Electrical Impedance Spectroscopy Measurements Research Articles

Investigation and Characterization of Interfacial Transport Phenomena in the Catalyst Layer Using Rheo-Impedance Measurement

Electrodes or catalyst layers (CLs) are the heart of fuel cell and electrolyzer cell devices. They are mainly heterogeneous porous electrodes composed of catalyst particles, ion-conducting polymer material, and void spaces that make up the triple-phase boundary (TPB). It is important to tailor the CL’s microstructure such that there are abundant TPBs where reactions take place to maximize catalyst utilization and improve cell performance. However, this is a critical challenge due to lack of fundamental understanding of the interfacial transport within the CL. Understanding how catalyst ink parameters affect ink properties and how ink components interact, and ultimately, their relationship with CL microstructure formation and cell performance, are essential to designing electrodes. Electrode morphology is important and is controlled by the ionomer/catalyst interactions formed in precursor inks that evolve during mixing and electrode fabrication.In this study, we probe interactions in catalyst inks with different formulations (ionomer-to-carbon ratio and IPA/water) using a new experimental method to unravel the complexities of ionomer/catalyst particle interactions. The new experimental method is a combination of rheological and electrical impedance spectroscopy measurements (rheo-EIS) that takes advantage of the dynamic nature of catalyst ink and the fact that the rheological and electrical behaviors of the ink are coupled to the microstructure of the material. Using rheo-EIS tool, in combination with zeta (ζ) potential and dynamic light scattering (DLS) measurements, we were able to systematically study how the level of agglomeration of the inks and microstructures evolve with respect to different I/C ratios, solvent formulation, and external shear forces. Results from the three-phase rebuilt test designed to simulate the ink coating condition with single-frequency EIS measurement give information on how the ionomer/catalyst particle interactions form and recover during the coating process. In addition, the full frequency range EIS measurements provide complementary data of the ionic and electrical resistance of the ink before and after high shear applications. Furthermore, the observations of the effect of I/C and IPA/water ratios from this study provide insights on how to better engineer suitable catalyst inks and how to control specific CL microstructure without the need for time-consuming optimization and empirical studies.

Development of the passive film during passivation in passivating electrolytes containing sodium molybdate

The impact of sodium molybdate on passive films formed on lean duplex stainless steel (STS 329 FLD) was investigated. Elemental depth distribution was examined using glow discharge optical emission spectroscopy, while the analysis covered passive film capacitance, molybdenum's chemical state, and corrosion resistance. The addition of sodium molybdate to the passivation electrolyte resulted in a reduction of iron content in the iron-rich layer (from 48 % to 38 %), an increase in chromium content in the enhanced chromium layer (from 33 % to 42 %), and the presence of molybdenum on the film surface. Electrical impedance spectroscopy measurements indicated a significant increase in the capacitance of the passive film. Furthermore, molybdenum was identified as molybdate. Electrochemical anodic polarization curves revealed that the corrosion potential rose with the addition of sodium molybdate to the nitric acid electrolyte. This improvement in corrosion resistance was attributed to molybdate adsorption on the outermost part of the passive film, preventing chloride adsorption or penetration. Additionally, the corrosion current density decreased due to the presence of the chromium-rich layer.

Verbena officinalis (VO) leaf extract as an anti-corrosion inhibitor for carbon steel in acidic environment

