Electrode Impedance Research Articles

Conducting Polymer Microelectrode Arrays for Simultaneous Electrophysiology and Advanced Brain Imaging

AbstractIn neuroscience research and clinical practice, electrophysiology is used to record and stimulate specific parts of the brain with high temporal resolution. This capability can be augmented by magnetic resonance imaging (MRI), which provides anatomical and functional information about the brain with large spatial coverage. However, metallic electrodes, commonly used in electrophysiology, are fundamentally incompatible with MRI due to heating concerns and imaging artefacts. Here, it is demonstrated that flexible micro‐electrocorticography (µECoG) arrays, with electrodes made of poly(3,4‐ethylenedioxythiophene) doped with polystyrene sulfonate (PEDOT:PSS), are compatible with ultra‐high magnetic field MRI up to 9.4 T. A scalable fabrication process is adopted that results in very repeatable electrochemical properties across devices. The volumetric capacitance of PEDOT:PSS leads to low electrode impedance and enables high‐resolution neural recordings of single‐unit activity from the cortical surface of rodents. Furthermore, the µECoG array creates minimal distortion in T2‐weighted anatomical brain MRI. Multimodal brain monitoring is demonstrated by performing simultaneous blood oxygen level‐dependent functional MRI (BOLD fMRI) in parallel with electrical stimulation from the µECoG array. The results show that the PEDOT:PSS µECoG arrays enable the combination of high‐resolution electrophysiology and advanced brain imaging in vivo.

Electrochemical Switching of Laser-Induced Graphene/Polymer Composites for Tunable Electronics

Laser reduction of graphene oxide (GO) is a promising approach for achieving flexible, robust, and electrically conductive graphene/polymer composites. Resulting composite materials show significant technological potential for energy storage, sensing, and bioelectronics. However, in the case of insulating polymers, the properties of electrodes show severely limited performance. To overcome these challenges, we report on a post-processing redox treatment that allows the tuning of the electrochemical properties of laser-induced rGO/polymer composite electrodes. We show that the polymer substrate plays a crucial role in the electrochemical modulation of the composites’ properties, such as the electrode impedance, charge transfer resistance, and areal capacitance. The mechanism behind the reversible control of electrochemical properties of the rGO/polymer composites is the cleavage of polymer chains in the vicinity of rGO flakes during redox cycling, which exposes rGO active sites to interact with the electrolyte. Sequential redox cycling improves composite performance, allowing the development of devices such as electrolyte-gated transistors, which are widely used in chemical sensing applications. Our strategy enables the engineering of the electrochemical properties of rGO/polymer composites by post-treatment with dynamic switching, opening up new possibilities for flexible electronics and electrochemical applications having tunable properties.

Electrodeposited Nitrate-Intercalated NiFeCe-Based (Oxy)hydroxide Heterostructure as a Competent Electrocatalyst for Overall Water Splitting.

Electrochemical water splitting is a promising method for the generation of "green hydrogen", a renewable and sustainable energy source. However, the complex, multistep synthesis processes, often involving hazardous or expensive chemicals, limit its broader adoption. Herein, a nitrate (NO3-) anion-intercalated nickel-iron-cerium mixed-metal (oxy)hydroxide heterostructure electrocatalyst is fabricated on nickel foam (NiFeCeOxHy@NF) via a simple electrodeposition method followed by cyclic voltammetry activation to enhance its surface properties. The NiFeCeOxHy@NF electrocatalyst exhibited a low overpotential of 72 and 186 mV at 10 mA cm-2 for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively, in 1.0 M KOH. In a two-electrode system, the NiFeCeOxHy@NF obtained a low voltage of 1.47 V at 10 mA cm-2 in 1.0 M KOH with robust stability. Results revealed that the notable activity of the NiFeCeOxHy@NF catalyst is primarily due to (i) hierarchical nanosheet morphology, which provides a large surface area and abundant active sites; (ii) NO3- anion intercalation enhances electrode stability and eliminates the need for binders while simultaneously promoting a strong catalyst-substrate adhesion, resulting in decreased electrode resistance and accelerated reaction kinetics; and (iii) the unique superhydrophilic surface properties facilitate electrolyte penetration through capillary action and minimize gas bubble formation by reducing interfacial tension.

