilized, the Hull cell test relies on trial and error and operator experience, providing only qualitative assessments. CVS, which measures changes in the rate of copper deposition to reflect additive concentration, may not be universally suitable for all electroplating baths due to their varying complexities.Prior Electrochemical Impedance Spectroscopy (EIS) investigations on copper plating baths have qualitatively linked impedance changes with aging [1]. Our objective was to quantify additives using EIS. To achieve this, experimental data were analyzed in terms of resistive and capacitive components to calculate the distribution of relaxation times (DRT) via Lasso regression [2]. The resulting data were subjected to multivariate analysis to address this challenge.The promising outcomes [3] render this method highly appealing in both industrial and academic contexts. Its application in the galvanic field is particularly advantageous for gaining insights into the function of individual additives, their interactions, and the aging process of plating baths.Project funded under the National Recovery and Resilience Plan (NRRP), Mission 4 Component 2 Investment 1.3 - Call for tender No. 341 of 15 March 2023 of Italian Ministry of University and Research (MUR) funded by the European Union - NextGenerationEU - Project code PE_00000004, CUP B83C22004890007, Project title "3A-ITALY - Made-in-Italy circolare e sostenibile".

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.

Impedance Based Comparison of PEMFC Cathode Catalyst Layer Materials

The performance of Polymer Electrolyte Membrane Fuel Cells (PEMFC) is strongly dependent on the oxygen reduction reaction and therefore the cathode catalyst layer. Different catalyst layers with the same platinum loading can achieve vastly different performances. The exact composition of ionomer, carbon support and catalyst has a big impact on important electrode characteristic. These characteristics define the contributions of the loss processes that occur in the electrode. By improving one of the performance defining features of the catalyst layer, another one is oftentimes worsened. This creates a trade-off between the loss contributions and the catalyst design parameters.Impedance spectroscopy (EIS) is a powerful tool to make these trade-offs visible. By calculating the distribution of relaxation times (DRT) the different loss processes can be deconvoluted and by fitting the impedance spectra to a physicochemical meaningful transmission line model, the loss processes can be quantified. In addition the electrochemical active surface area (ECSA) can be determined by cyclic voltammetry (CV) and correlated to the charge transfer losses.In this contribution PEMFCs with different cathode catalyst layers and the same anodes are compared in a wide spectrum of operating conditions by means of EIS and DRT. On the basis of these measurements a transmission line model (TLM) is fitted to the impedance spectra and the loss contributions are quantified. The results enable a direct comparison of the cathode catalyst specific loss processes in different operating conditions. By means of CV and Hydrogen Underpotential Desorption, the ECSA is estimated and correlated with the loss contributions.