In the present work, Verbena Officinalis (VO) leaf extract was used as potential corrosion inhibitor for the corrosion of carbon steel (CS) in 0.5 M H2SO4 medium. Further, the corrosion inhibiting nature of VO leaf extract towards the CS was evaluated using mass loss (ML), potentiodynamic polarization (PDP), electrical impedance spectroscopy (EIS) and surface morphological analyses using atomic force microscope (AFM) and X-ray photoelectron spectroscopy (XPS) techniques. Calculation of activation energy Ea∗\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\left( {{\ ext{E}}_{{\ ext{a}}}^{*} } \\right)$$\\end{document} using Arrhenius equation shows the increase in activation energy when adding the VO leaf extract in 0.5 M H2SO4 medium and the maximum activation energy (Ea∗\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ ext{E}}_{{\ ext{a}}}^{*}$$\\end{document} = 49.9 kJ mol−1) was observed for 1000 mg L−1 VO leaf extract in acid medium. The negative free energy values suggested the spontaneous and the stability of the adsorbed layer of VO leaf extract on the CS surface. Using EIS measurements, high percent inhibitory effectiveness of 91.1% for 1000 ppm solutions was achieved. With an increase in VO leaf extract dose, the double layer capacitance (Cdl) values fall while the values of charge transfer (Rct) increase. This showed that a protective layer of VO leaf extract on CS surface was formed. The polarization curves showed that the VO leaf extract acts as a mixed-type inhibitor. It is discovered that the adsorption of VO leaf extract molecules adhering to the CS surface followed the Langmuir isotherm. The anti-corrosion action of VO leaf extract is fully demonstrated by some surface techniques.

Glass-sulfur composite cathodes: A new strategy for improving the performance of lithium-sulfur batteries

In this study, we investigated the potential of glass-sulfur composites to improve lithium–sulfur battery (LSB) performance. Glass-sulfur composites were prepared by the precipitation method, and the effect of varying carbon black content was studied. The results showed that glass addition improved the battery performance due to the high ion-conductivity of its structural motif. The 75 % glass variant demonstrated the best results, in both the low carbon and high carbon cases. The cyclic voltammetry (CV) and electrical impedance spectroscopy (EIS) measurements showed that glass-sulfur composites had lower resistivity than pure sulfur, which was beneficial for battery performance. The XANES analysis revealed that the incorporated glass interacted with and modified the properties of sulfur, leading to a higher proportion of sulfur in the -1 oxidation state (S−1). This suggests that the high proportion of S−1 phase benefitted battery capacity. Overall, glass-sulfur composites prepared using the precipitation method and incorporating a high content of carbon show promise as a novel and improved cathode material for LSBs.

Dielectric And Mechanical Properties Of PLA-Carbon Composites

This study focuses on the development and characterization of Carbon-based Polylactide (PLA) composites for 3D printer filaments. The aim is to enhance the electrical and mechanical properties of PLA by incorporating recovered carbon black (RCB) in different mesh sizes (500, 1000, 1500, and 2000 mesh). Electrical impedance spectroscopy and dielectric constant measurements were performed to investigate the electrical properties of the composites. Results showed that the addition of RCB increased the dielectric constant, with values ranging from 2.5 to 7.1, indicating improved electrical performance. Scanning electron microscopy (SEM) analysis revealed the dispersion of carbon particles within the composites, enhancing their electrical conductivity. The effect of RCB particle size on electrical properties was also explored, with smaller particle sizes (2000 mesh) resulting in the highest conductivity of 6.2 S/m. Tensile testing demonstrated that the addition of RCB increases the tensile strength of PLA, with values ranging from 28.6 MPa to 47.2 MPa, and the elastic modulus, ranging from 832 MPa to 1.56 GPa, depending on the mesh size. The optimal combination of RCB content and mesh size resulted in a composite with a tensile strength of 43.8 MPa. Overall, this research provides insights into the development of Carbon-based PLA composites with improved electrical and mechanical properties.

Electrical Impedance Spectroscopy Quantifies Skin Barrier Function in Organotypic In Vitro Epidermis Models