Stretchable impedance electrode array with high durability for monitoring of cells under mechanical and chemical stimulations

Electrochemical impedance spectroscopy (EIS) serves as a non-invasive technique for assessing cell status, while mechanical stretching plays a pivotal role in stimulating cells to emulate their natural environment. Integrating these...

Prussian Blue and Polyvinylpyrrolidone‐Embedded Hollow Fiber Gradient Polysulfone Membrane for Uric Acid Biosensor Application

ABSTRACTTraditional biosensors have drawbacks such as temperature sensitivity and cross‐reactivity. An innovative UA biosensor was developed. It combined Prussian Blue, carbon nanotubes, PVP with uricase oxidase in a polysulfone hollow fiber gradient membrane, forming a multilayer 3D structure. The optimal pH and temperature for the biosensor were determined to be 8.0 and 37°C, respectively. Electrochemical impedance spectroscopy (EIS) showed that the nanoparticles significantly reduced the working electrode's impedance, enhancing electron transfer. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were used to study the electrochemical behavior of UA oxidation. A distinct oxidation peak for UA was observed at 0.7 V. The sensor exhibited a sensitivity of 0.33 × 10−6 A/mM, a linear working range from 1.2 to 12 mM, and a detection limit of 0.424 mM. The porous structure of the membrane and the nanoparticles' synergistic effect contributed to high sensor stability. After continuous use for a week, the sensor maintained approximately 90% of its initial performance. This research demonstrates the effectiveness of our method in developing highly sensitive and stable biosensors for UA detection, providing a promising solution for accurate and reliable uric acid level monitoring.

Multifunctional Cyclized Polyacrylonitrile (cPAN) as a Coating for Sb-Based Anodes in Sodium-Ion Batteries.

Conversion electrodes, such as antimony (Sb), are high energy density electrode materials for sodium-ion batteries (NIBs). These materials are limited in their performance due to the mechanical instability of these systems resulting from volume expansion of the material during cycling. Stabilizing conversion materials using a conductive polymer binder (CPB) protective layer is an effective way to enhance the performance of these materials. There is, however, a lack of a clear understanding of how CPBs affect the (de)insertion and surface chemistry of these systems. Herein, we report the systematic investigation of the effects on Na-ion (de)insertion chemistry of a cyclized-polyacrylonitrile (cPAN) layer on Sb-based conversion electrodes in NIBS. Through electrochemical characterization, it was determined that the inclusion of a cPAN layer increases the achievable capacity of the electrode system due to the storage of Na ions by the cPAN layer and facilitates Na-ion transport to the Sb active material at early cycles by reducing the charge transfer resistance of the ensemble electrode.

STUDI NILAI RESITENSI ELEKTRODA PENTANAHAN MENGGUNAKAN METODE TIGA KUTUB PADA KONDISI TANAH BERBEDA

The grounding system serves as a safe path for electrical current to flow to the ground, which is important in preventing the risk of equipment damage and safety hazards. One of the critical parameters in this system is the resistance of the ground electrode, which can be measured using the three-point method. Based on PUIL 2000, the recommended grounding resistance value for electrical installations must be less than 5 ohms so that the system can work optimally and safely. The three-pole method is known to be accurate because it minimizes the influence of the environment around the electrode. However, factors such as soil type, humidity, and mineral content greatly influence the resistance of the ground electrode. Therefore, this study aims to evaluate the resistance of grounding electrodes in various types of soil, such as clay, swamp soil, damp sandy soil, dry soil, and rocky soil. Research results: The best grounding electrode resistance values ​​were obtained in clay and moist sandy soil (coastal). Meanwhile, the resistance value of the ground electrode for dry soil, rocky soil, and swamp soil does not meet the standard of ≤ 5 ohms. The factors that cause the resistance value of the ground electrode not to meet the standard are because in swampy soil the soil is dominated by insulating organic material and low content of conductive minerals. Also, moisture imbalance, electrode corrosion, and less-than-optimal electrode installation contribute. At the same time, dry soil and rocky soil are characterized by having a high level of resistivity due to low water and mineral content and a texture that does not support optimal electrical conductivity where field measurement results are not yet available. Meets the standard ≤ 5 Ω

Long-Term Stable Reference Electrodes with High-Pressure Tolerance and Salinity-Independence.