3 D human epidermal equivalents (HEEs) are a state-of-the-art organotypic culture model in pre-clinical investigative dermatology and regulatory toxicology. Here, we investigated the utility of electrical impedance spectroscopy (EIS) for non-invasive measurement of HEE epidermal barrier function. Our setup comprised a custom-made lid fit with 12 electrode pairs aligned on the standard 24-transwell cell culture system. Serial EIS measurements for seven consecutive days did not impact epidermal morphology and readouts showed comparable trends to HEEs measured only once. We determined two frequency ranges in the resulting impedance spectra: a lower frequency range termed EISdiff correlated with keratinocyte terminal differentiation independent of epidermal thickness and a higher frequency range termed EISSC correlated with stratum corneum thickness. HEEs generated from CRISPR/Cas9 engineered keratinocytes that lack key differentiation genes FLG, TFAP2A, AHR or CLDN1 confirmed that keratinocyte terminal differentiation is the major parameter defining EISdiff. Exposure to pro-inflammatory psoriasis- or atopic dermatitis-associated cytokine cocktails lowered the expression of keratinocyte differentiation markers and reduced EISdiff. This cytokine-associated decrease in EISdiff was normalized after stimulation with therapeutic molecules. In conclusion, EIS provides a non-invasive system to consecutively and quantitatively assess HEE barrier function and to sensitively and objectively measure barrier development, defects and repair.

Novel, compact electrochemical and impedance instrumentation

This paper presents the development of a novel, compact electrochemical and impedance instrumentation utilizing an analog integrated circuit (IC) for biosensing applications. Given the increasing availability of multifunctional integrated circuits (ICs), there is a growing need for devices capable of versatile applications spanning multiple fields. To address this requirement, a design was tailored to accommodate multifunctional techniques for biosensing. By combining multi-layer printed circuit board (PCB) techniques with 3D printing, the module was compact and capable of cyclic voltammetry (CV) and electrical impedance spectroscopy (EIS) measurements. Additionally, a comparison was conducted between the CV functionality of a commercial and the customized module. The results demonstrated that the customized module outperformed the commercial module. The Bode and Nyquist plots obtained from the EIS measurements accurately depicted the impedance values of resistance (R) and capacitance (C) in basic RC circuits. The experimental results show the error of R was below 2% and C was below 4% across the full frequency range from 500 Hz to 10 kHz. Furthermore, the high performance of this system was demonstrated by its successful application in monitoring the ripeness of bananas through EIS measurements. These measurements specified the total impedance and phase to assess the ripening stages accurately. This suggests the potential of the proposed system for utilizing impedance measurements in controlling fruit quality. Based on the achieved results, the proposed system holds promise for various electrochemical research and monitoring applications, particularly for electrochemical sensors and biosensors.

Circuital modelling in muscle tissue impedance measurements

Electrical impedance spectroscopy (EIS) stands as a widely employed characterization technique for studying muscular tissue in both physio/pathological conditions. This methodology commonly involves modeling tissues through equivalent electrical circuits, facilitating a correlation between electrical parameters and physiological properties. Within existing literature, diverse equivalent electrical circuits have been proposed, varying in complexity and fitting properties. However, to date, none have definitively proven to be the most suiTable for tissue impedance measurements. This study aims to outline a systematic methodology for EIS measurements and to compare the performances of three widely used electrical circuits in characterizing both physiological and pathological muscle tissue conditions. Results highlight that, for optimal fitting with electrical parameters relevant to tissue characterization, the choice of the circuit to be fitted closely hinges on the specific measurement objectives, including measurement parameters and associated physiological features. Naturally, this necessitates a balance between simplicity and fitting accuracy.

Skin Barrier Function Assessment: Electrical Impedance Spectroscopy Is Less Influenced by Daily Routine Activities Than Transepidermal Water Loss.

Skin barrier function assessment is commonly done by measuring transepidermal water loss (TEWL). An important limitation of this method is the influence of intrinsic and extrinsic factors. Electrical impedance spectroscopy (EIS) is a lesser-established method for skin barrier function assessment. Some influential factors have been described, but no guidelines exist regarding the standardization of these measurements. To evaluate the effect size of daily routine activities on TEWL and EIS, as well as their correlation with age and anatomical differences. Healthy participants (n=31) were stratified into three age groups (18-29, 30-49, and ≥50 years). In a climate-controlled room, EIS and TEWL measurements were performed on the left and right volar forearm and abdomen. Body cream application decreased TEWL and EIS values after 15 and 90 minutes. Skin washing decreased TEWL for 15 minutes and EIS values for at least 90 minutes. TEWL was increased 5 minutes after moderate to intense exercise. Coffee intake increased TEWL on the abdomen after 60 minutes. TEWL and EIS values did not correlate with participants' age and no anatomical differences were observed. No correlation was observed between TEWL and EIS. Body cream application and skin washing should be avoided at least 90 minutes prior to measurements of TEWL and EIS. Exercise and coffee intake should also be avoided prior to TEWL measurements. EIS may be a promising tool for skin barrier function assessment as it is less affected by daily routine activities than TEWL.