The reference electrode's performance is essential for ensuring the accuracy of electrochemical sensors in marine environments. Yet, the many existing reference electrodes can exhibit sensitivity to salinity variations, potentially leading to inaccuracies in the measurement process. Herein, we have designed a reliable solid-state reference electrode by introducing SiOx-stabilized 1-methyl-3-octylimidazolium bis(trifluoromethyl sulfonyl)imide ([C8mim+] [Ntf2-]) into a P(VdF-co-HFP) matrix with a SPEEK/[C8mim+] [Ntf2-] coated Ag/AgCl as substrate. The SPEEK/[C8mim+] [Ntf2-] coating protects the AgCl substrate, and the incorporation of SiOx improves the compatibility of the IL with the polymer matrix, thereby increasing the electrode's resistance to interference and extending its long-term stability and lifespan. The developed reference electrode showed a stable and rapid response, with potential variations of less than 0.7 mV across various salinity solutions, including practical seawater, lake water, and their mixture samples. During extended periods of 18 days in deionized water and artificial seawater, the electrode demonstrated negligible potential drifts of 0.36 and 0.14 mV/d, respectively. Notably, the electrode could maintain a stable potential even after being stored in a preservative solution for 67 days. Furthermore, the electrode showed a stable response to withstand pressures of up to 100 MPa, covering the vast majority of the seafloor. This innovative reference electrode is capable of maintaining a stable reference potential across various salinities, ionic strength, and full ocean depth, making it versatile for use in diverse aquatic environments, underscoring its significant potential for advancing oceanographic research and enabling new insights into the unexplored depths of oceans.

Effect of Different Binders on the Power Characteristics for Carbon Fluorides in Lithium Primary Batteries

Abstract This study demonstrates the effect of different binders on the power characteristics of carbon fluorides (CFx) cathode material for power-type lithium primary batteries. Specifically, polymer binders, such as polyacrylic latex (LA133), poly(vinylidene fluoride) (PVDF) and carboxymethyl cellulose (CMC) are utilized in the preparation of CFx composite electrodes. The selection of binders significantly influences the rate performance of Li/CFx batteries. Among the binders tested, the LA133 binder notably reduces the electrode resistance and interface impedance of the batteries compared to PVDF and CMC, resulting in outstanding rate performance at 1C. Additionally, this study discusses the impact of binder chemistry on the overall performance of the batteries.

Past, present, and future of electrical impedance tomography and myography for medical applications: a scoping review.

This scoping review summarizes two emerging electrical impedance technologies: electrical impedance myography (EIM) and electrical impedance tomography (EIT). These methods involve injecting a current into tissue and recording the response at different frequencies to understand tissue properties. The review discusses basic methods and trends, particularly the use of electrodes: EIM uses electrodes for either injection or recording, while EIT uses them for both. Ag/AgCl electrodes are prevalent, and current injection is preferred over voltage injection due to better resistance to electrode wear and impedance changes. Advances in digital processing and integrated circuits have shifted EIM and EIT toward digital acquisition, using voltage-controlled current sources (VCCSs) that support multiple frequencies. The review details powerful processing algorithms and reconstruction tools for EIT and EIM, examining their strengths and weaknesses. It also summarizes commercial devices and clinical applications: EIT is effective for detecting cancerous tissue and monitoring pulmonary issues, while EIM is used for neuromuscular disease detection and monitoring. The role of machine learning and deep learning in advancing diagnosis, treatment planning, and monitoring is highlighted. This review provides a roadmap for researchers on device evolution, algorithms, reconstruction tools, and datasets, offering clinicians and researchers information on commercial devices and clinical studies for effective use and innovative research.

Effect of Bi(iii)-to-metal ion concentration ratios on stripping voltammetric response of bismuth-film glassy carbon electrodes.

The effect of Bi-to-metal ion concentration ratio (c Bi/c M ratio) on key evaluation indicators, including sensitivity, precision, and cathodic potential range, has been investigated for the determination of Cd and Pb at in situ prepared bismuth film electrodes. Unlike the usual recommendation of at least a 10-fold excess of Hg(ii) for anodic stripping experiments at in situ prepared mercury film electrodes, it is found that the c Bi/c M ratios in the 1-10 range are sufficient to obtain a high determination sensitivity, but that the signal decreases significantly when the ratio exceeds 40. Further analysis shows that the precision of the analytical results is good when the c Bi/c M ratio is in the range of 5-10. The precision is even better in the range of 10-20, but too high a ratio cannot further improve the precision of the results. Therefore, it is recommended to keep the c Bi/c M in the range of 5 to 40 to balance the sensitivity and precision in detection. The study also finds that the optimum cathodic potential range is related to the total concentration of metal ions. Therefore, for metals susceptible to hydrogen evolution (e.g., zinc), additional consideration should be given to inhibiting the hydrogen evolution reaction when selecting the c Bi/c M ratio. This work is the first to investigate the effect of the c Bi/c M ratio on the morphology and thickness of deposits using EIS, SEM, and AFM. It is found that increasing the c Bi/c M ratio leads to an increase in the coverage and thickness of the bismuth film on the electrode surface, which enhances the sensitivity of the determination. However, this change is also accompanied by an increase in the electrode resistance, resulting in a significant decrease in signal when the ratio is too large. In addition, when the c Bi/c M ratio is <5, the precision of the bismuth film electrode is relatively poor due to the rapid increase of the bismuth coverage on the electrode surface. The uneven thickening of the deposit also affects the cathodic potential range. Based on these findings, standard curves with c Bi/c M ratios ranging from 5-25 are prepared and successfully applied to the analysis of river water and wastewater.

Comparative Study of Potassium Ion-Selective Electrodes with Solid Contact: Impact of Intermediate Layer Material on Temperature Resistance.

This paper presents a comparative study on the temperature resistance of solid-contact ion-selective electrodes, depending on the type of solid-contact material. Five types of potassium electrodes, with a valinomycin-based model membrane, were developed using different types of mediation layers, namely a conductive polymer (poly(3-octylthiophene-2,5-diyl) and a perinone polymer), multi-walled carbon nanotubes, copper(II) oxide nanoparticles, and a nanocomposite consisting of multi-walled carbon nanotubes and copper(II) oxide. We examined how the measurement temperature (10 °C, 23 °C, and 36 °C) affects the sensitivity, measurement range, detection limit, selectivity, as well as the stability and reversibility of the electrode potential. Electrodes modified with a nanocomposite (GCE/NC/ISM) and a perinone polymer (GCE/PPer/ISM) showed the best resistance to temperature changes. An almost Nernst response and a stable measurement range and the lowest detection limit values for each temperature were obtained for them. The introduction of mediation layers significantly improved the stability and potential reversibility of all the modified electrodes relative to the unmodified electrode (GCE/ISM). Still, it was the GCE/PPer/ISM and GCE/NC/ISM that stood out from the others, with stability of 0.11 and 0.12 µV/s for 10 °C, 0.05 and 0.08 µV/s for 23 °C, and 0.06 and 0.09 µV/s for 36 °C, respectively.

Enhancing the Pseudocapacitive Energy Storage of Coordination Polymers by Artificially Constructed Defective Sites Anchoring Redox-Active Species.