Electrical impedance spectroscopy detects skin barrier dysfunction in childhood atopic dermatitis.

Skin barrier dysfunction is associated with the development of atopic dermatitis (AD), however methods to assess skin barrier function are limited. We investigated the use of electrical impedance spectroscopy (EIS) to detect skin barrier dysfunction in children with AD of the CARE (Childhood AlleRgy, nutrition, and Environment) cohort. EIS measurements taken at multiple time points from 4 months to 3-year-old children, who developed AD (n = 66) and those who did not (n = 49) were investigated. Using only the EIS measurement and the AD status, we developed a machine learning algorithm that produces a score (EIS/AD score) which reflects the probability that a given measurement is from a child with active AD. We investigated the diagnostic ability of this score and its association with clinical characteristics and age. Based on the EIS/AD score, the EIS algorithm was able to clearly discriminate between healthy skin and clinically unaffected skin of children with active AD (area under the curve 0.92, 95% CI 0.85-0.99). It was also able to detect a difference between healthy skin and AD skin when the child did not have active AD. There was no clear association between the EIS/AD score and the severity of AD or sensitisation to the tested allergens. The performance of the algorithm was not affected by age. This study shows that EIS can detect skin barrier dysfunction and differentiate skin of children with AD from healthy skin and suggests that EIS may have the ability to predict future AD development.

Method for fabricating self-powered cement sensors based on gold nanoparticles

Nowadays, cement industry researchers are working hard to develop cement sensors based on nanocomposites because they can be used to develop intelligent and sustainable civil structures, self-powered, self-healing, or self-monitoring. In this light, this paper shows a methodology to obtain piezoelectric cement sensors, which produce enough energy not to require an external power source in sensing-strain applications. Mainly, two proposed experimental procedures increased the piezoelectric properties of these cement-based composites: add gold nanoparticles in the proper concentrations and apply a constant electric field during the curing stage. Firstly, the gold nanoparticles were obtained through a pulsed laser ablation system, and their particle size distribution was measured with a particle analyzer Litesizer 500 from Anton Paar, and their morphology was corroborated using a scanning electron microscope. Two concentrations (442 ppm and 658 ppm) of gold nanoparticles were obtained by changing the total ablation time. Next, we fabricated the cement sensors as described by ASTM standards C39-C39M. Hence, the cement was hand mixed with a water-to-cement ratio (w/c) of 0.47 for then poured on cylindrical molds saving the proportions recommended by the ASTM standard; in this stage, the gold nanoparticles were already part of the water ratio. Then, the cement sensors were cured under an external electric field and dried for 24 hours more in an oven to be finally ready for electromechanical characterization. Meanwhile, the electric response in altern current and the piezoelectric behavior were corroborated through electrical impedance spectroscopy and open circuit potential measurements, respectively. The piezoelectric behavior was obtained when a compressive strength was applied to the sensor, and the generated voltage was simultaneously measured. Finally, the electrical and mechanical characterization measurements were processed and analyzed using Python scripts.•The particle size and the families amount of Au NPs are affected by the ablation time.•The correct proportion of Au NPs increases the inherent piezoelectricity of cement paste.•The piezoelectric response can be addressed by coupling electric and mechanical tests.

Improving the polyethylene oxide/carboxymethyl cellulose blend's optical and electrical/dielectric performance by incorporating gold quantum dots and copper nanoparticles: nanocomposites for energy storage applications

Herein, nanocomposite polymer electrolyte films were prepared from the blend of two polymers, polyethylene oxide (PEO) and carboxymethyl cellulose (CMC), stuffed with various contents of gold quantum dots (AuQDs) and copper nanoparticles (CuNPs) as hybrid nanofiller via the solution casting method. AuQDs were prepared using laser ablation in liquid (LAL). TEM images showed that the average size of AuQDs is nearly 6.21 nm with a spherical shape. The effects of AuQDs and the hybrid nano-filler (AuQDs and CuNPs) on the PEO/CMC blend structural, optical, and electrical/dielectric characteristics have been investigated and discussed. XRD results revealed that the crystallinity degree of the nanocomposite samples decreased with increasing AuQDs/CuNPs content. Also, UV–Vis spectroscopy analysis uncovered that the optical energy gap reduced as the hybrid nanofillers' content increased. At room temperature, the electrical impedance spectroscopy (EIS) measurements showed that the hybrid nanofiller loading increases the electrolyte films’ electrical conductivity. In the dielectric properties, space charges polarization revealed higher values, where the dielectric constant (ε′) increased at lower frequency regions. The Nyquist diagram showed a semicircular shape at the lower frequencies part with a linear shape at the higher frequencies part with decreasing radius; two equivalent circuit models could be the best fit. These results suggest that these nanocomposite electrolyte films could be candidates for capacitors and flexible energy storage devices.

Development of Distillation Sensors for Spirit Beverages Production Monitoring Based on Impedance Spectroscopy Measurement and Partial Least-Squares Regression.

During spirit beverages production, the distillate is divided into three parts: the head, the heart, and the tail. Acetaldehyde and ethanol are two key markers which allow the correct separation of distillate. Being toxic, the elimination of the head part, which contains a high concentration of acetaldehyde, is crucial to guarantee the consumer's health and security. Plus, the tail should be separated from the heart based on ethanol concentration. Nowadays, online or in-line sensors for acetaldehyde monitoring during distillation do not exist, and the online sensors for alcohol monitoring, based on density measurement, remain expensive for producers. In this work, we demonstrate the development of distillation monitoring sensors based on electrical impedance spectroscopy (EIS) measurements, combined with PLS-R (partial least-squares regression) modeling. Four types of sensors are proposed and tested with wine-based distillates. Using PLS-R, the best correlations were found for one electrode, named "SpotsSym". With an R 2 up to 89.9% for acetaldehyde concentration prediction and an R 2 up to 86.8% for ethanol, the obtained results indicate the promising potential of the proposed approach. To our knowledge, this is the first report of sensors capable of simultaneously measuring ethanol and acetaldehyde concentrations. Furthermore, these sensors offer the advantages of being low cost and nondestructive. Based on these results, the development of an in-line distillation monitoring system is possible in the near future, providing a promising tool for spirit beverages producers.

Differentiation using minimally-invasive bioimpedance measurements of healthy and pathological lung tissue through bronchoscopy.

To use minimally-invasive transcatheter electrical impedance spectroscopy measurements for tissue differentiation among healthy lung tissue and pathologic lung tissue from patients with different respiratory diseases (neoplasm, fibrosis, pneumonia and emphysema) to complement the diagnosis at real time during bronchoscopic procedures. Multi-frequency bioimpedance measurements were performed in 102 patients. The two most discriminative frequencies for impedance modulus (|Z|), phase angle (PA), resistance (R) and reactance (Xc) were selected based on the maximum mean pair-wise Euclidean distances between paired groups. One-way ANOVA for parametric variables and Kruskal-Wallis for non-parametric data tests have been performed with post-hoc tests. Discriminant analysis has also been performed to find a linear combination of features to separate among tissue groups. We found statistically significant differences for all the parameters between: neoplasm and pneumonia (p < 0.05); neoplasm and healthy lung tissue (p < 0.001); neoplasm and emphysema (p < 0.001); fibrosis and healthy lung tissue (p ≤ 0.001) and pneumonia and healthy lung tissue (p < 0.01). For fibrosis and emphysema (p < 0.05) only in |Z|, R and Xc; and between pneumonia and emphysema (p < 0.05) only in |Z| and R. No statistically significant differences (p > 0.05) are found between neoplasm and fibrosis; fibrosis and pneumonia; and between healthy lung tissue and emphysema. The application of minimally-invasive electrical impedance spectroscopy measurements in lung tissue have proven to be useful for tissue differentiation between those pathologies that leads increased tissue and inflammatory cells and those ones that contain more air and destruction of alveolar septa, which could help clinicians to improve diagnosis.