Coordination polymers (CPs) have emerged as potential energy storage materials for supercapacitors due to their tunable chemical composition, structural diversity, and multielectron redox-active sites. However, besides poor cycling stability, the practical application of dense CPs in supercapacitors is generally limited by low specific capacitance and high resistance, which are caused by their low specific surface area and dense frameworks, resulting in insufficient redox reactions of metal sites and poor ion diffusion, respectively. Here, we synthesize a new dense CP {CP-1: [Ce(obb)(HCOO)]∞} via self-assembly of the Ce cation and 4,4'-oxidibenzoate (obb2-). The specific capacitance of CP-1 increases by 156.7 times, and its lifetime after charge-discharge for 5000 cycles is elevated from 62 to 86.7%; meanwhile, the resistance of the positive electrode is reduced from 1.05 to 0.73 Ω through this defect engineering strategy (DES), i.e., cyclic voltammetry sweep in a sulfuric acid electrolyte to artificially construct defects for anchoring the redox-active species (ferricyanide anions). To investigate the universality of this strategy, we have applied it to the other two previously reported CPs {CP-2: [Ce4(obb)6(H2O)9·(H2O)]∞ and CP-3: [Ce2(obb)3(OH)(H2O)(DMF)]∞}, which are also obtained by self-assembly of the Ce cation and obb2- ligand. By comparing the electrochemical performances of the three pristine CPs and their corresponding defect-engineered CPs obtained through the DES, we have found that (i) this strategy is effective in enhancing the electrochemical performances for all three CP materials and (ii) the effect of this strategy on improving the electrochemical performance of CP-1 with a three-dimensional dense network is better than that of CP-3 with a layered structure, and both are better than that of CP-2 with small pores. This work demonstrates a new effective universal strategy for boosting the electrochemical performances of CPs, thus advancing their application in the energy storage field.

Investigation into the impedance, dielectric behavior, and conductivity within p-silicon/n-nanocrystalline iron disilicide heterojunctions and equivalent circuit model in relation to temperature

The p-Si/n-nanocrystalline FeSi2 heterojunctions constructed through facing-targets sputtering were characterized for impedance under various frequencies and temperatures of between 160−400 K. Imaginary and real impedance plots for all temperatures demonstrated single semicircular arc with negative temperature dependency. From the arc, a circuit model equivalent to electrode resistance serially connected to several loops, each consisting of a parallel circuit comprising a resistance//constant phase element (Q), corresponding to the crystallite, crystallite boundary, and interface. All resistances increased with decreasing temperatures, while the Q values decreased but behaved as ideal capacitors for all temperatures. The dielectric constants versus increasing temperature demonstrated a linear increase. At 300 K and 1 MHz, the dielectric constant was 24.5 with 0.1 loss tangent, denoting its possible usage for filtration and storage. The alternating-current conductivities disclosed that direct-current conductivities increased as the temperature increased. The exponents from Jonscher's fit were 1 or less around 180 K and the values beyond 1 at higher temperatures, indicating the shift from long transitional transport to localized hopping transport. The activation energy based on conductivities was higher than the one based on relaxation times, implying that excess charge led to more energy requirements for transportation.

Impact of Na-Carboxymethyl Cellulose Binder Type on Hard Carbon Performance and SEI Formation in Sodium-Ion Batteries.

The development of hard carbon (HC) electrodes using biobased binders, formulated in water solvent, is of great interest for Na-ion batteries. Five Na-carboxymethyl cellulose (CMC) binders with different molecular weights and degrees of substitution were investigated. The increase in the CMC molecular weight led to an increase in the volume of water necessary for slurry preparation and a decrease in the electrode mass loading. Moreover, the adhesion of the slurry was strongly impacted by the aluminum current collector properties. A high initial Coulombic efficiency, iCE (up to ∼90%), and reversible capacity (up to 334 mAh g-1 at C/10) were obtained in Na half-cells. Post-mortem XPS analyses performed on several electrodes under various conditions allowed a better understanding of the formation and composition of the solid electrolyte interphase (SEI) layer. The genesis of SEI was initially chemically driven: to a small extent, by HC and to a greater extent, by the Na metal. However, SEI formation was mainly governed by the electrochemical-driven degradation of the electrolyte salt and solvent. The SEI layer composed of an inorganic-rich core and an organic-rich shell significantly decreased the resistance of the HC electrode, allowing superior iCE while maintaining high capacity retention (96.2%), after 100 cycles at 1C.