Electrochemical Impedance Spectroscopy Integrated with Environmental Transmission Electron Microscopy.

The concept of combining electrical impedance spectroscopy (EIS) with environmental transmission electron microscopy (ETEM) is demonstrated by testing a specially designed micro gadolinia-doped ceria (CGO) sample in reactive gasses (O2 and H2 /H2 O), at elevated temperatures (room temperature-800 °C) and with applied electrical potentials. The EIS-TEM method provides structural and compositional information with direct correlation to the electrochemical performance. It is demonstrated that reliable EIS measurements can be achieved in the TEM for a sample with nanoscale dimensions. Specifically, the ionic and electronic conductivity, the surface exchange resistivity, and the volume-specific chemical capacitance are in good agreement with results from more standardized electrochemical tests on macroscopic samples. CGO is chosen as a test material due to its relevance for solid oxide electrochemical reactions where its electrochemical performance depends on temperature and gas environment. As expected, the results show increased conductivity and lower surface exchange resistance in H2 /H2 O gas mixtures where the oxygen partial pressure is low compared to experiments in pure O2 . The developed EIS-TEM platform is an important tool in promoting the understanding of nanoscale processes for green energy technologies, e.g., solid oxide electrolysis/fuel cells, batteries, thermoelectric devices, etc.

The acceptability of cervical electrical impedance spectroscopy within a multi-modal preterm birth screening package: a mixed methods study

BackgroundReducing the rate of preterm birth is a cornerstone of global efforts to address child mortality, however existing screening tests offer imperfect prediction. Cervical electrical impedance spectroscopy (EIS) is a novel technique to quantify the ripening changes which precede labour. Mid-trimester EIS measurements have been shown to accurately predict preterm birth in asymptomatic women. This study aimed to comprehensively evaluate the acceptability of cervical EIS to low and high-risk women as part of a package of screening tests performed during a larger prospective trial.MethodsIn this parallel convergent mixed methods study, 40 women completed questionnaires before and after screening tests (EIS, cervical length measurement and fetal fibronectin quantification). Quantitative outcomes were anxiety levels before and after screening (Spielberger State Trait Anxiety Inventory, STAI-6), pain (Short Form McGill Pain Questionnaire) and ratings of EIS device appearance and test acceptability (visual analogue scales). Twenty-one women (11 high-risk, 10 low-risk) also attended a semi-structured qualitative interview. Interviews were recorded and transcribed, then thematic analysis was performed. A convergence coding matrix was constructed to enable triangulation of quantitative and qualitative results.ResultsHigh risk women demonstrated a significant reduction in anxiety following screening (mean STAI-6 score 34.5 vs. 29.0, p = 0.002). A similar trend was observed among low-risk participants. Ratings of pain, EIS device appearance and procedural acceptability did not differ between groups. Mean pain ratings were low (visual analogue scale 0.97 and 1.01), comparing favourably to published evaluations of conventional screening tests. Qualitative analysis provided insight into both the physical consequences and emotional experiences of screening. Additional determinants of the screening experience included device design, pre-existing perspectives on intimate examination, attitudes to knowledge in pregnancy and interaction with clinical staff. Finally, a range of practical considerations regarding wider use of EIS were identified, with valuable complementary detail regarding acceptability for use in antenatal care.ConclusionsCervical EIS is well tolerated and acceptable to both low and high-risk women when performed as part of a multi-modal screening package. These results provide useful insights to inform the design of future study and screening protocols.

Effective Capacitance from Equivalent Electrical Circuit as a Tool for Monitoring Non-Adherent Cell Suspensions at Low Frequencies.