Fast Numerical Optimization of Electrode Geometry in a Two-Electrode Electric Resistance Furnace Using a Surrogate Criterion Derived Exclusively from an Electromagnetic Submodel

The Joule heat generated by current flow between electrodes in a resistance furnace not only melts and heats the charge but also induces mixing of the molten material. Increased mixing promotes improved chemical and temperature uniformity within the bath. This paper presents a novel approach to effectively optimizing electrode geometry in resistance furnaces. The method relies on a surrogate criterion derived exclusively from an electromagnetic submodel, which governs the process hydrodynamics. This criterion is based on the location of the Joule heat generation center in the bath. Its idea is to lower this center as much as possible while keeping it close to the vertical bath axis. Owing to this, the best conditions for the development of natural convection were obtained. The developed methodology was demonstrated through an application to a two-electrode furnace. The results showed that the influence of forced MHD convection is negligible in this furnace (with a Lorentz force of only about 0.0015 N/kg). The validation of the optimized geometry, derived using solely the electromagnetic submodel, was carried out using a full process model, including time-consuming hydrodynamic calculations. The proposed optimization methodology enabled a 10-fold increase in the average mixing velocity (from 0.0008 to 0.0084 m/s). The main significance of the presented study is the introduction of a surrogate criterion that allows for a multiple reduction in the time of numerical optimization of the mixing intensity in electrode resistance furnaces in comparison to the standard solution based on the flow velocity criterion determined from the hydrodynamic model.

Analysis of Species Concentrations in Bifunctional Air Electrodes Using Mathematical Modeling and Simulation

Metal-air secondary batteries using aqueous alkaline solutions are attracting attention as a next-generation large-scale energy storage system. However, the large overpotential of the bifunctional air electrode is a challenge for its practical application. In order to reduce the overvoltage, one approach is to optimize the design of the electrode to enhance both electrochemical as well as transport properties within. We have previously estimated the oxygen diffusion resistance in bifunctional air electrodes with different thicknesses and electrolyte solutions from the difference in the steady state potential under air and oxygen flow. We identified that the reaction zone for the oxygen reduction and evolution reactions concentrated on the gas and electrolyte sides of the catalyst layer, respectively. 1 On the other hand, it is difficult to analyze local reaction rates in more detail since gas diffusion electrodes have a complex structure with a mixture of solid, gas, and liquid. In this study, we analyzed the local conditions in gas diffusion electrodes by combining digital simulations using finite difference methods and electrochemical measurements. The electrolyte solution's distribution significantly affects the simulation result since the electrolyte solution works as both an ionic conductiont and an obstacle to oxygen transport.2 Therefore, the electrolyte solution distribution in the electrode was determined by impedance analysis using a transmission line model, and a simulation model was constructed based on this impedance analysis.Figure 1 shows the Nyquist plot of a gas diffusion electrode at OCV. A transmission line-type frequency dependency is observed in the high-frequency region. The impedance simulated with an equivalent circuit where the ion transport resistance in the electrode does not change in the thickness direction shows a relatively significant difference from the measured one. On the other hand, the impedance simulated with an equivalent circuit with the linear decrease in the ionic conductance from the electrolyte to gas diffusion layer sides showed good agreement with the measured one. This result indicates that the amount of electrolyte in the gas diffusion electrode decreases from the electrolyte side to the gas diffusion layer side. Simplifying the pore structure with the porosity and average pore size obtained with the Barrett-Joyner-Halenda (BJH) method and the tortuosity calculated from the Bruggeman’s equation, the electrolyte thickness was calculated to be 2.1 and 1.1 nm at the electrolyte and gas sides, respectively. The local conditions in the electrode obtained with a one-dimensional simulation model based on the obtained electrolyte solution distribution will be presented at the site. Acknowledgment This work was financially supported by RP-LEAD with DFG (JPJSJRP20221602 and SCHR 1756/1-1).

Developing Routes for 3D Printed Carbon Aerogel Electrodes

Aerogels are porous solids used in a number of electrochemical applications including catalysis, batteries, and supercapacitors due to their high internal surface, composition, and small pore/particle size. Carbon electrodes (e.g. nanotubes, graphene, etc.) are particularly attractive due to their low electrical resistance. The efficient transport of charged species within energy storage devices, in particular, is critical to realizing both high power and energy densities, especially when operating under extreme conditions (e.g. ultralow temperatures, high charge/discharge rates, etc.). A number of resistances can contribute to sluggish ion/electron transport in a cell such as charge transfer at interfaces, electrolyte resistance, electrode resistance, and diffusive transport within porous electrodes. Several strategies have been pursued to address these transport limitations. Electrode materials discovery and development is a popular strategy as the charge storage mechanism and electrode resistance play a key role in kinetics of the device. Within electrode materials development, engineering of the electrode pore architecture is an extremely effective strategy to decrease the diffusive transport lengths and electrode resistances. This pore engineering can be achieved through synthetic chemistry for small pores (e.g. <10 um) and via additive manufacturing for larger pores (> 10 um). Here we show how electrode materials development can be used to overcome sluggish transport in aerogel-inspired electrodes. Particular focus will be given to the use of synthetic means to tune to the properties of electrode material (e.g. surface area, pore size, mechanical properties) and 3D printing to define the larger pore structure to improve the ultimate performance of the device. We explore a number of additive manufacturing techniques (e.g. direct ink write, projection microstereolithography, etc.) to print a variety of simple and complex structures to determine the optimal electrode architecture. The impact of these different methods on both aerogel properties and device function will be discussed.This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Equivalent Circuit Modelling for Electrode-Supported Solid Oxide Cell Based on Analysis of Gas and Temperature Dependence

Electrochemical impedance spectroscopy (EIS) measurement is used to determine the performance of solid oxide cells (SOCs). In the commercial-type of SOC such as an electrode-supported cell (ESC), all reaction resistance is sometimes combined into one spectrum, making it difficult to deconvolute the reaction resistance. The distributed-relaxation times (DRT) is often used to deconvolute the impedance spectra into a several reaction resistances. However, the DRT analysis cannot give any physical meaning to each reaction resistance of SOC’s components. Thus, it is necessary to build an equivalent circuit model to describe the physical meaning of each resistance.In this study, the ESC (Nexceris, USA) with a composition of Ni-YSZ (yttria stabilized zirconia) as a fuel electrode, 8YSZ as an electrolyte, Ce0.9Gd0.1O1.95 as an interlayer, and La0.6Sr0.4CoO3- δ (LSC) as an electrode was measured by EIS as a function of oxygen partial pressure, hydrogen partial pressure, water vapor partial pressure, temperature, and carbon dioxide partial pressure under open circuit voltage (OCV). At first, the impedance spectra were analyzed by the DRT method using software “FTIKREG” [1] based on Tikhonov regularization. After that, the complex nonlinear least square (CNLS) equivalent circuit was developed and fitted to the obtained impedance spectra.The gas conversion and diffusion at a very low-frequency region were analyzed by the Warburg impedance, meanwhile, the electrode resistance was perfectly fitted by the Gerischer impedance. The analysis result on the air electrode resistance of LSC showed the transport properties such as oxygen exchange coefficient and oxide ion diffusivity of the LSC air electrode close to the reported data on the bulk electrode [2]. Meanwhile, the analysis result on the Ni/YSZ fuel electrode resistance showed a good agreement on the reaction resistance and chemical capacitance from the reported data [3].Despite the developed model is “well-fitted” with the obtained impedance spectra, the analysis only done at OCV. In the real operating condition such as fuel cell or electrolysis mode the applied bias is used. Thus, the impedance spectra will slightly be different to those obtained under OCV. Therefore, the developed model will be also fitted to the impedance spectra under applied bias. The analysis result will be used to discuss the application of the developed equivalent circuit model. Acknowledgement This study was supported by the New Energy and Industrial Technology Development Organization (NEDO), grant number JPNP16002. Reference [1] J. Weese, Computer Physics Communications, 69 (1992) 99-111.[2] D. K. Hohnke et al., Solid State Ionics,5 (1981) 531-534.[3] M. Takeda, K. Yashiro, R. A. Budiman, S. Hashimoto, T. Kawada, J. Electrochem. Soc., 170 (2023) 034505.