Analyzing the electrical double layer (EDL) in electrical impedance spectroscopy (EIS) measurement at low frequencies remains a challenging task for sensing purposes. In this work, we propose two approaches to deal with the EDL in measuring impedance for particles and non-adherent cells in an electrolytic suspension. The first approach is a simple procedure to compute a normalized electrical impedance spectrum named dispersed medium index (DMi). The second is the EIS modeling through an equivalent electric circuit based on the so-called effective capacitance (Cef), which unifies the EDL phenomena. Firstly, as an experiment under controlled conditions, we examine polymer particles of 6, 15, and 48 μm in diameter suspended in a 0.9% sodium chloride solution. Subsequently, we used K-562 cells and leukocytes suspended in a culture medium (RPMI-1640 supplemented) for a biological assay. As the main result, the DMi is a function of the particle concentration. In addition, it shows a tendency with the particle size; regardless, it is limited to a volume fraction of 0.03 × 10-4 to 58 × 10-4. The DMi is not significantly different between K-562 cells and leukocytes for most concentrations. On the other hand, the Cef exhibits high applicability to retrieve a function that describes the concentration for each particle size, the K-562 cells, and leukocytes. The Cef also shows a tendency with the particle size without limitation within the range tested, and it allows distinction between the K-562 and leukocytes in the 25 cells/µL to 400 cells/µL range. We achieved a simple method for determining an Cef by unifying the parameters of an equivalent electrical circuit from data obtained with a conventional potentiostat. This simple approach is affordable for characterizing the population of non-adherent cells suspended in a cell culture medium.

Experimental Investigation on the Compressive Stress-Sensing Ability of Steel Fiber-Reinforced Cement-Based Composites under Varying Temperature Conditions

This study investigates the piezoresistive (self-sensing) properties of short stainless-steel fiber-reinforced mortar under varying temperature conditions. Different reinforced mortars were produced by varying fiber and aggregate content. First, Electrical Impedance Spectroscopy (EIS) measurements were used to characterize the electrical properties of the mortar specimens. EIS measurements were performed at temperatures of 24 °C, 35 °C, and 50 °C. Second, to investigate the self-sensing capacity of the different composites, the fractional changes of electrical impedance at 1 kHz were monitored under two conditions: temperature variation alone (cooling down from 35 °C or 50 °C to room temperature), and temperature variation combined with cyclic compressive loading (up to 5 MPa). The results of the former were used to compensate for the effect of temperature variations in the latter. Both temperature and mechanical loading produced meaningful variations in the electrical impedance and piezoresistivity of the investigated composites. Conclusions are drawn with respect to the stress and temperature sensitivity of the composites. The real and imaginary parts of the electrical impedance of the mortar produced with the highest fiber volume fraction (0.01%) and higher aggregate content (volume fraction of 60%) were distinctly sensitive to temperature and stress, which suggests the possibility of using the same composite as a stress and temperature sensor.

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

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

Syntheses and Photovoltaic Properties of New Pyrazine-Based Organic Photosensitizers for Dye-Sensitized Solar Cells

Three novel pyrazine-based organic photosensitizers denoted as TPP, TPPS, and TPPF were synthesized for dye-sensitized solar cell (DSSC) studies. Chemical structures of the pyrazine-based photosensitizers were designed with pyrazine derivatives as acceptors, triphenylamine groups as donors, and the thiophene–cyanoacryl group as an auxiliary heterocyclic linkers-acceptor. Using UV-vis spectrophotometry, cyclic voltammetry, and density functional theory calculations, optical and electrochemical characteristics of these pyrazine-based photosensitizers were examined and explored in relation to photovoltaic parameters. The effects of the molecular structures of these photosensitizers on the performances of DSSCs were also investigated. The overall conversion efficiencies of DSSCs based on pyrazine-based photosensitizers were 1.31~2.64% under AM 1.5 irradiation of 100 mW/cm2. To confirm the effect of interfacial charge transfer on photovoltaic performances of DSSC based on pyrazine-based photosensitizers, interfacial charge transfer resistances were investigated by electrical impedance spectroscopy (EIS) measurements.