(Invited) Analysis of Electrochemical Reaction in Polysulfide-Insoluble Lithium Sulfur Battery with in-Situ Electrochemical Impedance Spectroscopic Method

Lithium-Sulfur battery (LiSB) has attracted attention as a new generation secondary battery. However, one of the major problems is dissolution of discharge products of lithium polysulfides (Li2S n ) that cause the self-discharge. Ionic liquids and super-concentrated electrolyte solution (SCES) have been attracting attention as a LiSB electrolyte due to its low solubility of the polysulfides. SCESs are electrolyte solutions which consist of only two or three times as much solvent as lithium salt. Watanabe and Dokko et al. [1] proposed polysulfides insoluble LiSBs using lithium-glyme based solvate ionic liquid (Li-Gn SIL) and sulfolane (SL)-based SCES. Various battery materials have been proposed for LiSBs; on the other hand, the discharge behavior strongly depends on the battery materials. Both the Li-Gn SIL and SL-based SCES are polysulfide-insoluble electrolytes, whereas the LiSB with the SL-based SCES has better battery performance than that with the Li-Gn SIL, implying that the discharge behavior is different between the LiSB with the SCES and LiSB with the SIL [1]. In this contribution, we carried out in situ electrochemical impedance spectroscopic measurement (EIS) [2,3] to reveal influence of different electrolytes on electrode reactions.A positive electrode slurry was obtained by mixing a sulfur S8, a Ketjen black (KB, EC600JD, Lion Corporation) and a carboxymethyl cellulose (CMC2200, Daicel) at a weight ratio of 60 : 30 : 10. The Slurry was spread on an Al foil to obtain a KB-S composite electrode. A negative electrode and a separator were used a lithium metal foil (Honjo Metal) and a glass separator (GA-55, Advantec), respectively. SL-based SCES and Li-Gn SIL are used as electrolyte solutions. The cells were assembled using three-electrode typed cell in an Ar-filled glove box. In situ EIS measurements were conducted at 0.025~0.1C-rate using an electrochemical measurement system (SP-150e, BioLogic). The DC current was superimposed with a small AC current adjusted so that the response voltage amplitude did not exceed 5~10 mV. The measurements were carried out in the frequency range from 500 kHz to 10 mHz. The measured impedance spectra during discharging/charging include the contribution of changes over time. Accordingly, the instantaneous impedance spectra at an arbitrary time were determined using the method to compensate for the changes over time [2,3].In discharge curves of the LiSB with Li-Gn SIL, a voltage drop was observed at DOD = 20−35% during discharge at a high C-rate (0.1C). This voltage drop did not appear in the discharge curve at a low C-rate (0.025C). The capacitive semicircle at 457 Hz appeared in the instantaneous impedance spectra of the LiSB during discharging. The diameter of this semicircle increased as the voltage dropped and the semicircle could be assigned to the charge transfer resistance of the lithium negative electrode. The charge transfer resistance of the negative electrode is related to the resistance of the Li+ ion dissolution/deposition reaction. During discharging at a high C-rate, the Li+ ion dissolution reaction could be suppressed.In the instantaneous impedance spectra of positive electrode in LiSB with SL-based SCES exhibited three capacitive semicircles and an inductive loop at DOD = 5%. Upon further discharging, the inductive loop changed into a capacitive semicircle. The Warburg impedance appeared at the end of the discharge period. This low-frequency impedance behavior was attributed to the Faradaic impedance due to elementary reactions on the electrode, such as intermediate reactions and redox species adsorption/desorption processes. This suggests that multi-step reactions occur in each DOD for the LiSB battery using SL based SCES.References1) A. Nakanishi et al., J. Phys. Chem. C, 123, 14229-14238 (2019).2) Z. B. Stoynov et al., J. Electroanal. Chem., 183, 133-144 (1985).3) M. Itagaki et al., J. Power Sources, 135, 255-261 (2004).